Answer: b. Answer: a. Answer: d

Transcription

1 Practice Test IV Name 1) In a single slit diffraction experiment, the width of the slit is m and the distance from the slit to the screen is 2.2 m. If the beam of light of wavelength 600 nm passes through the slit and forms a diffraction pattern on the screen, what is the linear distance on the screen from the center of the diffraction pattern to the first dark fringe? A) 2.1 cm B) 4.3 cm C) 6.3 cm D) 8.5 cm 2) In a single-slit diffraction experiment, a beam of monochromatic light of wavelength 640 nm is incident on a slit of width mm. If the distance between the slit and the screen is 1.80 m, what are the positions of the first dark fringes? A) m B) m C) m D) m 3) In a single-slit diffraction experiment, the width of the slit through which light passes is reduced. What happens to the central bright fringe? A) It stays the same. B) It becomes narrower. C) It becomes wider. D) None of the other answers is correct. 4) A single-slit diffraction pattern is formed on a distant screen. Assuming the angles involved are small, by what factor will the width of the central bright spot on the screen change if the slit width is doubled? A) It will be cut to one-quarter its original size. B) It will be cut in half. C) It will double. D) It will become four times as large. 5) In a double-slit interference experiment you are asked to use laser light of different wavelengths and determine the separation between adjacent maxima. You observe that this separation is greatest when you illuminate the double slit with A) blue light. B) green light. C) red light. D) The separation is the same for all wavelengths.

2 6) Helium-neon laser light ( = m) is sent through a 0.30 mm-wide single slit. What is the width of the central maximum on a screen 1.0 m from the slit? a. 2.0 cm b. 4.2 mm c. 1.1 cm d. 2.0 mm e mm Answer: b 7) Monochromatic light from a He-Ne laser ( = nm) is incident on a diffraction grating containing 5000 lines/cm. Determine the angle of the first-order maximum. a b c d e Answer: a 8) White light is spread out into spectral hues by a diffraction grating. If the grating has 1000 lines per cm, at what angle will red light ( = 640 nm) appear in first order? a b c d e Answer: d 9) When you look at a single slit diffraction pattern produced on a screen by light of a single wavelength, you see a bright central maximum and a number of maxima on either side, their intensity decreasing with distance from the central maximum. If the wavelength of the light is increased, a. the pattern shrinks in size. (central maximum less wide; other maxima in closer to it) b. the pattern increases in size. (central maximum wider; other maxima farther from it) c. it does not affect the size of the pattern. d. the width of the central maximum increases, but the other maxima do not change in position or width. e. the width of the central maximum decreases, but the other maxima do not change in position or width.

3 10) What is the maximum velocity (in km/s) of a photoelectron emitted from a surface whose work function is 5.0 ev when illuminated by a light whose wavelength is 200 nm? a. 460 b. 650 c. 420 d. 550 e Answer: b 11) A photon whose wavelength is = m is scattered straight backward. What is the wavelength of the scattered wave? a m b m c m d m e m Answer: c 12) A photon collides with an electron. After the collision the wavelength of the scattered wave is a. greater than or equal to the initial wavelength. b. equal to the initial wavelength. c. less than or equal to the initial wavelength. d. greater than the initial wavelength. e. less or greater depending on the scattering angle. Answer: A 13) An electron is accelerated through a potential difference of V. What is the de Broglie wavelength of the electron (in m)? a b c d e Answer: d

4 14) When a photon collides with a free electron at rest and the direction of motion of the photon changes, a. the magnitude of the momentum of the photon does not change. b. the momentum of the electron does not change. c. the kinetic energy of the electron does not change. d. the total energy of the photon does not change. e. both the magnitude of the momentum and the total energy of the photon decrease. Answer: E 15) A photon has energy of 4.20 ev. To what wavelength does this energy correspond? A) 321 nm B) 103 nm C) 296 nm D) 412 nm 16) A certain photon after being scattered from a free electron at rest moves at an angle of 120 with respect to the incident direction. If the wavelength of the incident photon is nm, what is the kinetic energy of the recoiling electron? A) J B) J C) J D) J 17) What is the uncertainty in determining the momentum of an electron if the speed of the electron is 6000 m/s within an accuracy of 0.004%? A) kgχm/s B) kgχm/s C) kgχm/s D) kgχm/s 18) Protons are being accelerated in a particle accelerator. When the speed of the protons is doubled, their de Broglie wavelength will A) increase by a factor of 2. B) decrease by a factor of 2. C) increase by a factor of 2. D) decrease by a factor of 2. 19) When you decrease, by a factor of two, the wavelength of the light causing photoelectrons to be emitted from a metal surface, the kinetic energy of the photoelectrons will A) decrease by a factor of 2.

5 B) double C) more than double. D) decrease by a factor of 2. 20) A proton and an electron are both accelerated to the same final kinetic energy. If λ p is the de Broglie wavelength of the proton and λ e is the de Broglie wavelength of the electron, then A) λ p > λ e. B) λ p = λ e. C) λ p < λ e. D) Not enough data to answer this question. 21) A certain crystal has an interatomic spacing of nm. If a beam of electrons moving with a speed of 1400 m/s is diffracted from this crystal, what is the de Broglie wavelength of the electron? A) 420 nm B) 130 nm C) 260 nm D) 520 nm 22) A beam of white light of a certain frequency is incident on a metal surface. If the work function of this surface is 2.20 ev, what frequency of light would give a maximum kinetic energy of 0.25 ev to the photoelectrons ejected from this surface? A) Hz B) Hz C) Hz D) Hz 23) The value of a wavelength in the Balmer series is nm. What is the value of n? A) 6 B) 3 C) 10 D) 12 24) What is the longest wavelength in the Paschen series? A) 2.01 nm B) 2.01 µm C) 1.88 nm D) 1.88 µm

6 25) An electron in the hydrogen atom has a wavelength of m. To what state of hydrogen atom does this electron belong? A) n = 1 B) n = 3 C) n = 4 D) n = 6 26) What is the wavelength of the photon emitted when an electron in a hydrogen atom which is in the initial state n i = 8 jumps to the final state n f = 2? A) nm B) nm C) nm D) nm 27) What is the surface temperature of a star, given that its radiation peak occurs at a frequency of Hz? A) 17,000 K B) 14,500 K C) 20,400 K D) 18,000 K 28) In the spectrum of white light which one of the following colors corresponds to the highest temperature? A) Yellow B) Violet C) Green D) Red 29) What is the number of photons per second given off by a light bulb with a power of 100 Watts operating at an efficiency of 4.80%? Assume the wavelength of light to be 600 nm. A) photons/s B) photons/s C) photons/s D) photons/s 30) Which one of the following is the correct expression for the energy of the photon? A) E = h/f B) E = hλ/c C) E = hc/λ D) E = hλ

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