Online test/2021/1-MCQ

 

MULTIPLE CHOICE QUESTIONS

CBSE TERM 1 PRACTICE QUESTIONS

CLASS X

TERM 1

Chapter : Light – Reflection and Refraction

(To download the MCQ pdf - click the link MCQ - Light: reflection and refraction)

To check your score in MCQs, attempt the online test  - Online Test -Light reflection and refraction

Electric Current

 ELECTRIC CURRENT :

If electric charges such as electrons, ions, charged particles flows we say that there exist an electric current.

Consider a cell is connected to a torch bulb through metallic wires and a switch. On switching on the circuit, electric current is produced which flow through the wire and filament of the torch bulb, heat it up and the filament begins to glow.

Here in this case, electrons starts flowing when the cell was connected to the torch bulb through wires and switch. This flow of electrons in the metallic wire constitute the electric current.

Definition OF Electric Current: 
Electric current is defined as the rate of flow of charge flowing through a cross-section of a wire/conductor. 

Formula: If a net charge Q, flows across any cross-section of a conductor in time t, then the current I, through the cross-section is 

\[I = \frac{Q}{t}\]

SI Unit :
The SI unit of electric charge is coulomb (C) and time is second (s). Thus the SI unit of electric current is coulomb/second (C/s). This unit is given a special name called ampere (A), named after the French scientist, Andre-Marie Ampere (1775–1836). 

Definition of 1 ampere :

One ampere is that amount of current when an electric charge of one coulomb flows through a cross section of wire in one second. That is, 

\[1A=\frac{1C}{1s}\]

Small units of electric current: 

Small quantities of current are expressed in 
(i) milliampere

\[1mA=10^{-3}A\]

(ii) microampere

\[μA=10^{-6}A\]

Device used to measure current :

An instrument called ammeter measures electric current in a circuit. 

Symbol:

Connection in circuit: 

It is always connected in series in a circuit through which the current is to be measured. 

The Red terminal (positive terminal) is connected to the positive terminal of the battery and black terminal (negative terminal) is connected to the negative of the battery.

Direction of electric current :
Conventionally, in an electric circuit the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges. In an electric circuit electric current flows from the positive terminal of the cell to the negative terminal of the cell through the bulb and ammeter.


Electric circuit :
A continuous and closed path of an electric current is called an electric circuit.

Electric switch :
A switch makes a conducting link between the cell and the bulb. If the switch of the circuit is turned off, the current stops flowing and the bulb does not glow. 
Charge of an electron: 

\[1.6 \times 10^{-19}C\]

Number of electrons in 1C of charge: 

\[6.25 \times 10^{18}\]

NOW CHECK YOUR PROGRESS!!! 

1. What does an electric circuit mean? 
2. Define the unit of current. 
3. Calculate the number of electrons constituting one coulomb of charge. 
4. A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of charge that flows through the circuit. 
5. Name the instrument used to measure electric current in a circuit. How is this instrument connected in a circuit? Draw a simple circuit diagram to explain your answer. 
6. Which particles constitute electric current in a metallic conductor? 
7. Name two units for expressing the small values of current. Also write their symbols. How are these units related to ampere? 
8. Write the use of following components in an electric circuit 
(a) Cell/battery 
(b) Ammeter 
(c) Connecting wires 
(d) Switch/plug key 

Why the colour of clear sky is blue?

Why the colour of clear sky is blue?

The atmosphere of earth is full of particles or molecules like N2, O2, O3, H2, H2O, dust particles etc. These are so small that we cannot see them with naked eyes. Even with powerful microscope of 100X or higher available in school labs, air particles are not visible (except dust particles). When sunlight encounters these particles there is a change in the direction of sun rays which lead to a phenomenon known as scattering of light.The sunlight consists of different frequencies from 430 – 770 THz (or wavelengths 390 -700 nanomoetres). The colour of the scattered light depends upon the size of the encountered particles. The process of selective scattering is known as Rayleigh scattering.

The size of the air particles has size comparable to the wavelength of visible light at the blue end. These particles are more suitable in scattering light of blue and violet colours as compared to red colour. This is the reason why sky appears blue in colour.

Due to pollution, large size particles are introduced in the atmosphere. These particles are efficient in scattering light of longer wavelengths also. This causes the pale blue or grey colour of the sky in a polluted atmosphere. 

Watch the video shown below on youtube. This video shows how a laser light is scattered by water and talcom powder. The scattering of laser by water or talcom powder makes its path visible (known as Tyndall's  effect) and this property can be used to study relection or refraction.

Uses of spherical mirrors

Uses of spherical mirrors 

Uses of Concave Mirror

1. A concave mirror is used as a reflector of light in headlights of automobiles to obtain a parallel beam of light. In a similar way concave mirrors are also used in torch lights and search lights.

In such a case, the source of light such as bulb is placed at the focus of the concave mirror. The light rays which fall on the concave mirror are reflected parallel to the principal axis and thus a parallel beam is obtained.

