OCR - P1: Radiation and waves

Radiation is a 'scientific model' that can be used to describe and predict the effects of some processes in which one object affects another some distance away.

If one object (the source) emits radiation (of some kind) this spreads out from the source and transfers its energy to other object(s) some distance away.

Light energy is one of a family of radiation, called the electromagnetic spectrum.

All radiations in the electromagnetic spectrum travel at the same speed through space

1. Describe the main parts of the electromagnetic spectrum

– radio, microwave, infrared, visible (red to violet), ultraviolet, X-rays and gamma rays

Know how these range from long to short wavelengths, from low to high frequencies, and from low to high energies

2. Recall that our eyes can only detect a very limited range of frequencies in the electromagnetic spectrum. (380 - 740 nm)

- see S.I. Prefixes

3. Recall that all electromagnetic radiation is transmitted through space with the same very high (but finite) speed - the speed of light - 3.0 x 10⁸ m/s.

4. Explain, with examples, that electromagnetic radiation transfers energy from source to absorber

When electromagnetic radiation strikes an object, some may be transmitted (pass through it), or be reflected, or be absorbed.

When the radiation is absorbed it ceases to exist as radiation; usually it raises the temperature of the absorber.

Some types of electromagnetic radiation do not just cause a rise in temperature when absorbed - they can cause ionisation;

X-rays, gamma rays and high energy ultraviolet radiation photons have enough energy to remove an electron from an atom or molecule (undergo ionisation).

5. Recall that substances may

absorb,

transmit, or

reflect electromagnetic radiation

depending on the wavelength of the radiation that hits them

(Look at the work on reflection, refraction and dispersion in P1.4)

6. Recall that in each atom its electrons are arranged at different distances from the nucleus (from your chemistry), and that such arrangements may change with absorption or emission of electromagnetic radiation, and that atoms can become ions by loss of outer electrons

Exposure to large amounts of ionising radiation can cause damage to living cells; smaller amounts can causes changes to cells which may make them grow in an uncontrolled way, they can cause cancer.

Oxygen is acted on by radiation to produce ozone in the upper atmosphere. This ozone absorbs ultraviolet radiation, and protects living organisms, especially animals, from its harmful effects.

Radio waves are produced when there is an oscillating current in an electrical circuit. Radio waves are detected when the waves cause an oscillating current in a conductor.

Different parts of the electromagnetic spectrum are used for different purposes due to differences in the ways they are reflected, absorbed, or transmitted by different materials.

Developments in technology have made use of all parts of the electromagnetic spectrum; every development must be evaluated for the potential risks as well as the benefits.

Data and scientific explanations of mechanisms, rather than opinion, should be used to justify decisions about new technologies.

7. Recall that changes in molecules, atoms and nuclei can generate and absorb radiations over a wide frequency range, including:

a) gamma rays are emitted from the nuclei of atoms (they are nuclear radiation)

b) X-rays, ultraviolet and visible light are generated when electrons in atoms lose energy by moving to lower energy states within the electron shells of the atom

c) high energy ultraviolet, gamma rays and X-rays have enough energy to cause ionisation when absorbed by electrons orbiting some atoms

d) ultraviolet is absorbed by oxygen to produce ozone, which also absorbs ultraviolet, protecting life on Earth.

e) infrared is emitted and absorbed by atoms and molecules

8. Describe how ultra-violet radiation, X-rays and gamma rays can have hazardous effects, notably on human bodily tissues

9. Give examples of some practical uses of electromagnetic radiation in the radio, microwave, infrared, visible, ultraviolet, X-ray and gamma ray regions of the spectrum

10. Recall that radio waves can be produced by, or can themselves induce, oscillations in electrical circuits