light & the EM spectrum
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How are electromagnetic waves defined?
Transverse waves that transfer energy from source to absorber.
All electromagnetic waves …
• are transverse • can travel through a vacuum • travel at same speed in a vacuum
The sun emits several types of EM radiation such as…
• visible light (to see) • infared (heat earth) • ultraviolet (energy for photosynthesis)
Radiation with higher energy is…
• highly ionising • harmful to cells & tissues causing cancer
Radiation with lower energy…
• useful for communications • less harmful to humans
What are the positives & negatives of microwaves?
Used for communications, cook food. Risk of internal heating since humans contain a lot of water.
What are the positives & negatives of ultraviolet?
Suntanning, detecting forged banknotes. Can cause severe eye damage, ionising so can kill cells resulting in skin cancer.
What are the positives & negatives of x rays & gamma rays?
Look at bones & structures inside body, sterilize food & medical equipment. Most ionising, can cause internal damage & cancer.
What colours have the shortest & longest wavelength?
Red, violet.
What happens in the transmitting antenna? What happens in a receiving aerial?
Charge from alternating current oscillates up & down antenna producing radio waves. Metal aerial absorbs radio waves creating alternating current.
The denser the substance…
The slower the wave.
What’s the method for refraction?
• Draw around the glass block • Draw a normal • Turn on ray box & draw Xs to indicate paths of light rays • Turn off ray box & remove block • Join Xs to show light rays • Measure angles of reflection & refraction