SP5a Ray diagrams
A ray diagram is a way of modelling what happens when light is refracted or reflected.
The rays are lines that show the direction the waves are travelling.
A normal is a line drawn at right angles to the mirror or barrier.
The angles of the incident ray and reflected ray are always measured from the normal.
When waves are reflected, angle of reflection = angle of incidence - law of reflection
Total Internal Reflection - when light passes from water/glass to air with small angles of incidence, most of the
light passes through the interface but a little is reflected. As the angle of incidence increases so does the angle
of refraction until the refracted light passes along the interface. If the angle of incidence is greater than the
critical angle, the light is completely reflected inside the glass.
Core Practical - Investigating refraction
Investigate refraction in rectangular glass blocks in terms of the interaction of
electromagnetic waves. Set up power supply, ray box and a single slit so a single light ray
can be shone. Draw around a glass block then draw on the light rays and measure angles.
SP5b Colour
diffuse reflection- rough surfaces, most reflected light is scattered in all directions
specular reflection- smooth surfaces (mirrors), light is reflected evenly
White light is a mixture of different colours of light that we see as white. It can be split up into the the colours
of the visible spectrum using a prism.
When white light hits a coloured surface some of the colours that make it up are absorbed and some are
reflected.
For example, a yellow object looks yellow because it reflects yellow light and absorbs all the other colours. A
white object looks white because it reflects all the other colours.
Filters can be used to make coloured light from white light. Filters are pieces of transparent material that
absorb some of the colours in white light. For example, a blue filter transmits blue light and absorbs the other
colours.
,SP5c Lenses
A lens is a piece of transparent material shaped to refract light in particular ways. The power of a lens
describes how much it bends the light that passes through it.
A converging lens is fatter in the middle than at the edges. It makes
parallel rays of light converge at the focal point. The focal length is
the distance from the middle of the lens to the focal point.
A diverging lens is thinner in the middle than at the edges. The focal
point is the point at which the rays seem to be coming after passing
through the lens.
A converging lens creates a real image that can be projected onto a screen
A diverging lens creates a virtual image because it can’t be projected onto a screen
SP5d Electromagnetic waves
We see things when light travels from a source and is reflected by an object into our eyes. Light is a type
of electromagnetic wave.
Our eyes can detect certain frequencies of light and we call those frequencies visible light. Lower frequencies
appear more red and higher frequencies appear more blue.
SP5e The electromagnetic spectrum
There are seven colours in the spectrum- red, orange, yellow, green, blue, indigo, violet
The colour of visible light depends on its frequency. If the frequency of an electromagnetic wave is lower than
that of red light, human eyes cannot detect it. Infrared, microwaves and radio waves have lower frequencies
than red light.
Ultraviolet radiation has a higher frequency than visible light. X-rays and gamma rays have even higher
frequencies and shorter wavelengths.
The range of electromagnetic waves is called the electromagnetic spectrum
Higher frequency waves have shorter wavelengths and lower frequency waves have longer wavelengths.
, Radio waves
Uses: to transmit radio broadcasts and TV programmes
Dangers: can cause cancer
Microwaves
Uses: to heat food and send communications and satellite transmissions
Dangers: internal heating of body cells
Infrared
Uses: to cook food and for communications at short ranges
Dangers: skin burns
Visible light
Uses: light bulbs emit visible light
Dangers: no dangers
Ultraviolet
Uses: can be used to disinfect water by killing microorganisms
Dangers: sun burn, eye problems, blistering and skin cancer
X-rays
Uses: can pass through muscle and fat, used to make images of inside the body
Dangers: over exposure cause cells to die and can cause mutations in DNA
Gamma rays
Uses: to sterilise medical instruments
Dangers: can cause mutations in DNA
Radio waves are produced by oscillations in electrical circuits. A metal rod or wire can be used as an aerial to
receive radio waves. The radio waves are absorbed by the metal and cause oscillations in electric circuits
connected to the aerial.
Waves travel in straight lines unless they reflected or refracted.
Some frequencies of radio waves can be refracted by a layer
called the ionosphere. However, some radio waves and all
microwaves pass through this layer so are not refracted.
