CIE iGCSE Co-Ordinated Science P4.4 Electrical safety Exam Style Questions Paper 4
Question
A gardener cuts grass with an electric mower.
(a) Use the information in Fig. 12.1 to explain why the cut in insulation is an electrical hazard.
▶️Answer/Explanation
Hazard explanation:
1. Exposed live wires can cause electric shock if touched
2. Damp grass increases conductivity (water is a good conductor when contains ions)
3. Risk of short circuit if conductors touch
4. Potential fire hazard from sparks
Safety implications:
– 230V mains electricity can be lethal
– Current as low as 50mA can cause cardiac arrest
– Damaged insulation violates electrical safety regulations
– Proper repair requires complete rewrapping with insulating tape or cable replacement
(b) The mower is noisy. Sound waves from the lawn mower pass through the air as a series of compressions and rarefactions.
(i) State what is meant by a compression.
▶️Answer/Explanation
A region of high pressure where air particles are closer together
Sound wave details:
– Longitudinal wave characteristic
– Particles vibrate parallel to wave direction
– Alternates with rarefactions (low pressure regions)
– Distance between compressions = wavelength
– Frequency of compressions determines pitch
(ii) Describe the wavelength of a sound wave in terms of compressions.
▶️Answer/Explanation
The distance between two consecutive compressions (or between two consecutive rarefactions)
Wave characteristics:
– Measured in meters (m)
– Inversely proportional to frequency (λ = v/f)
– Typical audible sound wavelengths range from 17mm to 17m
– Determines the pitch we perceive – shorter wavelengths = higher pitch
(iii) Sound waves are longitudinal waves.
Describe the differences between longitudinal and transverse waves.
▶️Answer/Explanation
| Characteristic | Longitudinal Waves | Transverse Waves |
|---|---|---|
| Particle motion | Parallel to wave direction | Perpendicular to wave direction |
| Examples | Sound waves, seismic P-waves | Light waves, seismic S-waves |
| Medium required | Yes (solid, liquid, gas) | Only for mechanical waves |
| Wave features | Compressions and rarefactions | Crests and troughs |
Key difference: The relationship between particle motion and wave propagation direction
(c) The gardener places mirrors in his garden to scare cats away. When a cat sees its image in the mirror it runs away.
Describe the image formed in a plane mirror by using three words or phrases from the list.
laterally inverted magnified not upside down real
same size smaller upside down virtual
▶️Answer/Explanation
1. Virtual
2. Laterally inverted
3. Same size
Plane mirror image properties:
– Virtual: Cannot be projected on a screen (light rays appear to come from behind mirror)
– Laterally inverted: Left-right reversal (like text in a mirror)
– Same size: Magnification = 1 (object and image dimensions identical)
– Additional correct properties: Upright, same distance behind mirror as object is in front
(d) Fig. 12.2 shows a heater in the garden. The heater burns butane gas.
The underside surface of the hood is shiny and light in colour.
Suggest why this is a more suitable surface than a dull and dark colour.
▶️Answer/Explanation
Thermal radiation benefits:
1. Shiny surface reflects infrared radiation downwards
2. Light color emits less thermal radiation upwards
3. Increases heating efficiency by directing heat where needed
Physics principles:
– Good reflectors are poor emitters/absorbers (Kirchhoff’s Law)
– Dark surfaces would absorb and re-radiate heat upwards
– Shiny aluminum has low emissivity (ε ≈ 0.03)
– Maximizes downward heat transfer to people below