AP Physics IV.B

Physical Optics

27.1 Linear Superposition

27.2 Young’s Double Slit Experiment and Wave Properties

of light

First, what is diffraction of light?

Bright and dark fringes

Position of the fringes

“Order in the fringe!”

Intensity of the fringes

Two equations for double-slit interference

Ex. The distance between two slits is 1.20 EE –4 m. An interference pattern is projected onto a screen 2.75 m away. Find the distance on the screen between the central bright fringe and and the third order bright fringe.

p. 858: 1-6 (omit 4), 77B5.b-c; Rev. p. 662: 5-7

2. a) 0.68º b) 1.4º c) 2.0º

3. For 2nd dark fringe order is ?

6. 0.43 EE -2 m

77B5

b. Drawing (in your notes)

c. What is d in terms of wavelength? (f = 90 Hz)

p. 662, 6: 58º

24.2 The electromagnetic Spectrum

All wave of e-m spectrum travel at c. Note the relationship between

wavelength, frequency and energy.

E-m spectrum

• Radio (AM, FM, TV) > 30 cm• Microwaves (radar, atomic-molecular research, m-

wave ovens) between 30 cm and 1 mm• Infrared between 1 mm and 700 nm• Visible light between 400 nm and 700 nm• Ultraviolet between 400 nm and 60 nm• X-rays between 60 nm and 10 EE -4 nm• Gamma rays between 0.1 nm and 10 EE -5 nm

24.6 Polarization of Light

Let’s look at unpolarized light first

The fence and the rope

27.3 Thin Film Interference

Soap bubbles, parking lots and CDs

For each case give the equation for constructive and destructive

interference at the top interface.

Ex. A soap bubble appears green (wavelength 540 nm) on its front surface at a point nearest the viewer. What is the minimum thickness of the film if the index of refraction for soap is 1.35?

Ex. A very fine wire with a diameter of 7.35 EE -3 mm is placed between two glass plates. Light with a wavelength in air of 600 nm falls perpendicular to the plates and a series of bright and dark bands is seen. How many dark bands are seen from the point at which the plates come in contact to the location of the wire?

p. 859: 10-14, 84B5; Rev. p. 79: 21, 24

10. 183 nm, 366 nm

12. a) 140 nm b) 200 nm

14. 1.18

84B5

a) 5 EE 14 Hz

b) 480 nm

c) 120 nm

d) 240 nm

p. 79• 30.0 m

24. 18 m/s

27.5 Diffraction of Light and Huygen’s Principle

Huygen’s Principle – every point on a wave acts as a source of tiny wavelets that move forward with the same speed as the wave. The wave front at a later instant is a

line tangent to the wavelets.

When the width of the opening is large compared to the wavelength

of light, the bending is small. When the width of the opening is

small compared to the wavelength, the bending is large.

Interference pattern for single slit diffraction

Single slit interference

Ex. The width of a single slit is 4.0 EE –6 m. The slit is 0.40 m from a screen. The distance between the middle of the central bright fringe and the first dark fringe is y. Find the width of the central bright band when red light (wavelength 690 nm) and violet light (wavelength 410 nm) fall upon the slit.

27.7 Diffraction Gratings

Interference pattern for a diffraction grating

Ex. A mixture of violet light (wavelength 410 nm) and red light (wavelength 660 nm) falls on a diffraction grating that has 1.0 EE 4 lines/cm. For each wavelength, find the angle for the first order maximum.

p. 859: 21-23; 80B4, 85B5

22. 1.5

80B4 – drawings

85B5

a. 5.0 EE -3 m

b. i. 380 nm ii. 790 nm

c. yours