Electromagnetic Waves — Physics STD 12 Science — Question

A light ray is incident by grazing one of the face of a prism and after refraction ray does not emerge out, what should be the angle of prism while critical angle is C

(a) Equal to 2C

(b) Less than 2C

(c) More than 2C

(d) None of the above

Solid targets of different elements are bombarded by highly energetic electron beams. The frequency (f) of the characteristic X-rays emitted from different targets varies with atomic number Z as

(a) f ∝

(b) f ∝

(c) f ∝ Z

(d) f ∝

Arrange the following in the increasing order of magnetic susceptibility.

A barometer kept in an elevator reads 76cm when it is at rest. If the elevator goes up with increasing speed, the reading will be:

1. zero.
2. 76cm.
3. < 76cm.
4. > 76cm.

Three electric bulbs of rating 60W each are joined in series and then connected to electric mains. The power consumed by these three bulbs will be

(a) 180 W

(b) 60 W

(c) 20 W

(d)

The forces in which sum of kinetic energy and potential energy is conserved are called as:

An object 1 cm tall is placed 4cm infront of a mirror. In order to produce an upright image of 3cm  height one needs a

(a) Convex mirror of radius of curvature 12 cm

(b) Concave mirror of radius of curvature 12 cm

(c) Concave mirror of radius of curvature 4 cm

(d) Plane mirror of height 12 cm

A point source of light is used in an experiment on photoelectric effect. Which of the following curves best represents the variation of photo current (i) with distance (d) of the source from the emitter

(a) a

(b) b

(c) c

(d) d

In a transistor, a change of 8.0 mA in the emitter current produces a change of 7.8 mA in the collector current. What change in the base current is necessary to produce the same change in the collector current

(a) 50 mA

(b) 100 mA

(c) 150 mA

(d) 200 mA