Question

Remember, all energy answers should be given in eV. You will lose convention marks for not doing this.

1. What is the energy of light with a frequency of 6.5 × 104Hz?

2. What wavelength does a photon of energy 2.00eV have?

3. What is the momentum of a photon with a wavelength of 725nm?

4. A photon with wavelength of 450nm ejects an electron with 0.5eV of kinetic energy. What is the work function of the material the electron belonged to?

5. An electron (9.11 × 10−31kg) is moving at 3.00 × 106m/s. A photon of what wavelength would have the same momentum?

6. How many photons of wavelength 5.89 × 10−7m would it take to equal the momentum of a 5.00g pingpong ball moving at 8.25m/s?

7. A photon ejects an electron from some platinum (work function 5.65eV) with a kinetic energy of 4.35 × 104eV. What was the wavelength of the photon?

8. What is the speed of an electron that has a wavelength of 3.32 × 10−10m?

Answer 1

1. The energy of the light and its frequency are related as
E = h
Where h is the Planck's constant
E = 6.63 x 10^-31 J s x 6.5 × 10⁴ Hz
E = 4.3095 x 10^-26 J = 2.69 x 10^-7 eV
2. The wavelength and the energy are related as
E = h c /
Where c is the velocity of light.
E = 2.0 e V = 2.0 x 1.6 x 10^-19 J = 3.2 x 10^-19 J
= h c / E
= 6.63 x 10^-31 Js x 3 x 10⁸ m/s / 3.2 x 10^-19 J
= 6.215x 10^-4 m
3. The wavelength and the momentum are related as
p = h / = 6.63 x 10^-31 Js / 725 x 10^-9 m = 9.1448 x 10^-25