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Dr Pusey
www.puseyscience.com
Q: Are light waves longitudinal or transverse?
Light waves are electromagnetic waves that can travel through a vacuum.
Light Energy Light is a form of energy and can be changed from one
form into another.
For example in solar panels
For example in plants
Light energy Electrical energy
Light energy Chemical energy
Different light frequencies produce different ‘colour’. The range of colours that we can see are known as the visible spectrum.
Outside of the visible spectrum, we cannot see the electromagnetic waves.
Higher frequency = Higher Energy!!
The Electromagnetic Spectrum
https://en.wikipedia.org/wiki/Electromagnetic_spectrum
Ones you need to knowRadio Waves – Very long wavelength
Walky Talkies
Radio (Even digital)
Television
Infra-red – Frequency is just below the colour red
Associated with HEAT
The warm part of sunlight
Ones you need to knowVisible Waves
Different colours are different frequencies within a small range
White light is a combination of all visible frequencies!
Ultra-Violet (UV) – Frequency is just above the colour violetAssociated with skin burnsCan cause other types of damage (cancers)
Ones you need to know Microwaves – Short wavelength
PlayStation controller Bluetooth
X-rays - Very short wavelength Can pass through soft human tissue (good for
looking at bones) More risk of causing damage to humans
Gamma-rays – Super short wavelength Travels through nearly everything High risk of causing damage to humans (if it is
absorbed!)
Quick Quiz Sort the following in their order of wavelength
(shortest to longest)
Radio Waves
Microwaves
Gamma Rays
X Rays
Visible Light
Ultra-Violet
Infra-Red
Quick Quiz Now, sort the following in their order of their Energy,
(lowest to highest)
Radio Waves
Microwaves
Gamma Rays
X Rays
Visible Light
Ultra-Violet
Infra-Red
The Electromagnetic Spectrum
https://en.wikipedia.org/wiki/Electromagnetic_spectrum
How do we see things? An object that gives out light = luminous
Light travels in a straight line from the object into your eyes. E.g. a light bulb
How do we see things? An object that does not give out light = non-luminous
Light hits the rock and some of it is reflected into your eyes. E.g. a rock
Reflection There are 2 types of reflectors
Regular reflectors…
…these produce regular reflection
Diffuse reflectors…
…these produce diffuse reflection
Regular Reflectors
Surface that is extremely smoothand shiny (E.g. A mirror)
Light rays bounce off (reflect) in an orderly way.
Diffuse Reflectors Most surfaces around
us are not super smooth, even if they might look it.
A rough surface will cause light to be reflected imperfectly, in all different directions.
Diffuse reflection occurs from these
rough surfaces and no clear image is
formed
Many surfaces appear
smooth but are rough compared with the
surface of a mirror.
Reflectors What type of reflection are these diagrams showing? Give
two examples of surfaces which show that type of reflection.
Law of Reflection:The angle of incidence is equal to the angle of reflection
https://en.wikipedia.org/wiki/Reflection_%28physics%29
Incident RayReflected RayAngle of IncidenceAngle of ReflectionNormal (to the surface)
Fit the above terms to the diagram!
Law of Reflection:The angle of incidence is equal to the angle of reflection
https://en.wikipedia.org/wiki/Reflection_%28physics%29
Incident RayReflected RayAngle of IncidenceAngle of ReflectionNormal (to the surface)
Angle of Incidence (i)
Angle of Reflection(r)
30°
50°
80°
65°
Reflection Quiz
Convex & Concave Mirrors Concave – Dug out Like a Cave
Can magnify things – useful for make-up mirrors!
Can focus light
Torches & Telescopes
Convex – Bulges out Makes things appear smaller
Security mirrors
“objects in mirror are closer than they appear”
www.physicsclassroom.com
