BRAINCAKEWaves and radioactivity
Revision notes for Waves and radioactivity in OCR Combined Science A (J250). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Wave motion: amplitude, wavelength, frequency and periodA wave transfers energy from one place to another without transferring matter.
- Defining wavelength and frequencyThe wavelength of a wave is the distance from a point on one wave to the identical point on the next wave.
- The wave speed equationThe speed of a wave is how far the wave travels each second.
- Calculations with wave speed, frequency and wavelengthUse the same method for every wave calculation.
- Transverse and longitudinal wavesWaves are classed by how the vibrations relate to the direction the wave travels.
- Ripples, sound waves and measuring wave speedRipples on the surface of water are used as a model of transverse waves.
- Evidence that the wave travels, not the mediumWhen a wave passes through a material, it is the wave that travels from place to place.
- Electromagnetic waves are transverse and travel at the same speed in spaceElectromagnetic waves (EM waves) are transverse waves.
- Electromagnetic waves transfer energy from a source to an absorberEvery EM wave carries energy.
- Frequency and wavelength across the electromagnetic spectrumThe wave equation links the three quantities of any wave: wave speed (m/s) = frequency (hertz, Hz) × wavelength (m), or v = f × λ.
- The groupings of the electromagnetic spectrumEM waves form a continuous spectrum that is split into seven main groups.
- What our eyes can detectThe electromagnetic spectrum is very wide, but our eyes can only detect a very small part of it.
- Light is an electromagnetic waveVisible light is one group of electromagnetic waves, so it has all the properties of the family.
- Uses of electromagnetic wavesEach part of the electromagnetic spectrum has uses that depend on its properties.
- Hazards of ultraviolet, X-rays and gamma raysUltraviolet waves, X-rays and gamma rays have high frequencies and carry a lot of energy.
- Radio waves and electrical circuitsRadio waves can be produced by oscillations in an electrical circuit.
- Absorption, transmission, reflection and refractionWhen an electromagnetic wave meets a substance, four things can happen.
- Wave velocity in different substances and refractionIn a vacuum all electromagnetic waves travel at the same speed, 300 000 000 m/s.
- Atomic nuclei: protons and neutronsEvery atom has a tiny nucleus at its centre.
- Isotopes and neutron numberAll atoms of one element have the same number of protons, which is its atomic number.
- Nuclear notation and isotopesA nucleus is written as the symbol of the element with two numbers beside it.
- Unstable nuclei and types of radiationSome nuclei are unstable.
- Changes to the nucleus on emissionWhen a nucleus emits radiation, its mass number or its charge (atomic number), or both, can change.
- Balanced equations for radioactive decayA decay equation shows the nucleus before and after emission.
- Balancing equations for alpha, beta and gamma emissionA nuclear equation must balance.
- Electron energy levels, excitation and ionisationIn an atom the electrons are arranged at different distances from the nucleus.
- Radiation from atoms and nucleiChanges in atoms and in nuclei can generate and absorb radiation over a wide range of frequencies.
- Half-life and random decayRadioactive decay is random.
- Half-life calculations and decay graphsAfter each half-life the activity (or the number of unstable nuclei) halves again.
- Penetrating power of alpha, beta and gammaThe three types of nuclear radiation differ in how far they can pass through materials.
- Contamination and irradiationContamination means that unwanted radioactive atoms have got on to or into an object or person.