Light and the Electromagnetic Spectrum Flashcards
What is the relationship between the incident angle and the reflection angle?
incident angle = reflection angle
Explain specular reflection on smooth surfaces
On a smooth surfaces, all light incident rays exist at the same angle.
Describe diffuse reflection
For diffusion reflection, this is where light hits a rough surface and the incident ray is reflected at many angles.
How does light behave when entering a denser material during refraction?
Light bends towards the normal line.
How does light behave when entering a less denser material during refraction?
Light bends away from the normal line.
Explain the concept of Total Internal Reflection (TIR)
TIR occurs when light travels from a denser medium to a less dense one and the angle of incidence exceeds the critical angle, causing the light to reflect back into the denser medium instead of refracting out.
What is different between each colour in visible light?
Each colour has a specific wavelength.
How does white light form?
White light is composed if all colours together.
Why do objects appear to have a specific colour?
Objects appear to gave a certain colour because they reflect only that specific colour of light, absorbing all other colours.
Define focal length
The distance between the lens and the focal point.
What is the focal point?
The focal point is where all horizontal rays converge after passing through the lens.
Explain the relationship between focal length and lens power.
Power of lens is inversely proportional to the focal length; Thicker lens means shorter focal length, so greater power.
What are concave lenses? (3)
- Caves inwards
- Thinner at centre than the edges
- Spreads light outwards and further – used for short sightedness. This is because light is focused in front of the retina, so needs to be spread out slightly to be able to be focused onto retina.
What are convex lenses? (4)
- Thicker at centre
- Focuses light inwards
- Horizontal rays focus onto focal point
- Used for magnifying glasses, binoculars and to correct long-sightedness as it focuses the rays closer.
Describe electromagnetic waves
They are transverse waves, all travel at the same speed in a vacuum (3 x 10 to the power of 8m/s) and in space all waves have the same velocity of speed of light.
EM waves do not need particles to move.
What are the EM waves?
radio waves, microwaves, infra-red, visible light, ultraviolet, x-ray, gamma
radio waves - highest wavelength
How do materials interact with electromagnetic waves?
Materials interact with EM waves differently depending on the wavelength; for example glass can transmit visible light, reflect/absorb UV and IR.
Explain how bodies emit radiation
All bodies emit radiation: the higher the temperature the more intense and more wavelengths will be emitted. Temperature of the earth is also maintained this way; amount of energy received and emitted from the sun.
It must radiate the same average power than it absorbs to remain at a constant temperature.
What happens if a body absorbs more power than it emits?
If it absorbs more power than it emits – the temperature will increase
Describe the role of short wavelength infrared radiation from the sun in maintaining the Earth’s temperature
Short wavelength infra-red radiation from the sun reaches the earth, some is reflected by the atmosphere, most reaches the atmosphere. The energy is absorbed and reemitted as longer length IR radiation. This is mostly absorbed by the atmosphere and keeps Earth warm.
What are the dangers with high EM waves?
Higher frequency EM waves have more energy, so exposure can transfer too much energy to cells, causing them to mutate and potentially damage them (causing cancer).
What are the dangers with microwaves?
internal heating of body cells
What are the dangers with infra-red waves?
skin burns
What are the dangers with UV waves?
damage to surface cells and eyes, leading to skin cancer
What are the dangers with x-ray or gamma rays?
mutation or damage to cells in the body
What are the uses of radiowaves?
Communications, satellite transmissions (they can be produced by oscillations in electrical circuits or they can induce oscillations in electrical circuits).
What are the uses of microwaves?
cooking, communication
What are the uses of infra-red waves?
cooking, thermal imaging, short range communications, optical fibres
What are the uses of visible light?
vision, photography, illumination
What are the uses of x-rays?
observing structures of objects, airport/medical scanners
What are the uses of gamma rays?
sterilising food/medical equipment, treating cancer
What can changes in atoms and nuclei do?
It can generate radiations over a wide frequency range and be caused by absorption of a range of radiation.
