# Force Generated From A Changing Magnetic Field

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Contents

## Introduction

In this experiment, we will study the force generated from a changing magnetic field. We will determine the induced magnetic force because of the changing magnetic field (Lenz law) by dropping a magnet on conducting metal tubes.

## Aim

To measure the induced magnetic force because of the change in a magnetic field.

## Theory

1. Lenz law states that the change in the direction of electric current is such that it always opposes the direction which has induced it.

2. Change in a magnetic field produces an induced electric current.

3. According to Faraday’s law, changing the magnetic field within a wire produces an electric current whose magnitude depends upon the changing magnetic field. When a bar magnet is brought toward a loop of wire, it increases the magnetic field in the loop When a bar magnet is moved away from a loop of wire, it decreases the magnetic field in the loop

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## Requirements

1. Two Neodymium-Iron-Boron (NIB) magnets of different magnetic strengths.

2. Aluminum and Copper tubes of length 0.91 meters.

3. Ammeter

## Procedure

Step 1: Drop two NIB magnets down on aluminum and copper tubes.

Step 2: As each magnet passes through the portion of the metallic tube, it will produce a changing magnetic field that will exert a magnetic force on the falling magnet to slow it down.

Step 3: Magnetic material will fall much slower than non-magnetic material due to this repulsion.

Step 4: Measure the magnetic force using Newton’s second law (F = ma) by joining the NIB magnets with a string connected to the cart that was pulled up on an incline ramp using a pulley as you drop down the magnet into the aluminum tube.

## Observation

1. The measured free-fall time of NIB magnets was 12.6 and 23.2 times greater than the reference weight of aluminum and copper tubing because of the Lenz law.

2. For copper tubes, the NIB magnet takes the longest time to fall, and it is also a good conductor as compared to aluminum. So, it will generate a large breaking force.

3. Mass of the cart, the magnetic force, and their velocity were experimentally found to be linear.

4. For a 0.635 cm thick aluminum tube, the measured force of the large NIB magnet was between 0.5 to 0.84 newtons, and the smaller NIB magnet was between 0.15 and 0.29 meters.

## Result

1. The greater NIB magnet and the thicker copper tube produces the larger magnetic force, which opposes the falling of the magnet and takes the longest time to fall.

2. Changing the tubing from aluminum to copper for a large NIB magnet increases the magnetic force from 0.94 to 1.8 newton.

3. When we drop the NIB magnet into the conductive metal tube, it establishes a changing magnetic field that produces the current and creates an induced magnetic field to oppose the falling of the magnet.

## Precaution

1. Use copper and aluminum tubes only.

## Conclusion

In this way, we have measured the force generated from a changing magnetic field, and we have measured the induced magnetic force because of the change in a magnetic field.

Q.1 What was the aim of your experiment?

ANS. To measure the induced magnetic force because of the change in a magnetic field.

Q.2 What do you understand about Lenz’s law?

ANS. Lenz law states that the change in the direction of electric current is such that it always opposes the direction which has induced it.

Q.3 A changing electric field produces what?

ANS. A changing electric field produces an induced current.

Q.4 A changing magnetic field produces what?

ANS. A changing magnetic field creates an induced current into the wire.

Q.5 What was the result of your experiment?

ANS. When we drop the NIB magnet into the conductive metal tube, it establishes a changing magnetic field that produces the current and creates an induced magnetic field to oppose the falling of the magnet.

Q.6 What is the formula for Lenz’s law?

ANS. ε = -Ndჶ/dt

where N is the number of turns in the coil,

dჶ is the induced emf,

dt is the change in time, and

ε is induced electromotive force.