Electrostatic Potential and Capacitance — Physics STD 12 Science — Question

The wave front due to a source situated at infinity is:

An electron enters a magnetic field whose direction is perpendicular to the velocity of the electron. Then(a) The speed of the electron will increase(b) The speed of the electron will decrease(c) The speed of the electron will remain the same(d) The velocity of the electron will remain the same

A river is flowing from west to east at a speed of 5 metres per minute. A man on the south bank of the river, capable of swimming at 10 metres per minute in still water, wants to swim across the river in the shortest time. He should swim in a direction:

1. Due north.
2. 30° east of north.
3. 30° north of west.
4. 60° east of north.

To get line spectrum, the substances are excited in their:

The vertical component of earth's magnetic field is zero at or The earth's magnetic field always has a vertical component except at the(a) Magnetic poles(b) Geographical poles(c) Every place(d) Magnetic equator

A particle of mass 'm' and charge 'q' enters in an uniform magnetic field B perpendicularly. The radius of its path will be :

Before using the tangent galvanometer, its coil is set in 

In a situation the contact force by a rough horizontal surface on a body placed on it has constant magnitude. If the angle between this force and the vertical is decreased, the frictional force between the surface and the body will:

1. Increase.
2. Decrease.
3. Remain the saint.
4. May increase or decrease.

Coherent sources of light produce constructive interference while there is a phase difference between them is :