Topic 5 Light and EM spectrum

• Refraction is when a ray of light moves into a material where it travels at a different speed it usually changes direction.
• law of reflection says that the angle of incidence is equal to the angle of reflection
• Total internal reflection is when the angle of incidence is greater than the critical angle
• when the angle of incidence equals the critical angle the refracted light passes along the interface boundary of the glass block
• Diffuse reflection is when rough surfaces reflect they scatter light in all direction
• When light is reflected on very smooth surfaces, the light is reflected evenly this is called specular diffusion
• Filters emit different colours of light by transmitting their colouring and absorbing all other colours
• An object looks a certain colour because it reflects light of that colour and absorbs all other colours
• A more powerful lens is more curved and bends light more,
• converging lens makes parallel rays of light converge at the focal point
• diverging lens, the focal point is the point which the rays seem to be coming after passing through the lens
• An object close to a converging lens will always make a virtual image, called virtual because it cannot be projected onto a screen.
• Diverging lenses always produce virtual images that are the same way up, much smaller and close to the lens than the object
• All electromagnetic waves are transverse and they travel at the same speed in a vacuum
• electromagnetic waves transfer energy from source to observer
• 1. The order of the electromagnetic waves from low to high frequencyRadio waves 2. Microwaves 3. Infrared 4. Visible light (the light we can see) 5. Ultraviolet 6. X-rays 7. Gamma radiation
• our eyes can only detect a limited range of frequencies of electromagnetic radiation
• different substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength
• The more dense the medium gets, the slower the EM wave travels, meaning the smaller its wavelength
• The less dense the medium gets, the faster the EM wave travels, meaning the larger its wavelength
• All bodies emit radiation and the intensity and wavelength distribution of any emission depends on their temperature
• For a body to be at a constant temperature it needs to radiate the same average power that it absorbs
• The amount of radiation emitted by an object increases as its temperature increases
• The amount of energy transferred in a certain time is its power
• For a system to stay at a constant temperature it must absorb the same amount of power as it radiates
• For the temperature of the earth to stay the same it must radiate energy into space at the same average rate it is absorbed
• The temperature of the earth is affected by factors controlling the balance between incoming radiation and radiation emitted
• The potential danger associated with an EM wave increases with increasing frequency
• A certain microwave frequency can heat water, this could be dangerous to people because our bodies are mostly water and so microwaves could heat cells from the inside
• Infrared radiation is used to cook food, our skin absorbs infrared which we feel as heat. Too much can damage or destroy cells causing skin burns
• The energy transferred by UV radiation to our cells can cause sunburn and damage DNA. Too much exposure can lead to skin cancer, and UV radiation can cause eye conditions because too much UV radiation is reflected into them
• Xrays and Gamma rays are higher frequency than UV radiation and so transfer more energy. This can penetrate the body and may cause mutations in DNA that can kill cells or cause cancer
• Radio waves can be produced by or can themselves induce oscillations in electrical circuits
• changes in atoms and nuclei can generate radiations over a wide frequency range
• changes in atoms and nuclei can be caused by absorption of a range of radiations
• EM radiation is produced by the changes in the electrons or the nuclei in atoms
• Radio waves can be used for broadcasting, communications and satellite transmissions.
• microwaves can be used for communications and satellite transmissions and cooking. In cooking energy is transferred to the food, heating it up
• infrared waves can be used for communication in short ranges eg between computers in the same room. The information sent along optical fibres is also sent using infrared radiation.
• Cooking food is done by infrared radiation, and in thermal imaging by showing how much infrared radiation is emitted by a person