Electromagnetic Waves (AQA GCSE Physics): Flashcards
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Define electromagnetic waves.
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Define electromagnetic waves.
Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber.
What do all electromagnetic waves have in common in terms of speed and medium?
All EM waves are transverse, can travel through a vacuum and travel at the same speed in a vacuum.
How many types of electromagnetic wave make up the electromagnetic spectrum?
There are seven types of electromagnetic wave, which together form a continuous spectrum.
The electromagnetic spectrum is arranged in order from the longest wavelength (lowest frequency) to the ______ wavelength (highest frequency).
The electromagnetic spectrum is arranged in order from the longest wavelength (lowest frequency) to the shortest wavelength (highest frequency).
Why is radiation with a higher frequency more dangerous than radiation with a lower frequency?
Higher frequency EM radiation carries higher energy, making it more highly ionising and more harmful to cells and tissues, which can cause cancer.
Define visible light.
Visible light is the range of wavelengths that are visible to humans; it is the only part of the EM spectrum detectable by the human eye.
Which colour of visible light has the longest wavelength, and which has the shortest?
Red light has the longest wavelength (lowest frequency and energy); violet light has the shortest wavelength (highest frequency and energy).
True or False?
Humans can perceive infrared and ultraviolet wavelengths of light.
False.
Humans can only detect visible light; some animals, such as birds, bees and certain fish, can perceive infrared and UV wavelengths.
Define EM radiation as an energy transfer pathway.
EM radiation is an energy transfer pathway that carries energy from one point to another.
Which EM waves carry the most energy, and why does this matter?
Waves with a shorter wavelength carry more energy, including UV, X-rays and gamma rays; the higher the energy, the more dangerous the radiation.
How does a microwave oven transfer energy to food?
Water molecules in the food absorb certain wavelengths of microwave radiation, transferring energy by radiation to the thermal store of the food.
How does infrared radiation transfer energy between objects?
All hot objects emit infrared radiation, which can be absorbed by other objects, transferring energy by radiation to their thermal store and warming them up.
Ultraviolet waves from the Sun cause ______ and sunburn.
Ultraviolet waves from the Sun cause suntans and sunburn.
Name the three types of EM radiation emitted by the Sun, and give one effect of each.
The Sun emits visible light (allows living creatures to see), infrared (heats up the Earth) and ultraviolet (causes suntans and sunburn); energy from the Sun is transferred by radiation.
True or False?
Microwave ovens transfer energy to food by conduction.
False.
Microwave ovens transfer energy by radiation to the thermal store of the food, since water molecules absorb certain microwave wavelengths.
List the four ways an electromagnetic wave might interact when moving from one medium into another.
An EM wave may be transmitted, absorbed, reflected or refracted.
What two factors determine how an EM wave interacts with a material?
The interaction depends on the wavelength of the wave and the material it is travelling through.
Describe how glass interacts with visible light, UV radiation and infrared radiation.
Glass transmits and/or refracts visible light, and absorbs both UV radiation and infrared radiation.
Although all electromagnetic waves travel at the same speed in a vacuum, they ______ down when they encounter certain materials such as water, glass or oil.
Although all electromagnetic waves travel at the same speed in a vacuum, they slow down when they encounter certain materials such as water, glass or oil.
Why do electromagnetic waves refract when they enter a different material?
Refraction occurs because of the difference in velocity of the wave between the two substances; how much the wave slows down depends on the material.
Using a wavefront diagram, explain why a wave changes direction when it enters a new medium.
Different parts of the wave enter the new medium at different times, causing a change in speed; this difference in speed between the parts in the first and second medium causes the wave to bend, changing its direction.
True or False?
All parts of a wavefront enter a new medium at the same time.
False.
Different parts of the wave enter the new medium at different times, which causes the change in speed that makes the wave bend.
Define refraction.
Refraction is the change in direction of light as it passes a boundary between two different transparent media.
What is the "normal" in a ray diagram?
The normal is a hypothetical line perpendicular to the boundary between two media, usually drawn as a dashed or dotted line, from which the angle of refraction is measured.
Which way does light bend when passing from a less dense to a more dense medium (e.g. air to glass)?
Light bends towards the normal.
Which way does light bend when passing from a more dense to a less dense medium (e.g. glass to air)?
Light bends away from the normal.
When light travels along the normal, it ______ at all.
When light travels along the normal, it does not bend at all.
Which two properties of light change during refraction, and which property stays the same?
Speed and wavelength change during refraction, but the frequency does not change.
True or False?
Light changes colour when it refracts.
False.
Light does not change colour when it refracts because its frequency stays the same; only its speed and wavelength change.
In the infrared investigation, what is the independent variable and what is the dependent variable?
The independent variable is the colour of the flask; the dependent variable is the temperature of the water.
Give three control variables in the infrared radiation investigation.
Control variables include: identical flasks (except colour), the same amount of hot water, the same starting temperature, and the same time interval.
What is the resolution of the thermometer and the stopwatch used in this investigation?
Thermometer resolution = 1 °C; stopwatch resolution = 0.01 s.
Any difference in heat loss between the flasks must, therefore, be due to ______ radiation.
Any difference in heat loss between the flasks must, therefore, be due to infrared radiation.
