The EM Spectrum And Light Rays Flashcards
What are the uses of radio waves
Radio broadcast
What are 2 uses for microwaves
Communication + cooking
What is the speed of EM waves
3x10^8 m/s (the speed of light)
What is infrared used for
Night vision, remote controls
What is visible light used for
Seeing, photography
What is UV light used for
Detecting counterfeit documents and currency
What are x-rays used for
Observation of the bones of the human body
What are gamma rays used for
Sterilising food and medical equipment
What are some sources of radiowaves
Radio transmitters, tv transmitters
What are some sources of microwaves
Microwaves and ovens
What is the source of IR
Hot objects
What is the source of visible light
Luminous objects
What is the source of UV
The sun and UV lamps
What are the sources of x-rays
X-ray tubes
What is the source of gamma rays
Radioactive materials
Which has the highest frequency
Gamma rays
Which wave type on the EM spectrum has the largest wavelength
Radiowaves
What are the dangers of microwaves
They heat water molecules because they absorb the microwaves - meaning they could also heat human body tissue
Do all object emit IR
Yes
What are some of the dangers of IR
Skin burns
What are the dangers of radio waves
Heats human body tissue
What are the dangers of visible light
Retina damage
What are the dangers of ultraviolet light
Causes skin to age prematurely and skin cancer
What are the dangers of x-rays
Cell damage and cancer
What are the dangers of gamma rays
Damaging DNA and cancer
What is reflection
When a ray of light strikes a plane (flat) mirror, it is reflected so that the angle of incidence (i) is equal to the angle of reflection (r)
What is a normal line
A perpendicular line drawn at the point where the ray meets the mirror
What is refraction
When light passes through a medium like air, water, glass etc, the ray is slowed down, therefore refracted towards the normal, assuming it is going into an object with a greater refractive index e.g. from air into glass
Where is the normal line for refraction
Perpendicular to the boarder between mediums
When does refraction happen
When a light ray passes from one medium to another
When is there no refraction
When the light ray hits the medium at a perpendicular angle to the boarder
What equation is used to calculate the refractive index
n = sin i/sin r
What is i
The angle of incidence
What is r
The angle of reflection/refraction
What is total internal reflection
When all of the light ray is reflected back into the medium off the boarder, rather than passing through the medium
What is the critical angle in refraction
The angle of incidence when the refracted ray runs along the boarder
Where are the two light rays produced when a light ray passes through a medium
- The refracted ray that passes over the boundary
- A weak ray is reflected, with the same angle of the angle of incidence
How do ships find out how far they are from the bottom of the surface
- Send a sound wave down to the sea floor
- Measure how long it takes for you to receive it again
- You already know the speed of the wave
Use speed = distance/time to find distance (be careful that you divide time by two because it has to go down and up to be received)
What equation links critical angle and refractive index
Sin critical angle = 1/refractive index
What letter represents refractive index
n
What happens to a ray of light when it refracts towards the normal
It slows down
What happens to a ray of light when it refracts away from the normal
It speeds up
Where are angles drawn from on a refraction/reflection diagram
Between the ray and the normal (not the border
How to draw the normal line
Perpendicular to the tangent at the point at which the light ray enters a new medium (for non straight borders)
Perpendicular to the point of intersection with the border (straight line border)
