Topic 5: Light and the Electromagnetic Spectrum Flashcards
Total internal reflection
the complete reflection that takes place within a medium when the angle of incidence of light striking the surface boundary is equal to or more than the critical angle
Explain why light can be TIR’ed at the water surface from inside the water and why sound can be TIR’ed at the water surface from inside the air [6]
- the critical angle is the angle of incidence that gives an angle of refraction of 90° along the boundary
- sound going from air to water bends away from the normal
- because sound is slower in air than water
- so r° is always bigger than i°
- so TIR is possible in this direction
- light is quicker in air than in water so TIR will be in the opposite direction
State what can be deduced from this diagram (light traveling through a 45 degree glass prism) about the value of the critical angle for glass
The critical angle is below 45 degrees
Give a reason why high quality optical instruments use prisms instead of mirrors to reflect light
Light can undergo total internal reflection in prisms, no light is scattered
Explain the difference between specular and diffuse reflection
Specular:
- occurs on a smooth flat surface
- all light incident at the same angle all exit at the same angle
Diffuse:
- occurs on a rough surface
- incident ray is reflected at many angles rather than just one angle
Explain how colour of light is related to:
- a differential absorption at surfaces
- b transmission of light through filters
If a coloured object is opaque:
- out of the incident white light only
a certain colour light (e.g purple light) is reflected, all other colours are absorbed
Filters:
-All other colours are absorbed, and only a certain colour is allowed to pass through - so only
a certain wavelength is transmitted through the filter
How is the power of the lens related to its focal length and shape?
- power is inverse of focal length
- shorter focal length = higher lens power
- a thicker lens will have more power since its focal length will be shorter.
focal length
the distance from the center of a lens to the focal point
Use ray diagrams to show the similarities and differences in the refraction of light by converging and diverging lenses
to draw a ray diagram:
draw a ray from the object to the lens that is parallel to the principal axis. Once through the lens, the ray should pass through the principal focus.
draw a ray which passes from the object through the centre of the lens.
Explain the effects of different types of lens in producing real and virtual images
A Real image:
- an image produced at the opposite side of the lens to the object.
- For converging lenses the image is inverted and smaller than the object
Virtual images
- appear to come from the same side of the lens to the object
-this is if the object lies closer to the lens
than the focal point
- for diverging lenses the images are the same way up and much smaller and closer to the lens than the object.
Compare and contrast converging and diverging lenses
Converging lenses:
- convex
- Focuses light inwards
- They are used for magnifying glasses,
binoculars and to correct longsightedness
Diverging lenses:
- concave
- Spreads light outwards
- used to correct short-sightedness
What do all electromagnetic waves have in common?
They all travel at the same speed through a vacuum - the speed of light (300,000,000m/s)
They are all transverse waves
The wavelength of a UV wave is 360 nm
Calculate its frequency
frequency = velocity/wavelength
all waves in the EM spectrum travl at light speed (in a vacuum): 3×10⁸
1nm= 1×10⁻⁹m
frequency= 3×10⁸/360×10⁻⁹
frequency= 8.3 ×10¹⁴
Explain, with examples, that all electromagnetic waves transfer energy from ______ to ________?
- Source to observer
- for example with microwave ovens the microwaves transfer energy from the source to the food
Core Practical: Investigate refraction in rectangular glass blocks in terms of the interaction of electromagnetic waves with matter
- place a glass block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
- switch on the ray box and direct a beam of light at the side face of the block
- mark on the paper a point on the ray close to the ray box, the point where the ray enters the block, the point where the ray exits the block and a point on the exit light ray which is a distance of about 5 cm away from the block
- draw a dashed line normal (at right angles) to the outline of the block where the points are
- remove the block and join the points marked with three straight lines
- replace the block within its outline and repeat the above process for a ray striking the block at a different angle
- repeat the procedure for each shape of perspex block (prism and semi-circular)
Recall the main groupings of the continuous electromagnetic spectrum including (in order) radio waves, microwaves, infrared, visible (including the colours of the visible spectrum), ultraviolet, x-rays and gamma rays
The order of the electromagnetic waves from longest to highest is
1. Radio waves
2. Microwaves
3. Infrared
4. Visible light (the light we can see)
5. Ultraviolet
6. X-rays
7. Gamma radiation
describe the electromagnetic spectrum
continuous from radio waves to gamma rays and that the radiations within it can be grouped in order of decreasing wavelength and increasing frequency
recall that our eyes can only detect a limited range of frequencies of electromagnetic radiation
our eyes can only detect a limited range of frequencies of electromagnetic radiation
Explain that all bodies emit radiation, that the intensity and wavelength distribution of any emission depends on their temperature
for hotter objects, the peak wavelength will be at a shorter wavelength and at a higher intensity
What shape is a Converging lens ?
shape of diverging lens
how does converging lens refract light
how does a diverging lens refract light
