Light belongs to the electromagnetic spectrum, a family of electromagnetic waves that travel at a speed of 300 000 km/s through space, which is a vacuum.
What is a 'photon'?
A tiny packet of energy that behaves similar to a wave, but also as a stream of particles.
A picture taken of light.
The intensity of [blank_start]electromagnetic[blank_end] radiation gets less as you move [blank_start]further[blank_end] away from the source. The intensity of the Sun's radiation decreases further away from it because it is spread over a [blank_start]larger[blank_end] area. This is why planets more distant from the Sun than the Earth are much [blank_start]cooler[blank_end] than our planet. The earth receives more of the Sun's electromagnetic radiation because the intensity of the radiation is [blank_start]greater[blank_end] closer to the Sun.
[blank_start]Intensity[blank_end] = energy transferred per second per m^2.
If you move a torch closer to a surface, its light spreads over a smaller area and becomes [blank_start]brighter[blank_end]. The total energy from the torch each second is the [blank_start]same[blank_end], but the intensity of light on the surface increases. This happens because as the distance [blank_start]doubles[blank_end], the area the energy spreads over increases four-fold, and so the intensity [blank_start]decreases[blank_end] four-fold.
X-Rays have a higher frequency than gamma rays.
Radiation workers increase their risk of exposure to X-rays and [blank_start]gamma[blank_end] rays. They can choose whether to accept this [blank_start]risk[blank_end]. The risk can be monitored using [blank_start]dosimeters[blank_end], allowing problems to be spotted before too much harm is done.
People who have mobile phone [blank_start]masts[blank_end] built near their homes have exposure to [blank_start]microwaves[blank_end] forced upon them. They tend to be less [blank_start]willing[blank_end] to accept any level of risk, and are more likely to [blank_start]overstate[blank_end] possible risks.
We are surrounded by ionising radiation all the time. The risk to health is very low, but people tend to overstate it. Why?
people want to deter new projects eg. nuclear power stations
people are unsure of risks due to lack of education
Why does a substance warm up when it absorbs radiation?
the energy from the absorbed radiation is transferred to thermal (heat) energy
the radiation excites the particles, generating thermal energy
The risks to living cells from microwaves are very low because microwaves have a low frequency.
What is ozone?
A form of oxygen containing three oxygen atoms.
A substance that increases the amount of UV radiation on Earth.
Ozone is produced when oxygen [blank_start]molecules[blank_end] absorb high energy UV radiation and react together. Ozone molecules may split into an oxygen molecule and a free oxygen [blank_start]atom[blank_end] if they absorb low energy UV radiation. In both these reactions, [blank_start]infrared[blank_end] radiation is emitted. Ozone also reacts with nitrogen, hydrogen, chlorine and bromine [blank_start]compounds[blank_end].
The absorption of [blank_start]ultraviolet[blank_end] radiation in the ozone layer reduces the amount of ultraviolet radiation reaching the Earth's [blank_start]surface[blank_end]. It also causes [blank_start]chemical[blank_end] changes in this part of the atmosphere.
Using the diagram, explain what the Greenhouse effect is and how it affects the Earth.
The increase in average temperature worldwide caused by an increase in the greenhouse effect.
The extinction of antarctic species.
A digital signal is a type of signal that can take one of a small number of fixed (discrete) values. The values change is discrete steps, and cannot take any values in-between.
Which of these describes an analogue signal?
A signal that can take one of a small number of fixed (discrete) values. The values change is discrete steps, and cannot take any values in-between.
A signal which can vary continuously.
There are several advantages of sending information using [blank_start]digital[blank_end] signals:
- different types of [blank_start]information[blank_end] can be sent at the same time
- digital signals can be sent more accurately than [blank_start]analogue[blank_end] signals
- digital information can be stored and [blank_start]processed[blank_end] by computers.
- digital signals can only take certain [blank_start]values[blank_end], so it is easy to tell which part of the signal is real and what is [blank_start]noise[blank_end] (unwanted information mixed in with the original signal).