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# Millikan experiment, Compton effect, photoelectric effect

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1. In a Millikan oil drop experiment the terminal velocity of the droplet is observed to be vt = 1.5 mm/s. The density of the oil is = 830 kg/m3 and the viscosity of air is = 1.82 10-5 kg/m s. Use the following equations to find the values below.

Calculate the droplet radius.
µm
(b) Calculate the mass of the droplet.
kg
(c) Calculate the coefficient of friction.
kg/s

12. A gamma ray of 630 keV energy Compton scatters from an electron. Find the energy of the photon scattered at 89°, the kinetic energy of the scattered electron, and the recoil angle of the electron.
keV (photon)
keV (electron)
°

3. What is the threshold frequency for the photoelectric effect of barium ( = 2.5 eV)?
Hz
What is the stopping potential if the wavelength of the incident light is 420 nm?
eV

4. Light from a slit passes through a transmission diffraction grating of 330 lines/mm, which is located 2.2 m from a screen. What are the distances on the screen (from the unscattered slit image) of the three brightest visible (first-order) hydrogen lines?
Red cm

Blue-green cm

Violet cm

3. In a Millikan oil drop experiment the terminal velocity of the droplet is observed to be vt = 1.5 mm/s. The density of the oil is = 830 kg/m3 and the viscosity of air is = 1.82 10-5 kg/m s. Use the following equations to find the values below.

(b) Calculate the droplet radius.
µm
(b) Calculate the mass of the droplet.
kg
(c) Calculate the coefficient of friction.
kg/s

4. Light from a slit passes through a transmission diffraction grating of 330 lines/mm, which is located 2.2 m from a screen. What are the distances on the screen (from the unscattered slit image) of the three brightest visible (first-order) hydrogen lines?

Red cm

Blue-green cm

Violet cm

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#### Solution Preview

1. In a Millikan oil drop experiment the terminal velocity of the droplet is observed to be vt = 1.5 mm/s. The density of the oil is = 830 kg/m3 and the viscosity of air is = 1.82 10-5 kg/m s. Use the following equations to find the values below.

Calculate the droplet radius.
µm
(b) Calculate the mass of the droplet.
kg
(c) Calculate the coefficient of friction.
kg/s

Solution : _______________________
a) Radius r = = 3 √1.82x10-5x1.5x10-3/2x9.8x830 = 0.039x10-4 m

r = 0.039x10-4 m = 0.039x10-4 x 106 μm = 3.9 μm

b) Mass of the droplet m = Volume x Density = (4/3 Πr3)ρ = 4/3 Π (0.039x10-4)3 x 830 = 0.206 x 10-12 kg

m = 0.206 x 10-12 kg

c) Coefficient of friction f = mg/vt = 0.206 x 10-12 x 9.8/1.5x10-3 = 1.35 x 10-9 kg/s

f = 1.35 x 10-9 kg/s

12. A gamma ray of 630 keV energy Compton scatters from an electron. Find the energy of the photon scattered at 89°, the kinetic energy of the scattered electron, and the recoil angle of the electron.
keV (photon)
keV (electron)
°
Y
Solution :

Electron Scattered photon
Incident photon φ ...

#### Solution Summary

This set of miscellanious problems on Millikan oil drop experiment, Compton scattering, photoelectric effect and diffraction grating have been solved explaining the underlying principles involved.

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