Wave Optics — Physics STD 12 Science — Question

Photoelectric effect was successfully explained first by:

The length of a solenoid is 0.4m and the number turns in it is 500. A current of 3 amp, is flowing in it. In a small coil of radius 0.01m and number of turns 10, a current of 0.4 amp. is flowing. The torque necessary to keep the axis of this coil perpendicular to the axis of solenoid will be:

The net resistance of an ammeter should be small to ensure that:

1. It does not get overheated.
2. It does not draw excessive current.
3. It can measure large currents.
4. It does not appreciably change the current to be measured.

Electron and proton beams are travelling parallel to each other in the same direction. There will be ___________ between them.

What causes changes in the colours of the soap or oil films for the given beam of light

(a) Angle of incidence

(b) Angle of reflection

(c) Thickness of film

(d) None of these

A short magnetic needle is pivoted in a uniform magnetic field of strength 1 T. When another magnetic field of strength   is applied to the needle in a perpendicular direction, the needle deflects through an angle q, where q  is

(a) 30o

(b) 45o

(c) 90o

(d) 60o

For the propagation of light wave, medium is required. This is according to:

The height of a T.V. transmission tower at any place on the surface of the earth is 245 m. The maximum distance upto which transmission of tower will reach is :

A molecule with a dipole moment p is placed in an electric field of strength E. Initially the dipole is aligned parallel to the field. If the dipole is to be rotated to be anti-parallel to the field, the work required to be done by an external agency is

(a) – 2pE

(b) – pE

(c) pE

(d) 2pE

In a photo cell, the photo-electrons emission takes place

(a) After 10–1 sec on incident of light rays

(b) After 10–3 sec on incident of light rays

(c) After 10–6 sec on incident of light rays

(d) After 10–8 sec on incident of light rays