Waves and optics summary (O level Physics)
- A wave is a periodic disturbance that transmit energy from one point to another.
- 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.
- 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.
- 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.
- All waves obey the wave equation: v = fλ, whereby v is the wave velocity, f is the frequency and λ is the wavelength.
- 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).
- Sound is produced by vibrations in a medium and it needs a medium to travel.
- An echo is sound reflected from smooth hard surfaces.
- 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.
- 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.
- 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.
- 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
- 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.
- 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.
- Total internal reflection is used in:
- Binoculars
- Periscopes
- Optic fibres
- Endoscopes
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