Practically, there are two bulbs one above the focus to obtain low beam (to light the ground nearby) and the other bulb slightly below the focus to obtain a high beam (to illuminate a larger distance but this will blind the driver approaching from opposite side).

In some reflectors the position of the bulb can be shifted slightly to obtain a low beam/high beam.


2. A concave mirror is used as a dentist’s mirror.
Dentists use a concave mirror to obtain the enlarged image of a tooth. The focal length of concave mirror used is large enough so that object (tooth) is placed between Focus and Pole. Thus a virtual, erect and magnified image of the tooth is obtained.

The position of object (tooth) is very important. Imagine what would happen if dentist view an inverted image using a concave mirror if it is placed between C and F. the image obtained will be magnified but inverted. In confusion, dentist may remove a healthy tooth.

3. Concave mirrors are used as concentrator of heat and light in solar furnace.
A solar furnace can be constructed by using a huge concave mirror or an array of plane mirrors mounted on a curved surface giving rise to a concave shape. The huge concave mirror is directed towards the sun. The sun’s rays get focused at F. At focus F, the temperature will be very high as all heat rays (infra red) get converged there. The temperature can reach up to 3500°C which can be used to melt metals.

One such solar furnace is installed in Mount Louis in France.

4. A concave mirror can be used as a shaving mirror.
Such a mirror will have a large focal length say 1m or 1.5m so that the person standing nearby would be placed between F and P. A virtual, erect and magnified image of the face is obtained which helps the person to see an enlarged image of his face while shaving.



Uses of Convex mirrors

1. It is used as a rear view mirror in automobiles.

Since a convex mirror provides a wider field of view and erect image of the object, it is a perfect choice for the rear view mirror.

The driver can view the wide view of traffic behind the vehicle.

The only disadvantage with the convex mirror is that the driver may be confused about the actual distance of the traffic behind his own vehicle. The image formed by the convex mirror is diminished and it gives an illusion that the object is very far. Even a closer object may appear very far in a convex mirror.

You can find this caution in every rear view mirror of automobile “Objects in the mirror are closer than they appear”.

2. Convex mirror are also used at the intersection of a busy traffic and at sharp curve.

Power of a lens

Power of a Lens

The power of a lens tell us its ability to converge or diverge a  beam of light falling on it.

Observe the following two convex lenses

The convex lens (A) with the short focal length converge the light rays by large angles and focus the rays close to the optical centre. Thus the lens with short focal length has a high converging power. 

The other lens (B) with longer focal length converge the light rays by small angle and focus the rays far from the optical centre. This lens with larger focal length has a low converging power.

Similarly for a concave lens, the shorter the focal length more is the diverging power of the lens.

Thus power of a lens may be defined as the reciprocal of its focal length in metres.

\[P=\frac{1}{f}\]
\[P=\frac{100}{f}\]  (if f is expressed in cm)

SI unit of power of a lens is dioptre. It is denoted by the symbol D.

Power of lens is said to be one dioptre if its focal length is 1m.
\[P=\frac{1}{f}\] 
\[P=\frac{1}{1}=1\]

Convex lens has a positive power as the focal length of convex lens is positive.

A concave lens has a negative power as the focal length of concave lens is negative.

Power of a combination of a lens

If lenses are combined then power of the combination is simply the algebraic sum of power of individual lenses.

Spherical lenses

Spherical Lenses
A spherical lens is a transparent medium bounded by two surfaces. Atleast one of the two surfaces must be spherical.
If the lens has one spherical surface then other surface will be plane. This results into two types of lenses.
(a) Plano convex lens
(b) Plano concave lens

If both the surfaces of the lens are spherical then following lens are obtained.
(c) Double convex lens ( or simply known as convex lens)
(d) Double concave lens ( or simply known as concave lens)

(e) Convexo concave
(f) Concavo convex 

Few terms related to spherical lens

Optical centre (O) : The centre of the lens is known as optical centre.

Principal axis : The line passing through the centre of curvatures of spherical surfaces of lens and the optical centre is called principal axis.

Principal focus of a convex lens

When incident rays parallel to the principal axis falls on a convex lens then after refraction through the lens, all rays meet at a point on the other side of the lens. This point is known as the principal focus of a convex lens.

Since a lens is transparent light can enter the lens from either of the two surfaces. Hence a lens has two foci labeled as F1 and F2.

Focal length (f): The distance between optical centre and focus of a spherical lens is called focal length.

2F1 and 2F2 are the points located at twice the distance of focal length from the optical centre of the lens.

Principal focus of a concave lens

When incident rays parallel to the principal axis falls on a concave lens then after refraction through the lens, all rays diverge and appears to coming from a point on the principal axis. This point is known as the principal focus of a concave lens.

Since a lens is transparent light can enter the lens from either of the two surfaces of the concave lens. Hence a concave lens has two foci labeled as F1 and F2.

Watch a video for formation of image by a convex lens from our YouTube partner 'Learn n Hv Fun'.

