Physics Waves

"What do all waves transfer, and what do they NOT transfer?

All waves transfer energy from one place to another. They do NOT transfer matter — the medium (e.g. air or water) only vibrates, it does not travel with the wave."

"What are the four key properties used to describe any wave?

Amplitude, wavelength, frequency and period."

"What is the amplitude of a wave?

The maximum distance a point on the wave moves from its rest (undisturbed) position."

"What is the wavelength of a wave?

The distance from one point on a wave to the same point on the next wave (e.g. peak to peak)."

"What is the frequency of a wave, and what unit is it measured in?

The number of waves passing a point each second. Measured in hertz (Hz)."

"What is the period of a wave?

The time taken for one complete wave to pass a point. Measured in seconds."

"What is the equation linking period and frequency?

T = 1 ÷ f. Period (s) equals 1 divided by frequency (Hz). Rearranged: f = 1 ÷ T."

"How do you identify amplitude and wavelength on a wave diagram?

Amplitude: measure from the rest line up to a peak (or down to a trough). Wavelength: measure from one peak to the next peak (or trough to trough)."

"What is wave speed?

The speed at which energy is transferred through the medium by the wave."

"What is the wave equation?

wave speed = frequency × wavelength, written as v = fλ. Rearranged: f = v ÷ λ, or λ = v ÷ f."

"If wave speed stays the same, what happens to wavelength when frequency increases?

Wavelength decreases. Because v = fλ, if v is constant then f and λ are inversely related."

"How can you measure the speed of sound in air?

Measure a known distance, then time how long the sound takes to travel it (e.g. using an echo, or two microphones connected to a timer). Calculate speed using v = distance ÷ time. Repeat to improve reliability."

"In the speed of sound experiment, what are the variables?

Independent variable: distance. Dependent variable: time. Control variables: wind, temperature, and the same sound source."

"What does Required Practical 20 (RP20) investigate?

How to measure the frequency, wavelength and speed of waves — both ripples in a ripple tank and waves on a stretched string (a wave on a solid)."

"How do you measure the speed of ripples on water in a ripple tank?

Read the frequency from the dipper's vibration setting. Measure the wavelength using a ruler against the projected pattern (a stroboscope freezes the image). Then calculate speed using v = fλ."

"What are the main sources of error in ripple tank measurements, and how can you reduce them?

Parallax error when reading wavelength, reaction-time error when timing, and stroboscope flicker. Reduce by using a stroboscope to freeze the pattern, taking repeats, and timing several waves at once."

"What is a longitudinal wave?

A wave where the particles vibrate parallel to (in the same direction as) the direction of energy transfer. This creates compressions and rarefactions."

"What is a transverse wave?

A wave where the particles vibrate perpendicular (at right angles) to the direction of energy transfer."

"What is a compression in a longitudinal wave?

A region where the particles are pushed close together — an area of high pressure."

"What is a rarefaction in a longitudinal wave?

A region where the particles are spread further apart — an area of low pressure."

"Give an example of a longitudinal wave.

Sound waves travelling through air."

"Give an example of a transverse wave.

Ripples on a water surface. (Other examples: light, all EM waves, vibrations on a guitar string.)"

"What is the key difference between longitudinal and transverse waves?

The direction the particles vibrate. Longitudinal: parallel to the direction of energy transfer. Transverse: perpendicular to it."

"What evidence shows that waves transfer energy without transferring matter?

On water, a floating object bobs up and down but doesn't move along with the wave. For sound, air doesn't flow from a speaker to your ear — only the vibration travels."

"What is the electromagnetic (EM) spectrum?

A continuous spectrum of transverse waves that transfer energy from a source to an absorber. All EM waves travel at the same speed in a vacuum (or air) and are grouped by their wavelength and frequency."

"What are the 7 types of EM wave, in order from longest to shortest wavelength?

Radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays. (Memory aid: Roman Men Invented Very Unusual X-ray Guns.)"

"At what speed do all EM waves travel through a vacuum?

The speed of light: 3 × 10⁸ m/s (300,000,000 metres per second)."

"Why can our eyes only see a small part of the EM spectrum?

Our eyes only detect visible light — a narrow band between infrared and ultraviolet. The rest of the spectrum is invisible to us."

"Give examples of energy being transferred by EM waves.

Sunlight warming a surface (infrared), a microwave oven heating food, radio waves carrying signals to an aerial, X-rays forming a medical image."

"(HT) What four things can happen to an EM wave when it meets a substance?

It can be absorbed, transmitted (passed through), refracted (bent), or reflected. Which happens depends on the wavelength and the substance."

"(HT) What causes refraction?

A change in the wave's speed when it crosses the boundary between two media. The change in speed makes the wave change direction."

"How do you draw a ray diagram for refraction?

Draw the incident ray hitting the boundary, then a normal line at 90° to the boundary at that point. The refracted ray bends towards the normal when entering a denser medium, and away from the normal when entering a less dense medium."

"(HT) How do wave front diagrams explain refraction?

When a wave front meets a boundary at an angle, one end enters the new medium first and changes speed before the other end. This makes the whole wave front pivot, so the wave changes direction."

"What does Required Practical 21 (RP21) investigate?

How the amount of infrared radiation absorbed or emitted by a surface depends on the nature of that surface (e.g. matt black vs shiny silver)."

"How is RP21 carried out?

Use a Leslie cube (or hot can) with different surfaces, kept at the same starting temperature. Place an infrared detector the same distance from each surface and record the reading. Vary only the surface type to keep it a fair test."

"What are the main uses of each type of EM wave?

Radio — TV and radio broadcasting. Microwave — satellite communications, cooking. Infrared — heaters, cooking, IR cameras. Visible light — fibre optic communications. Ultraviolet — energy-efficient lamps, tanning. X-rays and gamma rays — medical imaging and treatments."

"(HT) Why are microwaves used for cooking?

They have a wavelength that penetrates food and is absorbed by water molecules, which heats the food from inside."

"(HT) Why are X-rays used for medical imaging?

They pass easily through soft tissue but are absorbed by bone, so bones show up clearly on a detector."

"(HT) Why is visible light used in fibre optic cables?

It can be reflected along the inside of glass fibres without escaping, allowing signals to travel long distances with little loss."

"What harm can ultraviolet (UV) radiation cause?

UV can cause skin to age prematurely and increases the risk of skin cancer."

"What harm can X-rays and gamma rays cause?

They are ionising radiation, which can cause gene mutation and cancer."

"What is meant by ionising radiation?

Radiation with enough energy to knock electrons off atoms, turning them into ions. This can damage cells and DNA. X-rays and gamma rays are ionising; UV is partly ionising."

"What is radiation dose, and what unit is it measured in?

A measure of the risk of harm to the body from exposure to radiation. Measured in sieverts (Sv). 1000 millisieverts (mSv) = 1 Sv."

"How are EM waves produced and absorbed by atoms?

Changes in atoms and their nuclei can produce or absorb EM waves across a wide range of frequencies. Gamma rays specifically come from changes in the nucleus."

"(HT) How are radio waves produced?

By oscillations (alternating currents) in electrical circuits — the oscillating charges send out radio waves."

"(HT) What happens when radio waves are absorbed by a circuit?

They induce an alternating current in the circuit with the same frequency as the radio wave. This is how a radio aerial picks up a signal."