Interference

A parallel beam of monochromatic light is incident on a slit of width 2 cm. The light passing through the slit falls on a screen 2 m away. As the slit width is decreased: 

A. the width of the pattern on the screen continuously decreases 

B. the width of the pattern on the screen at first decreases but then increases 

C. the width of the pattern on the screen increases and then decreases 

D. the width of the pattern on the screen remains the same 

E. the pattern on the screen changes color going from red to blue

A light spectrum is formed on a screen using a diffraction grating. The entire apparatus (source, grating and screen) is now immersed in a liquid of refractive index 1.33. As a result, the pattern on the screen: 

A. remains the same 

B. spreads out 

C. crowds together 

D. becomes reversed, with the previously blue end becoming red 

E. disappears because the refractive index isn’t an integer

Light from a small region of an ordinary incandescent bulb is passed through a yellow filter and then serves as the source for a Young’s double-slit experiment. Which of the following changes would cause the interference pattern to be more closely spaced? 

A. Use slits that are closer together 

B. Use a light source of lower intensity 

C. Use a light source of higher intensity 

D. Use a blue filter instead of a yellow filter 

E. Move the light source further away from the slits.

As more slits with the same spacing are added to a diffraction grating the lines: 

A. spread farther apart 

B. move closer together 

C. become wider 

D. becomes narrower 

E. do not change in position or width

If two light waves are coherent: 

A. their amplitudes are the same 

B. their frequencies are the same 

C. their wavelengths are the same 

D. their phase difference is constant 

E. the difference in their frequencies is constant

A light beam incident on a diffraction grating consists of waves with two different wavelengths. The separation of the two first order lines is great if: 

A. the dispersion is great 

B. the resolution is great 

C. the dispersion is small 

D. the resolution is small 

E. none of the above (line separation does not depend on either dispersion or resolution)

Yellow light is viewed by reflection from a thin vertical soap film. Let λ be the wavelength of the light within the film. Why is there a large dark space at the top of the film?

A. no light is transmitted through this part of the film 

B. the film thickness there is λ/4 

C. the film thickness there is much less than λ 

D. the film is too thick in this region for thin film formulas to apply 

E. the reflected light is in the infrared

Huygens’ construction can be used only: 

A. for light 

B. for an electromagnetic wave

C. if one of the media is vacuum (or air) 

D. for transverse waves 

E. for all of the above and other situations

The widths of the lines produced by monochromatic light falling on a diffraction grating can be reduced by: 

A. increasing the wavelength of the light 

B. increasing the number of rulings without changing their spacing 

C. decreasing the spacing between adjacent rulings without changing the number of rulings

D. decreasing both the wavelength and the spacing between rulings by the same factor 

E. increasing the number of rulings and decreasing their spacing so the length of the grating remains the same

In a Young’s experiment, it is essential that the two beams: 

A. have exactly equal intensity 

B. be exactly parallel 

C. travel equal distances 

D. come originally from the same source 

E. be composed of a broad band of frequencies