Working of electric motor

ELECTRIC MOTOR

An electric motor is a rotating device which converts electrical energy into mechanical energy.
It means it takes energy from electricity and using this energy the motor system rotates its rotator. The motion of rotator means that it possesses mechanical energy.
It appears so simple but we have to understand the process by which this energy change take place.

Image Credit -Lookang many thanks to Fu-Kwun Hwang and author of Easy Java Simulation = Francisco Esquembre, Ejs Open Source Direct Current Electrical Motor Model Java Applet ( DC Motor ) 20 degree split ring, CC BY-SA 3.0

The basic principle behind the working of motor is that when a current carrying wire is placed in a magnetic field it experiences a force. The direction of this force can be determined by Fleming’s left hand rule.

Thus using electrical energy we setup an electric current in a coil
and in an electromagnet. The electromagnet thus behaves like a magnet. The current carrying coil when placed in magnetic field of electromagnet experiences a force. Using suitable arrangement and designing, the coil can be made to rotate.

Construction
A simple electric motor consists of a rectangular coil ABCD of insulated copper wire placed between two opposite poles magnets as shown in the figure. The ends of the coil are connected to two half of a split ring (S1 and S2) attached to the axle. The split rings are connected to two carbon brushes B1 and B2 as shown in the figure. The carbon brushes are connected to a battery through connecting wire and a key (or switch).

©Udvita.org

Working:
First Half Cycle

Let the plane of coil is initially placed horizontally as shown in the figure. The direction of current in the coil is along ABCD. The direction of magnetic field is from North pole to the south pole.
By applying Fleming’s left hand rule on arm AB, the direction of force on arm AB is downward. Similarly the direction of force on arm CD is upward. Under the action of two equal and opposite will make the coil mounted on an axle to rotate anticlockwise.

Second Half Cycle
After half a rotation, arms AB and CD will interchange its position. The split ring S1 is now in contact with brush B2 and the split ring S2 is in contact with brush B1. The direction of current in the coil is now DCBA, reversed as compared to first half cycle. A device which reverses the direction of current in a circuit is called commutator. In electric motor, split rings acts as commutator.

©Udvita.org

By applying Fleming’s left hand rule on arm AB, the direction of force on arm AB is upward. Similarly the direction of force on arm CD is downward. Again under the action of two equal and opposite will make the coil mounted on an axle to rotate anticlockwise.

Commercial motor
A commercial motor consists of an electromagnet instead of permanent magnets. The current carrying coil consists of a large number of turns (in thousands). A soft iron core is used on which the coil is wound.
The soft iron core along with the coil is called the armature.

Image credit-Abnormaal, Electric motor, CC BY-SA 3.0

Uses of electric motor
Electric motor is used in electric fans, water pumps, mixer, MP3 player, computer etc

Simplest Electric Motor
Watch the Simplest electric Motor video made by our YouTube Channel partner 'Learn n hv Fun'.
The motor is simply made using a copper coil and few neudymium magnets using a 1.5V  electric cell.

Human Eye - Accomodation

HUMAN EYE – ACCOMMODATION

A human eye with normal vision can see nearby objects as close as 25cm clearly and distinctly and far away objects as far as infinity clearly without any strain in eyes. 

To see an object clearly the eye lens must focus the image on the retina. This sharp focusing is achieved by eye lens with the help of ciliary muscles. The ability of eye lens to adjust its focal length to focus objects at different distances on the retina is called accommodation.

How Accommodation is achieved?

An eye lens is a jelly like material made up of protein. The curvature/shape of the eye lens can be changed to some extent by the action of ciliary muscles. When ciliary muscles contract, curvature of eye lens increases. This decreases focal length of eye lens. This enables us to see nearby objects clearly. 

Similarly when ciliary muscles relax, curvature of eye lens decreases. This increases focal length of eye lens. This enables us to see far away objects clearly. 

The following steps would be easier to understand the process.

To view nearby objects:

Ciliary muscles contracts → curvature of eye lens increases → eye lens becomes thicker → focal length of eye lens decreases → image of nearby objects focused on the retina 

The above action of ciliary muscles and eye lens enables us to see nearby objects clearly.

To view far away objects:

Ciliary muscles relaxes in this situation → curvature of eye lens decreases → eye lens becomes thinner → focal length of eye lens decreases → image of far away objects focused on the retina. 

The above action of ciliary muscles and eye lens enables us to see far objects clearly.

The power of accommodation for a normal vision is 4 dioptre.

The power of eye lens when a nearby objects is viewed is 44 D. The power of eye lens when a far away object is viewed is 40 D. Thus the maximum variation in the power of eye lens achieved is 44D – 40D = 4D. 

Least distance of distinct vision (Near point)

The minimum distance at which the object can be see clearly and distinctly without any strain in the eyes is called the least distance of distinct vision or near point of the eye. 

For a person with normal vision this value is 25 cm.

What would happen if the object is closer than 25 cm? Would any image be formed on eye lens?

