# Demo: Print: Supplies: pennies, set of styro-cups.

## Presentation on theme: "Demo: Print: Supplies: pennies, set of styro-cups."— Presentation transcript:

Demo: Print: Supplies: pennies, set of styro-cups

REMINDER: QUIZ, Monday REMINDER: QUIZ, Monday  Convex and concave lenses Look at money under UV light Look at money under UV light Optic Illusions Optic Illusions Convex lenses Convex lenses Concave lenses Concave lenses

The change in direction of a wave due to a change in its speed The change in direction of a wave due to a change in its speed Most commonly observed when a wave passes from one medium to another Most commonly observed when a wave passes from one medium to another – When does light change speed?

Activities Have students in a line bounce off a wall Demonstrate refraction In fluids In lenses Light changes speed when it travels from one optical density to another

A transparent item used to change the direction and control the distribution of light rays A transparent item used to change the direction and control the distribution of light rays Where are lenses used? Where are lenses used?

Because when light hits different mediums, its speed changes. In this case, the light hit the water, which made the light become more spread out. This allowed us to see the penny at further distances.

Swamp

Mirror GlassAir

In transparent media, normal lines guide transmission of ray, not reflection In transparent media, normal lines guide transmission of ray, not reflection When light travels from lower to higher optical density (i.e. from air to glass) light bends toward the normal When light travels from lower to higher optical density (i.e. from air to glass) light bends toward the normal

Glass AirGlassWater Air Water

Convex A converging lens is thickest in the middle Concave A diverging lens is thinnest in the middle

At least one side of the outer lenses curves outwards At least one side of the outer lenses curves outwards Are thicker in the middle and thinner on the outer edges Are thicker in the middle and thinner on the outer edges Used for magnifying an object Used for magnifying an object

Since the lens is a different medium than air, the light rays refract Since the lens is a different medium than air, the light rays refract Convex lenses refract parallel light rays so that they meet at a focal point. (“convergence”) Convex lenses refract parallel light rays so that they meet at a focal point. (“convergence”)

Using normal lines, demonstrate the light rays through the convergent lens: Using normal lines, demonstrate the light rays through the convergent lens:

At least one side curves inwards. At least one side curves inwards. Thinner in the middle Thinner in the middle Make an object appear smaller Make an object appear smaller

Concave lenses cause light rays to “diverge” Concave lenses cause light rays to “diverge” Divergence Divergence – To separate/curve outwards

1.Concave 2.Convex

1.Concave 2.Convex

1.Concave 2.Convex

It’s a number that indicates the amount that a transparent medium decreases the speed of light. It’s a number that indicates the amount that a transparent medium decreases the speed of light. It can be measured as: It can be measured as: Index of refraction of material= speed of light in vacuum Index of refraction of material= speed of light in vacuum speed of light in medium speed of light in medium

Snell was a Dutch astronomer who was credited with identifying the exact relationship between the angle of incidence and angle of refraction Snell was a Dutch astronomer who was credited with identifying the exact relationship between the angle of incidence and angle of refraction The formula is used to calculate the new angle that a ray will take as a beam of light strikes the interface. The formula is used to calculate the new angle that a ray will take as a beam of light strikes the interface. Indices of refraction: n 1, n 2 Indices of refraction: n 1, n 2 Angle of incidence and angle of refraction ө 1, ө 2 Angle of incidence and angle of refraction ө 1, ө 2

n 1 sin ө 1 = n 2 sin ө 2

Light reflects completely off the inside wall of a denser medium rather than passing through the wall into a less dense medium. Light reflects completely off the inside wall of a denser medium rather than passing through the wall into a less dense medium.