Question

A uniform magnetic field exists in the plane of paper point from left to right as shown in figure. In the field, an electron and a proton move as shown. The electron and the proton experience forces.

• A. Both pointing into the plane of paper
• B. Both pointing out of the plane of paper
• C. pointing into the plane of paper and out of the plane of paper, respectively
• D. pointing opposite and along the direction of the uniform magnetic field respectively.

Answer 1

The correct option is A Both pointing into the plane of paper

When a conductor carrying current is placed perpendicular to the direction of magnetic field, the force acing on it is given by Fleming's left hand rule. Since the direction of current is the same as that of the motion of a positive charge, the direction of force acing on it when it is moving perpendicular to the direction of magnetic field is the same a sthat acting on a current -carrying conductor placed perpendicular to the direction of magnetic field. Obviously, the force acting on an electron (which is negatively charged) is opposite to that acting on a positive charge while moving perpendicular to the direction of magnetic field. In this case, the force on the electron is directed into the page.