# Frequency of a ticker-timer

##### Class practical

This develops the idea of frequency, and explores accuracy of measurement.

#### Apparatus and materials

For each student group

Ticker-timer with power supply unit

Ticker-tape

Stopwatch or stopclock

#### Procedure

a Pull a tape steadily through the ticker-timer for a measured amount of time, such as 10 seconds. The dots should be just far enough apart for you to count them.

b Count how many dots were made in the measured time.

c Work out how many dots were made in each second. That is the frequency of the ticker-timer.

d Repeat this at least twice again. Do you get the same answer each time? How can you make your answer for the frequency as accurate as possible?

#### Teaching notes

1 The frequency for most types of ticker-timer is that of the mains, but don't tell pupils this until they have completed the exercise.

2 Ways of achieving an accurate result might include good experimental technique (such as starting and finishing the ticker timer and the timing together), and repeated results allowing calculation of an average.

3 When they are using a ticker-timer to analyze motions, students need to know the time interval between each dot. This time is the inverse of frequency. Mains frequency is 50 Hz, so the time interval between each dot is 1/50 s = 0.02 s.

Make sure that they count intervals and not dots. The first dot is effectively 0 on a scale of time.

This experiment was safety-checked in March 2005