Topic 5 - light and the electromagnetic spectrum Flashcards
What is total internal reflection?
When a light is completely reflected back at a boundary between two mediums
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 has the highest frequency?
Blue
What colour of visible light has the largest wavelength?
Red
What is meant by ‘speculate reflection’?
Rays are reflected from a smooth surface in a single direction
WhT is meant by ‘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 the red range of the spectrum
So only red light passes through
What is meant by ‘opaque’?
Not see through
What governs the colour of an opaque object?
Different objects reflect different wavelengths of light by different amounts
The wavelengths that are most strongly reflected determine the colour
What happens to the wavelengths of light that aren’t reflected by any 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 type of waves are electromagnetic waves?
Transverse
What do electromagnetic waves transfer?
Energy (not matter))
What type of spectrum do electromagnetic waves form?
A continuous spectrum
List the order of the electromagnetic spectrum in order of increasing wavelength
Gamma, X-rat, Ultraviolet, visible, infrared, microwaves, 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?
All transverse
All travel at 3x10^8 m/s
Can all travel through a vacuum
What range of frequencies of electromagnetic waves can be detected by the human eye?
400-700 manometers
How do the speeds of EM radiation differ in a vacuum and in air?
They travel at the same speed
What can happen when radiation strikes an object?
It can be transmitted, reflected or absorbed
What do all objects emit and absorb?
Infrared radiation
WhT 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 bu an object as temperature increases?
The hotter the body the shorter the wavelength of radiation releases
What is required for an object 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 is meant by intensity?
The power transferred per unit area, it is a measure of the energy transferred by a wave
What will happen if the average power that an object radiates is less than it absorbs?
The temperature of the object will decrease
Hat can be said about the rates of emission and absorption for an object increasing in temperature?
The object is absorbing radiation faster than it is emitting it
Give two factors that affect the temperature of the earth
The amount of reflection of radiation into space
The earth”’s rate of absorption and emission of radiation
How does the Earth’s atmosphere effect radiation?
It absorbs of reflects radiation from the sun, preventing it from reaching earth
Some is allowed to pass through and warms the earth
What happens to the radiation emitted from the earth?
It is absorbed and re-emitted in all direction but greenhouse gases, resulting in the greenhouse effect which warms the earth
What type of waves can be produced by oscillations in an electrical circuit?
Radio
How can radio waves created an alternating current in a circuit?
When they are absorbed, they induce oscillations in a circuit with the same frequency as the waves themselves
Where do gamma rays originate from?
Changes in the nuclei of atoms
What health effects can untraviolet waves cause?
Premature skin aging
Can increase the risk of developing skin cancer
What health effects can X-rays and gamma rays cause?
Are ionising radiation so can cause mutations in genes
Can lead to increased risk of developing various cancers
What health effects can infrared rays cause?
Can cause burns to skin/tissue
How does electromagnetic 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 or gaining outer electrons
What are the effects of body cells absorbing radiation?
Large amounts can damage cells
Smaller amounts cause mutation, Causing cells to divide rapidly, which can lead to cancer
State and explain the main use of radio waves
Communication
Because they are long wavelength and can travel long distances without losing quality
State and explain the main use of microwaves
Cooking, as microwaves are absorbed by and heat fat/water in foods
State uses of infrared radiation
Cooking food
Infrared cameras
Short range communication
State and explain uses of UV radiation
Sterilisation, as it kills bacteria
Energy efficient lamps, as it radiates low heat but high energy
Sun tanning
State and explain uses of X-rays
Medical imaging and treatment p, because they are very high energy and can easily penetrate body tissues
State a use of gamma rays
Medical treatments, such as radiotherapy in the treatment of cancer
Which waves of the EM spectrum are regarded as most dangerous?
Gamma and X-rays as they have the highest energy
