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Dr Pusey www.puseyscience.com Q: What are the differences between a convex and concave mirror?

Yr9 - Refraction, Lenses and The Eye

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Page 1: Yr9 - Refraction, Lenses and The Eye

Dr Pusey

www.puseyscience.com

Q: What are the differences between a convex and concave mirror?

Page 2: Yr9 - Refraction, Lenses and The Eye

Recap - Convex & Concave Mirrors Concave – Dug out Like a Cave

Can form real and virtual images

Can focus light

Torches & Telescopes

Convex – Bulges out

Makes things appear smaller

Security mirrors

“objects in mirror are closer than they appear”

www.physicsclassroom.com

Page 3: Yr9 - Refraction, Lenses and The Eye

Recap

MIRROR

Show:• Angle of incidence• Angle of reflection• Normal• Reflected Ray• Incident Ray

Page 4: Yr9 - Refraction, Lenses and The Eye

Recap

MIRROR

Normal

Reflected RayIncident Ray

i r

Page 5: Yr9 - Refraction, Lenses and The Eye

Refraction Bending of light

Occurs when the light wave enters a different medium and changes speed

Light is the fastest in a vacuum (space)

Speed (vacuum) = 3x108 m/s

When light slows down, it bends TOWARDS the normal

Page 6: Yr9 - Refraction, Lenses and The Eye

Why is light refracted?The speed of light depends on the material through which the light is travelling. When light enters a different material (e.g. when moving from air into glass), the speed of light changes.

This causes the light to bend or refract.

The speed of light is affected by the density of the material through which it is travelling.

When light enters a more dense medium, its speed decreases and this is why refraction occurs.

air

glass

Page 7: Yr9 - Refraction, Lenses and The Eye

Your Turn As a wave enters a

medium where it travels slower, it bends towards the normal

As a wave enters a medium where it travels faster, it bends away from the normal

Faster speed

Slower speed

Normal

Normal

i

r

Page 8: Yr9 - Refraction, Lenses and The Eye

Your Turn

Glass

Show:• Angle of incidence• Angle of refraction• Normal• Refracted Ray• Incident Ray

Page 9: Yr9 - Refraction, Lenses and The Eye

Your Turn

Glass

Normal

i

r

Incident Ray

Refracted Ray

What happens when the ray leaves the glass block? Draw it!

Page 10: Yr9 - Refraction, Lenses and The Eye

Your Turn

Glass

Normal

Normal

i

r

i

r

Page 11: Yr9 - Refraction, Lenses and The Eye

Total Internal Reflection If the angle of incidence is large enough, light won’t

actually refract through to the next medium. It will instead reflect!

Diamonds

NBN Fibre Optics!

Page 12: Yr9 - Refraction, Lenses and The Eye

Lenses Transparent material that

direct/refocus light using the principles of refraction

Two types for you to learn:

Convex – Bulges on each side

Concave – Caves in on each side

https://en.wikipedia.org/wiki/Lens_%28optics%29

Page 13: Yr9 - Refraction, Lenses and The Eye

Convex Lens Focusses light (e.g. magnifying

glass)

The point at which light focusses is the “focal point”

https://en.wikipedia.org/wiki/Lens_%28optics%29

Page 14: Yr9 - Refraction, Lenses and The Eye

Concave Lens Spreads (diverges) the light

The point where the diverging light appears to come from is known as the “focal point”

https://en.wikipedia.org/wiki/Lens_%28optics%29

Page 15: Yr9 - Refraction, Lenses and The Eye

Your turn Finish these ray diagrams:

Page 16: Yr9 - Refraction, Lenses and The Eye

Your turn Finish these ray diagrams:

Page 17: Yr9 - Refraction, Lenses and The Eye

Focuses Light to the Retina to form an image

Changes the shape of the lens to focus on near and far objects

Contains light receptors.Where images areformed from light

Carries signals to the brain

Let’s light intothe eye!

Controls how much light is let into the eye

Refracts light into the lens for

focussingExtension!

The Eye