Refraction when light passes from one material aka

Refraction • when light passes from one material (aka medium) to another, it bends because the speed of light travels at different speeds in different mediums

• Light bends toward the normal when it slows down, and away from the normal as it speeds up. - vacuum: 3. 0 x 108 m/s - water: 2. 26 x 108 m/s - acrylic: 1. 76 x 108 m/s

Light travels thru water (why we see blue best)

This bending of light can play tricks on our minds. Ie. Broken/Bend pencil/spoon.

This is why a fish in the water looks just below the surface, and may be deeper and further away.

Another Trick Light travels faster at higher altitudes because the air is less dense.

Another example of refraction of light is the twinkling of a star in the night sky As starlight travels from space into the Earth’s atmosphere, the rays are refracted. Since the atmosphere is constantly changing, the amount of refraction also changes.

• Light can undergo partial reflection and refraction at the same time at a surface. Ex. Sunglasses, two way mirrors (buildings = less air conditioning)

Refraction Lab Purpose: To determine relative speeds of light through different mediums Observations: 1. Trace a petri dish, label the normal and draw in an incident light ray for you to follow. 2. Fill the petri dish with water 3. Shoot the light ray down the incident ray. 4. Trace the light ray coming out of the petri dish 5. Remove petri dish and connect the lines and label ‘water’ 6. Repeat steps 2 – 5 with glycerin in petri dish. 7. Use a protractor to label the incident angle and both of the refracted angles.

Analysis: 1. Which ray bends most toward the normal; air, water, glycerin? Which ray bends the least? 2. Which substance is the light travelling the fastest in and why? 3. Which substance is the light travelling the slowest in and why?

Dispersion - The refraction of white light into different colours. (Pink Floyd – dark side of the moon) - Since each colour travels at a different speeds, it bends at different angles

• Ex. Rainbows – in order to see a complete rainbow, you need to stand so that its raining in front of you, and the sun is directly behind you.

Total Internal Reflection Sometimes light bends (refracts) so much that it hits the inside wall of a substance at 90 degrees, and totally reflects off (no refraction occurs). The light gets trapped inside the object.

Ex. Fiber Optics – used to send signals quickly over long distances – glasses, phone cables, surgery Demo – dollar store fibre optics Demo –laser follows stream of water (2 L water bottle)

Ex. Diamonds – jewellers cut angles surfaces (facets) to make the light become trapped in diamond, and reflect out the top, making it sparkle.

Prisms