GCSE · Physics · Edexcel · Spec 1PH0
Danger of EM waves increasing with frequency
Gamma rays have a scary reputation. Yet a weak beam of gamma rays can be less harmful than very intense infrared from hot charcoal. How can the scarier radiation lose?
Physics · Electromagnetic waves
Which radiation can knock an electron off an atom?
Sort each band: ionising or non-ionising? Commit first, then read the reason.
Still to sort
Ionising (0)
One packet carries enough energy to push an electron off an atom.
Where the line is: The line falls at ultraviolet. Ultraviolet, X-ray and gamma packets can push an electron off an atom.
Non-ionising (0)
One packet does not carry enough energy to do that.
Where the line is: Radio, microwave, infrared and visible light packets fall short of the line: they don't carry enough energy.
Radiation delivers its energy in small packets, one by one. If a single packet carries enough energy to push an electron off an atom, the radiation is ionising. Your job: decide which side of that line each band falls on.
Cells and cancer
Reason it through
How can ionising radiation increase the risk of cancer?
First link · your turn
A packet of ionising radiation reaches an atom inside a living cell. What can it do to that atom?
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
Why some radiation is harmless to atoms, and some can knock electrons clean off them.
What you need to know
- Electromagnetic waves of every frequency carry energy from a source to an absorber, in small packets, one by one.
- The higher the frequency, the more energy in a single packet. So potential harm rises with frequency.
Have a goRadiation X has a higher frequency than radiation Y. Which one carries more energy in a single packet?
Radiation X.
Higher frequency means more energy in each packet, which is exactly why potential harm rises with frequency.
- But total energy also depends on intensity. A weak gamma beam can be less harmful than very intense infrared from hot charcoal.
Have a goGamma packets are the heavyweights. So how on earth does charcoal's infrared end up out-delivering a weak gamma beam?
Through its intensity: very intense infrared transfers more energy per second.
Total energy depends on intensity as well as frequency, so a higher-energy packet doesn't guarantee a more harmful beam.
- Ionisation is an atom losing or gaining electrons. That gives it an overall charge, and it's now an ion.
Have a goSam insists that only LOSING electrons counts as ionisation. Is Sam right?
No. Losing or gaining electrons both count.
Either way the atom ends up with an overall charge, and an atom that has lost or gained electrons is an ion.
- Only ultraviolet, X-rays and gamma rays are ionising: one packet can carry enough energy to push an electron off an atom.
- Radio waves, microwaves, infrared and visible light are non-ionising, because their packets don't carry enough energy.
- Higher frequency means more ionising: gamma rays beat X-rays, and X-rays beat ultraviolet.
- Ionisation in a living cell can change the cell's chemical reactions. The damaged cell may not work properly, or may be killed.
- If DNA is ionised, the cell's instructions can change (a gene mutation). Damaged cells can sometimes reproduce uncontrollably, so cancer risk rises.
- Ultraviolet causes tanning and sunburn and increases the risk of skin cancer.
The big picture
Electromagnetic radiation delivers its energy in small packets, and the higher the frequency, the more energy each packet carries. That is why potential harm rises with frequency. From ultraviolet upwards, a single packet can push an electron off an atom (ionising radiation), which can damage cells and DNA and raise the risk of cancer. But frequency isn't the whole story: total energy also depends on intensity.
Key points
Worked example
Problem
A neutral atom has 6 protons and 6 electrons. A packet of ionising radiation pushes one electron off it. Describe the atom now, and say what it is called.
⚠ Watch out
Assuming the highest-frequency radiation always means the most harmful beam. Frequency only sets the energy in each packet. How intense the beam is also changes the total energy it transfers.
Memory hook
Remember U-X-G: ultraviolet, X-rays, gamma. Those are the ionising three, and the line falls at ultraviolet. Frequency sets what each packet carries. It is never the whole story.
Check yourself
Radiation Z is non-ionising. What does that tell you about a single packet of Z, and does it mean Z transfers no energy?
Flashcards
(12)What happens to energy stores when electromagnetic waves are emitted and absorbed?
In what form does electromagnetic radiation transfer its energy?
As frequency rises, what happens to the energy in one packet, and to potential harm?
Besides frequency, what else decides the total energy a beam transfers?
What are ionisation and an ion?
Name the ionising radiations.
Which radiations are non-ionising, and why?
Gamma, X-ray or ultraviolet: which packet carries the most energy, and which the least?
How can ionising radiation damage a living cell?
What can happen if ionising radiation ionises an atom in a DNA molecule?
Why does ionising radiation increase the risk of cancer?
Name three effects of ultraviolet radiation on people.
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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