P1P5 - Light + Electromagnetic spectrum Flashcards
What are the 7 waves on the Em spectrum?
(High freq - low)
gamma, X-ray, ultraviolet (UV), visible, infrared, microwave, and radio waves.
Whats the wavelength + frequency of a gamma and radio waves?
Gamma rays have the shortest wavelength and the highest frequency.
Radio waves have the longest wavelength and the lowest frequency.
What are the uses of a gamma ray?
medical imaging and therapy, astronomy, sterilisation and food preservation.
What are the risks of gamma rays?
Extremely penetrating and damaging to living tissues and cells.
What are the uses of X-rays?
Low-energy X-rays are used for medical and industrial imaging.
High-energy X-rays are used to treat cancer.
Security purposes
What are the precautions for using x-rays?
Barriers
Materials between them (metal and lead
How do x-rays get images of our bones?
X-rays penetrate soft materials.
Bones are dense materials that absorb X-rays.
We can use X-rays to build a shaded image of bones and body tissue.
How do ultraviolet light work?
In lamps, UV photons excite atoms. The atoms then release visible light.
In sun tanning, UV excites (gives energy to) skin cells. The skin cells then change colour.
Why can microwaves be a risk?
Because humans are largely made up of water, exposure to microwaves could have a harmful effect.
What are the uses of microwaves?
Satellite communications
Transmit signal from a nearby phone mast to a mobile phone.
Cooking food
How do microwaves work?
Microwaves have a high enough frequency to penetrate the Earth’s atmosphere and to reach satellites.
Microwaves travel in straight lines through the atmosphere. This makes them good for transmitting (sending) signals.
What are the uses of radiowaves?
Radios
TV communications
How do radiowaves work?
Long wavelengths,
so they can be transmitted around the Earth’s surface and around buildings without interference.
What are the 7 colours in VL? (increasing freq)
Red, Orange, Yellow, Green, Blue, Indigo and Violet.
How does visible light work?
We use visible light in optical fibres because it can be totally internally reflected.
This means that we can transmit signals along optical fibres without the signals getting lost.
Opaque
Reflect or absorb
(No light passes through)
Transparent
Transmit light without scattering the rays
Translucent
Transmit light but scatters rays
What is specular reflection?
Light reflected off smooth surface
What is diffuse reflection?
Light reflected off a rough surface
What is a convex/converging lens?
Curved on both sides and is wider at the middle than at the edges.
What is the focal length?
The distance from the lens to the principal focus
What is a concave/diverging lens?
Wider at the edges than in the middle.
What happens when light enters a concave/diverging lens?
They disperse and spread out.
What is the principal focus in a convex lens?
The place where all the rays hitting the lens parallel to the axis meet.
