- Waves are a transfer of energy.
- Longitudinal waves: the vibrations are parallel to the direction of the wave (sound) e.g. | | | ||| ||| | | ||
- Transverse waves: the vibrations are perpendicular to the direction of the wave (water, EM waves)
- Wavelength: the distance from a point on one wave to the equivalent point on the adjacent wave.
- Amplitude: the maximum displacement of a point on a wave away from its undisturbed position (high amplitude = high volume).
- Frequency: the number of waves passing a point each second (high frequency = high pitch).
- Period: the time taken for one wave to pass a point.
- T = 1/f
- v = fλ
- T: time period (s), f: frequency (Hz), v: speed (m/s), λ: wavelength (m)
- Electromagnetic waves are always transverse, travel at the same velocity through a vacuum.
- HIGHEST WAVELENGTH, LOWEST FREQUENCY
- Uses: RADIO: tv and radio, MICROWAVES: satellite communications, cooking food, INFRARED: electrical heaters, cooking food, infrared cameras, VISIBLE LIGHT: fibre optic communications, ULTRAVIOLET: energy efficient lamps, sun tanning, X-RAYS and GAMMA: medical imaging and treatments.
- LOWEST WAVELENGTH, HIGHEST FREQUENCY
- Radio waves can be produced by oscillations in electrical circuits.
- When they are absorbed they may create an alternating current with the same frequency, so radio waves can themselves induce oscillations in an electrical circuit.
- Different substances may absorb, transmit, refract or reflect electromagnetic waves.
- Refraction: when waves change direction as they enter a new medium. For example, when light enters glass from air, it slows down, so it bends (towards the normal).
- Diagrams: the normal is perpendicular (90 degrees) to the boundary. If the ray slows down, it bends towards the normal. If it speeds up, it bends away from the normal.
- Reflection: when a wave bounces back off a surface.
Triple Science Only
- Angle of incidence = angle of reflection (measure both using the normal).
- Sound waves can travel through solids causing vibrations.
- In the ear, sound waves cause the ear drum to vibrate which causes sound.
- The frequency range of human hearing is 20-20,000 Hz.
- Ultrasound waves have a frequency above 20,000 Hz.
- Ultrasound waves are partially reflected when they meet a boundary between two media. The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is. This allows ultrasound waves to be used for both medical and industrial imaging.
- Medical and industrial imaging: time taken for the reflections to reach a detector can be used to determine how far away such a boundary is.
- Earthquakes produce seismic waves (S and P).
- P-waves: longitudinal, seismic waves. P-waves travel at different speeds through solids and liquids.
- S-waves are transverse, seismic waves. S-waves cannot travel through a liquid.
- P-waves and S-waves provide evidence for the structure and size of the Earth’s core.
- Echo sounding, using high frequency sound waves is used to detect objects in deep water and measure water depth.
- Gamma rays originate from changes in the nucleus of an atom.
- Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range.
- Lense:
- Visible Light: each colour has a certain frequency and wavelength.
- Specular reflection: reflection from a smooth surface in a single direction.
- Diffuse reflection: reflection from a rough surface causes scattering.
- Colour filters work by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour).
- If all wavelengths are reflected equally the object appears white. If all wavelengths are absorbed the objects appears black.
- Objects that transmit light are either transparent or translucent.
- All bodies emit and absorb infrared radiation. Hotter = more radiation.
- A perfect black body is an object that absorbs all of the radiation incident on it. A black body does not reflect or transmit any radiation.
- A good absorber is a good emitter, so a perfect black body would be the best possible emitter.
- The temperature of a body increases when the body absorbs radiation faster than it emits radiation, and vice versa.