Wave Optics — Physics STD 12 Science — Question

The layered lens is made of two kinds of glass. A point source of light is placed on its principal axis. If the reflections from the boundaries between layers are ignored, the lens will form

The temperature of an object is observed to rise in a period. In this period:

1. Heat is certainly supplied to it.
2. Heat is certainly not supplied to it.
3. Heat may have been supplied to it.
4. Work may have been done on it.

A parallel plate capacitor is first charged and then a dielectric slab is introduced between the plates. The quantity that remains unchanged is

(a) Charge Q

(b) Potential V

(c) Capacity C

(d) Energy U

What is the potential energy of the equal positive point charges of 1μC each held 1 m apart in air

(a) 9

(b) 9

(c) 2 eV/m

(d) Zero

A and B are two concentric circular conductors of centre O and carrying currents  and  as shown in the adjacent figure. If ratio of their radii is 1 : 2 and ratio of the flux densities at O due to A and B  is 1 : 3, then the value of   is

(a)

(b)

(c)

(d)

Force between two identical bar magnets whose centres are r metre apart  is 4.8 N, when their axes are in the same line. If separation is increased to 2r, the force between them is reduced to

(a) 2.4N

(b) 1.2N

(c) 0.6N

(d) 0.3N

The following four wires are made of the same material and are at the same temperature. Which one of them has highest electrical resistance

(a) Length = 50 cm, diameter = 0.5 mm	(b) Length = 100 cm, diameter = 1 mm
(c) Length = 200 cm, diameter = 2 mm	(d) Length = 300 cm, diameter = 3 mm

A current carrying coil is placed with its axis perpendicular to N-S direction. Let horizontal component of earth's magnetic field be H_o and magnetic field inside the loop is H. If a magnet is suspended inside the loop, it makes angle θ with H. Then θ =

(a)

(b)

(c)

(d)

The current in the given circuit is

(a) 8.31 A

(b) 6.82 A

(c) 4.92 A

(d) 2 A