Q.

Under the influence of the Coulomb field of charge +Q, a charge q is moving around it in an elliptical orbit. Find out the correct statement(s).          [2009]

1 The angular momentum of the charge q is constant  
2 The linear momentum of the charge q is constant  
3 The angular velocity of the charge q is constant  
4 The linear speed of the charge q is constant  

Ans.

(1)

According to the question, under the influence of the Coulomb field of charge +Q, a charge -q is moving around it in an elliptical orbit. This situation is shown in the figure which is similar to a planet revolving around the Sun.

The distance of -q from +Q is changing; therefore, the force between the charges will change. The speed of the charge -q will be greater when the charge is nearer to +Q as compared to when it is far. Hence, the angular velocity of charge -q is not constant.

The direction of the velocity changes continuously; therefore, the linear momentum is not constant. The angular momentum of charge (-q) about Q is constant because the torque about charge +Q is zero.