Yes, the image would be formed but that will be blurred, not well focused. Try focusing on the object. Some of you may be able to focus the object but if would cause strain in your eye after few seconds. 

Try holding a pen or a pencil close to your eye or nose. At first the object will appear blurred but if you try to focus object may get focused to some extent causing strain in your eye. You have to either shift your focus or have to move away the object from you.

Reason:

The curvature of the eye lens can be change up to some extent only and that with the help of cilicary muscles. Thus focal length of eye lens cannot be decreased beyond a certain minimum limit. Hence there is minimum distance at which objects can be seen comfortably. That minimum comfortable distance is 25 cm. This is called near point or least distance of distinct vision.

Far point

The farthest point up to which a human eye with normal vision can see is infinity and this is called the far point of human eye. 

Try focusing a star. These stars are hundred, thousand light years from us. The nearest star Alpha centuri is 4.2 LY away. ( 1 LY = 9.46 X \(10^{15}\) m)

Question of the day 15 Nov 2107

Question of the day 15 Nov 2017

A student has two resistors A and B of resistance 4 ohm and 6 ohm respectively.  The student was challenged by the Physics teacher to connect them to a 12 V battery so as to draw maximum current from the voltage source.

How would you advice the student to connect the resistors and what would be the current obtained?

Question of the day 14/11/2017

Question of the day - 14 Nov 2017

The resistance of an electric heating device is 20 ohms. If an electric current of 5 A flows through the device for 30 seconds. Determine

(i) Potential difference applied across the device.

(ii) heat produced in the device in 30 seconds.

The Story of Electricity

THE STORY OF ELECTRICITY

Imagine a world without any electricity. Imagine your home now… no televisions, no air conditioners, no light, no refrigerator, no machines, no mobile phones, no electronic gadgets to assist you, no apps, no facebook, no twitter… The only form of electricity available to us would be that of lightning.

Ohh.. what a boring life…

But life would be very close to nature. Sun and fire will be the only source of light. Watching birds, animals would be your favorite pass time. Crude handmade gadgets like magnetic compass, hammer, knife would be your apps. Pigeon would serve as twitter, FB…

So my dear friend, electricity is an integral part of our modern life. The study of electricity is necessary so that such a vast knowledge is not lost overtime. It must be passed to the next generation.

I am doing my duty as I am passing the story to electricity to you..

Take a piece of copper metal. If you view the copper at the microscopic level you would find a lot of empty space with copper atoms suspended in space in the cloud of electrons. Most of the electrons in the cloud are orbiting to some copper atoms or the other. Some electrons in the cloud are wandering from one atom to the other, colliding with other atoms and electrons. At this microscopic level, everything happens very fast. Electrons are moving at 10⁶m/s, atoms are vibrating very rapidly with a frequency of ……..

Suddenly, in the macroscopic, outer world, a human connected the metal plate to a battery.

In the inner atomic world, there is a change in the scene now. The cloud of wandering electrons  start moving towards positive terminal of the battery with a very slow speed of 1mm/s. The number of wandering electrons are however enormous. About 10²² in few grams of copper.

We call this flow of electrons as electric current.

When such moving electrons are made of pass through a filament of electric bulb, it heats up to approx 2700°C and starts glowing. 

This is how we use electricity of light a bulb.

Watch the video from YouTube to understand electricity in a more detail.

Ohm's Law

Ohm's Law is a relationship between potential difference applied across a conductor to the electric current flowing in it.

You must have experienced the following situations in daily life:

(1) Fluctuations in voltage which leads to dimming or brightening of electric bulb. (This is the reason why we use stabilizers for ACs - to prevent any damage due to voltage fluctuations ) 
(2)  While playing with LEDs, torch bulb, electric cells and connecting wires you must have observed that by increasing the number of cells in the circuit the LEDs glows brighter.
(3) A 12V battery provides a large amount of current than a 3V battery.

This suggests that there must be a relation between voltage (potential difference) and electric current. This relationship is known as Ohm's Law.

Ohm's law was given by George Simon Ohm in the year 1827. This is a relation between potential difference (V) applied across the ends of a conductor to the electric current (I) flowing in the conductor

According the Ohm's Law, the electric current flowing in a conductor is directly proportional to the potential difference (V) applied across the ends of a conductor provided the temperature of the wire remains the constant.

Mathematically,
                              I    ∝    V
or it can also be written as

                            V  ∝    I
removing the proportionality sign and introducing a constant

                            V   =  R I

Where R is a constant known as the resistance of the given conductor.

Graph:

The V–I graph is a straight line that passes through the origin of the graph, as shown in Figure. Thus,
\[\frac{V}{I}\]
is a constant ratio.

Resistance

Physically, resistance is defined as a property of a conductor to resist the flow of charge through it.

The SI unit of resistance is ohm (Ω)  (Greek symbol omega)

A conductor is said to have a resistance of 1Ω when a potential difference of 1V is applied across the ends of a conductor and a current of 1A flows through it.
\[R=\frac{V}{I}\]
\[1Ω=\frac{1V}{1A}\]

A fan regulator is actually a variable resistor. It changes the resistance of the circuit and thereby we can control the speed of the fan.

