Radiation and Waves (OCR)
What are the Risks and Benefits of Using Radiations?
Radiation as a Model
A model of radiation helps explain how energy is transferred from a source to an object some distance away.
The source emits radiation, which spreads out and carries energy through space.
This radiation can interact with matter by being transmitted, reflected, or absorbed.
The Electromagnetic Spectrum
Light is a type of electromagnetic radiation.
The electromagnetic spectrum includes several types of radiation, all of which travel at the same speed in a vacuum (approximately 3 × 10⁸ m/s).
The spectrum consists of:
Radio waves
Microwaves
Infrared
Visible light (red to violet)
Ultraviolet
X-rays
Gamma rays
These are ordered from:
Long to short wavelength
Low to high frequency
Low to high energy
Interaction with Matter
When radiation strikes an object, it may:
Be transmitted (pass through)
Be reflected (bounce off)
Be absorbed (energy taken in)
When absorbed, the radiation usually heats the object.
Some forms of electromagnetic radiation have enough energy to cause ionisation:
X-rays, gamma rays, and high-energy ultraviolet radiation can remove electrons from atoms or molecules.
This ionisation can lead to chemical changes or biological effects.
Risks and Benefits of Electromagnetic Radiation
Benefits
Used in medical imaging (e.g., X-rays)
Communication technologies (e.g., radio, microwaves)
Infrared radiation for heating
Gamma rays for sterilisation of medical equipment
Risks
Ionising radiation (X-rays, gamma rays, and high-energy ultraviolet rays) can damage living tissue.
May lead to mutations or increase cancer risk.
Excessive exposure to ultraviolet can cause skin damage or eye problems.
Effects of Ionising Radiation on Living Cells
High doses of ionising radiation can damage or destroy living cells, potentially leading to radiation sickness or death.
Smaller doses can cause mutations or changes in DNA, which may cause cells to grow uncontrollably, leading to cancer.
Protection from Harmful Radiation
In the upper atmosphere, oxygen is affected by radiation and forms ozone (O₃).
This ozone layer absorbs harmful ultraviolet (UV) radiation from the sun.
The ozone layer protects animals and other living organisms on Earth by reducing their exposure to UV radiation.
Production and Detection of Radio Waves
Radio waves are produced by oscillating currents in electrical circuits.
These waves are detected when they cause an oscillating current in a receiver circuit (e.g., an aerial or antenna).
Uses of the Electromagnetic Spectrum
Different parts of the electromagnetic spectrum are suited to different tasks because of how materials absorb, reflect, or transmit them.
For example:
Microwaves are absorbed by water molecules and used for heating.
X-rays pass through soft tissue but are absorbed by bone, making them useful in medical imaging.
Evaluation of New Technologies
Advances in technology use all parts of the electromagnetic spectrum.
When assessing new technologies, it is important to:
Consider both benefits and potential risks.
Use data and scientific explanations, not opinions, to justify decisions about their use.
What is Climate Change and What is the Evidence for It?
All objects emit electromagnetic radiation.
The type (wavelength) and intensity (strength) of radiation depend on the temperature of the object:
Cooler objects emit longer wavelengths (infrared).
Hotter objects emit shorter wavelengths (visible or ultraviolet).
The higher the temperature, the:
Greater the intensity of radiation emitted.
Peak wavelength of the radiation shifts to shorter wavelengths.
This is known as black body radiation – an ideal object that absorbs and emits all radiation perfectly.
Energy Balance and Temperature:
The temperature of an object depends on the balance between:
Incoming radiation (e.g. from the Sun)
Absorbed radiation
Radiation emitted by the object
If an object absorbs more radiation than it emits → it gets hotter.
If an object emits more radiation than it absorbs → it gets cooler.
When the rates are equal, the object’s temperature stays constant.
The Earth’s Energy Balance and the Greenhouse Effect:
The Earth receives short-wavelength radiation (mostly visible light) from the Sun.
Some of this radiation is:
Reflected by clouds or the surface (especially ice and snow).
Absorbed by the surface, warming the planet.
The Earth emits longer-wavelength infrared radiation back into space.
Some gases in the atmosphere (e.g. carbon dioxide, methane, water vapour) absorb and re-emit this infrared radiation in all directions.
