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The difference between EMF and voltage is that the EMF is the potential difference measured across a power source without a load connected to it whereas voltage is the potential difference measured between any two points in a circuit. The article covers important MCQs on the Difference Between EMF and Voltage.
Difference Between EMF and Voltage
Ques 1: For accurate measurements, the resistance of a voltmeter should be
- infinite
- as small as possible
- as large a possible
- equal to the resistance across which potential difference is to be measured
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Answer: The correct answer is (c) as large as possible
Explanation: Voltmeter when connected across any circuit element should not draw any current from it. If the voltmeter resistance is not high as compared to the resistance of the circuit element, across which it is connected, the measured voltage becomes less. Thus the resistance of the voltmeter should be as large as possible.
Ques 2: If a wire of resistance 2Ω is covered with ice and a voltage of 210V is applied across the wire, then the rate of melting ice would be
- 0.85g/s
- 1.92g/s
- 6.56g/s
- none of the above
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Answer: The correct answer is (c) 5.56g/s
Explanation: The rate at which heat is produced in the wire is heat/time = V2/R = 2205Js−1
Latent heat of ice = 80c/gm = 80x4.2J/gm
Hence rate of melting ice would be = 2205/80X4.2 = 6.56g/s
Ques 3: If the ammeter shows a reading of 10A and the voltmeter having internal resistance of 3000 Ω measures a voltage of 200V, the resistance R is given by
- 201.3 Ω
- 2013 Ω
- 20.13 Ω
- 20.00 Ω
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Answer: The correct answer is (c) 20.13 Ω
Explanation: Applying Ohm’s law in section PQ
V=IR
The resistances, R and internal resistance of the voltmeter are connected in parallel
I/V = 1/R + 1/Rv
or
1/R = I/V − 1/Rv
Thus, R = V/I−V/Rv
putting the respective values and calculating we find R=20.13Ω
Ques 4: Two battery having unequal emf
- cannot be connected in parallel.
- cannot be connected in series.
- both a and d
- can be connected in series only
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Answer: The correct answer is (c) both a and d
Explanation: We cannot connect the two batteries in parallel, when they have unequal voltage. If we connect them in parallel, then the low voltage battery will be charged by the high voltage battery. So, there is a chance of causing damage to the circuit. But, if we connect them in series, then both voltages are added together and we get that added voltage at output side. Hence, two batteries having unequal voltage can be connected in series only.
Ques 5: When the battery is being charged, the terminal voltage decreases with
- increasing charging rate
- increasing temperature
- increasing state of charge
- none of these
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Answer: The correct answer is (b) increasing temperature
Explanation: Whenever a battery is being charged, the terminal voltage of the battery changes a small amount whenever the battery temperature changes. As the battery temperature increases, its terminal voltage decreases or as the terminal voltage decreases, its temperature increases. This is usually called as temperature compensation in a storage battery.
Ques 6: The induced voltage will oppose the flux producing it. State True/False.
- True
- False
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Answer: The correct answer is (a) True
Explanation: According to Lenz law, the induced voltage acts in such a way that it opposes the flux producing it. This is indicated by a negative sign.
Ques 7: Calculate the emf when a coil of 100 turns is subjected to a flux rate of 0.3 tesla/sec.
- 3
- 30
- -30
- -300
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Answer: The correct answer is (c) -30
Explanation: The induced emf is given by Vemf = -dλ/dt = -Ndψ/dt. Thus emf will be -100 x 0.3 = -30 units.
Ques 8: According to Faraday’s law, EMF stands for
- Electromagnetic field
- Electromagnetic force
- Electromagnetic friction
- Electromotive force
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Answer: The correct answer is (d) Electromotive force
Explanation: The force in any closed circuit due to the change in the flux linkage of the circuit is called as electromotive force EMF. This phenomenon is called as Faraday’s law.
Ques 9: Calculate the emf when the flux is given by 3sin t + 5cos t
- 3cos t – 5sin t
- -3cos t + 5sin t
- -3sin t – 5cos t
- 3cos t + 5sin t
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Answer: The correct answer is (b) -3cos t + 5sin t
Explanation: The electromotive force is given by Vemf = -dλ/dt. Thus Vemf = -dλ/dt = -(3cos t – 5sin t) = -3cos t + 5sin t.
Ques 10: Two parallel plates are separated by a distance D charged by V volt. The field intensity E is given by,
- V × D
- V / D
- V × D²
- V² / D
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Answer: The correct answer is (b) V / D
Explanation: Electric field intensity between two points is always expressed as the potential difference between these two points divided by the distance between them. The strength of electric field or electric field intensity is measured by volt per meter or newton per meter.
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