AQA Waves
Transverse and Longitudinal waves
Waves in air, fluids and solids
Transverse wave | Vibration causing the wave is at right angles to the direction of energy transfer | Energy is carried outwards by the wave. | Water and light waves, S waves. |
Longitudinal wave | Vibration causing the wave is parallel to the direction of energy transfer | Energy is carried along the wave. | Sound waves, P waves. |
Electromagnetic waves
Black body radiation
Properties
Wavelength | Distance from one point on a wave to the same point of the next wave |
Amplitude | The maximum disturbance from its rest position |
Frequency | Number of waves per second |
Period | Time taken to produce 1 complete wave |
| Units |
Distance | Metres (m) |
Wave speed | Metres per second (m/s) |
Wavelength | Metres (m) |
Frequency | Hertz (Hz) |
Period | Seconds (s) |
Measuring speed
Wave speed | Wave speed = frequency X wavelength | |
Wave period | Wave period = 1 ÷ frequency | T = 1 ÷ f |
Speed | Speed = distance ÷ time | v = d ÷ t |
In water, use a ripple tank.
In air, use echoes.
PHYSICS ONLY |
Reflection | Wave bounces off the surface. |
Refraction | Waves changes direction at boundary. |
Transmitted | Passes through the object. |
Absorbed | Passes into but not out of, transfers energy and heats up the object. |
Sound waves travelling through different mediums, the frequency stay constant.
Air Water
Angle of incidence = angle of reflection (i) = (r)
Light refracts as it slows down in a denser substance
Hearing | Frequencies between 20 – 20,000 Hz | Longitudinal waves cause ear drum to vibrate, amplified by three ossicles which creates pressure in the cochlea. |
P wave | S wave | Seismograph |
Longitudinal | Transverse | Shows P and S waves arriving at different times. |
Fast | Slow | |
Travel through solids and liquids | Travels through solids | By using the times the waves arrive at the monitoring centres, the epicentre of earthquake can be found. (v = x ÷ t). |
Produced by earthquakes. | ||
PHYSICS HIGHER ONLY |
Ultra sound | Partially reflected off boundary | Used for medical and foetal scans. |
Sonar | Reflected off objects | Used to determine depth of objects under the sea. |
PHYSICS ONLY |
Black body radiation | All objects absorb or reflect infrared radiation | Hotter objects emit more infrared radiation. |
Constant temperature | Rate of absorption = rate of radiation | Intensity and wavelength of energy affects temperature. |
Ultraviolet, visible light, infra-red radiation penetrate atmosphere and heat up Earth’s surface.
Earth and Global warming
Longer wavelengths are radiated back, trapped by atmosphere.
Energy lost is not at the same rate as energy being absorbed so Earth heats up.
PHYSICS ONLY |
Convex | Real or virtual images. |
Concave | Only virtual images. |
Electromagnetic wave | Continuous spectrum of transverse waves |
Short wavelengths have high frequency and high energy.
e.g. Gamma
Seismic waves
Absorbed light changes into thermal energy store.
Black surfaces | Good emitters, good absorbers |
White surfaces | Poor emitters, poor absorbers |
Shiny surfaces | Good reflectors |
EM waves refract
EM wave | Danger | Use |
Radio | Safe. | Communications, TV, radio. |
Microwave | Burning if concentrated. | Mobile phones, cooking, satellites. |
Infrared | Heating, remote controls, cooking. | |
Visible | Damage to eyes. | Illumination, photography, fibre optics. |
Ultra violet | Sunburn, cancer. | Security marking, disinfecting water. |
X-ray | Cell destruction, mutation, cancer. | Broken bones, airport security. |
Gamma | Sterilising, detecting and killing cancer. |
HIGHER: Properties
Low frequency, long wavelength.
High frequency, short wavelength
Magnification = image size ÷ object size
Specular | Flat surface reflection. |
Diffuse | Rough surface reflection. |
White | Wave lengths reflected |
Black | Wave lengths absorbed |
HIGHER: Lenses
2F | Image same size, upside down, real. |
2F - F | Image larger, upside down, real. |
< F | Image bigger, right way, virtual. |