Wave Optics — Physics STD 12 Science — Question

There is force of repulsion between two parallel current carrying conductors. What idea we get about direction of flow of current?

Light passes through a closed cylindrical tube containing a gas. If the gas is gradually pumped out, the speed of light inside the tube will:

1. Increase.
2. Decrease.
3. Remain constant.
4. First increase and then decrease.

Two converging lenses of unequal focal lengths can be used to reduce the aperture of a parallel beam of light without losing the energy of the light. This increases the intensity. Describe how the converging lenses should be placed to do this.

Power factor of an ac circuit is 0.5. What is the phase difference between current and voltage in the circuit?

Write the relation between threshold frequency and work function.

Choose the correct alternative from the clues given at the end of the each statement:
A classical atom based on .......... is doomed to collapse. (Thomson’s model/ Rutherford’s model.)

Light is incident normally on a small plane surface. If the surface is rotated by an angle of 30° about the incident light, does the illuminance of the surface increase, decrease or remain same? Does your answer change if the light did not fall normally on the surface?

Answer carefully:
Guess a possible reason why water has a much greater dielectric constant (= 80) than say, mica (= 6).