Topic 1: Measurements

Question 1

Order of magnitude

Answer 1

The size of a number rounded to the nearest power of ten.

Question 2

SI units

Answer 2

The International System of units is the one most scientists have agreed to use.

Question 3

Fundamental units

Answer 3

Seven units of basic quantities from which all other units can be derived. Eg metre, second, kilogram, mol, A, K, cd

Question 4

Derived units

Answer 4

Units which are made by combining fundamental units. Eg m/s2, newton

Question 5

Error

Answer 5

The way a measurement may vary from the true value.

Question 6

Uncertainty

Answer 6

A measure of the size of the error.

Question 7

Random error

Answer 7

When repeated readings give slightly different values, some higher, some lower than the true value.

Question 8

Systematic error

Answer 8

When the measurement is incorrect due to a fault in the apparatus or method.

Question 9

Precision

Answer 9

A measurement with a low random error. ie does not vary much but could be wrong.

Question 10

Accuracy

Answer 10

A measurement with a low systematic error. ie it is close to the true value though individual readings may vary.

Question 11

Absolute uncertainty

Answer 11

The size of an error measured in the same units as the quantity. eg 10.2 ± 0.1 m

Question 12

Relative uncertainty

Answer 12

The size of an error compared with the original quantity. It can be expressed as a percentage. eg 10.2 m ± 1%

Question 13

Error bars

Answer 13

Lines drawn through a point on a graph to show the size of the uncertainty.