Cambridge International AS and A level Physics
Stopwatch
Top pan balance
Protractor
Measuring cylinder A
Analogue voltmeter
Analogue thermometer
Micrometer
Callipers
30 cm ruler
Metre rule
2 Copy and complete this table, giving units for any values. Include columns for all instruments that you have available or for which there is a diagram in your textbook.
Is there a possibility of a zero error? What is the smallest scale division? What is the uncertainty (assume no zero error)? What is the largest possible reading? What is the percentage uncertainty in the largest possible reading?
Exercise P1.2 Finding the uncertainty in a reading 220
This exercise considers different uncertainties in measurements and how they arise. Calculated quantities should be given to the same number of significant figures as (or one more than) the measured quantity with the least accuracy, except when produced by addition or subtraction. 1 When a student hears the starting pistol at the start of the race, he starts his stopwatch and stops it as he sees a runner crossing the finishing line. The reading on the stopwatch is 26.02 s. a Suggest the value that the student should write down as his best estimate for the time and for the uncertainty in the time, based on only one reading. b Three other students also record the same time and the readings on their stopwatches are: ●
25.90 s
●
26.34 s
●
26.14 s.
Calculate the mean value of all four readings and an estimate of the uncertainty of the time. c The true value of the time is 26.40 s. Explain how this value shows that the students’ readings have a systematic error. d Suggest one cause of a systematic error and one cause of a random error in the readings. 2 A student times a number of oscillations of a ball along a track. one complete oscillation ball