CBSE Class 10 Physics Electricity Worksheet

Question : Two resistors of resistances 2 Ω and 4 Ω when connected to a battery will have
a) Same current flowing through them when connected in parallel
b) Same current flowing through them when connected in series
c) Same potential difference across them when connected in series
d) None of these
Answer : B

Question : The resistance of an electric iron drawing a current of 4A when connected to a 220V mains would be
a) 1000 Ω
b) 55 Ω
c) 44 Ω
d) 64 Ω
Answer : B

Question : If 25 joule of work is done in moving a charge of 5C across two points A and B the potential difference between these points would be
a) V
b) 125V
c) 5V
d) 625V
Answer : C

Question : Ohm’s law states the relationship between
a) Electric current and heat produced in it
b) Electric power and work done
c) Electric current and potential difference
d) Electric current and electric charge
Answer : C

Question : If electrons flow from A to B, current will flow from
(a) A to B
(b) B to A
(c) It will not flow
(d) None of these
Answer : B

Question : Unit of electric power may also be expressed as
a) Volt ampere
b) Kilowatt hour
c) Watt second
d) Joule second
Answer : A

Question : Electric current flows from ‘A’ to ‘B’ in metallic conductor. The point is at higher potential is
(a) A
(b) B
(c) Both have equal potential
(d) Both have lower potential
Answer : A

Question : When a 4V battery is connected across an unknown resistor there is a current of 100 mA in the circuit.
The value of the resistance of the resister is:
(a) 4 Ω
(b) 40 Ω
(c) 400 Ω
(d) 0.4 Ω
Answer : B

Question : In an electric circuit three incandescent bulbs of rating 40W, 60W and 100W respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness
a) Brightness of all the bulbs will be the same
b) Brightness of bulb A will be the maximum
c) Brightness of bulb B will be more than that of A
d) Brightness of bulb C will be less than that of B
Answer : C

Question : Electrical resistivity of a given metallic wire depends upon
(a) its length
(b) its thickness
(c) its shape
(d) nature of the material
Answer : D

Question : The unit of resistivity is
a) Ohm
b) Ohm metre²
c) Ohm metre
d) Ohm per metre
Answer : C

Question : The resistivity does not change if
a) The material is changed
b) The temperature is changed
c) The shape of the resistor is changed
d) Both material and temperature are changed
Answer : C

Question : An electric kettle consumes 1kW of electric power when operated at 220V. The rating of fuse wire that must be used would be
a) 1A
b) 2A
c) 4A
d) 5A
Answer : D

Question : A cylindrical conductor of length l and uniform area of cross section A has resistance R. Another conductor of length 2l and resistance R of the same material has area of cross section
a) A / 2
b) 3A / 2
c) 2A
d) 3A
Answer : C

Question : Two students (A) and (B) connect their two given resistors R₁ and R₂ in the manners shown below :

Student (A) connects the terminal marked (b₁) and (c₁) while student (B) connects the terminals marked (d₂) and (c₂) in their respective circuits at the points marked X and Y.

Which one of the following is correct in relation to above arrangements? 

 

a. Student (A) will determine the equivalent resistance of the series combination while student (B) will determine the equivalent resistance of the parallel combination of the two resistors.

b. Both the students will determine the equivalent resistance of the parallel combination of the two resistors.

c. Both the students will determine the equivalent resistance of the series combination of the two resistors.

d. Student (A) will determine the equivalent resistance of the parallel combination while student (B) will determine the equivalent resistance of the series combination of the two resistors.

Answer : A 

Explanation: R₁ and R₂ has one common point in (A) and two common points in (B).

 

Question :  Match the following with the correct response: 

(1) Electric current                                                         (A) Ammeter

(2) Small deflection in the circuit                                     (B) Battery

(3) Maintains potential difference between two points       (C) Galvanometer

(4) Variable Resistance                                                   (D) Rheostat

a. 1-B, 2-D, 3-A, 4-C

b. 1-C, 2-B, 3-D, 4-A

c. 1-A, 2-C, 3-B, 4-D

Assertion and reasoning questions

The following questions consists of two statements –Assertion(A) and Reason (R). Answer these questions selecting the appropriate option given below.
a) Both A and R are true and R is the correct explanation for A
b) Both A and R are true and R is not the correct explanation for A
c) A is true but R is false
d) A is false but R is true.

