Rules Radiowaves Increasing frequency↓
Very Visible light
Uneasy Ultra violet
Xing X rays
Girls Gamma rays Increasing wavelength↑
Richard Red Increasing frequency↓
Vain Violet Increasing wavelength↑
Using waves cont. Analogue and digital.
The speed of all electromagnetic waves are constant
Higher frequency=Shorter wavelength.
Digital and analogue
Analogue electrical signals are continuously variable voltages
- must be amplified
- pick up 'noise'
Digital electrical signals can have only two possible values 0 and 1 (binary number system)
- more information can be transmitted.
Reflection of light
normal: at right angles to the mirror surface where the light rays strike at it.
i: angle of incidence r: angle of reflection
Law of reflection:
The angle of incidence = the angle of reflection
An image on a mirror is a virtual image. It appears to be the same distance behind the mirror as it is infront.
Refraction of light
When a light ray travels from air into glass it is bent towards the normal and when a light ray travels back out of glass into air, it is bent away from the normal.
Law of refraction:
refractive index, n = sin i / sin r OR 1/ sin c
Critical angle, c: the angle at which the reflection travels at a 90degree angle to the normal.
Refraction is used in optical fibres. Light can be diffracted.
Sound travels as a longitudinal eave through gases, liquids and solids. They cannot travel through a vacuum. The speed of sound in gases is lower than in liquids and slower in liquids than solids.
Humans can hear 20Hz to 20kHz. These frequencies are known as audio frequencies.
Stethoscopes are an example of total internal reflection of soundwaves.
Pitch: how quickly the sound producer is vibrating: T=1/f
Oscilloscopes use small voltages that vary with time in the same way as the changing pressure of the air. It produces a graph to show how the voltages are changing with time. The greater the loudness, the higher the amplitude.