# Determining Uncertainty(Edexcel International A Level Physics)

Author

Katie M

Expertise

Physics

## Percentage Uncertainty in Single Readings

• Percentage uncertainty for a single reading (measured value) is defined by the equation:

Percentage uncertainty = × 100 %

#### Worked example

A student measures the potential difference on an analogue voltmeter with resolution 0.2 V as 15 V.

Calculate the percentage uncertainty in the student's reading of the potential difference.

1. Determine the absolute uncertainty

• The absolute uncertainty of the reading is half the resolution of the analogue voltmeter

= 0.1 V

2. Calculate the percentage uncertainty

× 100 % = 0.67 %

#### Exam Tip

Always make sure your percentage uncertainty is at least one significant figure smaller than the measurement.

## Percentage Uncertainty in Multiple Readings

• The percentage uncertainty in measurements from multiple readings (e.g., repeat readings) use half the range of the readings
• The range of the readings is the difference between the highest and lowest reading

#### Worked example

A student achieves the following results in their experiment for the angular frequency, ω.

0.154, 0.153, 0.159, 0.147, 0.152

Calculate the percentage uncertainty in the mean value of ω.

1. Calculate the mean value

mean ω = 0.153 rad s–1

2. Calculate half the range (this is the uncertainty for multiple readings)

× (0.159 – 0.147) = 0.006 rad s–1a

3. Calculate percentage uncertainty

× 100 % = × 100 %

× 100 % = 3.92 %

#### Exam Tip

Remember that percentage uncertainties have no units, only the % sign!

You will not be expected to compound percentage uncertainties for AS.

### Get unlimited access

to absolutely everything:

• Unlimited Revision Notes
• Topic Questions
• Past Papers