Optics Unit

10.1 Nature of Light

Properties of Light• Light travels very fast, nearly 300, 000, 000 m/s

• Light travels in a straight line

• Light is a form of energy that can travel through a vacuum (radiation)

• Light is an electromagnetic wave

Light Travels in a Straight Line

• How do we know that light travels in a straight line? Can you think of any examples in your life that would point to this conclusion?– Shadows– Flashlight beam– Eclipses

Flashlight

Solar Eclipse

Light is a Form of Energy

• What happens when you sit outside on a sunny day?– You warm up and might even get a sunburn– These phenomena point to the fact that light is a form

of energy

• What biological process makes use of light energy?– Photosynthesis (converts light energy into chemical

energy)

Light Energy is Transmitted via Radiation

• Do you remember how heat energy can be transmitted?– Via conduction or convection

– These methods require a physical substance (medium) through which energy is transferred

• Does light energy require a medium?– Think about how light gets to us from the Sun

– Energy transfer without a medium is called Radiation

Light is an Electromagnetic Wave

• Under certain conditions light displays wave-like properties

• This wave is created by a changing electric field and a changing magnetic field

• The hypothesized electromagnetic wave was finally proven by the discovery of radio waves– the wavelength was able to be measured – since they travel at the speed of light, they are a form

of light

The Electromagnetic Spectrum

• We classify light based on how much energy it carries

• From least energetic to most energetic:– Radio waves, microwaves, infrared light, visible

light, ultraviolet light, X-rays, and gamma rays

Energy of Light• If the speed of light is constant, how can

different waves of light have different energy levels?– Higher energy light has shorter wavelengths and

lower energy light has longer wavelengths

Spectrum of Visible Light

• Visible light can also be classified based on how much energy it carries

• From least to most energetic:– Red, orange, yellow, green, blue, indigo, violet– Remember the acronym ROY G BIV

Putting the Electromagnetic Spectrum to Use

The Electromagnetic Spectrum

Bill Nye: Light and Colour

Part 1

Part 2

“White” Light• “White” light is actually a mixture of all seven

colours of visible light

• “White” light can be broken down into these different colours by passing it through a prism

“White” Light

• Another way to see that “white” light is actually a combination of coloured light is by shining the primary colours upon one another

Visible Light: Only a Part of the Picture