ATP Guidebook: O Levels Physics 5054 and IGCSE Physics 0625

Errors in Measurements

Definition

• Error: Difference between actual value and calculated value of any physical quantity.

Types of Errors

1. Systematic Errors:

   • Occur due to faults in experimental instruments.
   • Examples:
     • Dead space in rulers
     • Broken edges of a ruler
     • Improperly calibrated thermometer
     • Zero Error (Positive and Negative)

2. Random Errors:

   • Fluctuate from measurement to measurement.
   • Causes: Human reaction time, atmospheric conditions, parallax error.
   • Mitigation: Take multiple readings and average them.

Zero Error

• Occurs when instrument gives a false reading when the true value is zero.

Types of Zero Errors

1. Positive Zero Error:
   • Zero mark on vernier scale ahead of main scale zero.
   • Correction: Correct Value = Measured Value - Zero Error.
2. Negative Zero Error:
   • Zero mark on vernier scale behind main scale zero.
   • Correction: Correct Value = Measured Value + Zero Error.

Solutions

• Systematic Errors: Identify and change faulty instruments.
• Random Errors: Use averaging to reduce impact.

Graph Plotting

Key Points

1. Scale: Cover at least 75% of the graph.
2. Axis: Linear scales preferred. Avoid non-uniform plotting.
3. Readability: Use multiples of 2 and 5; avoid multiples of 3.
4. Labeling: Axis should be labeled with Symbol/Unit (e.g., L/cm).
5. Plotting: Use x or . to mark points.
6. Starting Point: Follow examiner's instructions; not necessarily from origin.
7. Best Fit Line/Curve: Balance points above and below line.

Calculating Gradient

• Select two points at least covering half the graph.
• Use dotted triangle to indicate points.
• Gradient formula applies.
• Dependent variable on y-axis; independent variable on x-axis.

Specific Tips for Practicals

• Number of observations specified in examination.
• Ensure uniform intervals between readings.
• Column headings must include Quantity/Unit.
• Consistency in decimal places and significant figures.

Measurement Instruments

Common Precautions

• Avoid parallax error; use perpendicular line of sight.

Instruments

1. Ammeter: Measures current, negligible resistance, always in series.
2. Galvanometer: Sensitive ammeter for small current changes.
3. Voltmeter: Measures voltage, connected in parallel, infinite resistance.
4. Meter Rule: Measure lengths shorter than 1m, avoid parallax.
5. Measuring Tape: For lengths >1m, measures curved surfaces too.
6. Measuring Cylinder: Volume of liquids and irregular shapes, use meniscus for reading.
7. Set Square: Ensures perpendicular alignment.
8. Protractor: Measures angles; avoid parallax error.
9. Vernier Caliper: Measures internal/external diameter; max reading 20cm.
10. Micrometer Screw Gauge: For small dimensions, least count 0.01mm.

Pendulum Experiment

• Time Period: Time for one oscillation.
• Frequency: Oscillations per second.
• Amplitude: Maximum displacement from mean position.
• Length: Measured from the thread to pendulum bob's center.