## Measurement of the Acceleration Due to Gravity Using an Electromagnet and Trap Door

Apparatus:

Electromagnet free fall apparatus with timer and metre rule.

Diagram (simplified): Procedure:

1. Wire up the apparatus.

2. Set height to be about 30 cm. Record the actual value of h.

Then do the following in the order specified.

(a) press the switch closed (and keep it closed until stage (e))

(b) close the gate of the trap door

(c) reset the timer to zero (it should stay at zero until stage (e))

(d) attach the ball bearing to base of electromagnet (it should hold)

(e) release the switch

3. If the apparatus works correctly the timer should record the time taken for the ball bearing to fall from the electromagnet to the trap door. If this does happen; record time t.

If the above does not happen; then check your wiring and try again.

4. Repeat once more and in order to obtain an average value for t at height h.

5. Repeat the above for four more different values of h.

6. For each of the five heights calculate the average value of t and the average value of t2. Tabulate your results clearly.

7. Plot a graph of ( - axis) against ( - axis). It should be a straight line. Measure the gradient of your graph.

8. The acceleration of free fall, should be equal to twice the value of your gradient. Calculate your value of 9. Use the equation to explain why the gradient of your graph, m should be equal to [Hint: notice that and ]

10. Your value of g is probably about 8.5 m/s 2 . Explain why it is less than the accepted value of 9.8 m/s 2 .