Quick Quiz on Uncertainties

1.
	An experiment to measure the speed of a toy car is repeated several times. The results are similar but not identical. This could be due to approximate uncertainty.

2.
	The results of an experiment produce a straight line graph but it does not pass through the origin. This may be due to uncertainty.

3.
	The acceleration of a girl falling is repeatedly measured under identical conditions. The results are: a(ms^-2): 9.7, 10.3, 9.6, 10.0 Calculate the best estimate for the acceleration. acceleration = ms^-2.

4.	A uncertainty will tend to affect all results in the same way.

5.	By taking more readings you can reduce the approximate uncertainty.

6.
	What type of device has a "scale-reading" uncertainty of +/- a half of its smallest division?

7.	A voltage is measured as 25 V (+/- 20%). The absolute error for this measurement is +/- V.

8.	The equation: error = (max - min) / n is used to calculate approximate uncertainty.

9.

During an experiment the following readings are recorded.

Quantity	Value	Uncertainty	Units
current	6.4	+/- 0.8	A
time	95	+/- 15	s
voltage	12	+/- 3	V

is the quantity with the largest percentage uncertainty.

10.	A metre stick has the end marked zero worn away by 2 mm. This will introduce a uncertainty.

11.	A pupil's reaction time is repeatedly measured and produces these results. t (s): 0.25, 0.21, 0.24, 0.17 The mean value of these results for the pupil's reaction time is t = 0.22 s. The approximate random uncertainty in this mean value is +/- s.

12.	A timer records a value of (4.0 +/- 0.8) s. The percentage error in this reading is %.

13.	To calculate the power of a lightbulb a pupil measures the current as 2.4 A +/- 4% and the voltage as 12.7 V +/- 2%. Using P = I V the overall percentage uncertainty in the final value for the power is %.

14.
	What type of device has a "scale-reading" uncertainty of +/- the smallest division on the scale?

15.	A voltmeter is used to check the voltage output of a 24 V powersupply. The meter has an uncertainty of +/- 0.1 V The same meter is then used to check a 12 V battery. Assuming that both sources are working properly, which source will produce the largest percentage error in its reading?

See your overall score.