This traps heat and keeps Earth warmer than it would be without an atmosphere.
This is called the greenhouse effect.
Factors that Determine the Earth’s Temperature:
The amount of greenhouse gases – more gases = more heat trapped.
Cloud cover – can reflect or trap radiation depending on type and height.
Surface reflectivity (albedo) – ice reflects more radiation than oceans or forests.
Solar activity – changes in the Sun’s output affect incoming energy.
Volcanic activity – can increase atmospheric particles that reflect sunlight.
Evidence for Climate Change:
Carbon dioxide levels have been rising due to:
Burning fossil fuels (coal, oil, gas).
Deforestation (reduces CO₂ absorption by trees).
Computer climate models:
Use data from satellites, weather stations, and ocean buoys.
Predict temperature rises and help understand long-term climate trends.
Support the conclusion that human activity is contributing to global warming.
Everyday Example:
A car parked in the sun:
Absorbs visible light.
Re-emits it as infrared radiation.
Glass windows trap infrared, warming the interior — similar to the greenhouse effect.
How Do Waves Behave?
1. Wave Basics
A wave is a regular disturbance that transfers energy through a medium or space.
Waves do not transfer matter, only energy.
The disturbance in the medium moves differently depending on the type of wave:
Transverse wave: the medium moves perpendicular to the direction of wave travel.
Longitudinal wave: the medium moves parallel to the direction of wave travel.
2. Types of Waves
Transverse Waves:
Particles move at right angles to the wave direction.
Examples:
Waves on a rope
Ripples on water
Light and other electromagnetic waves
Longitudinal Waves:
Particles move in the same direction as the wave.
Examples:
Sound waves in air
Compression waves in a slinky spring
3. Wave Properties
Amplitude:
The maximum displacement from the rest position.
Linked to the energy carried by the wave.
Wavelength (λ):
The distance between two matching points on a wave (e.g., crest to crest or compression to compression).
Frequency (f):
The number of waves passing a point each second.
Measured in Hertz (Hz).
Period (T):
The time it takes for one wave to pass a point.
Formula:
Wave Speed (v):
The speed at which the wave moves through a medium.
Formula:
where
v = speed (m/s),
f = frequency (Hz),
λ = wavelength (m)
4. Wave Behaviour
It is the wave that travels, not the medium itself.
In both water ripples and sound waves, the particles oscillate but stay in place.
5. Reflection and Refraction
Reflection:
Waves bounce back when they hit a surface.
Example: light reflecting off a mirror.
Refraction:
Waves change direction and speed when passing from one medium to another.
Example: light bending when it enters glass from air.
These behaviours can be demonstrated using water waves, making them a useful model for understanding light and sound.
6. Measuring Waves (PAG4 and PAG8)
PAG4 – Using a ripple tank:
Measure the speed, frequency, and wavelength of waves.
Observe transverse wave behaviour.
PAG8 – Light waves:
Measure refraction using a prism.
Investigate reflection using a plane mirror.
7. Practical Applications
A wave model helps predict and explain the behaviour of light and sound:
How they travel
How they interact with surfaces (reflection and refraction)
Refraction of Light and Sound
What is Refraction?
Refraction is the bending of a wave when it enters a different medium at an angle.
It occurs due to a change in wave speed in different substances.
Why Does Refraction Happen?
When a wave moves from one material to another (e.g., air to glass):
The speed of the wave changes.
This causes a change in wavelength, because the frequency stays the same.
The change in wavelength leads to a change in direction (refraction).
Key Points:
Frequency stays constant during refraction.
Wavelength and speed change depending on the medium.
Angle of incidence and angle of refraction are used to describe the direction change.
Electromagnetic Waves
11. Light as an Electromagnetic Wave
Light is part of the electromagnetic spectrum.
It does not need a medium to travel; it can move through a vacuum.
Electromagnetic waves include:
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
12. Nature of Electromagnetic Waves
All electromagnetic waves are transverse.
This means the electric and magnetic fields oscillate at right angles to the direction of wave travel.
They all travel at the same speed in a vacuum (approximately 3.0×1083.0 \times 10^83.0×108 m/s).