Model Paper 3 — Physics STD 12 Science — Question

The resistance of a wire of iron is 10 ohms and temp. coefficient of resistivity is  5 . At  20 it carries 30 milliamperes of current. Keeping constant potential difference between its ends, the temperature of the wire is raised to 120. The current in milliamperes that flows in the wire is

(a) 20

(b) 15

(c) 10

(d) 40

In rear-wheel drive cars, the engine rotates the rear wheels and the front wheels rotate only because the car moves. If such a car accelerates on a horizontal road, the friction:

1. On the rear wheels is in the forward direction.
2. On the front wheels is in the backward direction.
3. On the rear wheels has larger magnitude than the friction on the front wheels.
4. On the car is in the backward direction.

An ammeter gives full scale deflection when current of 1.0 A is passed in it. To convert it into 10 A range ammeter, the ratio of its resistance and the shunt resistance will be

(a) 1 : 9

(b) 1 : 10

(c) 1 : 11

(d) 9 : 1

The unit of magnetic moment is

(a) Wb/m

(b)

(c) A.m

(d)

If  is the original mass of the substance of half life period   years, then the amount of substance left after 15 years is

(a)

(b)

(c)

(d)

The slit of a collimator is illuminated by a source as shown in the adjoining figures. The distance between the slit S and the collimating lens L is equal to the focal length of the lens. The correct direction of the emergent beam will be as shown in figure

(a) 1	(b) 3
(c) 2	(d) None of the figures

In a transformer, the coefficient of mutual inductance between the primary and the secondary coil is 0.2 henry. When the current changes by 5 ampere/second in the primary, the induced e.m.f. in the secondary will be

(a)  5 V

(b) 1 V

(c)  25 V

(d) 10 V

The current carrying wire and the rod AB are in the same plane. The rod moves parallel to the wire with a velocity v. Which one of the following statements is true about induced emf in the rod

(a) End A will be at lower potential with respect to B

(b) A and B will be at the same potential

(c) There will be no induced e.m.f. in the rod

(d) Potential at A will be higher than that at B

A man wearing glasses of focal length +1m cannot clearly see beyond 1m:

1. If he is farsighted.
2. If he is nearsighted.
3. If his vision is normal.
4. In each of these cases.