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# 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