Cells, Emf, and Internal Resistance MCQ

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Cells, emf and internal resistance are all components of an electrical circuit. A cell has both emf and internal resistance and thus are interrelated to one another. Cells, emf and Internal resistance topic is part of Class 12 Physics Chapter 3 Current Electricity.

Cell: It is the electrical component which supplies electricity to the electric circuit. A cell converts chemical energy into electrical energy.
Emf: Emf or Electromotive force is a force that is developed from the source which is used to drive the charges from one point to another. It is denoted by the symbol ε.
Internal Resistance: Every component in an electrical circuit has an internal resistance that is due to the material in which it is made. This resistance reduces the amount of current flowing through the circuit.

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MCQs on Cells, emf, Internal Resistance

Ques. What is the dimensional formula of emf?

[M¹L²T^-³A^-1]
[M¹L³T^-³A^-1]
[M¹L³T^-³A^-2]
[M¹L²T²A^-2]

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Ans. a

Explanation: Emf is a potential difference across the ends of the battery when no current is drawn from it. The dimensional formula emf (????) is the same as that of the potential difference.

The formula of potential difference is

V = W/q

where

q is the charge.
W is the work done

Dimensions of work is, [W] = [M¹L²T^-2]

Dimensions of charge is, [q] = [A¹T¹]

Therefore, the dimensional formula of emf is

[????]= [V] = [M¹L²T^-2] / [A¹T¹]

⇒ [????] = [ML²T^-3A^-1]

The SI unit of emf is Joule/Coulomb or JC^-1.

Ques. Which of the following factors does internal resistance not depend upon?

Distance between electrodes
Temperature of electrolyte
Nature of electrode and electrolyte
Area of electrode

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Ans. b

Explanation: Internal resistance of a cell depends on the distance of electrodes, nature of the material of the electrodes and area of electrodes. But it does not depend on the temperature of the electrolyte in any way.

Ques. A 3A current passes through an electric circuit for 5 minutes and 900 J of work is done. Find the emf.

2v
3v
5v
1v

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Ans. d

Explanation: Current = 3A

Time = 5 minutes = 300 sec

Work done = 900J

Power = Work done/time

Power = 900/300 = 3W

Power = emf x current

Emf = Power/ current

Emf = 3/3

Emf = 1V

Ques. The emf of a battery is 6v, current of 0.5A and internal resistance is 1 ohm. If the cell is connected to a resistor, find the resistance.

10 ohm
11 ohm
12 ohm
13 ohm

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Ans. b

Explanation: emf = 6v

Current = 0.5A

Internal resistance = 1 ohm

We know that,

I = e/R + r

0.5 = 6/ R + 1

R = 11 ohms

Ques. Which device is suitable to measure emf?

Voltmeter
Potentiometer
Multimeter
Galvanometer

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Ans.: b

Explanation: Potentiometer is a very sensitive device and can be used to measure accurate emfs. Unlike a voltmeter, a potentiometer does not draw current from the circuit.

Ques. What is the value of internal resistance of an ideal cell?

1v
2v
3v
0v

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Ans. d

Explanation: An ideal cell should be such that it should offer no resistance in the electric circuit.

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Ques. Which of the following has the highest internal resistance?

Voltmeter
Potentiometer
Multimeter
Galvanometer

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Ans. a

Explanation: Voltmeter is a device that is used for measuring the potential difference between 2 points in a circuit. In an ideal condition, the voltmeter should not draw any current from the circuit. Therefore it should have the maximum resistance among the given options.

Ques. How much electricity can one solar cell produce?

0.8W
0.6W
0.7W
0.1W

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Ans. c

Explanation: A standard solar photovoltaic cell can produce 0.7 Watts of electricity.

Ques. A battery converts ____ energy into electrical energy

Mechanical
Chemical
Solar
Hydro

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Ans. b

Explanation: A typical battery converts chemical energy into electrical energy by the use of cathode, anode and electrolyte through the process of electrolysis.

Ques. What will be the potential difference if a cell of emf E and internal resistance

r is connected to resistor of resistance r?

E
E/2
2E
4E

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Ans. b

Explanation: We know that, E-V = Ir

By Ohms law,

V = Ir

Substituting V,

E - Ir = Ir

E = 2Ir

I = E/2r

From Ohm’s law,

V = E/2r x r

V = Er/2r

Thus,

V = E/2

Ques 11. What is the purpose of connecting cells in parallel?

Increase internal resistance
Increase voltage output
Increase current capacity
Decrease current capacity

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Answer: d

Explanation: When cells are connected in parallel, the voltage remains constant, internal resistance decreases and current capacity increases.

Ques. In a dry cell, the cathodic material is usually?

MgO
MgBr
MnO₂
ZnO

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Ans. c

Explanation: In a dry cell, the following are the components.

Anode - Zinc

Cathode - Graphite rod (carbon)

Cathodic material - Manganese oxide and carbon

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