IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

# Magnetic Force on a Current Carrying Conductor

## Objective

To study magnetic force on a current carrying conductor.

## Introduction

The force on a current carrying wire placed in a magnetic field is given by $$\vec{F}=i\vec{l}\times\vec{B}$$.

## Apparatus

a strip of aluminium foil, two ring magnets, a battery, connecting wires.

## Procedure

Take about 1 cm wide and 10 cm long aluminium foil. The kitchen foil works very well. On a flat wooden surface, tape about 2 cm of the strip from each end. The middle portion should be very loose. Press this portion to touch the surface at the middle. Place two ring magnets in vertical position on the sides of the strip so that their magnetic filed at the strip adds up. Thus, the magnetic field is perpendicular to the length of the strip and horizontal. Now connect the two ends of the strip to battery through a switch.

Press the switch and see what happens to the strip. Did the middle portion jump? If not, reverse the direction of current. Now, it will jump up.

## Discussion

The current and magnetic field are both in horizontal plane. Hence, the force on the middle portion is vertical. For one direction of the current, force will be upward and for another direction, it will be downward. You can also change the direction of magnetic force by changing direction of the magnetic field.