RP 3 - Determination of g

How can an electromagnet system be used to determine g?

A magnetic ball bearing can be released by an electromagnet clamped at a know height. Timing system starts when the electromagnet is switched off, and the timer is stopped when the ball lands on the finish pad.

Why does experimental value of g differ from the actual value?

Delays in timing Resitive forces may be significant Error in height measurement More likely to be lower than actual value due to resistive forces.

What is meant by free fall?

Motion under the influence of gravitational pull only

Why should there be a gap between the release position and the first light gate?

To ensure that the time in which the ball is passing the light gate is negligible

What safety precaution should you take when using an electromagent?

Turn it off when not in use to avoid overheating.

When using a clamp stand in this experiment, what safety precaution should be taken?

Use a counterweight of clamp the stand to the desk to prevent toppling

How should you ensure light-gates are positioned correctly

Use plumb line to show expected path of the ball

What is g?

acceleration due to gravity

Why it better to use a small ball-bearing over a larger one?

less air resistance

Required practical 3 graphs and calculations

○ Plot a graph of 2h/t against t and draw a line of best fit. The gradient will be g. ○ The y-intercept is 2u, where u is the speed of the ball bearing when it reaches the top light gate

Required Practical 3 equipment

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

Required practical 3 improvements and notes

○ 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.

Required Practical 3 method

○ 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.

Required practical 3 safety

○ Use a counterweight or clamp the stand to the table to avoid it toppling over and causing injury