Measurements and their errors:

Question 1

How do you convert mega electron volts to joules? (MeV -> J)

Answer 1

1eV = 1.6x10^-19

Question 2

How do you convert kilowatt hours to joules?
(kWh -> J)

Answer 2

1 kWh -> 3.6MJ

Question 3

What is a random error?

Answer 3

Measurements that vary due to unpredictable circumstances
They cannot be corrected only minimised

Question 4

How can you reduce a random error?

Answer 4

Take at least 3 repeats and calculate a mean
Use computers/ data loggers to reduce human error
Use appropriate equipment such as a micrometer not a ruler

Question 5

What is a systematic error?

Answer 5

Measurements that differ from the true value by a consistent amount each time.

Question 6

How do you reduce systematic errors?

Answer 6

Calibrate the equipment using a known value
In radiation experiments correct for background radiation
Read values at eye level to remove parallax errors.

Question 7

What is precision?

Answer 7

Consistent measurements that vary slightly about a mean value.

Question 8

What is accuracy?

Answer 8

A measurement very close to the true value

Question 9

What is repeatability?

Answer 9

If the same person, can repeat the same experiment and get the same results

Question 10

What is reproducibility?

Answer 10

If a different person, does a different experiment and get the same results

Question 11

What is resolution?

Answer 11

The smallest change in the quantity being measured that will give a recognisable change in the reading.

Question 12

What is uncertainty?

Answer 12

The uncertainty of a measurements is the bounds in which the accurate value can be expected to lie. e.g. 20 +- 2 is equal to 18-22

Question 13

What is absolute uncertainty?

Answer 13

Uncertainty given as a fixed quantity. e.g. 7 +_ 0.6

Question 14

What is fractional uncertainty?

Answer 14

Uncertainty given as a fraction of the quantity. e.g. 7+- 3/5

Question 15

What is percentage uncertainty?

Answer 15

Uncertainty given as a percentage of the measurement

Question 16

What is a reading?

Answer 16

A reading is when one value is found

Question 17

What is a measurement?

Answer 17

A measurement when at least 2 values are found

Question 18

How do you work out the uncertainty in a reading?

Answer 18

The uncertainty in a reading is +- half the smallest division. e.g. 1º uncertainty = +- 0.5º

Question 19

How do you work out the percentage uncertainty in a measurement?

Answer 19

Add at least +-1 of the smallest division at a minimum, however if it is say a ruler you have to add the uncertainty from both ends of the ruler.

Question 20

How do you work out the uncertainty for repeated data

Answer 20

mean + (range/2)

Question 21

How many sig figs should the uncertainty be?

Answer 21

The same number of sig figs as the data

Question 22

What do you do when you add/subtract data?

Answer 22

Add the absolute uncertainties

Question 23

What do you do when multiplying/dividing data?

Answer 23

Add the percentage uncertainties

Question 24

What do you do when raising a power?

Answer 24

Multiply percentage uncertainty by the power

Question 25

How do you find percentage uncertainty for gradients?

Answer 25

draw a best and worst line of best fit
((best gradient - worst gradient)/ best gradient) x 100%

Question 26

What is estimation?

Answer 26

Estimation is a skill physicists must use to approximate the values of physical quantities in order to make comparisons, or to check the value they have calculated is reasonable.