Waves & The Electromagnetic Spectrum (Edexcel IGCSE Physics)

True.

The highest point above the rest position of a transverse wave is called the peak or the crest of the wave.

The name of the lowest point below the rest position of a transverse wave is the trough.

The wave shown is a transverse wave because it oscillates at right angles of the direction of wave motion.

A correctly labelled longitudinal wave is as follows:

Amplitude is the distance from the central undisturbed position to the peak or trough of a wave.

The wavelength of a wave is the distance from one point on the wave to the same point on the next wave.

Frequency is the number of waves passing a point in a second.

Wave speed is the speed at which a wave travels.

The symbol used for amplitude is .

The units of amplitude are metres (m).

Amplitude is drawn from the central equilibrium position to the peak.

Wavelength is drawn between consecutive peaks (or troughs).

The wave property indicated by the arrow on the diagram is time period, T.

The units of wave speed are metres per second (m/s).

The symbol for wave speed is .

False.

The symbol for frequency is .

True.

The units of frequency are hertz (Hz)

The units for wavelength are metres (m).

The symbol for wavelength is lambda, .

The wave equation in terms of wave speed is

Where:

• = wave speed, measured in metres per second (m/s)

• = frequency, measured in hertz (Hz)

• = wavelength, measured in metres (m)

False.

The wave speed equation in terms of wavelength is

Where:

• = wavelength, measured in metres (m)

• = wave speed, measured in metres per second (m/s)

• = frequency, measured in hertz (Hz)

True.

The wave speed equation in terms of frequency is

Where:

• = frequency, measured in hertz (Hz)

• = wave speed, measured in metres per second (m/s)

• = wavelength, measured in metres (m)

The equation linking time period, and frequency, is:

Where:

• = time period, measured in seconds (s)

• = frequency, measured in hertz (Hz)

The Doppler effect is the apparent change in the observed wavelength and frequency of a wave emitted by a source moving relative to an observer.

The frequency of a siren decreases as it moves past a stationary observer.

The Doppler effect, when observed with galaxies, shows that light waves have redshifted (wavelength increases) as the stars move away from Earth.

Waves from a stationary source sound spread out symmetrically.

False.

The Doppler effect occurs when the source of the waves is moving (towards or away from an observer).

The wavelength of waves appears shorter for an observer positioned in front of a moving source.

The wavelength of waves for an observer behind a moving source appears to get longer.

Wave speed stays constant when the Doppler effect is observed.

The equally spaced wavefronts on the diagram identify that the car is stationary when sound is emitted from the horn.

The feature of the diagram that shows that the observer hears a higher pitch as the source moves towards them is that the wavefronts are closer together next to the observer.

True.

The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies.

The order of the electromagnetic spectrum from longest to shortest wavelength is:

• Radio waves

• Microwaves

• Infrared

• Visible light

• Ultraviolet

• X-rays

• Gamma rays

All electromagnetic waves share the following properties:

• transverse

• can travel through a vacuum

• travel at the same speed in a vacuum

• form a continuous spectrum

Electromagnetic waves are transverse waves with oscillating electric and magnetic fields that transfer energy from the source of the waves to an absorber.

True.

The speed of electromagnetic waves in air can be approximated to the speed of light in a vacuum because the difference in speed is so small.

The higher the frequency, the higher the energy of the radiation, and vice versa.

One possible mnemonic for remembering the correct order of radiation in the electromagnetic spectrum is:

Raging Martians Invaded Venus Using X-ray Guns.

The electromagnetic radiation type with the shortest wavelength is gamma rays.

The electromagnetic radiation type with the highest frequency is gamma rays.

The electromagnetic radiation type with the lowest frequency is radio waves.

Fluorescence is the process where certain substances absorb ultraviolet light and re-emit it as visible light, causing them to glow.

The main application of radio waves is in wireless communications.

The two main applications of microwaves are:

• heating food

• wireless communications

True.

One application of infrared radiation is night vision cameras.

False.

Infrared and visible light are used in optic fibre communications. Gamma rays are used for sterilising medical equipment and treating cancer.

False.

Sterilising water and detecting fake bank notes are two applications of ultraviolet radiation (UV). X-rays are used for imaging in medicine, dentistry, airport security and industry.

True.

Human eyes can only detect wavelengths of electromagnetic radiation in the visible light section of the electromagnetic spectrum.

False.

Ultraviolet radiation carries too much energy and would be harmful if used for this purpose. Remote controls are one application of infrared radiation.

The device in the diagram is a microwave oven and uses microwaves.

True.

As the frequency of electromagnetic waves increases, the energy they transfer increases, and therefore so does the danger associated with them.

Ultraviolet, X-rays, and gamma rays can all ionise atoms, which can damage cells and cause mutations, which can lead to cancer.

False.

There are no known harmful effects of radio waves.

True.

Microwaves can be harmful to humans in high levels of exposure, because higher-frequency microwaves cause internal heating.

True.

Mobile phones do emit microwave radiation, but only at low energies which are not known to cause any harm.

True.

Ultraviolet radiation can cause sunburn, eye damage and skin cancer.

True.

X-rays and gamma rays (and UV) are ionising radiation which can remove electrons from atoms, causing damage to DNA which can lead to cell and tissue damage, mutations and cancer.

True.

Sunscreen absorbs ultraviolet light, preventing it from damaging the skin.

True.

The ionising forms of electromagnetic radiation are ultraviolet, X-rays and gamma rays, all of which have higher frequencies than visible light.

False.

The shorter the wavelength (and therefore, the higher the frequency), the more ionising the electromagnetic radiation.

The device in the image is a radiation badge and its purpose is to measure a person's exposure to radiation.