AS2 Physics Definitions

• Waves


  Periodic disturbance which results in a vibration
• Progressive waves


  • Transport energy from one place to another by causing vibrations in the material or medium through which it moves
• Transverse waves


  • Vibrations of the particles in the medium are perpendicular to the direction in which the wave travels
• Longitudinal waves


  • Vibrations of the particles in the medium are parallel to the direction in which the wave travels
• Period (T)


  Time taken for one complete vibration
• Frequency (f)


  Number of complete waves that pass a point in a second
• Amplitude (A)


  Maximum displacement of a particle from its rest position
• Wavelength (λ)


  Distance the wave travels in the periodic time, T
• In Phase


  Two waves where the particles are vibrating so at the same instant they are at the same displacement (distance and direction) from their equilibrium positions
• Out of Phase


  Two waves where the particles are vibrating so at the same instant they are at different displacements (distances and directions) from their equilibrium positions
• Phase difference


  Time interval or phase angle by which one wave leads or lags another
• Unpolarised wave


  Wave vibrating in more than one plane
• Polarised wave


  Wave where all the vibrations are confined to one plane
• Refraction


  Bending of a wave when it travels from one medium to another at an angle of incidence greater than 0°
• Snell's Law


  For light travelling from one material to another, the ratio sin i/sin r is a constant
• Critical angle


  Angle of incidence which results in an angle of refraction of 90°
• Endoscope


  • Flexible tube that uses total internal reflection down optical fibres to illuminate the inside of the body and transmit images back
• Real image


  Image where the rays of light which make it up, pass through it and can be formed on a screen
• Virtual image


  Image where the rays of light which make it up do not pass through it but appear to come from it, and cannot be formed on a screen
• Optical Centre


  Exact centre of the lens
• Principal Axis


  Imaginary line passing through the optical centre at right angles to the plane of the lens
• Principal focus


  Point on the principal axis where rays of light originally parallel and close to the principal axis pass through a converging lens
• Focal length


  Distance from the principal focus to the optical centre of the lens
• Principal focus


  Point on the principal axis where rays of light originally parallel and close to the principal axis pass through a diverging lens
• Linear Magnification (m)


  Height of image/height of object
• Power of a lens

  1/f (f is in m)
• Far point


  Furthest point which can be seen clearly by the unaided eye
• Near point


  Nearest point which can be seen clearly by the unaided eye
• Myopia (short sight)


  Unable to see distant objects clearly
• Long sight


  Unable to see near objects clearly
• Principle of Superposition


  Resultant displacement at a point at a given time is the algebraic (vector) sum of the displacements of each wave at that point at that time
• Constructive Interference


  When two waves meet in Phase they produce a wave of greater amplitude
• Destructive Interference


  When two waves meet exactly out of phase they produce a wave of smaller amplitude (zero if the amplitude of the waves were the same)
• Coherent sources


  Produce waves of the same wavelength or frequency and be in phase or have a constant phase difference between them
• Standing waves


  Produced by the interference of two waves, of the same type and having the same wavelength moving in opposite directions and meeting
• Diffraction


  Spreading out of waves when they meet an obstacle or aperture (gap)
• Diffraction grating


  Rectangular piece of glass treated on one side to make it opaque and then scored on the opaque side to produce parallel lines of equal width and equal separation
• Monochromatic


  Single wavelength
• Photoelectric emission


  Emission of electrons from the surface of a metal when electromagnetic radiation of sufficiently high frequency falls on it
• Work function (Ø)


  Minimum quantity of energy needed to liberate electrons from the surface of a metal and to just allow it to escape to an infinite distance from the metal