Electromagnetic Waves Flashcards
All 39 cards in this deck
What type of wave are all electromagnetic waves?
Transverse.
How do the speeds of different electromagnetic waves in a vacuum compare?
They all travel at the same speed ( m/s).
e.g. radio waves and light waves travel at the same speed in space.What do all electromagnetic waves transfer from a source to an observer?
Energy.
e.g. microwaves transfer energy that makes water molecules in food vibrate more, heating it.True or false? The human eye can detect every frequency of electromagnetic radiation.
False. The eye detects only a limited range of frequencies — visible light.
In the refraction core practical, which angles are measured, and from which line?
The angle of incidence and the angle of refraction, both measured from the normal with a protractor.
In the refraction practical, which way does a ray bend as it enters a glass block at an angle to the normal?
Towards the normal, because the light slows down in the glass.
How does the ray leaving the far side of a rectangular glass block compare with the ray that entered?
It is parallel to the incident ray, but shifted sideways.
Give one way to reduce error when measuring the angles in the refraction core practical.
Use a narrow ray and a sharp pencil, marking each ray with two dots far apart before joining them with a ruler.
Name the seven groups of the electromagnetic spectrum in order of increasing frequency.
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Name the colours of the visible spectrum in order of decreasing wavelength.
Red, orange, yellow, green, blue, indigo, violet.
What does it mean that the electromagnetic spectrum is continuous?
There are no gaps between the groups — wavelength decreases and frequency increases smoothly from radio waves to gamma rays.
Name the four things a substance may do to an electromagnetic wave.
Absorb, transmit, refract or reflect it — and this varies with the wavelength of the wave.
What causes white light to split into colours when it crosses the boundary from air into glass?
The colours have different wavelengths and travel at different speeds in glass, so they refract by different amounts.
Why can a radio-wave remote control work from behind an armchair when an infrared one may not?
Infrared is absorbed/blocked by the armchair, while radio waves are transmitted through it, because they have different wavelengths.
True or false? UVA, UVB and UVC all pass through the Earth's atmosphere equally well.
False. The shorter the wavelength the more is absorbed — UVA is mostly transmitted and UVC is completely absorbed.
As you go along the electromagnetic spectrum, how does the potential danger of the waves change?
The potential danger increases as frequency increases.
True or false? Higher-frequency electromagnetic waves are more dangerous because they travel faster.
False. All EM waves travel at the same speed; the danger rises because higher frequency means higher energy.
What is the harmful effect on people of excessive exposure to microwaves?
Internal heating of body cells.
What is the harmful effect on people of excessive exposure to infrared radiation?
Skin burns.
What are the harmful effects on people of excessive exposure to ultraviolet radiation?
Damage to surface cells and to the eyes, leading to skin cancer and eye conditions.
What is the harmful effect on people of excessive exposure to X-rays and gamma rays?
Mutation or damage to cells in the body, which can cause cancer.
Give two uses of radio waves.
Broadcasting (TV and radio) and communications/satellite transmissions.
Give two uses of microwaves.
Cooking, and communications/satellite transmissions.
Give two uses of infrared radiation.
Cooking and thermal imaging. (Also optical fibres, TV remote controls, security systems, short-range communication.)
Give two uses of ultraviolet radiation.
Security marking and detecting forged banknotes. (Also fluorescent lamps and disinfecting water.)
Give two uses of X-rays.
Medical X-rays to observe internal structure, and airport security scanners.
Give two uses of gamma rays.
Sterilising food and medical equipment, and detecting and treating cancer.
How are radio waves produced in a transmitting aerial?
By oscillating (alternating) current — electrons oscillating up and down the aerial.
What happens when radio waves are absorbed by a receiving aerial?
They induce oscillations (an alternating current) in the electrical circuit.
How does the frequency of the radio waves emitted by an aerial relate to the current in it?
It is the same as the oscillation frequency of the alternating current.
Where in an atom are gamma rays produced?
In the nucleus, by energy changes/rearrangement that stabilise it, e.g. in radioactive decay.
How are X-rays produced in terms of electrons in atoms?
Electrons fall to a lower energy level; a large energy loss is emitted as high-frequency X-ray radiation.
What happens to an electron in an atom when it absorbs electromagnetic radiation?
It moves to a higher energy level, into an 'excited' state.
What is fluorescence?
A substance absorbs ultraviolet, its excited electrons de-excite and the energy is emitted as visible light.
e.g. security marks on banknotes glowing under UV.True or false? All electromagnetic waves travel at the same speed in every substance.
False. They all travel at the same speed in a vacuum, but their speeds change in other substances, which is why light refracts.
Give two uses of visible light.
Vision and photography. (Also illumination.)
Why are microwaves used to communicate with satellites?
The microwave wavelengths chosen are absorbed very little by the atmosphere, so they travel through cloud and water vapour to and from the satellite.
Why do bones show up clearly on an X-ray image?
Bone absorbs X-rays strongly, while soft tissue lets most of them through, so bone casts a clear shadow on the detector.
Which three types of electromagnetic radiation are ionising?
Ultraviolet, X-rays and gamma rays.