Potentiometer MCQ | Class 12 Physics |Enlight CBSE
Potentiometer MCQ | Class 12 Physics | Enlight CBSE
Q.1. A potentiometer does not:
A. Measure the emf of two cells
B. Measure the unknown temperature
C. Measure the cell Internal Resistance
D. Compare the emf of two cells
Answer: B. Potentiometer does not Measure the unknown temperature.
Explanation: A potentiometer is helpful in measuring the emf between two cells, comparing the EMFs, and measuring the unknown temperature in the circuit. However, a potentiometer is not capable of measuring the internal resistance of the cells.
Q.2. The length of wire in the potentiometer is 100 cm with a resistance of 30 ohms. It is connected in series with a resistance of 20 ohms and an accumulator of emf 8V having negligible internal resistance. 1.2 V source balances it against the length ‘L’ of the potentiometer wire. Calculate the length ‘L’ of the wire.
A. 30 cm
B. 35 cm
C. 20 cm
D. 25 cm
Answer: 25 cm
Explanation: Current through the wire, I = 8/(30+20) = 8/50 = 0.16 A
Potential difference across the wire:
V = current × resistance = 0.16 x 30 = 4.8 V
Length of the wire = 100 cm
Therefore, k = V / l
= 4.8/100 = 0.048
The EMF 1.2V is balanced against the length L of the wire, i.e. 1.2 = kL
Length = 1.2/k
= 1.2 / 0.048
= 25cm
Hence, L= 25 cm
Q.3. A potentiometer has 5 wires and the balance is obtained in the 2nd wire. If the balance is to be shifted to the 4th wire, the current should be reduced.
A. True
B. False
Answer: True
Explanation: When the balance has to be shifted to a higher length, the potential gradient should be reduced. This can be achieved by increasing the resistances (in series) with the potentiometer wire. This can thus be achieved by reducing the current flow in the circuit. Hence the above statement is true.
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