To test your knowledge on Ohm's Law, attempt the following test.

you will get your score immediately. 

Click the link below to attempt the test:

Online Test on Ohm's Law

Some more questions on Ohm's Law:

1. Name and state the law which relates the current in a conductor to the potential difference across a conductor and the current flowing through it.

2. Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

3. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.


4. (a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω? (b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω?

5. The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4A from the source. What current will the heater draw if the potential difference is increased to 120 V?

6. The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below –
I (amperes) 0.5    1.0     2.0      3.0       4.0
V (volts)     1.6    3.4     6.7     10.2     13.2
Plot a graph between V and I and calculate the resistance of that resistor.

7. Keeping the potential difference constant, the resistance of a circuit is doubled. By how much does the current change?

QUESTION OF THE DAY 09/05/2015

Question of the day September 9, 2015

Three electric lamps A, B and C are rated as follows:

Lamp A : 40 W, 220 V

Lamp B: 60 W, 220 V and

Lamp C: 100 W, 220 V

Which lamp has higher resistance? Give reason.

Question Bank - Magnetic effects of electric current

1.    Why does a compass needle got deflected when brought near a bar magnet?

2.    Draw magnetic field lines of a bar magnet.

3.    List any two properties of magnetic field lines.

4.    The magnetic field in a given region is uniform. Draw a diagram to represent it.

5.    Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right hand rule to find out the direction of magnetic field inside and outside the loop.

6.    Why don’t two magnetic field lines intersect each other?

7.    Explain different ways to induce current in a coil.

8.    State Fleming’s left hand rule.

9.     What is the principle of electric motor?

10.   State the principle of electric generator.

11.   State Fleming’s right hand rule.

12.   State right hand thumb rule.

13.   Name some sources of direct current.

14.   Which sources produces alternating current?

15.   Name two safety measures commonly used in electric circuit and appliances.

16.   What precautions should be taken to avoid the overloading of domestic electric circuit?

17.   An electric oven of a 2kW power rating is operated in a domestic circuit (220 V) that has a current rating of 5A. What result do you expect? Explain.

18.   Define electromagnetic induction.

19.   List three sources of magnetic field.

20.   How does a solenoid behaves like a bar magnet? Can you determine the north and south poles of a current carrying solenoid with the help of a bar magnet? Explain.

21.   When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

22.   Imagine you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?

23.   A coil of insulated copper wire is connected to a galvanometer. What would happen if a bar magnet is

  (i) Pushed into the coil.

  (ii) Withdrawn from inside the coil.

  (iii) Held stationary inside the coil.

24.   Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

25.   State the rule to determine the direction of a

  (i) Magnetic field produced around a straight conductor carrying current.

  (ii) Force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.

  (iii) Current induced in a coil due to its rotation in a magnetic field.

26.   When does an electric short-circuit occur?

27.   What is the function of an earth wire? Why is it necessary to earth metallic appliances?

28.   What is the effect of inserting a soft iron core inside a current-carrying solenoid? What is this arrangement known as?

29.   What is the capacity of an electric fuse used in (i)lighting circuit (ii) power circuit used in household supply?

30.   State two characteristics of electric fuse wire.

31.   State two ways by which the strength of an electromagnet can be increased.

32.   State three factors on which the magnitude of force on a current carrying –conductor placed in a magnetic field depends. Can this force be zero for some position of the conductor?

33.   Draw the magnetic field lines around a straight conductor carrying current.

34.   Draw the magnetic field lines due to a current-carrying circular wire.

35.   What is solenoid? Draw the magnetic field lines due to a current carrying solenoid.

36.   Compare the magnetic field produced by a bar magnet and a solenoid?

37.   What is the difference between a direction current and an alternating current? How many times does AC used in India change direction in one second?

38.   In what way can the magnitude of induced current be increased?

39.   How does AC differ from DC? What are the advantages and disadvantages of AC over DC?

40.   What is earthing? How does it work as a safety measure?

41.   What is the function of earth wire? Why is it necessary to earth the metallic appliances?

42.   What is the role of fuse used in series with any electrical appliance?

43.   Why should a fuse with defined rating not be replaced by one with a larger rating?

44.   How is the direction of magnetic field at a point determined?

45.   What is the direction of magnetic field at the centre of a current-carrying circular loop?

46.   A magnetic compass shows a deflection when placed near a current carrying wire. How will the deflection of the compass get affected if the cyrrent in the wire is increased? Support your answer with reason.

47.   What does the divergence of magnetic fied lines near the ends of a current carrying straight solenoid indicate?

48.   An electron enters a uniform magnetic field at right anges to it as shown in the figure. In which direction will this electron move? State the principle applied by you in finding the direction of motion of the electron?

49.   What is an electric fuse? How does it function?

50.   A fuse is rated at 8 A, it means:

   (a) It will not work if current is less than 8 A.

