P6.6. Waves

What is a wave?

A transfer of energy from one place to another without transferring matter.

What are the two types of wave?

Transverse and longitudinal.

What is a transverse wave?

A wave where the oscillations are perpendicular to the direction of energy transfer.

What is an example of a transverse wave?

Ripples on a water surface.

What is a longitudinal wave?

A wave where the oscillations are parallel to the direction of energy transfer.

What are compressions?

Regions where particles in a longitudinal wave are close together.

What are rarefactions?

Regions where particles in a longitudinal wave are spread further apart.

What type of wave is sound travelling through air?

A longitudinal wave.

What evidence shows that the water itself does not travel with a water wave?

A floating object oscillates rather than travelling with the wave.

What evidence shows that the air itself does not travel with a sound wave?

Air particles vibrate rather than travelling with the sound wave.

What is amplitude?

The maximum displacement of a point on a wave from its undisturbed position.

What is wavelength?

The distance from a point on one wave to the equivalent point on the adjacent wave.

What is frequency?

The number of waves passing a point each second.

What is frequency measured in?

Hertz (Hz).

What is the period of a wave?

The time taken for one complete wave.

What is the period measured in?

Seconds (s).

What is the equation linking period and frequency?

T = 1/f.

What is wave speed?

The speed at which energy is transferred, or the wave moves, through a medium.

What is the wave equation?

v = fλ.

What is wave speed measured in?

Metres per second (m/s).

What is wavelength measured in?

Metres (m).

What should you be able to identify from wave diagrams?

Amplitude and wavelength.

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

Measure the distance travelled and the time taken, then calculate speed = distance/time.

How can you measure the speed of ripples on a water surface?

Measure suitable wave quantities and use the wave equation, or measure distance travelled and time taken.

What should you consider when choosing apparatus to investigate waves?

Whether the apparatus is suitable for measuring frequency, wavelength and wave speed.

What should you investigate using a ripple tank?

The suitability of apparatus for measuring the frequency, wavelength and speed of waves.

What should you investigate using waves in a solid?

The suitability of apparatus for measuring the frequency, wavelength and speed of waves.

What measurements should you take in the wave practical?

Appropriate measurements of frequency, wavelength and wave speed.

What should you be able to do when investigating waves?

Make observations and select and use appropriate apparatus and measurements.

What are electromagnetic waves?

Transverse waves that transfer energy from a source to an absorber.

What do all electromagnetic waves have in common?

They are transverse and all travel at the same velocity through a vacuum or air.

What is the speed of electromagnetic waves in a vacuum?

About 3 × 10⁸ m/s.

What do electromagnetic waves form?

A continuous spectrum.

How are electromagnetic waves grouped in the spectrum?

According to their wavelength and frequency.

What is the order of the electromagnetic spectrum from longest to shortest wavelength?

Radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays.

What is the order of the electromagnetic spectrum from lowest to highest frequency?

Radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays.

What is the order of visible light from long to short wavelength?

Red to violet.

Which electromagnetic waves can human eyes detect?

Visible light.

What can electromagnetic waves transfer?

Energy from a source to an absorber.

What should you be able to give examples of?

Energy transfer by electromagnetic waves.

What can different substances do to electromagnetic waves?

Absorb, transmit, refract or reflect them.

How can the behaviour of electromagnetic waves depend on wavelength?

Different substances can absorb, transmit, refract or reflect electromagnetic waves differently at different wavelengths.

Why can refraction occur when an electromagnetic wave enters a different substance?

The velocity of the wave changes between the substances.

What should you be able to construct to show refraction?

Ray diagrams showing refraction at the boundary between two different media.

How can wavefront diagrams explain refraction?

They show how a change in wave speed causes the wavefronts to change direction.

What is the aim of the infrared practical?

To investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of the surface.

What should you compare in the infrared investigation?

Surfaces with different natures and the amount of infrared radiation they absorb or radiate.

How can radio waves be produced?

By oscillations in electrical circuits.

What can happen when radio waves are absorbed?

They may create an alternating current with the same frequency as the radio wave.

How can radio waves induce oscillations in an electrical circuit?

An absorbed radio wave can produce an alternating current at the same frequency.

What can changes in atoms and atomic nuclei produce?

Electromagnetic waves over a wide range of frequencies.

Where do gamma rays originate?

Changes in the nucleus of an atom.

Which electromagnetic waves can have hazardous effects on human tissue?

Ultraviolet, X-rays and gamma rays.

What does the hazard from electromagnetic radiation depend on?

The type of radiation and the size of the dose.

What is radiation dose?

A measure of the risk of harm from exposure of the body to radiation.

What is the unit of radiation dose?

Sieverts (Sv), although you do not need to recall the unit.

What is the relationship between sieverts and millisieverts?

1000 mSv = 1 Sv.

What should you be able to do with data about radiation exposure?

Draw conclusions about the risks and consequences of exposure.

What can ultraviolet radiation do to skin?

It can cause premature skin ageing and increase the risk of skin cancer.

Why are X-rays and gamma rays particularly hazardous?

They are ionising radiation that can cause gene mutations and cancer.

What are radio waves used for?

Television and radio.

What are microwaves used for?

Satellite communications and cooking food.

What is infrared used for?

Electrical heaters, cooking food and infrared cameras.

What is visible light used for?

Fibre optic communications.

What is ultraviolet used for?

Energy-efficient lamps and sun tanning.

What are X-rays used for?

Medical imaging and treatments.

What are gamma rays used for?

Medical imaging and treatments.

Why are radio waves suitable for television and radio?

They can be used to transmit information.

Why are microwaves suitable for satellite communications?

They can be used for communication with satellites.

Why are microwaves suitable for cooking food?

They transfer energy to the food.

Why is infrared suitable for electrical heaters?

It transfers energy as thermal radiation.

Why is infrared suitable for infrared cameras?

Objects emit infrared radiation that can be detected by the camera.

Why is visible light suitable for fibre optic communications?

It can transmit information through optical fibres.

Why is ultraviolet suitable for energy-efficient lamps?

It can cause fluorescent materials to emit visible light.

Why is ultraviolet suitable for sun tanning?

It can cause changes in skin cells that produce a tan.

Why are X-rays suitable for medical imaging?

They can pass through soft tissue but are absorbed more by denser materials such as bone.

Why are gamma rays suitable for medical treatments?

They can damage and destroy cancer cells.