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Physics 3204 Modern Physics

1. Convert 4.5 eV into joules.

a) 7.2 x 10-19 J

a) 2.8 x 10-19 J

c) 2.8 x 1019 J

d) 4.5 x 10-19 J

1. What statement must be true for the photoelectric effect to occur?

a) Wo > VStop

b) Wo < VStop

c) Ephoton > Vstop

d) Ephoton > Wo

2. What is the energy of a photon that has a wavelength of 460 nm?

a) 3.05 x 10-41 J

b) 4.32 x 10-28 J

c) 4.32 x 10-19 J

d) 3.05 x 10-9 J

3. When electromagnetic radiation with a frequency of 8.6 x 1014 Hz falls on a metal, the maximum kinetic energy of the ejected electrons is 3.8 x 10-19 J. What is the work function of the metal in eV?

a) 0.87 eV

b) 1.2 eV

c) 2.4 eV

d) 3.6 eV

4. If an electron requires 3.5 V to stop it from being liberated from the surface of a metal, which statement is true?

| | | |

| |Stopping Potential|Kinetic energy of ejected |

| |V |electron (J) |

| | | |

|(A) |3.5 |5.6 x 10-19 |

| | | |

|(B) |3.5 |3.5 |

| | | |

|(C) |5.6 x 10-19 |3.5 |

| | | |

|(D) |5.6 x 10-19 |5.6 x 10-19 |

6. A photoelectric surface requires a light of maximum wavelength 675 nm to cause electron emission. What is the work function of this material in eV?

[2]

7. Electrons are ejected from a photoelectric surface with a maximum speed of 4.20 x 105 m/s. If the work function of the surface is 2.55 eV, what is the wavelength of the incident light?

[2]

8. Explain, with reference to the photoelectric effect apparatus, how we could determine the stopping voltage VSTOP of an unknown metal.

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Compton discovered the scattering effect of x-rays, a pattern which could only be explained if electromagnetic radiation had momentum.

p = h / λ

9. What is the momentum of a photon whose wavelength is 450 nm?

10. Find the speed of an electron having the same momentum as a photon having a wavelength of 0.80 nm.

DeBroglie extended Compton’s work, and said that if waves had momentum, then perhaps all matter could be treated as a wave. He uses the same equation.

11. What is the DeBroglie wavelength of an electron that has been accelerated from rest to a velocity of 4.8 x 106 m/s?

12. Calculate the DeBroglie wavelength of a 1000 kg car moving at 90 km/hr.

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