1. What is the fundamental difference between a real image and a virtual one?

2. Parallel light rays are focused on the focal point of a concave mirror. Where do you want to place the bulb in a searchlight, which uses a concave mirror , to produce a parallel beam?

Atmospheric Refraction

Dispersion and Colors

One combination of light beams that produces most of the colors that we perceive is red, green and blue. These are primary colors.

Red + Green = Yellow

Blue + Green = Cyan

Red + Blue = Magenta

Two colors that produce white light when added together are called complementary colors.

Mixing Paints and Mixing Colored Lights

Mixing paints is different from mixing colored lights.

Mixing paints is subtractive process, whereas with light beams you are adding colors.

Why is the sky blue? Why is the sun yellow?

1. What color is produced by the overlap of a blue spotlight and a red spotlight?

2. A surface appear yellow under the white light. How it will appear under red light? Under green light? Under blue light?

3. A substance is known to reflect red and blue light. What color would it have when it is illuminated by white light? By red light?

4. If you remove all of the green light from white light, what color would you see?

Rainbows

Thin Lenses

Any lens that is thicker in the center than at the edges will make parallel rays converge to a point and is called a converging lens.

Lenses that are thinner in the center than at the edges are called diverging lenses because they make parallel light diverge.

Lenses in eyeglasses are made with one convex surface and one concave surface. How can you tell if the lenses are converging or diverging?

Finding the Image Position Formed by a Thin Lens

-ray 1 is drawn parallel to the axis; therefore it is refracted by the lens so that is passes along a line through the focal point;

-ray 2 is drawn on a line passing the other focal point F’ and emerges from the parallel to the axis;

-ray 3 is directed toward the very center of the lens, this ray emerges from the lens at the same angle as it entered.

The Lens Equation

Converging Lens: fdd i

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Diverging Lens:

fdd i

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1. The focal length is positive for converging lens and negative for diverging.

2. The object distance is positive if it is on the opposite side of the lens from where the light is coming; otherwise it is negative.

3. The image distance is positive if it is on the opposite side of the lens from where light is coming.

4. The height of the image is positive if the image is upright and negative if the image is inverted relative to the object.

Lateral Magnification

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