   (b) It has a resistance of 8 ohm.

   (c) It will work only if current is 8 A.

   (d) It will burn if current exceeds 8 A.

Question Bank Electricity

A Question Bank provides you a plenty of good questions for practice and meaningful discussion with your peers. It saves time and make you confident in the subject. The following is the Question Bank on Electricity Class 10 standard.

1.    What does an electric circuit mean?

2.    Define the unit of current.

3.    Calculate the number of electrons constituting one coulomb of charge.

4.    A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of charge that flows through the circuit. (Ans. 300 C)

5.    Name the instrument used to measure electric current in a circuit. How is this instrument connected in a circuit? Draw a simple circuit diagram to explain your answer.

6.    Which particles constitute electric current in a metallic conductor?

7.    Name two units for expressing the small values of current. Also write their symbols. How are these units related to ampere?

8.    Name a device that helps to maintain potential difference across a conductor.

9.    What is meant by saying that potential difference between two points is 1V?

10.   Write the relation which states the relation between potential difference and work done.

11.   How much energy is given to each coulomb of charge passing through a 6V battery?

12.   How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V?

13.   Name the device that measures the potential difference across two points in an electric circuit. How it is connected in an electric circuit?

14.   Name and state the law which relates the current in a conductor to the potential difference across a conductor and the current flowing through it.

15.   Define the SI unit of resistance.

16.   (a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω? (Ans. 0.183 A)

        (b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω? (Ans. 2.2 A)

17.   The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V? (Ans. 8 A)

18.   A wire of given material having length l and area of cross-section A has a resistance of 4 Ω. What would be the resistance of another wire of the same material having length l/2 and area of cross-section 2A? (Ans. 1 Ω)

19.   On what factors does the resistance of a conductor depend?

20.   Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

21.   Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

22.   Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

23.   When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor. (Ans. 4800Ω)

24.   Why is the tungsten used almost exclusively for filament of electric lamps?

25.   Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?

26.   How does the resistance of a wire vary with its area of cross-section?

27.   Why copper and aluminium wires are usually employed for electricity transmission?

28.   Keeping the potential difference constant, the resistance of a circuit is doubled. By how much does the current change?

29.   Give two examples of materials which are (i) good conductor (ii) resistor (iii) insulator (iv) poor conductor.

30.   Why do electricians wear rubber hand-gloves while working with electricity?

31.   Name the device used to change resistance in a circuit to regulate current without changing the voltage source.

32.   What is nichrome? State its one property and one use.

33.   Define resistivity. What is its SI unit? On what factor does it depends?

34.   A wire of resistance 20 Ω is stretched to double its length. What will be its new (i) resistivity (ii) resistance? (Ans. New R = 80 Ω)

35.   The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below –

                    I (amperes)    0.5     1.0      2.0      3.0      4.0


                    V (volts)       1.6       3.4      6.7     10.2     13.2

Plot a graph between V and I and calculate the resistance of that resistor.

36.   Write the use of following components in an electric circuit
        (a) Cell/battery
        (b) Ammeter
        (c) Connecting wires
        (d) Switch/plug key

37.   A wire of resistance R is cut into five equal pieces. These five pieces of wire are then connected in parallel. If the resultant resistance of this combination be R then the ratio of resultant to the original will be?

38.   A radio set draws a current of 0.36 A for 15 minutes. Calculate the amount of electric charge that flows through the circuit. (Ans. 324 C)

39.   Potential difference between two points of a wire carrying 2 ampere current is 0.1 volt. Calculate the resistance between these points. (Ans. 0.05Ω)

40.   A simple electric circuit has a 24 V battery and a resistor of 60 ohms. What will be the current in the circuit? The resistance of the connecting wires is negligible. (Ans. 0.4 Ω)

41.   Find resistance between A and B in following network

42.   A resistance of 6 ohms is connected in series with another resistance of 4 ohms. A potential difference of 20 volts is applied across the combination. Calculate the current through the circuit and potential difference across the 6 ohm resistance. (Ans. 2 A, 12 V)

43.   Calculate the work done in moving a charge of 5 Coulombs from a point at a potential of 210 Volts to another point at 240 Volts. (Ans. 150 J)

44.   How many electrons pass through a lamp in one minute if the current be 200 mA? (72 x 10^18)

45.   Calculate the current supplied by a cell if the amount of charge passing through the cell in 4 seconds is 12 C ? (Ans. 4 A)

46.   A 2 Volt cell is connected to a 1 Ω resistor. How many electrons come out of the negative terminal of the cell in 2 minutes? (Ans. 1440 x 10^18)

47.   A torch bulb when cold has 1Ω resistance. It draws a current of 0.3 Ampere when glowing from a source of 3 V. Calculate the resistance of the bulb when glowing and explain the reason for the difference in resistance. (Ans. 10Ω)

48.   A current of 0.2 Ampere flows through a conductor of resistance 4.5 Ω. Calculate the potential difference at the ends of the conductor. (Ans. 0.9 V)

49.   You have two metallic wires of resistances 6 ohm and 3 ohm. How will you connect these wires to get the effective resistance of 2 ohm?

