Physics

Physics

1. Waves

   • General Properties of Waves
     • Waves transfer energy and information without transferring matter.
     • In a transverse wave, the oscillations are at 90° to the direction of energy transfer.
     • In a longitudinal wave, the oscillations are parallel to the direction of energy transfer.
     • Electromagnetic waves are transverse waves and sound waves are longitudinal wave. Mechanical waves may be longitudinal or transverse.
     • Waves can be reflected, refracted or diffracted
     • For appreciable diffraction to take place, the size of the obstacle or gap must be of the same order of magnitude as the wavelength of the wave.
     • The wavelength is the length of one complete wave, measured in metres. Be able to label the wavelength on a diagram.
     • The frequency is the number of waves that pass a certain point in one second, measured in Hz.
     • The time period is the time taken for one wave to pass a certain point, measured in seconds.
     • The amplitude is the maximum ‘height’ of the oscillation, measured from the centre of oscillations in metres.
     • v=f x λ.
   • The Electromagnetic Spectrum
     • The electromagnetic waves make up a continuous spectrum of waves.
     • All electromagnetic waves travel at the same speed through a vacuum (space).
     • The wavelengths of the waves in the spectrum range from 10-15m to 104m and beyond.
     • Radio waves, microwaves, infrared and visible light can be used for communication. • Radio waves are used for TV and radio (including Bluetooth). Microwaves are used for mobile phones and satellite TV. Infrared is used for remote controls. Visible light is used for photography. Ultraviolet is used for security marking. X-rays are used for medical imaging. Gamma rays are used for sterol sing surgical equipment and killing harmful bacteria in food.
     • Microwaves can cause heating of body tissue. Infrared can burn skin. Ultraviolet can cause skin cancer and blindness. X-rays in high doses can kill cells. Gamma rays can cause genetic mutations. X-rays have a very short wavelength and high energy and cause ionisation. They affect a photographic film in the same way as light. They are absorbed by metal and bone but are transmitted through healthy tissue. X-rays can be used to diagnose some medical conditions such as bone fractures and dental problems, and to kill cancer cells. X-rays are used in CT (computed tomography) scans. The use of high energy ionising radiation can be dangerous, and precautions need to be taken to monitor and minimise the levels of radiation that people are exposed to.

2. Forces and Motion

3. Energy