Question : Assertion (A): If a graph is plotted between potential difference and current the graph is a straight line passing through the origin.
Reason(R): current is directly proportional to the potential difference.
Answer : A

Question : Assertion (A): Longer wires have greater resistance and the smaller wires have lesser resistance.
Reason(R): Resistance is inversely proportional to the length of the wire.
Answer : C

Question : Assertion (A): A cell converts chemical energy into electrical energy.
Reason(R): A cell maintains a potential difference across its terminals due to chemical reactions.
Answer : B

Question : Assertion (A): Alloys are commonly used in electrical heating devices.
Reason(R): Alloys do not oxidize at high temperatures.
Answer : A

Question : Assertion (A): When resistances are connected between the same two points they are said to be in series.
Reason(R): When resistors are connected in series the current through each resistor is the same.
Answer : D

Very Short Answers

Question : Define resistance. Give its S.I. unit.
Answer : Resistance is the property of a conductor to oppose the flow of charges through it. SI unit of resistance is Ohm (Ω).  

Question : What will happen to the resistivity of a wire of length L if it is cut into three parts?
Answer : Resistivity of the wire will not change even when the wire is cut into three parts as resistivity is a characteristic of the material of the conductor and does not depend on the physical dimensions of the conductor.

Question : The potential difference across the wire having fixed resistance is tripled. By how much does the electric power increase?
Answer :  The electric power will increase by nine times when the potential difference across the wire having fixed resistance is tripled. According to Ohm’s law, potential difference V is proportional to current, I. Therefore, when V is made 3 times, I will increase 3 times. As Power P = VI, therefore, Power will increase by 9 times. 

Short Answers

Question :  Find the minimum rating of fuse that can be safely used on a line on which two 1.1 KW electric geysers are to run simultaneously.
The supply voltage is 220 V.
Answer : Power P = VI. As the two geysers have power rating 1.1 kW or 1100 W and are connected in parallel, each geyser draws a current I = P/V =
1100/220 A = 5 A. 

Question : The electric power consumed by a device may be calculated by either of the two expressions P = I2R or P = V₂/R. The frist expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality. How can the seemingly different dependence of P on R in these expressions be explained? 
Answer :  The expression P = I2R is used for calculating electric power when only current I and resistance R are known, whereas P = V₂/R is used for calculating power when voltage V and
resistance R are known.

Question : Why does the cord of an electric heater does not glow while heating element does? 
Answer : Heating effect = I²Rt
where I is the current flowing and R is the resistance and t is the time. Current is same in cord and in heating element. Resistance R of the cord is negligible since it is made of copper (which has very less resistivity) while heating element is made in nichrome whose resistivity is 6,000 times more than copper. Nichrome gets heated up much more than copper.

Question : How will the heat produced in a resistor R change if its resistance is reduced to half of its initial value, other parameters of the circuit remain unchanged?
Answer : The heat produced in a resistor R is given by Joule’s law of heating H = I2Rt, where I is the current and t is the time. When R becomes R/2, I will become 2I according to Ohm’s law.
Therefore, heat produced = (2I)2(R/2)t = 2H. The heat produced will become double.

Question : Why is parallel arrangement used in domestic wiring? 
Answer :  Parallel arrangement is used in domestic wiring due to the following reasons:
• Each device will have the same voltage which is equal to the voltage of the supply.
• If two or more devices are used at the same time, then each appliance will be able to draw the required current.
• If one of the devices fails, then the other keeps working.

