How To Understand Light And Color

Transcription

1 PRACTICE EXAM IV P202 SPRING In two separate double slit experiments, an interference pattern is observed on a screen. In the first experiment, violet light (λ = 754 nm) is used and a second-order bright fringe occurs at the same location as a third-order dark fringe in the second experiment. Determine the wavelength of the light used in the second experiment. A) 1320 nm B) 862 nm C) 594 nm D) 431 nm E) 388 nm 2. A nm thick film of kerosene (n = 1.2) is floating on water. White light is normally incident on the film. What is the visible wavelength in air that has a maximum intensity after the light is reflected? Note: the visible wavelength range is 380 nm to 750 nm. A) 380 nm B) 430 nm C) 480 nm D) 530 nm E) 580 nm 3. A lens that has an index of refraction of 1.61 is coated with a non-reflective coating that has an index of refraction of Determine the minimum thickness for the film if it is to be non-reflecting for light of wavelength nm. A) m B) m C) m D) m E) m 4. Light with a wavelength of 644 nm uniformly illuminates a single slit. What is the width of the slit if the first-order dark fringe is located at θ = 0.125? A) m B) m C) m D) m E) m Page 1

2 5. The Hubble Space Telescope in orbit above the Earth has a 2.4 m circular aperture. The telescope has equipment for detecting ultraviolet light. What is the minimum angular separation between two objects that the Hubble Space Telescope can resolve in ultraviolet light of wavelength 95 nm? A) rad B) rad C) rad D) rad E) rad 6. Red light of wavelength nm is incident on a grating. If the separation between the slits is m, at what angle does the first principal maximum occur? A) rad B) rad C) rad D) rad E) rad 7. For which one of the following problems did Max Planck make contributions that eventually led to the development of the "quantum" hypothesis? A) photoelectric effect B) uncertainty principle C) blackbody radiation curves D) the motion of the earth in the ether E) the invariance of the speed of light through vacuum 8. A laser emits a single, 2.0-ms pulse of light that has a frequency of Hz and a total power of W. How many photons are in the pulse? A) B) C) D) E) Which one of the following phrases best describes the term work function? A) the minimum energy required to vaporize a metal B) the work required to place a charged particle on a metal surface C) the minimum energy required to remove electrons from the metal D) the minimum energy required to remove an atom from a metal surface E) the work done by electromagnetic radiation when it hits a metal surface Page 2

3 10. Photons of energy 5.0 ev strike a metal whose work function is 3.5 ev. Determine which one of the following best describes the kinetic energy of the emitted electrons. A) 1.5 ev or less B) 1.5 ev or more C) 2.5 ev or more D) 3.5 ev or more E) 3.5 ev or less 11. What is the speed of an electron that has the same momentum as a photon with a wavelength in a vacuum of 380 nm? The mass of an electron is kg. A) m/s B) m/s C) m/s D) m/s E) m/s 12. Approximately, what is the de Broglie wavelength of an electron that has been accelerated through a potential difference of 150 V? The mass of an electron is kg. A) 0.1 nm B) 1 nm C) 10 nm D) 100 nm E) 1000 nm 13. What happens to the de Broglie wavelength of an electron if its momentum is doubled? A) The wavelength decreases by a factor of 4. B) The wavelength increases by a factor of 4. C) The wavelength increases by a factor of 3. D) The wavelength increases by a factor of 2. E) The wavelength decreases by a factor of The position of a 1-g object moving in the x direction at 1 cm/s is known to within ± 10 nm. In which range is the fractional uncertainty, ( p x ) / p x, in the x component of its momentum? A) 10 2 to 10 4 B) to C) to D) to E) less than Page 3

4 15. Which one of the following pairs of characteristics of light is best explained by assuming that light can be described in terms of photons? A) photoelectric effect and the effect observed in Young's experiment B) diffraction and the formation of atomic spectra C) polarization and the photoelectric effect D) existence of line spectra and the photoelectric effect E) polarization and the formation of line spectra 16. Determine the wavelength of incident electromagnetic radiation required to cause an electron transition from the n = 6 to the n = 8 level in a hydrogen atom. A) nm B) nm C) nm D) nm E) nm 17. In an X-ray tube, electrons with energy 35 kev are incident on a cobalt (Z = 27) target. Determine the cutoff wavelength for X-ray production. A) m B) m C) m D) m E) m 18. Two possible states for the hydrogen atom are labeled A and B. The maximum magnetic quantum number for state A is +3. For state B, the maximum value is +1. What is the ratio of the magnitudes of the orbital angular momenta, L A /L B, of an electron in these two states? A) 1.22 B) 1.73 C) 2.00 D) 2.45 E) 3.46 Page 4

5 Answer Key 1. D 2. C 3. D 4. E 5. A 6. C 7. C 8. A 9. C 10. A 11. A 12. A 13. E 14. D 15. D 16. E 17. E 18. D Page 5