Waves, light and sound, Year 11: uses and hazards of electromagnetic waves

nucleus

提示It is the same place that alpha and beta particles are thrown out from.

为什么Gamma rays are produced by changes in the nucleus of an atom, as met in radioactive decay. Other electromagnetic waves can be produced or absorbed by other changes in atoms, over a wide range of frequencies.

age prematurely; cancer

提示One shows up as wrinkles sooner than expected; the other is a serious disease.

为什么Ultraviolet from the Sun or from a sunbed is absorbed in the skin, where it can damage cells. The harm depends on the size of the dose, which is why shade, clothing and sunscreen reduce the risk.

They can cause mutations of the genes, which can lead to cancer

提示Think what could go wrong if the instructions inside a cell's DNA were altered.

为什么Ionising radiation can knock electrons out of atoms in living cells. If this damages DNA, a gene may be changed (a mutation), and some mutations lead to cancer. How serious the effect is depends on which radiation it is and how big the dose is, which is why medical X-ray doses are kept as low as possible.

0.008 Sv

提示A millisievert is the smaller unit, so the number has to get smaller.

为什么Divide by 1000: 8 ÷ 1000 = 0.008 Sv. The dose, in sieverts, tells you how great the risk of harm is when the body is exposed to radiation. AQA gives the conversion and does not expect the unit to be recalled, but pupils must be able to compare doses given as data.

By making the current in the circuit oscillate (an alternating current)

提示The electrons in the aerial must not flow steadily one way.

为什么When charge oscillates back and forth in a circuit, it sends out radio waves with the same frequency as the oscillation. A transmitter is a circuit built to do exactly this. It is how radio and television stations send out their signals.

frequency

提示It is the property that a receiver is tuned to in order to pick out one station.

为什么The wave makes electrons in the metal aerial oscillate in step with it, so the induced alternating current copies the wave's rate of oscillation. A receiver then picks out the station it wants. This is the reverse of what happens in the transmitter.

radio

提示It is the group with the longest wavelength in the spectrum.

为什么Television and radio broadcasts are both carried by radio waves. Satellite television is different: signals to and from satellites use microwaves.

microwaves

提示The same group of waves is used to heat food quickly in a kitchen.

为什么AQA lists satellite communications and cooking food as the uses of this group. Its list also gives fibre optic communications as a use of visible light: pulses of light sent along thin glass fibres. Each part of the spectrum has uses that suit its properties.

Infrared

提示It is given out by anything warm, and lies just beyond the red end of visible light.

为什么Hot objects emit this radiation, and surfaces that absorb it are heated: that is how an electric heater warms you and a grill browns toast. Thermal cameras detect the radiation that warm objects give out, so they can show people or heat leaks in the dark.

Ultraviolet

提示It is also the part of sunlight that sunscreen is designed to block.

为什么In an energy-efficient (fluorescent) lamp, this radiation is produced inside the tube and absorbed by a coating that then gives out visible light. Tanning beds use it to darken the skin, which carries the same risks as too much sun.

They pass through soft tissue but are absorbed by bone, so the bones show up as a shadow on the detector

提示Ask which parts of the body stop them and which do not.

为什么A use suits a wave when the wave's behaviour with the materials involved matches the job. X-rays are transmitted by flesh and absorbed by dense bone, so a detector behind the patient records where they got through. Because X-rays are ionising, the dose is kept as small as possible.