Chapter 16 Review

Interference and Diffraction

1. Define diffraction. When does diffraction occur?

Diffraction is the bending of a wave as it goes around obstructions or through openings.

2. Interference supports what property of light?

That light is a wave. Wave interference is well understood.

3. In Young’s double slit, what values of “m” correspond to bright spots? To dark spots?

When “m” is a whole number, that is a bright spot. A whole number plus ½ is a dark spot.

4. What is coherent light?

Light that is the same wavelength, the same phase, and is going the same direction.

5. What type of interference occurs when two crests arrive together on a screen? When two troughs arrive together? When a crest arrives with a trough?

Two crests or two troughs produce constructive interference. A crest and a trough produces destructive.

6. In single slit interference, how do the paths of selected wavelets differ?

By ½ of a wavelength.

7. In single slit interference, what values of “m” correspond to bright spots? To dark spots?

Single slit is the opposite of double slit. When “m” is a whole number, it produces a dark spot. If “m” is a number plus ½, it produces a bright spot.

8. What is a laser? What does the acronym “LASER” mean?

A device that produces very intense, coherent light.

Light Amplification by Stimulated Emission of Radiation.

9. Describe the pattern resulting from Young’s double slit. From a diffraction grating. From a single slit.

Young’s double slit produces a series of bright and dark spots, the bright spots where “m” is a whole number, starting at m = 1. The dark spots are where m is a whole number plus ½, starting at m = ½.

Diffraction gratings produce spots at the same points as Young’s Double slit.

In single slit interference, a series of bright and dark spots is still produced; however, the DARK spots are located where m is a whole number, starting at m = 1. The BRIGHT spots are located where “m” is a whole number plus ½, starting at m = 1 ½.

10. The distance between two slits in a double-slit experiment is 0.05 mm. The third order bright fringe is at an angle of 3.3º from the central maximum. What is the wavelength of the light?

= d sin /m= (0.05 mm)(1/1000) sin 3.3º /3

= 9.59 X 10-7

= 959 nm

11. The distance between two slits in a double-slit experiment is 0.004 mm. What is the angle of the second order bright fringe produced with light of 630 nm?

= d sin /m630 X 10-9= (0.004 mm)(1/1000) sin/2

= 18.4º

12. Monochromatic light is shined on a diffraction grating with 6.1 x 103 lines/cm. The first order maximum is seen at a 30º angle. Find the wavelength.

= d sin /m= (1/6100)(1/100) sin 30º /1

= 8.19 X 10-7

= 819 nm

13. Light, wavelength 500 nm passes through a 9000 lines /cm diffraction grating. What is the second order angle of diffraction?

= d sin /m500 X 10-9= (1/9000)(1/100) sin/2

= 64.2º

14. Light with a wavelength of 400 nm passes through a 4.47 x 105 lines/m diffraction grating. What is the first-order angle of diffraction?

= d sin /m400 X 10-9= 1/(4.47 x 105) sin/1

= 10.3º

15. The angle between the first order maximum and the zeroth order maximum for light of 2000 nm is 35º. Calculate the number of lines per centimeter on this grating.

= d sin /m2000 X 10-9= d sin35º /1d = 3.486 x 10-6m/line

1/(3.486 x 10-6)(1/100)

2868 lines/cm

16. Monochromatic light, λ = 532 nm, shines on a diffraction grating with 723,000 lines/m. Find the angles at which one would observe the first and second order maxima.

= d sin /m532 X 10-9= 1/(723,000) sin/1

= 22.6º

= d sin /m532 X 10-9= 1/(723,000) sin/2

= 50.3º