50.   State Ohm’s law. “The resistance of a conductor is 1Ω.” What is meant by this statement?

51.   Prove that 1 J is equivalent to 1 Vx A x s.

52.   How long does it take a current of 5.0 mA to deliver 15 C of charge? (Ans. 3000 s)

53.   What is the potential difference between two points if 1.0 kJ of work is required to move 0.5 C of charge between the two points? (Ans. 2000 V)

54.   What is the voltage of a source which provides 12.0 J to each Coulomb of charge present?

55.   What is the potential difference between two points when a charge of 80.0 C has 4.0 x 10^3J of energy supplied to it as it moves between the two points? (Ans. 50 V)

56.   There is a current of 0.50 A through an incandescent lamp for 5.0 min, with a voltage of 115 V. How much energy does the current transfer to the lamp? What is the power rating of the lamp? (Ans. 17250 J, 57.5 W)

57.   If there is a current of 2.0 A through a hair dryer transferring 11 kJ of energy in 55 s, what is the potential difference across the dryer? (Ans. 100 V)

58.   An electric drill operates at a potential difference of 120V and draws a current of 6.0 mA. If it takes 40 s for the drill to make a hole in a piece of wood, how much energy is used by the drill? (Ans. 28.8 J)

59.   An electric toaster operating at a potential difference of 115 V uses 3220 J of energy during the 20 sec it is on. What is the current through the toaster? (Ans. 1.4 A)

60.   A motor draws a current of 2.0 A for 20.0 sec in order to lift a small mass of 500 g. If the motor does a total of 9.6 kJ of work calculate the voltage drop across the motor. (Ans. 240 V)

61.   In a lightning discharge, 30.0 C of charge moves through a potential difference 108 V in 20 minute. Calculate the current of the lightning bolt. (Ans. 0.025 A)

62.   How much energy is gained by an electron accelerated through a potential difference of 3.0 x 10^2 V? (4.8 x 10­-17 J)

63.   A 12V car battery can provide 6 A for 1.0 h. how much energy is stored in the battery? (Ans. 259200 J)

64.   a) Describe the difference between current in a series circuit and current in a parallel circuit.
        b) Describe the difference between voltage in a series circuit and voltage in a parallel circuit.

65.   Draw a schematic diagram of the following circuit: One power source and a resistor are connected in series with a combination of 3 light bulbs connected in parallel with each other. Include a fuse, 4 switches, a voltmeter, and an ammeter. The fuse should protect the whole circuit, one switch should shut off the whole circuit and the other switches should control the individual bulbs. The ammeter should read current drawn from power source and the voltmeter the voltage of the resistor.

66.   Describe the effect on the rest of the bulbs in the above problem when one burns out. Will the remainder glow brighter or dimmer? What will be the effect on the source?

67.   a) What is a short circuit? b) Why is it dangerous? c) Give two ways to protect against short circuits.

68.   A conductor has a length of 2.0 m and a radius of 3.0 mm. If the resistance is R = 100 Ω, calculate the new resistance if the same material has:
        a) length = 6.0 m and r = 6.0 mm (Ans. 75 Ω)
        b) length = 1.0 m and r = 1.0 mm (Ans. 450 Ω)

69.   List two ways to increase the current drawn by a circuit.

70.   A voltmeter measures a voltage drop of 60.0 V across a heating element while an ammeter reads the current through it as 2.0 A. What is the resistance of the heating coil? (Ans. 30Ω)

71.   How much current flows through a 7.5 W light bulb with a potential difference of 1.5 V? (Ans. 5A)

72.   A set of 6 identical motors are connected in series to a 120 V source drawing 1.0 A of current. Find:
       a) R total
       b) R of each motor
       c) Voltage drop across each load. (Ans. 120Ω, 20Ω and 20 V)

73.   A set of 6 identical motors are connected in parallel to a 150 V source drawing 1.2 A of current. Find:
        a) R total
        b) R of each motor
        c) Current through each motor
        d) Voltage drop across each load. (Ans. 125Ω, 750Ω, 0.2 A and 150 V)

74.   Do resistors in parallel increase or decrease total resistance?

75.   What resistance must be added in series to a circuit containing a 45 ohm resistor in order to draw 2.0 A of current from a 120V source? (Ans. 15 Ω)

76.   What makes the electric charge to flow?

77.   The V–I graph is a straight line that passes through the origin of the graph. What do you conclude from this observation?

