Practical Skills

Systematic Uncertainty 

• Caused by consistent errors in the measurement process.

• Affects accuracy, not precision.

• Examples:

  • A scale that always reads 0.5 g too high.

  • A ruler with a worn-out edge.

• These errors shift all results in one direction.

Random Uncertainty

• Caused by unpredictable variations in the measurement process.

• Affects precision, not accuracy.

• Examples include environmental fluctuations or operator inconsistencies.

How many significant figures a piece of processed data should be given to?

Same number of significant figures as the least precise measurement used in the calculation.

How do you find the uncertainty in a single result?

Half the smallest division of the instrument

How do you find the uncertainty in repeated results?

Half the range of the repeated measurements

How do you find the percentage uncertainty in a result?

Percentage Uncertainty= (Measured Value ÷ Absolute Uncertainty​)×100

Parallax Error

the apparent shift in position of an object due to a change in the observer's point of view, affecting measurement accuracy.

How to avoid parallax error?

1. View the scale straight-on

   • Make sure your eye is level with the measurement mark.

   • This ensures the pointer or edge aligns correctly with the scale.

2. Use a mirror behind the scale (if available)

   • Many analogue meters have a mirror strip behind the pointer.

   • Adjust your eye position until the pointer covers its reflection — this means you're looking straight-on.

What is the SI unit of surface area and cross-sectional area?

m²

How is cross-sectional area related to diameter?

A=(πd²)÷4

How should a voltmeter be connected?

Connected in parallel with the component you want to measure the potential difference (voltage) across.

How should an ammeter be connected?

Connected in series with the component or section of the circuit where you want to measure the current.

What property should an ideal voltmeter possess?

Infinite resistance:
So no current flows through it.

• This ensures it doesn’t affect the circuit or change the voltage it’s trying to measure.

• In reality, voltmeters have very high resistance, but not truly infinite.

What property should an ideal  ammeter possess?

Zero resistance:
So it does not affect the current in the circuit.

• If it had resistance, it would reduce the current slightly, giving an inaccurate reading.

• In reality, ammeters have very low resistance, but not exactly zero.