Question : Draw a circuit diagram having the following components:
(a) Bulb (b) A two cell battery (c) Ammeter (d) A closed key
Answer : 

Question : (A) What is the resistance of a conductor?
(B) What happens to the electrical resistance when mercury is cooled to 4.12 k?
(C) What name is given to this phenomenon?
Answer :  (A) The property of a conductor due to which it opposes the flow of current through it is called resistance. The resistance of a conductor is numerically equal to the ratio of potential difference across its ends to the current flowing through it.
(B) When mercury is cooled to 4.12 K, the electrical resistance of mercury disappears completely and becomes zero and the mercury becomes super conductor.
(C) This phenomenon of loss of electrical resistance of a substance on cooling it to an extremely low temperature is known as superconductivity.

Long Answers

Question : Answer the following:
(A) Why ammeter is always connected in series?
(B) give dry cells each of 1.0 volt have internal resistance of 0.2, 0.3, 0.4, 0.5 and 1.2 ohms. When connected in series, what current will these five cells furnish through 10 ohm resistance?
Answer :  (A) An ammeter is used to measure the current flowing through a circuit. We know that current remains same in series connection. lso the resistance of an ammeter is verysmall due to which it doesn’t affect the current to be measured. So, an ammeter is always connected in series to measure current.
(B) Total voltage produced by the batteries
V = 5 x 1.5 = 7.5 V
Total resistance
R = R₁ + R₂ + R₃ + R₄ + R₅
R = (0.2 + 0.3 + 0.4 + 0.5 + 1.2) + 10
   = 12.6 W
Therefore, current
I  = V/R
   = 7.5/12.6 = 0.595 A.

Answer :  Let the current through the circuit be I which is divided into I₁ and I₂ in the arms AB and CD respectively, then we have

I = I₁ + I₂

In the arm AB, the total resistance is

R₁ =  6Ω + 3Ω = 9Ω

and the total resistance in the arm CD is

R₂   = 12Ω + 3Ω = 15Ω

i. Then current in the 6Q resistor i.e.,

 

Question : List two distinguishing features between the resistance and resistivity of a conductor. A wire is stretched so that its length becomes 6/5 times of its original length. If its original resistance is 25 W, find its new resistance and resistivity. Give justification for your answer in each case.
Answer : Resistance
(i) It is the ratio of voltage over current at a particular temperature.
(ii) Its S.I. unit is ohm.
(iii) It is the property of a conductor
Resistivity
(i) It is the resistance of a wire of length 1 m and area of cross section 1 m².
(ii) Its S.I. unit is ohm metre
(iii) It is the property of the material of the conductor
Since resistance is directly proportional to the length and is inversely proportional to the area of cross section.
∴ New Resistance:

When the wire is stretched, its length becomes 6/5 times of its original length, and area of cross-section will become 5/6. Resistivity will remain the same because it does not depend upon the length and area of cross section. It depends on the nature of material of the substance and the temperature.

Question : (i) Write an expression for the resistivity of a substance.
(ii) State the SI unit of resistivity.
(iii) Distinguish between resistance and resistivity.
(iv) Name two factors on which the resistivity of a substance depends and two factors on which it does not depend.
Answer : 1. (i) Resistivity (r) = RA/l
(ii) Its SI unit is W m.
(iii) Resistivity is a characteristic property of a material that does not depend upon the dimensions of the material whereas resistance depends upon the dimensions of the material.
(iv) Resistivity does not depend on the:
(a) length of conductor, (b) area of cross section of conductor Resistivity depends on the:
(a) nature of material of conductor (b) temperature of conductor

Question : 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 upto 120 V?
Answer : 12. V = 60 V, I = 4 A
R = V/I = 60/4 = 15Ω [By Ohm's Law; V = IR]
Now, V = 120 V, I = ? R = 15 Ω
I = V/R = 120/15 = 8A

Question : State Ohm’s law. Draw a labelled circuit diagram to verify this law in the laboratory. If you draw a graph between the potential difference and current flowing through a metallic conductor, what kind of curve will you get? Explain how would you use this graph to determine the resistance of the conductor.
Answer : Ohm’s Law: It states that ratio of potential difference and current is constant and is equal to the
resistance of the conductor at a particular temperature. In other words, the current flowing through a
conductor is directly proportional to the potential difference at a constant temperature.
The graph between V and I will be a straight line.
Slope = tan θ = ‘R’
Slope = BC/AC = R