What is the heatproof mat used for in this investigation?
The heatproof mat protects the surface and prevents heat loss from the bottom of the flasks.
State two random errors to consider in the infrared radiation investigation.
Random errors include: reaction time delays when starting or stopping the stopwatch, and parallax error if the thermometer is not read at eye level; taking repeat readings and finding a mean can reduce their effect.
State one systematic error precaution in this investigation.
Ensure the starting temperature of the water is the same for each flask, since water cools very quickly; working in pairs helps coordinate starting the stopwatch and immersing the thermometer.
True or False?
Using a data logger connected to a digital thermometer could improve the accuracy of readings in this investigation.
True.
A data logger connected to a digital thermometer gives more accurate readings than reading a manual thermometer.
Which two ways can atoms interact with electromagnetic waves?
Atoms can interact with EM waves by absorbing them or emitting them.
What happens to an electron when it absorbs an electromagnetic wave?
The electron gains energy and moves up to a higher energy level.
What happens when an electron moves down to a lower energy level?
The electron emits an electromagnetic wave.
In which regions of the EM spectrum do electron transitions typically occur?
Electron transition energies tend to be in the visible and ultraviolet range, and sometimes X-rays.
How can an atom produce gamma rays?
Gamma rays are only produced when electromagnetic waves interact with the nucleus, since these represent higher energies than electron transitions can achieve.
The nucleus of an atom can ______ and ______ EM waves in a similar way to electrons.
The nucleus of an atom can absorb and emit EM waves in a similar way to electrons.
True or False?
Atoms can only absorb electromagnetic waves, not emit them.
False.
Atoms can both absorb and emit electromagnetic waves, depending on whether electrons move to higher or lower energy levels.
How are radio waves produced?
By connecting an antenna to a high-frequency alternating current (a.c.) power source; the oscillation of charge produces the radio waves.
Describe what happens in the transmitting antenna.
The 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.
In a receiving aerial, the metal aerial absorbs the radio waves, creating an alternating current with the same ______ as the transmitted wave.
In a receiving aerial, the metal aerial absorbs the radio waves, creating an alternating current with the same frequency as the transmitted wave.
True or False?
Radio waves can only be produced using a direct current (d.c.) power source.
False.
Radio waves are produced using a high-frequency alternating current (a.c.) power source.
Define radiation dose.
Radiation dose is a measure of the risk of harm resulting from an exposure of the body to radiation.
What is radiation dose measured in?
Sieverts (Sv), where 1 Sv = 1000 millisieverts (mSv).
Typical background radiation is about ______ mSv per year.
Typical background radiation is about 1.5 to 3.5 mSv per year.
Why does the danger of an electromagnetic wave increase as its frequency increases?
As frequency increases, so does energy; beyond the visible part of the spectrum, the energy becomes large enough to ionise atoms, damaging human body tissue.
The ______ the wavelength of an electromagnetic wave, the more ionising the radiation, although intensity also plays an important role.
The shorter the wavelength of an electromagnetic wave, the more ionising the radiation, although intensity also plays an important role.
Why are microwaves used for mobile phone communication considered safe, unlike microwave ovens?
Communication microwaves emit very small amounts of energy that are not known to cause harm, whereas microwave ovens emit large amounts of energy, which is prevented from escaping by the oven's metal walls and metal grid.
How can the eyes and skin be protected from ultraviolet radiation?
Sunglasses absorb ultraviolet light to prevent eye damage, and sunscreen absorbs ultraviolet light to prevent skin damage.
True or False?
X-rays and gamma rays are the least ionising types of electromagnetic wave.
False.
X-rays and gamma rays are the most ionising types of EM wave; they can penetrate the body, cause internal damage, mutate genes and cause cancer.
True or False?
Radio waves are known to have harmful effects on the human body.
False.
Radio waves have no known harmful effects, unlike gamma rays, which are regarded as extremely dangerous and can cause cancer.
What three questions should you consider when interpreting data on the risks of radiation exposure?
What are the known risks and consequences of the type of radiation
Does the data correlate with the hypothesis
Are there other factors that could explain the results
Name two uses of radio waves.
Radio waves are used for television and radio.
Microwaves are used for cooking food and ______ communications.
Microwaves are used for cooking food and satellite communications.
Name three uses of infrared radiation.
Uses of infrared radiation include:
Electrical heaters
Cooking food
Infrared cameras
True or False?
Fibre optic communication uses visible light.
True.
In fibre optic communication, signals are carried by pulses of visible light along thin glass fibres.
Name two uses of ultraviolet radiation.
Uses of ultraviolet radiation include:
Security marking
Fluorescent lamps
Detecting forged bank notes
Disinfecting water
What are X-rays and gamma rays used for?
X-rays and gamma rays are used for medical imaging and medical treatments.
State three properties of an electromagnetic wave that affect its suitability for a particular purpose.
The suitability of an electromagnetic wave for a purpose is related to its:
Penetrating ability
Energy
Frequency
Explain why X-rays are suitable for medical imaging.
X-rays penetrate soft body tissue but are absorbed by denser materials, such as bone.
This allows an image of internal structures, such as broken bones, to be formed.
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