ZIMSEC O Level · Combined Science · Form 2, Form 3, Form 4
Heat transfer
- Conduction: through solids, as particles pass on vibrations. Metals are good conductors; wood and plastic are insulators.
- Convection: in liquids and gases, as warm fluid rises and cool fluid sinks (convection currents).
- Radiation: by infrared waves, which need no medium. Dull black surfaces absorb and emit radiation best; shiny white surfaces reflect it.
Uses: a vacuum flask reduces all three; houses are painted white to stay cool.
Light
- Light travels in straight lines, which is why shadows form.
- Reflection: angle of incidence = angle of reflection.
- Refraction: light bends when it passes between materials of different density, e.g. from air into water.
- A prism splits white light into the colours of the spectrum (dispersion).
Waves and sound
- Waves transfer energy without transferring matter.
- Sound needs a medium and cannot travel through a vacuum. Higher frequency gives higher pitch; larger amplitude gives louder sound.
- Wave speed = frequency × wavelength (v = fλ).
Worked example: A wave has frequency 50 Hz and wavelength 4 m. Find its speed.
v = 50 × 4 = 200 m/s
Exam tip: Name the method of heat transfer and explain it in terms of particles (or waves for radiation).
Check yourself
- Why are cooking pots often made of metal with plastic handles?
- State the law of reflection.
- Why can sound not travel through a vacuum?
Show answers
- Metal conducts heat to the food; plastic is an insulator so the handle stays cool.
- The angle of incidence equals the angle of reflection.
- Sound needs particles (a medium) to pass on its vibrations.
Questions about this topic (0)
No questions about this topic yet.
Sign in or create a free account to join in.