exam model answers

Question 1

Comment on precision (sig fig consistency)

Answer 1

Repeat reading, enough results, look for inconsistent intervals between readings.

Question 2

Making results more accurate

Answer 2

Parallax error (record at eye level), fiducial markers as reference points, set square to make sure rulers are vertical, averages to reduce random error.

Question 3

Absolute uncertainty

Answer 3

The uncertainty from the measuring device.

Question 4

Uncertainty of repeat readings

Answer 4

Uncertainty = half the range of the repeats. Data = mean ± uncertainty.

Question 5

Percentage uncertainty

Answer 5

Absolute uncertainty / reading * 100.

Question 6

Accurate

Answer 6

Near the true value.

Question 7

Precise

Answer 7

Results are grouped together.

Question 8

Compounding uncertainties

Answer 8

Convert absolute uncertainty to percentage uncertainty, combine the uncertainties, convert back to absolute uncertainties (multiply by value).

Question 9

Compound uncertainty rules

Answer 9

Multiplying/dividing ADD THE UNCERTAINTIES. Powers MULTIPLY BY EXPONENT.

Question 10

Systematic error

Answer 10

Fault with equipment (e.g. zero error).

Question 11

Random error

Answer 11

Due to human error (e.g. human reaction time).

Question 12

Reading of a micrometer

Answer 12

Read the first two digits off the barrel (e.g. line above and below is 0.5mm). Read the value that lines up with the horizontal line on the thimble and add this to the previous value.

Question 13

Reading of a vernier caliper

Answer 13

Read off the first two numbers (e.g. 0.8 by looking at where the second scale begins). Third number is how many notches along until the two lines completely line up.

Question 14

Resolution of a vernier caliper

Answer 14

0.05mm.

Question 15

Resolution of a micrometer

Answer 15

0.01mm.

Question 16

Resolution

Answer 16

The smallest division on an instrument.

Question 17

Why take means

Answer 17

To reduce the effect of random errors and spot anomalies.

Question 18

Error

Answer 18

An error is the difference between the (measured) result and the true value.

Question 19

Uncertainty

Answer 19

An uncertainty is the interval/range in which the (true) value can be considered to lie.

Question 20

Reasons for uncertainty

Answer 20

Instrument resolution, the way the measurement is made (parallax error, reaction times, zero error), a measured constant not being constant.

Question 21

How to ensure accurate results

Answer 21

Check for zero error, measure dimensions in multiple places, measure for multiple objects then divide by the number (reduces uncertainty).

Question 22

How is light emitted?

Answer 22

There are electron transitions between energy levels in the atoms. When electrons return to a lower level, they emit energy in the form of photons.

Question 23

Cathode ray oscilloscope construction

Answer 23

Electron gun, deflection system, and screen.

Question 24

Cathode ray oscilloscope uses

Answer 24

Measuring voltage, measuring frequency, looking at phase difference.

Question 25

Show a graph is a 1/x curve

Answer 25

Plot y against 1/x, it should be a straight line through the origin.