Atoms — Physics STD 12 Science — Question

Why is it easier to swim in sea water than in fresh water?

A room is illuminated by an extended source. The illuminance at a particular portion of a wall can be increased by:

1. Moving the source.
2. Rotating the source.
3. Bringing some mirrors in proper positions.
4. Changing the colour of the source.

Light from a point source falls on a small area placed perpendicular to the incident light. If the area is rotated about the incident light by an angle of 60°, by what fraction will the illuminance change?

"For any charge configuration, equipotential surface through a point is normal to the electric field." Justify.

The instantaneous current and voltage of an a.c. circuit are given by
i = 10 sin 300t A and v = 200 sin 300t V
What is the power dissipation in the circuit?

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.

An illuminated object is placed on the principal axis of a converging lens so that a real image is formed on the other side of the lens. If the object is shifted a little,

1. The image will be shifted simultaneously with the object.
2. The image will be shifted a little later than the object.
3. The image will be shifted a little earlier than the object.
4. The image will not shift.

Define the term 'stopping potential' in relation to photoelectric effect.

How are infrared waves produced?

An air bubble is formed inside water. Does it act as a converging lens or a diverging lens?