Topic 5 - Light And EM Flashcards
What is total internal reflection?
When 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 large 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?
Violet
What colour of visible light has the largest wavelength?
Red
What is meant by the term “specular reflection”?
Rays are reflected from a smooth surface in a single direction.
What is meant by the term “diffuse reflection”?
Reflection from a rough surface which caused scattering of light rays.
How does a red colour filter work?
A red filter absorbs all wavelengths of light other than those in red range spectrum
This means only red light passed through the filter.
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 lights that Aren’t reflected by an opaque object?
Wavelengths Absorbed by the object
What colour does an object appear if all wavelengths are reflected by equal amounts?
White
What colore does an object appear if all wavelengths are absorbed?
Black
What types of waves are EM waves.
Transverse
What do EM waves transfer?
Energy (not matter)
What type of spectrum do EM waves form?
A continous spectrum
Order of EM spectrum in terms of increasing wavelength
Smallest: Gamma X ray Uv Visible Infrared Microwaves Radio Largest:
Highest frequency EM wave:
Gamma waves
Highest ionising EM wave
Gamma waves
What properties are all shared by EM waves?
All transverse
All travel at the same speed in a vacuum and air (3x10^8 m/s)
What type of waves can be produced by oscillations in an electrical circuit?
Radio waves
How can radio waves create and alternating current in a circuit?
When radio waves 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 Ultraviolet waves cause?
Damage to the surface cells and eyes, leading to skin cancer and eye conditions
What health effects can X-rays and Gamma rays cause?
They are ionising radiation so can cause mutations in genes.
They can lead to increased risk of developing various cancers.
How does electromagnetic radiation affect electron arrangement in atoms?
Absorption or emission of electromagnetic radiation can cause electron arrangement to change. (It can excite electrons up or down energy levels or remove electron from atom)
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 a use of radio waves
Communications, because radio waves are long wavelength and can travel Long distance without losing quality
State and explain a use of microwaves
Cooking, as microwaves are absorbed by and heat water/fat in foods.
State and explain uses of infrared radiation
Cooking food (as it transfers thermal energy) infrared cameras, short range communication.
State and explain used of visible radiation
Illuminating (seeing) and fibre Optics as they reflect best in glass (other waves have wavelengths that are too long/short).
State and explain used of UV
Sterilisation, as it kills bacteria, energy efficient lamps, as it radiates low heat but high energy and sun tanning.
State an explain uses of X rays
Medical imaging and treatment because they are very high energy and can easily penetrate body tissues
State and explain used of gamma rays.
Gamma rays are used in 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/highly ionising
What is the focal length?
Focal length is the distance between lens and focal point.
How is the power of lens related to the focal length and the shape of the lens?
Power of the lens = inverse of the focal length
Shorter focal length, greater power.
Thicker lens means shorter focal length, so greater the power.
What happens in a converging lense? Draw an Example
In a converging lens, parallel rays of light are brought to a focus. (Focal point/principal focus)
Also know as convex lense
What happens to light in a diverging lense? Draw an example
In a diverging lens, parallel rays of light are made to diverge from a point.
Aka concave lens
