Electromagnetic Waves (Edexcel GCSE Physics): Flashcards
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Define electromagnetic wave.
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Cards in this collection (41)
Define electromagnetic wave.
Transverse waves that transfer energy from the source of the waves to an absorber.
List three properties shared by all electromagnetic waves.
They are all transverse; they can all travel through a vacuum; they all travel at the same speed in a vacuum.
How does wavelength affect the energy carried by an EM wave?
The shorter the wavelength, the higher the energy carried, for example by UV, X-rays and gamma rays.
Water molecules ______ certain wavelengths of microwave radiation, which is how a microwave oven heats food.
Water molecules absorb certain wavelengths of microwave radiation, which is how a microwave oven heats food.
Why do hot objects warm up other objects near them, without contact?
Hot objects emit infrared radiation, which is absorbed by other objects, warming them up.
Name three types of EM radiation emitted by the Sun and give one effect of each.
Visible light allows living creatures to see; infrared heats up the Earth; ultraviolet provides plants with energy for photosynthesis.
True or False?
All electromagnetic waves travel at different speeds in a vacuum.
False.
All electromagnetic waves travel at the same speed in a vacuum.
List the seven types of wave in the electromagnetic spectrum, in order of increasing frequency.
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
The electromagnetic spectrum is arranged from ______ wavelength (lowest frequency) to shortest wavelength (highest frequency).
The electromagnetic spectrum is arranged from longest wavelength (lowest frequency) to shortest wavelength (highest frequency).
Define visible light.
The range of wavelengths of electromagnetic radiation that are visible to humans.
What fraction of the whole electromagnetic spectrum does visible light take up?
Just 0.0035% of the whole electromagnetic spectrum.
Which colour of visible light has the longest wavelength, and which has the shortest?
Red has the longest wavelength; violet has the shortest wavelength.
What is the relationship between the wavelength and frequency of an EM wave?
Wavelength and frequency are inversely proportional: an increase in wavelength is a decrease in frequency, and a decrease in wavelength is an increase in frequency.
True or False?
Radiation with a higher frequency has lower energy and is less ionising.
False.
Higher frequency EM radiation has higher energy and is more ionising, for example UV, X-rays and gamma rays.
Define refraction of an EM wave.
The bending of an EM wave caused by a change in its speed as it passes from one medium into another.
Do all electromagnetic waves travel at the same speed in matter such as water or glass?
No. When EM waves pass into a material they slow down, and the amount of slowing depends on the material.
Define dispersion.
Different wavelengths of light slowing down by different amounts as they pass into a medium, causing them to refract by different amounts (Higher tier only).
In a prism, which colour of visible light is refracted the most, and which the least?
Violet light is refracted the most; red light is refracted the least (Higher tier only).
List the four ways an EM wave may interact with a new medium.
Transmitted, absorbed, reflected or refracted (Higher tier only).
Glass will transmit and/or refract visible light, ______ UV radiation, and ______ infrared radiation.
Glass will transmit and/or refract visible light, absorb UV radiation, and reflect infrared radiation.
True or False?
Which interaction occurs when an EM wave meets a new material depends only on the wavelength of the wave.
False.
It depends on both the wavelength of the wave and the material it is travelling through.
What happens to the energy of EM waves as frequency increases?
The energy increases; beyond the visible part of the spectrum, the energy becomes large enough to ionise atoms.
Define ionising radiation.
Radiation with enough energy to remove electrons from atoms. The higher the frequency, the more ionising the radiation.
Why are microwave ovens safe to use even though they use high-energy microwaves?
The metal walls and metal grid in the door prevent the microwave energy from escaping the oven.
What eye damage can ultraviolet radiation cause, and what everyday item protects against it?
High levels of UV exposure can cause severe eye damage; good quality sunglasses absorb UV, preventing it from entering the eyes.
Ultraviolet radiation is ionising, meaning it can kill cells or cause them to malfunction, resulting in premature ageing and diseases such as ______.
Ultraviolet radiation is ionising, meaning it can kill cells or cause them to malfunction, resulting in premature ageing and diseases such as skin cancer.
How do doctors and radiographers reduce their exposure to X-rays and gamma rays?
Doctors leave the room when taking X-rays; people working with gamma rays wear radiation badges and take precautions to minimise exposure.
Why can microwaves used for communications, such as in mobile phones, be considered safe?
They emit very small amounts of energy, which are not known to cause any harm.
True or False?
Radio waves and gamma rays are equally dangerous to human tissue.
False.
EM waves become more dangerous the shorter their wavelength; radio waves have no known harmful effects while gamma rays can cause cancer.
What happens to an electron when it absorbs energy from an EM wave?
It moves up to a higher energy level.
What happens when an electron moves down to a lower energy level?
It emits an electromagnetic wave.
Define emission, in the context of atoms and EM waves.
When an electron moves down to a lower energy level and releases an EM wave in the process.
What determines the frequency of the EM wave absorbed or emitted by an atom?
The size of the gap between the energy levels the electron moves between.
The energies associated with electron transitions tend to be in the ______ and ultraviolet range, and sometimes X-rays.
The energies associated with electron transitions tend to be in the visible and ultraviolet range, and sometimes X-rays.
True or False?
Gamma rays can only be produced by interactions with the electrons orbiting an atom.
False.
Higher energies such as gamma rays can only be achieved when EM waves interact with the nucleus of the atom, not the orbiting electrons.
How are radio waves produced?
By connecting an antenna to a high-frequency alternating current (a.c.) power source.
What determines the frequency of the radio waves produced by an antenna?
The frequency of oscillation of charge in the a.c. circuit — the radio waves produced have the same frequency as this oscillation.
Describe what happens in a transmitting antenna to produce radio waves.
Charge from the alternating current oscillates up and down the antenna, producing radio waves that can be absorbed by a similar aerial some distance away.
Describe what happens when a receiving aerial absorbs radio waves.
The metal aerial absorbs the radio waves, creating an alternating current with the same frequency as the transmitted wave.
In a transmitting antenna, charge from the alternating current oscillates ______ the antenna to produce radio waves.
In a transmitting antenna, charge from the alternating current oscillates up and down the antenna to produce radio waves.
True or False?
The alternating current induced in a receiving aerial has a different frequency to the transmitted radio wave.
False.
The induced alternating current has the same frequency as the transmitted radio wave.
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