# Light as a Wave

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Nurlanish va yutilish spektri

• Prepared by
• Mr. G. Shahin
• 22th of February, 2018
• Collège des Frère

## Light as a Wave

• Light (or electromagnetic radiation), can be thought of as either a particle or a wave. Light has various properties:
• a wavelength, (distance between waves)
• a frequency, f (number of waves passing you each second)
• a speed, c =  f (this is always the same: 300,000 km/s)
• an energy per photon, E = h f (where h is just a constant)
• Note that because the speed of light is a constant, , f, and E are linked: if you know one, you know the other two.

## Light as a Particle

• Light can also behave as particle. Each packet of light is called a photon, and each photon carries a specific amount of energy (associated with the photon’s wavelength or frequency).
• Photons emitted from a source will spread out in all directions at the speed of light. Since the amount of area surrounding a source increases as the distance squared, the density of photons will decrease as 1/r2. This is the inverse square law of light.

## Scattering of Light

• Dust in the Earth’s atmosphere (or in space) can scatter light. In general, short wavelength blue light gets scattered more than red light. That’s why the sky is blue.

## Scattering of Light

• The long path through the atmosphere means all the blue photons are scattered away. That’s why the Sun is red at sunset.

• Anything that is hot (i.e., above absolute zero) produces light at all wavelengths – a continuous spectrum. But the amount of light given off at each wavelength depends on the object’s temperature.
• For hotter objects:
• Peak intensity shifts to shorter (bluer) wavelengths
• peak1/T
• more light is created

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