physics : class12 Balance Point : Potentiometer : Current Electricity MCQ Questions and Answers
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Balance Point
MCQ questions and answers.
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MCQ Questions
1. In a potentiometer, the balance point is the position where the galvanometer shows:
A.
Maximum deflection
B.
Zero deflection
C.
Constant deflection
D.
Reversed deflection
Correct Answer:
Zero deflection
Explanation:
At the balance point, no current flows through the galvanometer, so its deflection is zero.
2. At the balance point of a potentiometer, the potential difference across the unknown cell is equal to:
A.
The potential drop across the balancing length
B.
The total potential drop across the potentiometer wire
C.
Zero potential difference
D.
The resistance of the galvanometer
Correct Answer:
The potential drop across the balancing length
Explanation:
At balance, the emf of the unknown cell equals the potential drop along the length of wire up to the balance point.
3. If the balance point is found at a distance of 40 cm from the zero end of a potentiometer wire, the balancing length is:
A.
20 cm
B.
40 cm
C.
60 cm
D.
100 cm
Correct Answer:
40 cm
Explanation:
The distance from the zero end to the null point is called the balancing length.
4. For a uniform potentiometer wire, if the potential gradient is k and the balance point is at length l, the emf E of the cell is:
A.
E = k/l
B.
E = l/k
C.
E = kl
D.
E = k + l
Correct Answer:
E = kl
Explanation:
At balance, the emf equals the potential drop across the balancing length, so E = potential gradient × length = kl.
5. A cell gives a balance point at 50 cm on a potentiometer wire. If the potential gradient remains unchanged, what happens to the balance point for a cell having greater emf?
A.
It shifts toward the zero end
B.
It shifts toward the other end
C.
It remains at 50 cm
D.
It becomes zero
Correct Answer:
It shifts toward the other end
Explanation:
With the same potential gradient, a greater emf requires a greater balancing length, so the balance point moves farther from the zero end.
6. Two cells are compared using the same potentiometer. Cell P has a balance length of 30 cm and cell Q has a balance length of 60 cm. Which cell has the greater emf?
A.
Cell P
B.
Cell Q
C.
Both have equal emf
D.
Neither cell has emf
Correct Answer:
Cell Q
Explanation:
For the same potentiometer gradient, emf is proportional to the balancing length. Since cell Q has the longer balance length, it has the greater emf.
7. When the jockey is at the balance point, the potential difference between the corresponding point on the potentiometer wire and the cell terminal is:
A.
Zero
B.
Maximum
C.
Equal to the total wire voltage
D.
Equal to the galvanometer resistance
Correct Answer:
Zero
Explanation:
At balance, the two potentials are equal, so their potential difference is zero and no current flows through the galvanometer.
8. If the balancing length for a cell is increased while the potential gradient remains constant, the emf calculated for the cell will:
A.
Decrease
B.
Increase
C.
Remain zero
D.
Become independent of length
Correct Answer:
Increase
Explanation:
The emf is given by E = kl. With constant potential gradient k, increasing the balance length l increases the emf.
9. The balance point on a potentiometer wire is also called the:
A.
Null point
B.
Heating point
C.
Current point
D.
Resistance point
Correct Answer:
Null point
Explanation:
It is called the null point because the galvanometer shows zero deflection at this position.
10. A potentiometer has a potential gradient of 0.02 V/cm. If the balance point for a cell is at 25 cm, the emf of the cell is:
A.
0.5 V
B.
1.25 V
C.
12.5 V
D.
0.05 V
Correct Answer:
0.5 V
Explanation:
Using E = kl, the emf is E = 0.02 V/cm × 25 cm = 0.5 V.