Phenomena Related to Refraction. Why do we see images in mirrors? We know that light travels in straight lines Our brains interpret the light that is.

Phenomena Related to Refraction

Why do we see images in mirrors?

• We know that light travels in straight lines

• Our brains interpret the light that is reflected off mirrors as coming from a source behind the mirror

Magic Penny?

If you were trying to spear a fish from this vantage point, where would you aim your

spear?A. Directly at the

fish?B. Above where

you see the fish?

C. Below where you see the fish?

Virtual Image of fish

Actual location of fish

• Our brains interpret the refracted light as coming from a source along the line of sight

• Our eyes extend the light rays backwards, forming a virtual image of the fish

Apparent Depth

• Apparent depth is always smaller than actual depth

• Apparent Depth – the depth that an object appears to be at due to the refraction of light in a transparent medium

• The chest is deeper than it appears to the observer in the boat

Pretty Wacky!

Mirages• Mirage – a virtual image that forms as a

result of refraction and total internal reflection of light as it passes through a non-uniform atmosphere

• E.g. when you see “puddles” ahead on a hot highway

• On a hot day, the road gets very hot.• The road heats the air directly above it, while the

air higher up remains cool.• Since the air molecules are farther apart in hot

air, the density is lower lower index of refraction

• The farther away from the road, the cooler the air and the higher the index of refraction.

COOL n = 1.08

WARM n = 1.07 HOT n = 1.06

COLD n = 1.09

ROAD

More dense

Less dense

1.06

1.091.081.07

sky eye

ROAD

• Rays of light incident towards the road gradually refracts more and more, causing it to bend away from the road.• Once the light is incident at an angle that is larger than the critical angle it will totally internally reflect.• The light will then travel away from the road, eventually entering your eye.Virtual Image

of Sky

• Our brains interpret the light that enters our eye as coming from a source that is on the road.

• The image of the “pool of water” is therefore an inverted virtual image of the sky and other objects on the horizon.

Dispersion of Light• White light is a mixture of all the wavelengths of

the visible spectrum (ROYGBIV)

• The individual wavelengths appear when light refracts through a medium such as glass.

• This occurs because each colour of light bends at a different angle.– Violet refracts the most and red refracts the least.

You can see a rainbow when you look directly at the storm while the Sun is at your back.

1. When white light from the sun enters a raindrop, it is dispersed, producing the seven colours of the spectrum.

2. When this light hits the back of the raindrop, it is undergoes total internal reflection.

3. The light then refracts (disperses) even more when it travels from the raindrop to the air.

rain drop

Sunlight (white light)

1. Refraction(dispersion)

2. Total internal reflection

3. Refraction(dispersion)

• When we see a rainbow, we are seeing the refraction of light from many raindrops at different elevations.

• Each drop disperses a full spectrum of light, but a person only sees one color from a small group of raindrops. – Red light comes from raindrops higher up in the

sky

– Violet light comes from raindrops lower in the sky.

• Our eyes extend the rays that enter our eyes, thus producing a virtual image = RAINBOW!

What makes a double ?

The secondary bow arises from two internal reflections…. It’s always higher in the sky, and the colors are reversed!!

Secondary

Primary

Secondary RainbowSecondary

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• Pg. 531 # 3,5,8,9• Pg. 539 # 1-7