A ray diagram is a way of modelling what happens when light is refracted or reflected.
The rays are lines that show the direction the waves are travelling.
A normal is a line drawn at right angles to the mirror or barrier.
The angles of the incident ray and reflected ray are always measured from the normal.
When waves are reflected, angle of reflection = angle of incidence - law of reflection
Total Internal Reflection - when light passes from water/glass to air with small angles of incidence, most of the
light passes through the interface but a little is reflected. As the angle of incidence increases so does the angle
of refraction until the refracted light passes along the interface. If the angle of incidence is greater than the
critical angle, the light is completely reflected inside the glass.
Core Practical - Investigating refraction
Investigate refraction in rectangular glass blocks in terms of the interaction of
electromagnetic waves. Set up power supply, ray box and a single slit so a single light ray
can be shone. Draw around a glass block then draw on the light rays and measure angles.
SP5b Colour
diffuse reflection- rough surfaces, most reflected light is scattered in all directions
specular reflection- smooth surfaces (mirrors), light is reflected evenly
White light is a mixture of different colours of light that we see as white. It can be split up into the the colours
of the visible spectrum using a prism.
When white light hits a coloured surface some of the colours that make it up are absorbed and some are
reflected.
For example, a yellow object looks yellow because it reflects yellow light and absorbs all the other colours. A
white object looks white because it reflects all the other colours.
Filters can be used to make coloured light from white light. Filters are pieces of transparent material that
absorb some of the colours in white light. For example, a blue filter transmits blue light and absorbs the other
colours.
,SP5c Lenses
A lens is a piece of transparent material shaped to refract light in particular ways. The power of a lens
describes how much it bends the light that passes through it.
A converging lens is fatter in the middle than at the edges. It makes
parallel rays of light converge at the focal point. The focal length is
the distance from the middle of the lens to the focal point.
A diverging lens is thinner in the middle than at the edges. The focal
point is the point at which the rays seem to be coming after passing
through the lens.
A converging lens creates a real image that can be projected onto a screen
A diverging lens creates a virtual image because it can’t be projected onto a screen
SP5d Electromagnetic waves
We see things when light travels from a source and is reflected by an object into our eyes. Light is a type
of electromagnetic wave.
Our eyes can detect certain frequencies of light and we call those frequencies visible light. Lower frequencies
appear more red and higher frequencies appear more blue.
SP5e The electromagnetic spectrum
There are seven colours in the spectrum- red, orange, yellow, green, blue, indigo, violet
The colour of visible light depends on its frequency. If the frequency of an electromagnetic wave is lower than
that of red light, human eyes cannot detect it. Infrared, microwaves and radio waves have lower frequencies
than red light.
Ultraviolet radiation has a higher frequency than visible light. X-rays and gamma rays have even higher
frequencies and shorter wavelengths.
The range of electromagnetic waves is called the electromagnetic spectrum
Higher frequency waves have shorter wavelengths and lower frequency waves have longer wavelengths.
, Radio waves
Uses: to transmit radio broadcasts and TV programmes
Dangers: can cause cancer
Microwaves
Uses: to heat food and send communications and satellite transmissions
Dangers: internal heating of body cells
Infrared
Uses: to cook food and for communications at short ranges
Dangers: skin burns
Visible light
Uses: light bulbs emit visible light
Dangers: no dangers
Ultraviolet
Uses: can be used to disinfect water by killing microorganisms
Dangers: sun burn, eye problems, blistering and skin cancer
X-rays
Uses: can pass through muscle and fat, used to make images of inside the body
Dangers: over exposure cause cells to die and can cause mutations in DNA
Gamma rays
Uses: to sterilise medical instruments
Dangers: can cause mutations in DNA
Radio waves are produced by oscillations in electrical circuits. A metal rod or wire can be used as an aerial to
receive radio waves. The radio waves are absorbed by the metal and cause oscillations in electric circuits
connected to the aerial.
Waves travel in straight lines unless they reflected or refracted.
Some frequencies of radio waves can be refracted by a layer
called the ionosphere. However, some radio waves and all
microwaves pass through this layer so are not refracted.
