Topic 5 - Light & The EM Spectrum Flashcards
Reflection
- Wave changes direction back to the same medium at a boundary
Refraction
- Wave changes direction when traveling into a different media at a boundary
Total Internal Reflection
- Light ray travels from denser to less dense material, and there is no refracted ray as it is on the boundary
Critical angle
- The angle of incidence when it causes the refacted ray to bend 90 degrees to the normal, and on the boundary
Specular Reflection
- Reflection in a single direction
Diffuse Reflection
- Reflection causing scattering
How is colour of light related to differential absorption at surfaces?
- Surface absorbs every frequency of light except the colour it is
How is colour of light related to transmission of light through filters?
- Filters absorb certain wavelength, and transmit others
Relate power to focal length
- Higher the power, the lower the focal length
Equation for power:
P=1/Focal length (meters)
Description of real images:
- Converging lenses only
2 rays are drawn: - 1 through the centre of the lens
- 1 parallel to the axis until it hits the lens, then refracts to the focal point
Description of virtual images:
- Both Converging and Diverging
3 rays are drawn: (Converging) - 1 through the centre of the lens
- 1 parallel to the axis until it hits the lens, then refracts towards the focal point
- 2 rays go opposite direction until they meet
3 rays are drawn: (Diverging)
- 1 throught the centre of the lens
- 1 parallel to the axis until it hits the lens, then refracts away from the focal point, and one in the opposite direction to that
EM waves transfer energy from source to:
observer
EM spectrum in order of increasing frequency:
- Radio waves
- Microwaves
- Infrared
- Visible Light
- Ultraviolet
- X-Rays
- Gamma
Effects of differences in the velocities of EM waves in different substances
Dispersion, which is:
- Light slowing down through different materials more for some colours more than others
All bodies emit:
- Radiation, dependant on temperature
For a body to be at a constant temperature, it needs to:
- Radiate the same average power that it absorbs
If a body’s average power it radiates is less than the average power it absorbs:
- Its temperature will increase
If a body’s average power it radiates is more than the average power it absorbs:
- Its temperature will decrease
Factors controlling the temperature of Earth
- Greenhouse effect
- Sun
- Human activities
Effects on people due to exposure of EM waves
- Microwaves: internal heating
- Infrared: skin burns
- UV: damage to surface cells. causing cancer and eye conditions
- Gamma: Mutations or damage to cells
Uses of EM waves:
Radio waves: Broadcasting and comms
Microwaves: Cooking and comms
Infrared: Thermal imaging, and TV controllers
Visible Light: Vision
UV: Security searching and forged bank notes
X-rays: Observing internal structure
Gamma: Sterilisng foods, detect cancer
Radiowaves are produced by:
oscillations in electrical currents
Finish the sentence - Changes in atoms and nuclei:
- can generate radiations
- are caused by absorbing a range of radiations
