Waves and Optics Summary Notes (O level Physics)

Waves and optics summary (O level Physics)

1. A wave is a periodic disturbance that transmit energy from one point to another.
2. There are two types of waves:
   • Transverse waves – in which the vibrations are perpendicular to the direction of wave travel. For example electromagnetic waves.
   • Longitudinal waves – in which the vibrations are parallel to the direction of wave travel. For example sound waves.
3. A wave can be described by the following properties:
   • Amplitude – the distance from the rest position to the peak position of a wave.
   • Wavelength (λ) –the distance between two similar successive points of a wave. For example, distance from peak to the next peak, or trough to the next trough.
   • Frequency (f) –the number of complete oscillations per second (measured in Hz).
   • Period –the time taken by the wave to complete one oscillation (in s).
   • Wave speed is the distance travelled by the wave per unit time.
4. All waves can be reflected, refracted and diffracted whereby,
   • Reflection is the bouncing of a wave off a surface.
   • Refraction is the bending of a wave when it crosses a boundary of two different media.
   • Diffraction is the spreading out of a wave when it passes through a narrow gap.
5. All waves obey the wave equation: v = fλ, whereby v is the wave velocity, f is the frequency and λ is the wavelength.
6. Sound is a longitudinal wave whose:
   • amplitude is related to its loudness (the greater the amplitude, the louder the sound.)
   • wavelength is related to its pitch (the shorter the wavelength the higher the pitch).
7. Sound is produced by vibrations in a medium and it needs a medium to travel.
8. An echo is sound reflected from smooth hard surfaces.
9. Ultrasound is a very high frequency sound wave that is used:
   • in medicine to "see" into the human body
   • to measure the depth of rivers
   • to study the earth’s crust.
10. Laws of reflection:
    • The angle of incidence is equal to the angle of reflection.
    • The incident ray, reflected ray and the normal all lie in the same plane.
11. Laws of refraction:
    • The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. (Also known as Snell’s law).
    • The incident ray, refracted ray and the normal all lie in the same plane.
12. Properties of the image formed by a plane mirror:
    • Laterally inverted
    • Same distance from the mirror as the image is in front of the mirror.
    • Same size as the object
    • Virtual
13. Properties of refraction:
    • If a wave enters a more dense medium it will be bent towards the normal.
    • If a wave enters a less dense medium it will be bent away from the normal.
14. Total internal reflection is when a wave reflects off the inside of a surface when it hits the boundary at an angle greater than critical angle.
15. Total internal reflection is used in:
    • Binoculars
    • Periscopes
    • Optic fibres
    • Endoscopes