Electromagnetic Waves Flashcards

All 36 cards in this deck

What type of wave is every electromagnetic wave?

Transverse.

What is the speed of electromagnetic waves in a vacuum?

$3 \times 10^8$ m/s — the same for every part of the EM spectrum.

What do all electromagnetic waves transfer, and between what?

Energy, from a source to an observer.
e.g. infrared from a fire transfers energy to your skin.

True or false? Electromagnetic waves need a medium to travel through.

False. They can travel through a vacuum, e.g. light from the Sun crossing space.

What are the steps to find the frequency of an electromagnetic wave from its wavelength?
e.g. an EM wave in a vacuum with wavelength $3$ m

1. Use $v = f\lambda$ with $v = 3 \times 10^8$ m/s
2. Rearrange: $f = v \div \lambda$
3. $f = 3 \times 10^8 \div 3 = 1 \times 10^8$ Hz

What are the steps to find how far an electromagnetic wave travels in a given time?
e.g. light from the Sun takes $500$ s to reach Earth

1. Use distance = speed × time, speed $= 3 \times 10^8$ m/s
2. Substitute: $3 \times 10^8 \times 500$
3. Distance $= 1.5 \times 10^{11}$ m

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.

Which colour of visible light has the longest wavelength?

Red. (Violet has the shortest wavelength.)

Going from radio waves to gamma rays, what happens to wavelength and to frequency?

Wavelength decreases and frequency increases.

True or false? There are gaps between the groups of the electromagnetic spectrum.

False. The spectrum is continuous from radio waves to gamma rays; the groupings just name regions of it.

Which part of the electromagnetic spectrum can the human eye detect?

Visible light only — the eye detects just a limited range of frequencies.

Name the four things a substance may do to an electromagnetic wave that reaches it.

Absorb it, transmit it, refract it or reflect it.

True or false? A substance treats all parts of the electromagnetic spectrum in the same way.

False. Whether a substance absorbs, transmits, refracts or reflects a wave varies with the wavelength.

What happens to infrared, and to radio waves, when they meet an object such as an armchair?

Infrared is absorbed/blocked (it needs line of sight); radio waves are transmitted through it.

As the wavelength of ultraviolet gets shorter, what happens to how much of it a substance such as glass transmits?

Less is transmitted and more is absorbed — absorption increases as wavelength decreases.

True or false? Sunglasses with photochromic lenses darken because they react to ultraviolet.

True. The darkened lenses then absorb more light and protect the eyes from UV damage.

How does the potential danger of an electromagnetic wave change across the spectrum?

It increases with increasing frequency (so gamma rays are the most dangerous, radio waves the least).

What is the harmful effect of excessive exposure to microwaves?

Internal heating of body cells.

What is the harmful effect of excessive exposure to infrared radiation?

Skin burns.

What is the harmful effect of excessive exposure to ultraviolet radiation?

Damage to surface cells and to the eyes, leading to skin cancer and eye conditions such as cataracts.

What is the harmful effect of excessive exposure to x-rays and gamma rays?

Mutation or damage to cells in the body.

True or false? The potential danger of an EM wave increases as its velocity increases.

False. All EM waves travel at the same speed; the danger increases with increasing frequency.

Give three uses of radio waves.

Broadcasting, communications and satellite transmissions.

Give three uses of microwaves.

Cooking, communications and satellite transmissions.

Give four uses of infrared radiation.

Cooking, thermal imaging, optical fibres and television remote controls (also short-range communications and security systems).

Give three uses of visible light.

Vision, photography and illumination.

Give four uses of ultraviolet radiation.

Security marking, fluorescent lamps, detecting forged bank notes and disinfecting water.

Give two uses of x-rays and two uses of gamma rays.

X-rays: medical x-rays and airport security scanners (observing internal structure). Gamma: sterilising food and medical equipment, and detecting and treating cancer.

What can changes in atoms and in the nuclei of atoms generate?

Electromagnetic radiation over a wide range of frequencies.

Which part of the electromagnetic spectrum is produced by changes in the nucleus of an atom?

Gamma rays.

True or false? Atoms and nuclei can only emit radiation, never be changed by it.

False. Changes in atoms and nuclei can also be caused by the absorption of a range of radiations.

How are radio waves produced?

By oscillations in electrical circuits (an alternating current in an aerial).

What happens in an aerial or electrical circuit when radio waves are absorbed by it?

They induce oscillations (an alternating current) in the circuit, of the same frequency as the waves.

Which group of the electromagnetic spectrum has the longest wavelength and lowest frequency?

Radio waves.

True or false? Radio waves can be made by electrical circuits but cannot themselves affect electrical circuits.

False. Radio waves can both be produced by, and induce, oscillations in electrical circuits.