Page 27 - Physics - XII

Q3. The current in a potentiometer wire is adjusted to give a null point at 56 cm with a standard
cell of 1.02 V. The emf of another cell for which a null point at 70 cm is

(a) 1 V (b) 1.02 V (c) 1.275 V (d) 1.5 V
Q4. Potentiometer is an electrical measuring device which measures

(a) E.M.F. of the cell (b) Internal resistance of the cell
(c) Both (a) and (b) (d) None of these

Answer key

1. (c), 2. (b), 3. (c), 4. (c)

Assertion-Reason Type Questions

These consist of two statements—Assertion (A) and Reason (R). Answer these questions by selecting
the appropriate option given below:
a. Both A and R are true and R is the correct explanation of A.

b. Both A and R are true and R is not the correct explanation of A.
c. A is true but R is false.
d. A is false but R is true.

1. Assertion (A) : In balanced condition of a Wheatstone bridge, there is no current fl ow through
the galvanometer.
Reason (R) : The potential of point B and D are same.
2. Assertion (A) : The balancing point of a metre bridge is obtained at L = 40 cm. When the area

of cross-section of the wire is doubled, the balancing point shifts to L = 60 cm.
Reason (R ) : Resistance of wire is directly proportional to its area of cross-section.
3. Assertion (A) : Metre bridge wire is generally made of Constantan.

Reason (R) : Constantan has a very low temperature coeffi cient of resistance.
4. Assertion (A) : In balanced condition, if the galvanometer and the voltage source is interchanged,
the balanced condition remains same.
Reason (R) : The balanced condition of Wheatstone bridge does not depend on the value of

the resistances.
5. Assertion (A) : The connecting wires are made of copper.
Reason (R) : Copper has a very high electrical conductivity.

Answer key

1. (a), 2. (d), 3. (a), 4. (c), 5. (a)

25