Light and electromagnetic waves Flashcards
what is the law of reflection
Angle of incidence (i) = Angle of reflection (r)
why do lights rays undergo a change in direction
because the light changes speed
what does the change in direction depend on
From less dense to more dense (e.g air to glass), light bends towards the normal
From more dense to less dense (e.g. glass to air), light bends away from the normal
what properties change during refraction
speed and wavelength – the frequency of waves does not change
what colour has the highest frequency
red has a low frequency, whilst blue has a high frequency
When light refracts, it does not change colour (think of a pencil in a glass of water), therefore, the frequency does not change
what is total internal reflection
The angle of incidence is greater than the critical angle and the incident material is denser than the second material
what is the critical angle
As the angle of incidence is increased, the angle of refraction also increases until it gets closer to 90°
When the angle of refraction is exactly 90° the light is refracted along the boundary
At this point, the angle of incidence is known as the critical angle θc
what are the conditions for the TIR
The angle of incidence > the critical angle (i > θc)
The incident material is denser than the second material
what is specular reflection
reflection from a smooth surface in a single direction
what is diffuse reflection
Reflection from a rough surface causes scattering, this is what gives objects a dull or matt appearance
what is absorption of colour
Energy is transferred from the wave into the particles of a substance
what are colour filters
Colour filters work by absorbing certain wavelengths and transmitting other wavelengths
These certain wavelengths correspond to certain colours
what happens when white light hits a red filter
Red light is transmitted
All the other colours are absorbed
what is a principal focus
parallel rays of light are brought to a focus
what is a focal length
The distance from the lens to the principal focus is called the focal length
what does focal length depend on
This depends on how curved the lens is
The more curved the lens, the shorter the focal length
what does the power of a lens depend on
The focal length of the lens
The shape of the lens
how is power changed
The more curved the lens, the shorter the focal length
The shorter the focal length, the greater the power of the lens
what 3 thins should you look for when describing a image
Real or virtual
Magnified (larger) or diminished (smaller)
Upright or inverted
how a real images presented on converging lens ray diagram
If an object is placed further from the lens than the focal length f then a real image will be formed
Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line
Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly through the principal focus f
The image is the line drawn from the axis to the point where the above two rays meet
how a real images presented on converging lens ray diagram
If an object is placed further from the lens than the focal length f then a real image will be formed
Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line
Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly through the principal focus f
The image is the line drawn from the axis to the point where the above two rays meet
how are virtual images presented on converging lens
If the object is placed closer to the lens than the focal length f then a virtual image will be formed
Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line
Draw a dashed line continuing this ray upwards
Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly through the principal focus f
Also, draw a dashed line continuing this ray upwards
The image is the line drawn from the axis to the point where the two dashed lines meet
what type of image is created on a diverging lens
virtual image
diverging lens presenting virtual lens
Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line
Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly upwards away from the axis
Draw a dashed line continuing this ray downwards to the focal point, f
The image is the line drawn from the axis to the point where the above two rays meet
