Singapore-Cambridge N(A)-Level Combined Science, Physics: Waves, Electricity and Magnetism, from waves, sound and light through the electromagnetic spectrum to current electricity and electromagnetism

What this module is about

The Waves, Electricity and Magnetism module is the second half of N(A)-Level Combined Science Physics (SEAB 5105 and 5106). It deals with two of the great themes of physics: how energy travels as waves, and how electricity and magnetism are linked. The thread is transfer without matter moving along: a wave carries energy through a medium, and a current and a magnetic field carry effects through a circuit and through space.

This overview pulls the threads together and links to every dot point page in the module, each with its own worked answers and practice questions.

Waves and sound

The module opens with sound and waves. A wave carries energy without moving matter along permanently. It is described by frequency (waves per second, in hertz), wavelength (the distance between repeats, in metres) and amplitude (the size of the disturbance, linked to loudness or brightness). The wave equation links them: speed equals frequency times wavelength. Sound is a wave that needs a medium to travel, so it cannot travel through a vacuum.

Light and the electromagnetic spectrum

Next comes light and the electromagnetic spectrum. Light reflects off surfaces, and for a plane mirror the angle of incidence equals the angle of reflection. Light refracts (changes direction) when it passes between media because its speed changes. Light is one part of the electromagnetic spectrum, which runs from radio waves through microwaves, infrared, visible light, ultraviolet and X-rays to gamma rays, each region with its own uses.

Current electricity and circuits

The third dot point is current electricity and circuits. Current is the rate of flow of charge (in amperes), voltage is the energy given to the charge (in volts), and resistance opposes the current (in ohms). Ohm's law links them: voltage equals current times resistance. In a series circuit the current is the same everywhere; in a parallel circuit the current splits between branches and the voltage across each branch is the same.

Magnetism and electromagnetism

The module finishes with magnetism and electromagnetism. A magnet has a north and a south pole, like poles repel and unlike poles attract, and a magnetic field is the region where the force acts. Passing a current through a coil makes an electromagnet, which can be switched on and off. Its strength is increased by raising the current, adding more turns, or using a soft iron core.

How this module is examined

• Use the wave equation carefully. Speed = frequency x wavelength, with hertz and metres, and keep amplitude separate.
• Apply Ohm's law and the circuit rules. Voltage = current x resistance; series has the same current throughout, parallel splits the current and shares the voltage.
• Make an electromagnet stronger three ways. More current, more turns, a soft iron core, and remember it can be switched off.

Check your knowledge

A mix of recall and application questions covering the module. Attempt them under timed conditions, then check against the solutions, and use the dot point pages for fuller practice.

1. Define frequency and state its unit. (2 marks)
2. A wave has frequency 10 Hz and wavelength 3 m. Calculate its speed. (2 marks)
3. State the law of reflection for a plane mirror. (1 mark)
4. State Ohm's law as a word equation. (1 mark)
5. A 12 V supply drives a current of 3 A through a resistor. Calculate the resistance. (2 marks)
6. State two ways to increase the strength of an electromagnet. (2 marks)