Practical Skills

Question 1

Random Error

Answer 1

when the same measurement will give different values each time it is measured

Question 2

How can random error be reduced?

Answer 2

Taking repeat measurements – averaging and drawring a graph

Question 3

Systematic error

Answer 3

a measurement that is consistantly too large or too small by the same amount

Question 4

How can systematic error occur?

Answer 4

• recording the wrong unit
• faliure to check zero error
• incorrect calibration of equipment

Question 5

Zero error

Answer 5

when the measuring instrument is not set to zero accurately

Question 6

How can a systematic error be spotted with a graph?

Answer 6

• line of best fit shifted up or down the y-axis
• gradient remains the same

Question 7

Precision

Answer 7

Consistency between values obtained by repeated measurments

Question 8

Accurate

Answer 8

How close to the true value a measurement is

Question 9

Percentage Uncertainty equation

Answer 9

uncertainty/value * 100

Question 10

What happens to uncertainties when quantites are ADDED or SUBTRACTED?

Answer 10

add the absolute uncertainties

Question 11

What happens to uncertainties when quantites are MULTIPLIED or DIVIDED?

Answer 11

add percemtage uncertainties

Question 12

What happens to uncertainties when quantites are RAISED TO A POWER?

Answer 12

multiply percentage uncertainty by the power

Question 13

how can uncertainties be affected in measurements?

Answer 13

• the resolution of instrument used
• how the experimenter uses instruments
• the procedures adopted (e.g repeated readings)

Question 14

calculating percentage error for repeat measurements

Answer 14

1/2(range) / mean value *100

Question 15

How to use micrometer accuratly

Answer 15

• use rachet to close jaws to prevent over-tightening
• measure diameter several times in several places to check uniformity

Question 16

Using set squares

Answer 16

• ensures vertical/horizontal alignment
  -use at eye level or clap with ruler

Question 17

Techniques for timing oscillations

Answer 17

• use fiducial marker to see when object passes equilibrium position
• only start timer when object has completed one or two oscillations
• time around 10 oscillations to reduce uncertainty (asjust for heavily damped systems)

Question 18

advantages of using data loggers:

Answer 18

• record data automatically
• record data at small intervals over long periods of time
• can output data on a computer as a graph or in a table
  -sensors enable a wide range of measurements
• can measure several variables simultaneously