(P1) Topic 5- Light And The Electromagnetic Spectrum Flashcards
Angle of incidence is (?) to angle of reflection
Equal to
Why can only very smooth surfaces reflect
If the surface is bumpy then the light is not reflected evenly
What is specular reflection
When all light rays are parallel and an image is formed
What is diffuse reflection
When light reflects off a surface that isn’t flat and no image is formed
What is a virtual image
an upright image that is achieved where the rays seem to diverge (isn’t real)
What does a convex lens do
Brings light rays closer together (they converge)
What does a convex lens look like
()
What is a convex lens used for
Long-sightedness
Where is the focal point of a convex lens
After the lens
What does a concave lens do
Spreads out light rays (diverges rays)
What are concave lenses used for
Short-sightedness
Where is the focal point of a concave lens
Before the lens
Define focal point
the point at which rays or waves meet after reflection or refraction, or the point from which diverging rays or waves appear to proceed
Define focal length
The distance between the centre of the lens and the focal point
What does it mean is light rays cross with imaginary lines on a diagram
The image is virtual, not real
What does a concave lens look like
)(
What are the rules for converging lens (convex)
-if ray goes to centre of lens, it keeps going straight
-ray parallel= through to focal point on right
What are the rules for diverging lenses (concave)
-if ray goes to the centre it keeps going straight
-ray parallel= through to focal to focal point on left
Calculation for optical power
Optical power= 1 / focal length
What is optical power
How strong a lens is
What are the EM spectrum waves made by
Vibrating electric and magnetic fields
What is the speed of all EM waves
3x10^8
EM waves are (?) waves
Transversal
EM spectrum in order, from long wavelength+low energy+low frequency to short wave+high energy+high frequency
Radio waves
Microwaves
Infrared
Visible light
Ultra-violet
X-rays
Gamma rays
Radio waves
-produced by oscillations in electrical currents
-information coded into the wave
-long wavelength, low frequency
Microwaves
-beamed up to a satellite which reflect back down into a device
-phone -> electrically charged satellite -> transmitter
Infrared
-photothermal heating
-the internal energy of the bonds increases when they absorb infrared, which causes heating
-incident later light -> reflected and IR emissions, emitted IR radiation -> infrared detector
Ultraviolet
-fluorescent. Substances absorb ultraviolet light and re-emit the energy as visible light
-shorter wavelength and higher energy than visible light
X-Rays
-X-rays are transmitted through body tissues with very little absorption, whereas dense structures absorb them. This shows up as an image on the screen
What happens in an object when it is heated
The particles in the object move faster as they gain energy
What is 0 kelvin
-273.15 degrees Celsius
-particles have no energy and don’t move at all
What does energy per second equal
Power
What would happen to the infrared that the earth absorbs from the sun if there was no atmosphere
The night side would emit al of the infrared
Infrared radiation core practical
Speed of cooling- water in 4 test tubes, one control, on in tin foil, one in white paper, one in black paper. See which one cools to room temp the slowest = best insulator
Danger level of radio waves
Very low danger
Danger level of microwaves
Low intensity (e.g mobile signals)- unlikely to cause danger
High intensity (e.g microwaves oven)- cooks your insides, very high danger
Danger level of infrared
Intense source- causes burns
Danger of visible light waves
Intense sources (e.g looking at the sun)- destroys your retina and can cause blindness
Danger of ultraviolet waves
Can cause sunburn and skin cancer
Danger of x-rays
Ionising radiation- can cause cancer as cells can be altered
Large dose leads to DNA breakdown, radiation sickness
Danger of gamma rays
Same as x-rays
Ionising radiation- can cause cancer as cells can be altered
Large dose leads to DNA breakdown, radiation sickness
