Module 2 - Definitions (part 1)

Module 2 - Definitions (part 1)

1. Waves

   • What is a transverse wave?
     • The vibrations of the particles in the medium is perpendicular to the direction of wave propagation.
     • EXAMPLES: (1) Water waves (2) EM waves (3) Waves on a string
   • What is a longitudinal wave?
     • The vibrations of the particles in the medium is parallel to the direction of wave propagation.
     • EXAMPLES: (1) Sound
   • What is amplitude?
     • The maximum displacement of a particle from its equillibrium position.
   • What is frequency?
     • The number of cycles/oscillations/vibrations of a particle in a wave per second or the number of complete waves passing a point per second.
   • What is time period?
     • Time taken for one complete oscillation.
   • What is wavelength?
     • The distance between two successive crests or troughs or the distance travelled by the wave in periodic time.
   • What is plane polarisation?
     • The vibrations are limited to one plane only.
   • How do you confirm if a beam of light is polarised?
     • Pass it through a sheet of polaroid (or an analyser) held in the path of the wave at 90 degrees to the wave and rotate it through 360 degrees. The light will be extinguished (darkened) twice during the 360 degree rotation.
   • Why can sound waves never be polarised?
     • The oscillations can only be parallel to the velocity.
   • What is phase difference?
     • The difference between two points vibrating in the same way expressed as a fraction of one complete wave.
   • What are common properties of all EM waves?
     • (1) They are all transverse (2) They all travel at the same speed in a vacuum (3) They can all travel in a vacuum (4) They can all be polarised
   • What is the order of the EM spectrum from longest to shortest wavelength?
     • (1) Radio--> 1m+ (2) Microwave--> 0.01cm-50cm (3) Infra-red (4) Visible light--> 400-700nm (5) Ultra violet (6) X-ray--> <1nm (7) Gamma rays

2. Refraction

   • What is refraction?
     • The bending of a wave caused by change in speed as it passes from one medium to another.
   • What conditions are necessary for refraction?
     • (1)Wave passes from one medium to another.
     • (2) Which has a different refractive index due to a different optical density.
     • (3) At an angle of incidence >0 degrees.
   • What is Snell's Law?
     • For a given pair of media the ratio of the sine of the angle of incidence and the sine of the angle of refraction is a constant.
   • What is the critical angle?
     • The angle of incidence which gives an angle of refraction of 90 degrees.
   • What conditions are necessary for TIR?
     • (1)Waves incident on a boundary travelling from a more optically dense to a less optically dense material.
     • (2)The angle of incidence must be greater than the critical angle.

3. Lenses

   • What is the principle focus of a converging lens?
     • The point on the principle axis through which incident rays parallel to the principle axis, pass after passing through the lens.
   • What is the principle focus of a diverging lens?
     • The point on the principle axis from which all rays, parallel to the principle axis, appear to diverge from after passing through the lens.
   • What is the focal length?
     • It is the distance between the principle focus and the optical centre of the lens.
   • What is a real image?
     • One which can be projected onto a screen. The rays actually meet to form an image.
   • What is a virtual image?
     • One which cannot be projected onto a screen. The rays appear to originate at the image.
   • What is the object distance(u)?
     • The distance between the object and the optical centre of the lens.
   • What is the image distance(v)?
     • The distance between the image and the optical centre of the lens.
   • What is magnification?
     • The ration of the image height against object height or the image distance against the object distance.
   • What is Myopia?
     • Short-sightedness caused by the lens being too strong or the eyeball being long. Corrected using a concave lens.
   • What is Hypermetropia?
     • Long-sightedness caused by the lens being too weak or the eyeball being too short.
   • What is the near point?
     • It is the closest distance from an eye an object can be seen and is still in focus.
   • What is the far point?
     • It is the furthest distance from the eye and the object can be seen and is still in focus.

4. Superposition, Interference and Standing waves

   • What is a travelling/progressing wave?
   • What is the principle of superposition?
   • What is interference?
   • What conditions are necessary for interference to occur?
   • What is meant by the term coherent?
   • What is meant by the term in phase?
   • What conditions are necessary for constructive interference?
   • What are the conditions necessary for total destructive interference?
   • What is meant by path difference?