Question

A charged particle begins to move from the origin in a region which has a uniform magnetic field in the x-direction and a uniform electric field in the y- direction. Its speed is when it reaches the point (x, y, z) will depend

• A. Only on x
• B. Only on y
• C. On both x and y, but not z
• D. On x, y and z

Answer 1

The correct option is B

Only on y

Initially the particle will move along the y-axis due to the force exerted by the electric field; then it gets sent in the y-z plane as the magnetic field imparts a radial force. However the effect of the magnetic field is to only change the direction - not the magnitude of the particle’s velocity-which is affected only by the y-component of the electrical force. This component increases the value of the y co-ordinate of the particle. The longer the electric field operates, the higher the value of its speed i.e. speed depends only on y.