78.   Define the commercial unit of energy. Relate it to joules.

79.   Discuss the activity to show that resistance of a conductor depends on its length and area of cross section.

80.   Which common factor affects both resistance as well as resistivity?

81.   Alloys are commonly used in electrical heating devices. Why?

82.   It is impracticable to connect an electric bulb and an electric heater in series. Why?

83.   What is heating effect of electric current? Name the various devices in which this effect is utilized.

84.   State the Joule’s law of heating. Derive the expression for the same.

85.   Which effect of current is responsible for the glow of an electric bulb? Explain.

86.   The bulbs are usually filled with few gases. Name those gases. Also discuss the cause for the same.

87.   Which metal is used as the filament of an electric bulb and why?

88.   How does a fuse work in the electric circuit?

89.   Which materials are preferred for a fuse wire and why?

90.   Give the ratings of various fuses used in the domestic circuit.

91.   A torch bulb is rated at 3V and 600mA. Calculate it’s a) Power b) Resistance c) Energy consumed if it is lighted for 4 Hrs. (Ans. 1.8 W, 5 Ω, 0.0072kWh/25920 J)

92.   Which will offer more resistance a 50W lamp or 25W lamp bulb and how many times? (ans. 25 W, 2 times)

93.   Why should the heating element of an electric iron be made of iron, silver or Nichrome wire?

94.   If a wire is stretched to triple its original length, what happens to its resistivity?

95.   Two identical resistors each of resistance 10 ohm are connected 1) in series 2) in parallel, in line to a battery of 6volts. Calculate the ratio of power consumed in the combination of resistors in the two cases. (Ans. 1:4)

96. A bulb is rated at 220V- 100W. What is its resistance? Five such bulbs burn for 4 hrs. What is the energy consumed? Calculate the cost if the rate is Rs. 5 per unit? (Ans. 484 Ω 2kWh, Rs 10)

97.   Two lamps rated 100W, 220V and 120W, 220V are connected in parallel to 220V supply. Calculate the total current through the circuit. (Ans. 1 A)

98.   How does the resistance of wire change when 1) Its length is doubled 2) Area is doubled?

99.   A wire of resistance 10ohm is bent in the form of a closed circle. What is the effective resistance between the two points at the end of any diameter of the circle? (Ans. 2.5 Ω)

100.  When resistances are connected in series, which physical quantity remains constant?

101.  When resistances are connected in parallel, which physical quantity remains constant?

102.  Resistance of an incandescent filament of lamp is more than that when it is at the room temperature. Why?

103.  The length of a wire is doubled and its cross sectional area is also doubled. What is the change in its (i) resistivity (ii) resistance?

104.  Name two characteristics of a heating element wire.

105.  For an electric iron of 1kW rating at 220V, fuse of how much capacity is to be used? (Ans. 5A)

106.  What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?

107.  How can three resistors of resistances 2Ω, 3Ω and 6Ω be connected to give a total resistance of (a) 4Ω (b) 1Ω ?

108.  Why does the cord of an electric heater not glow while the heating element does?

109.  Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50V. (Ans. 4800 kJ)

110.  An electric iron of resistance 20 Ω takes a current of 5A. Calculate the heat developed in 30 s. (Ans. 15 kJ)

111.  What determines the rate at which energy is delivered by current?

112.  An electric motor takes 5A from a 220 V line. Determine the power of the motor and the energy consumed in 2 hours. (Ans. 1.1 kW, 2.2 kWh)

113.  A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then obtain the ratio of .

114.  An electric bulb is rated 220 V and 100 W. What will be the power consumed when it is operated on 110 V ? (Ans. 25 W)

115.

V-I graph for two conductors A and B obeying Ohm’s law is given in figure 4. Which conductor has more resistance?

116.

V-I graph for parallel and series combination of two metallic resistors is shown as in figure 5. Which graph represents the parallel combination? Justify your answer.

117.  Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then connected in parallel in a circuit across the same potential difference. Obtain the ratio of heat produced in series and parallel combination. (Ans. 1:4)

118.  How many 176 Ω resistors in parallel are required to carry 5 A on a 220 V line? (Ans.4 resistors)

119.  Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A? (Ans. 110 bulbs)

120.  Compare the power used in the 2Ω resistor in each of the following circuits:
        (i) a 6 V battery in series with 1Ω and 2Ω resistors, and
        (ii) a 6 V battery in parallel with 12 Ω and 2Ω resistors. (Ans. 8W, 18 W)

121.  Which uses more energy, a 250 W TV set in 1 hour, or a 1200 W toaster in 10 minutes?

122.  An electric heater of resistance 8Ω draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater. (Ans. 1800 W)

123.  (i) State the formula showing how the current I in a conductor varies when the potential difference V applied across it is increased stepwise.
        (ii) Show this relationship on a schematic graph.
        (iii) Calculate the resistance of a conductor if the current flowing it is 0.2 A, when the applied potential difference is 0.8V.

124.  A torch bulb is rated 2.5 V and 750 mA. Calculate 
         (i) its power, 
         (ii) its resistance, and 
         (iii) the energy consumed if this bulb is lighted for 4 hours.                                                 (Ans. 1.875 W, 3.3Ω, 0.0075kWh)

125.  A wire of resistance 4Ω is doubled on it. Calculate the new resistance of the wire. (Ans. 1Ω)


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