Wave Behaviour (OCR GCSE Physics A (Gateway)): Flashcards

The wave equation states that wave speed equals frequency multiplied by wavelength.

The wave equation is v = f × λ, where v is wave speed in m/s, f is frequency in Hz, and λ is wavelength in metres.

False.

Doubling the frequency halves the wavelength, but wave speed stays the same as long as the medium does not change.

The unit for frequency is the hertz (Hz). One hertz means one wave passes a point per second.

Use the wave equation: λ = v ÷ f.

λ = 0.15 ÷ 0.5

Wavelength = 0.30 m

Complete the table for the wave equation. Fill in the missing values.

True.

The wave equation applies to all waves. Both transverse and longitudinal waves follow v = f × λ.

First, find frequency: f = 1 ÷ T = 1 ÷ 2 = 0.5 Hz.

Then use v = f × λ: λ = 0.15 ÷ 0.5 = 0.30 m.

A transverse wave is one where the vibrations are perpendicular (at 90 degrees) to the direction of energy transfer.

A longitudinal wave is one where the points along its length vibrate parallel to the direction of energy transfer.

Examples of transverse waves include:

1. Ripples on the surface of water

2. Vibrations in a guitar string

3. Electromagnetic waves (e.g. light, radio waves)

False.

Sound waves are longitudinal waves. The particles vibrate parallel to the direction of energy transfer, not perpendicular to it.

In a longitudinal wave, regions where particles are close together are called compressions, and regions where they are spread apart are called rarefactions.

The two key features of a longitudinal wave are compressions (where particles are close together) and rarefactions (where particles are spread apart).

Longitudinal waves make particles vibrate parallel to the wave direction, so they can travel through any medium with particles. Mechanical transverse waves need particles that can vibrate at 90° to the wave, which gases cannot support.

True.

Electromagnetic waves are transverse and do not need a medium. They can travel through a vacuum at the speed of light.

Complete the table comparing transverse and longitudinal waves.

The peak (or crest) is the highest point above the undisturbed position. The trough is the lowest point below it. Both are separated from the rest position by the wave's amplitude.

Waves transfer energy — but they do not transfer matter. The particles in the medium vibrate about fixed positions.

False.

The duck bobs up and down but does not travel with the wave. This shows that waves transfer energy without transferring matter.

An oscilloscope is the most accurate method because it measures time automatically, eliminating the effect of human reaction time, which can introduce errors of up to 0.2 s.

Waves transfer energy from one place to another, but do not transfer matter along with them.

Stand about 50 m from a wall and clap wooden blocks repeatedly in rhythm with the echoes. Time 20 claps, then calculate speed using: speed = total distance ÷ total time.

True.

Larger distances mean the time interval is longer, so reaction time errors become a smaller proportion of the total time measured.

Complete the table showing methods to measure the speed of sound and their key apparatus.

Two people stand a few metres apart on a calm water surface. One disturbs the water to create a ripple; the other starts a stopwatch when the ripple arrives. Speed = distance ÷ time.

Sound waves travel fastest in solids. The more molecules present, the faster energy is transferred between them.

False.

Sound travels fastest in solids and slowest in gases. More molecules in solids means energy is transferred more quickly between them.

When sound moves from air (less dense) into water (denser), both its wavelength and its wave speed increase. The frequency does not change.

When a sound wave moves from one medium to another, its wave speed and wavelength change, but its frequency stays the same.

Refraction is the change in direction of a sound wave when it moves from one medium to another, caused by a change in wave speed.

In warm air, molecules move faster and collide more frequently, so they carry sound energy more quickly. In cold air, slower molecules mean sound travels at a lower speed.

False.

Frequency does not change when a sound wave moves between media — only the wave speed (and wavelength) change.

At night, air near the ground is cooler and air higher up is warmer. Sound refracts towards the ground as it speeds up moving into warmer air, so it stays closer to the surface and travels further.

True.

Sound waves are longitudinal and need particles to vibrate — they travel through solids, liquids, and gases, but not a vacuum.

A metre ruler (resolution 1 mm) is used to measure wavelength and a stopwatch (resolution 0.01 s) is used to measure frequency.

in the ripple tank experiment, the independent variable is frequency and the dependent variable is wavelength.

The wavelength is measured by using a ruler to find the total length of the screen and dividing that distance by the number of wavefronts visible.

True.

The frequency is calculated by counting the number of wavefronts passing a fixed point and dividing by the time taken.

Wave speed = frequency × wavelength, or v = fλ, where v is in m/s, f is in Hz and λ is in m.

A stroboscope is a flashing light matched to the frequency of the waves. It makes the wavefronts appear stationary, making it easier to measure wavelength accurately.

False.

You should measure across multiple wavefronts (e.g. five) and divide the total distance by the number of waves to reduce random error.

Water conducts electricity, so contact between them could cause electric shock. Keeping them separate is an essential safety precaution.

Reflection occurs when a wave hits a boundary between two media and does not pass through, staying in the original medium.

True.

This is the law of reflection: the angle of incidence equals the angle of reflection, both measured from the normal to the surface.

On a rough surface, reflected waves scatter in many different directions rather than as a single beam, so the reflected wave is weaker than on a flat surface.

Transmission occurs when a wave passes through a substance and emerges from the other side. The more transparent the material, the more wave energy is transmitted.

when a sound wave passes through a wall, it may be partially absorbed so the transmitted wave has a lower amplitude.

Absorption occurs when energy is transferred from the wave into the particles of a substance. Waves can be partially or completely absorbed.

Only red light is reflected by the object. All other frequencies of visible light are absorbed by the material.

complete the table to show what happens to the wave in each case.

The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal to the surface.

False.

Both angles are measured from the normal, which is a line drawn at 90° to the mirror surface at the point where the light strikes.

Draw a line at 90° (perpendicular) to the mirror or block face at the point where the light ray strikes. Angles of incidence and reflection are measured from this normal.

in the refraction experiment, when a light ray enters a perspex block the angle of incidence is greater than the angle of refraction, so the ray bends towards the normal.

True.

When exiting the block, the ray bends away from the normal, so the angle of refraction is greater than the angle of incidence (i < r).

A sharpened pencil creates a thin, precise mark in the centre of the light beam, reducing random error when measuring angles with the protractor.

The independent variable is the angle of incidence (i). The angle of reflection (r) is the dependent variable.

The ray does not refract and passes straight through the block. The angle of incidence equals the angle of refraction (i = r = 0°).

A compression is a region in a longitudinal sound wave where particles are closer together, creating an area of higher density and higher pressure.

A rarefaction is a region in a longitudinal sound wave where particles are more spread out, creating an area of lower density and lower pressure.

False.

Sound is a longitudinal wave, not a transverse wave. It travels as compressions and rarefactions, which are regions of varying particle density and pressure.

The compressions and rarefactions of the sound wave create varying pressure on the surface of the solid, causing it to vibrate in sync with the wave.

Sound waves transfer their vibrations to solids because sound is a type of pressure wave, meaning it exerts a varying force on surfaces it contacts.

The ossicles (hammer, anvil and stirrup) are three small bones in the ear that amplify vibrations from the eardrum and transfer them to the inner ear.

A typical human can hear frequencies in the range of 20 Hz to 20,000 Hz (20 kHz).

False.

It is the shorter hairs in the cochlea that respond to high frequencies and stop working first with age, reducing the ability to hear high frequencies.

Sound travels down the auditory canal to the eardrum, which vibrates. The ossicles amplify the vibrations and pass them to the cochlea, where cilia produce electrical signals sent to the brain.