Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Gauss’s law is true only if force due to a charge varies as

(a)

(b)

(c)

(d)

An isolated solid metallic sphere is given +Q charge. The charge will be distributed on the sphere

(a) Uniformly but only on surface

(b) Only on surface but non-uniformly

(c) Uniformly inside the volume

(d) Non-uniformly inside the volume

In a Young's double slit experiment, the fringe width is found to be 0.4 mm. If the whole apparatus is immersed in water of refractive index 4/3 without disturbing the geometrical arrangement, the new fringe width will be

(a) 0.30 mm

(b) 0.40 mm

(c) 0.53 mm

(d) 450 micron

At zero Kelvin a piece of germanium

(a) Becomes semiconductor	(b) Becomes good conductor
(c) Becomes bad conductor	(d) Has maximum conductivity

The impact of an image on the retina remains for

(a) 0.1 sec

(b)  0.5 sec

(c) 10 sec

(d)  15 sec

The radiant energy of the sun results from:

Light takes 8 min 20 sec to reach from sun on the earth. If the whole atmosphere is filled with water, the light will take the time    (a

(a) 8 min 20 sec

(b) 8 min

(c) 6 min 11 sec

(d) 11 min 6 sec

Assertion  : Television signals are received through sky-wave propagation.

Reason      :  The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Choose the correct answer from the alternatives given.
The conduction current is the same as displacement current when the source is.

The plates of a parallel plate capacitor of capacity 50 μC are charged to a potential of 100  volts and then separated from each other so that the distance between them is doubled. How much is the energy spent in doing so

(a) 25

(b) -12.5

(c) -25

(d) 12.5