Optional Practical: Falling magnet

Introduction

In this practical a magnet will be dropped through a coil of wire. As the magnet passes through the coil an EMF is induced that is measured using the data logger. The acceleration due to gravity will be calculated by measuring the time taken for the magnet to pass through the coil.

Method

Set up the apparatus as shown in the diagram. Connect the coil to the data logger and make some test runs to adjust the sampling rate and ensure everything is working properly. You should get a graph something like the one shown.

The peaks on the graph are caused when the rate of change of flux is at a maximum; this is when the magnet goes in and out of the coil. Using the time between the peaks and the length of the coil it is possible to measure the  average velocity of the magnet as it passes through the coil.

Applying the constant acceleration equations, the velocity of the magnet after falling a height h is given by

v2 = 2gh

By measuring the time for the magnet to pass through the coil as it is dropped from different heights use a graphical method to find g.

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