Determination of g

Question 1

Equipment

Answer 1

○ Stand and clamp
○ Electromagnet
○ Steel ball bearing
○ Light gate
○ Stopwatch

Question 2

Method

Answer 2

○ Set up the apparatus as
shown in the diagram.

○ The position of the lower
light gate should be adjusted
such that the height h is
0.500m, measured using the
metre ruler.

○ Turn on the electromagnet and attach the ball bearing. Reset the stopwatch to zero and switch off the electromagnet. Read and record the time t on the stopwatch.

○ Reduce h by 0.050m by moving the lower light gate upwards and repeat this, reducing h by 0.050m each time down to 0.250m.

○ Repeat the experiment twice more and find and record the mean t for each h.

Question 3

● Graphs and calculations:

Answer 3

○ Plot a graph of 2h/t against t and draw a line of best fit. The
gradient will be g.

○ h=ut + 1/2 gt^2 - 2h/t = 2u + gt

○ The y intercept is 2u, where u is the speed of the ball bearing
when it reaches the top light gate (which we don’t need).

Question 4

Improvements

Answer 4

○ The distance between the upper light gate and the starting
position of the ball bearing must be kept constant so that it reaches the upper light gate with the same speed each time.

○ The ball bearing can be cushioned by a pad which is inside a
tray at the bottom of the clamp so it does not fall off
dangerously.

○ The ball bearing should be dense to help mitigate the effects
of air resistance.

○ To reduce parallax error in measuring the height, the ruler can
be clamped directly next to the light gates.