Light and Electromagnetic Spectrum Flashcards
What is total internal reflection?
When light is completely reflected back at a boundary between two mediums and it occurs when light meets a less dense medium at an angle of incidence larger than the critical angle
What is the critical angle?
The angle of incidence which causes the angle of reflection to be 90 degrees
What determines the colour of visible light waves?
The wavelength and frequency of the light waves
What colour of visible light had the highest frequency?
Blue
What colour of visible light has the largest wavelength?
Red
What is specular reflection?
Rays are reflected from a smooth surface in a single direction
What is diffuse reflection?
Reflection from a rough surface which causes scattering
How does a red colour filter work?
A red filter absorbs all wavelengths of light other than those in red range of the spectrum and this means only red light passes through the filter
What is opaque?
Not see through
What governs the colour of an opaque object?
Different objects reflect different wavelengths of light by different amounts and the wavelength that are most strongly reflected determine the colour
What happens to the wavelengths of light that aren’t reflected by an opaque object?
Any wavelengths that aren’t reflected are absorbed by the object
What colour does an object appear if all wavelengths are reflected by equal amounts?
White
What colour does an object appear if all wavelengths are absorbed?
Black
What do all bodies emit and absorb?
Infrared radiation
What happens to the quantity of infrared radiation emitted by an object as temperature increases?
The hotter the object, the more infrared radiation it will emit
What happens to the type of radiation emitted by an object as temperature increases?
The hotter the body the shorter the wavelength of radiation released?
What is required for a body to be at a constant temperature?
The body would need to emit radiation at the same rate it absorbs it - it needs to radiate at the same average power that it absorbs
What distributes any emissions that depends on temperature?
Intensity and wavelength
What is meant by intensity?
The power transferred per unit area, a measure of the energy transferred by a wave
What will happen if the average power that a object radiates is less than absorbs?
The temperature of the object will decrease
What can be said about the rates of emission and absorption for a body increasing temperature?
The body is absorbing radiation faster than it’s emitting it
What factors that affect the temperature of the Earth?
The Earths rate of absorption and emission of radiation and the amount of reflection of radiation into space
How does the Earths atmosphere affect radiation?
The atmosphere largely absorbs or reflects radiation from the sun, preventing it from reaching Earth and some radiation, however is allowed to pass through and warms the earth
What happens to the radiation emitted from the Earth?
It’s absorbed and re-emitted in all directions by greenhouse gases, resulting in the greenhouse effect which warms the earth
What types of waves are electromagnetic waves?
Transverse
What do electromagnetic waves transfer?
Energy
What type of spectrum do electromagnetic waves form?
A continuous spectrum
What is the order of the electromagnetic spectrum in order of increasing wavelength?
Gamma, x-ray, UV, visible, infrared, microwaves and radio
What is the highest frequency electromagnetic wave?
Gamma waves
What is the highest energy electromagnetic wave?
Gamma waves
What properties are shared by all electromagnetic waves?
They are all transverse waves, travel at the same speed (3x10^8) and they can travel through a vacuum
What range of frequencies of electromagnetic waves can be detected by the human eye?
400-700 nanometers
How do the speeds of EM radiation differ in a vacuum and in air?
EM waves all travel at the same speed in a vacuum and in air
What can happen when radiation strikes an object
It can be transmitted, reflected or absorbed
What type of waves can be produced by oscillations in an electrical circuit?
Radio waves
How can radio waves create an alternative current in a circuit?
When radio waves are absorbed, they can induce oscillation in a circuit with the same frequency as the wave themselves
Where do gamma rays originate from?
They originated from changes in the nuclei of atoms
What health effects can ultraviolet waves causes?
They can cause skin to age prematurely and increase the risk of developing skin cancer
What health effects can x-rays and gamma rays cause?
They are ionising radiation so can cause mutations in genes and can lead to increased risk of developing various cancers
What health effects can infrared rays cause?
burns to skin/tissues
How does EM radiation affect electron arrangement in atoms?
Absorption or emission of EM radiation can cause electron arrangement to change
How do atoms become ions?
By losing an outer electron
What are the effects of body cells absorbing radiation?
Large amounts can damage cells, smaller amounts cause mutations, causing cells to divide rapidly which can lead to cancer
What is the use of radio waves?
Communication because radio waves are long wavelengths and can travel long distances without losing quality
What is the use of microwaves?
Cooking, as microwaves are absorbed by and heat fat/water in foods
What is the use of infrared radiation?
Cooing food, infrared cameras and short range communications
What is the use of visible radiation?
Illuminating and fibre optics as they reflect best in glass
What is the use of UV radiation?
Sterilisation as it kills bacteria, energy efficient lamps as it radiates low heat but high energy and sun tanning
What is the use of x-rays?
Medical imaging and treatment because they’re very high energy and can easily penetrate body tissues
What is the use of gamma rays?
Medical treatment, such as radiotherapy in the treatment of cancer
Which waves of EM spectrum are regarded as most dangerous?
Gamma and x-rays as they have the highest energy
