Baby-Quiz 1.Why is the diamond more brilliant than a clear piece of glass having the same shape? 2.A surface appear yellow under the white light. How it will appear under red light? Under green light? Under blue light? 3.Most of us find that we really have to strain our eyes to focus on objects located close to our noses. You hold two mirrors 1 foot in front of your face. One is a plane mirror, and the other is a concave mirror with a 3-inch focal length. In which case are you more likely to have to strain your eyes to see the image of your nose? 4.When you mix red and green light from separate projectors, you get yellow spot on the wall. However, if you mix red and green paint, you get a muddy brown color. How do you account for this difference?

The Wave Nature of Light

Waves vs Particles

Huygens’ Principle Every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself. The new wave front is the envelope of all wavelets – the tangent to all of them.

The bending of waves behind the obstacles into the “shadow region” is known as diffraction.

Huygens’ Principle and the Law of Refraction

Important: When a light wave travels from one medium to another, its frequency does not change, but its wavelength does.

Does red or blue light have the slower speed in glass?

1.How does a particle theory of light account for the diffuse reflection of light? 2.How does Newton’s idea of light particles explain the law of refraction? 3.Does the wave’s frequency or its wavelength remain the same when the wave crosses from one medium into another? 4.Which color of light, white or yellow, travels faster in diamond?

1.Does the amplitude of a light wave increase, decrease or stay the same upon reflection from a transparent material? Explain. 2.Imagine that Newton knew that light slower in glass than in air but was unaware of the law of refraction. In what direction would he have predicted light to bend when passing from air into glass? 3.Why we do not notice any dispersion when light passes through a windowpane?

1.What does the dispersion of light tell us about the speeds of various colors of light in a material? 2.Will the converging lens focus blue light or led light at a closer distance to the lens? Explain.

Interference: Young’s Double Slit Experiment

Constructive Interference: Destructive Interference:

Line Spacing for Double-Slit Interference

Conceptual Example: Changing the Wavelength (a)What happens to the interference patter if the incident light (500 nm) is replaced by light of wavelength 700 nm? (b)What happens instead if the slits are moved farther apart?

1.Would yellow light or green light produce the wider two- slit interference pattern? 2.If light and sound are both wave phenomena, why can we hear sounds around a corner but cannot see around a corner? 3.Red light is used to form a two-slit interference pattern on a screen. As the two slits are moved farther apart, does the separation of the bright bands on the screen decrease, increase, or remain the same?