19. Two side-by-side coherent light sources radiate at 450 nm. The phase difference between these two sources at a point in space is 0.333 radians. The path difference between the two sources could be
A) 15.8 nm B) 20.3 nm C) 23.8 nm D) 29.7 nm E) 32.1 nm
20. Which of the following statements is true?
A) When two harmonic waves of the same frequency and wavelength but differing in phase combine, the resultant wave is a harmonic wave whose amplitude depends on the phase difference.
B) A phase difference between two waves can be the result of a difference in path length.
C) A path difference of one wavelength is equivalent to no phase difference at all.
D) A phase difference between two waves can be the result of reflection from a boundary surface.
E) All of these are correct.
21. You create a wedge-shaped film of air between two flat plates of glass 2.5 cm wide by laying one on top of the other and placing a small slip of paper 1.0 mm thick between their edges at one end. You illuminate the glass plates with normally incident monochromatic light of unknown wavelength. Observing the reflection, you see dark fringes at both ends of the plates. Between the ends you see three other dark fringes. What is the wavelength of the incident light?
A) 250 nm B) 400 nm C) 440 nm D) 500 nm E) 620 nm
22. Which of the following statements about Young's double-slit experiment is false?
A) The bands of light are caused by the interference of the light coming from the two slits.
B) The results of the double-slit experiment support the particle theory of light.
C) Double-slit interference patterns can also be produced with sound and water waves.
D) If the slits are moved closer together, the bands of light on the screen are spread farther apart.
E) The pattern of light on the screen consists of many bands, not just two bands.
23. The maximum wavelength for the photoemission of electrons from a metal surface depends on
A) applied voltage.
B) light intensity.
C) the metal that the light strikes.
D) current.
E) None of these is correct.
24. In a photoelectric experiment, the threshold frequency for a material is 3.2 × 10¹⁴ Hz. An electron ejected from this surface by a photon of frequency 9.4 × 10¹⁴ Hz can be stopped by a stopping potential of
A) 8.5 mV B) 1.6 V C) 0.26 nV D) 2.6 V E) 3.6 kV