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Physic Topic 5: Light and the electromagnetic spectrum (Electromagnetic…
Physic Topic 5: Light and the electromagnetic spectrum
Colour
Most light is white, which is a mixture of the seven different colours in the visible spectrum
Rainbows are caused when tiny droplets of water in the air split up the colours in white light
A filter is a transparent piece of paper that absorbs some of the colours in white light and transmit the others
E.g Yellow filter paper absorbs every of colour other than yellow which is transmitted so you get a yellow light
Flowers are certain colours as they reflect the colours they are and absorb the others
If you were to put a red filter or spotlight on a white flower it would look red.
But if you put it on a colour that does not contain red like blue flowers they would appear black
Forming different images
Reflection and refraction
Refraction
Sound and light waves change speed as the travel through mediums of different densities. This cause them to change direction
Refraction doesn't occur when the waves cross the boundary at an angle of 90 degrees which in that case it goes straight
If you increase the angle of incidence the angle of refraction will increase
Reflection
Law of reflection: the angle of incidence = angle of reflection
Smooth surfaces:
Reflects waves uniformly
to produce strong echoes for sound waves and light waves produce images
Rough surfaces:
Scatters the waves
reflected in all directions but each tiny bit of the surface still follows the
Law of reflection
Electromagnetic spectrum
Visible light
Use:
Seeing
Ultraviolet
Use:
Detecting forged bank notes, black-lights
Infrared
Use:
Optical fibre communication
Hazards:
Radiation is felt as heat causing skin to burn
X-rays
Use:
Medical images of bones
Hazards:
Damage cells causing mutations and cell death
Types of UV radiation
UVB
- It has a
middle frequency
out of all of them and causes severe
sunburn
and
cell damage
UVA
- It has the
lowest frequency
and causes
weaker
effects of
UVB
UVC
- It has the
highest frequency
and cause severe
cell damage
Microwaves
Use:
Cooking, mobile phones
Hazards:
Cause internal heating to body tissue
Gamma rays
(
Shortest wavelength, highest frequency and energy
)
Use:
Killing cancer cells
Hazards:
Can cause cell mutations and cell death
Radio waves
(
Longest wavelength, lowest frequency and energy
)
Use:
Television signals
Frequencies and wavelengths
Speed of sound = 3 x 10^8 m/s
Wave speed(m/s) = frequency(Hz) x wavelength(m)
All electromagnetic waves travel at a speed of 3 x 10^8 m/s in a vacuum or in air
Comparing light and sound waves
Sound
Can be refracted
Can be defracted
Can be reflected
Can't
travel through a vacuum
Longitudinal
wave
Light
Can
travel through a vacuum
Can be reflected
Transverse
wave
Can be refracted
Can be defracted