P13- electromagnetic waves

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Electromagnetic spectrum

Electromagnetic waves- electric and magnetic disturbances that can be used to transfer energy from a source to an absorber

Microwaves- energy is transferred from the source of microwave radiation to the food, heating it

radiators- IR radiation transfers energy from the heater to the surroundings

EM waves don't transfer matter, they transfer energy depending on their wavelength

radio waves- about 10km wavelength

microwaves

infrared

visible light

Ultraviolet

X-rays

Gamma Rays - about 0.000001nm

Our eyes can only detect visible light, just below 400nm and above 700 nm.

All waves travel at 3 x 10^8 m/s

Equation for wave speed:

Since wave speed is constant for electromagnetic waves, the shorter the wavelength, the higher the frequency. As frequency increases, the energy of the wave increases.

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13.2 Light, infrared, microwaves and radio waves

White Light- light that has all colours of the visible spectrum in it. Eg: lamps and sunlight

Wavelength increases from violet to red.

Camera

Film camera-camera lens focuses light onto a light sensitive film. The film needs to be developed to see the image

Digital(phone) camera- lens focuses light onto a sensor made up of thousands of light sensitive pixels. Each pixel makes up a dot on the image, which can be seen on a screen at the back of the camera. The image is stored digitally on a memory card.

Infrared radiation

All objects emit IR radiation. The hotter an object is, the more IR radiation it emits. If absorbed in excess by the skin, it can damage, burn and kill skin cells.

Optical fibres use IR radiation instead of visible light as IR is absorbed less in glass fibres

IR pulses are easily produced and detected electronically. Remote controls and video equipment transmit signals by sending out a sequence of IR pulses when a button is pressed.

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