**Q 1.**What is the Kinetic energy of the photo electrons ejected from a tungsten surface by UV light of wavelength 1940 Å ? Express the result in eV. The photoelectric threshold of tungsten is 2300 Å .

Ans. K=1 eV

**Q 2.**The work function of sodium is 2 eV.

(a) Find the maximum energy of the photo electrons ejected when a sodium surface is illuminated with light of 3105 Å.

(b) Calculate the maximum wavelength of the light that would produce photoelectric effect.

Ans. 2 eV , 6210 Å

**Q 3.**A small plate of metal (work function 1.17 eV) is placed at a distance 2 m from monochromatic light source of wavelength 4.8x 10

^{-7 }and power 1.0 watt. The light falls normally on plate. Find the number of photons striking the metal plate per square meter per second. If a constant uniform magnetic field of strength 10

^{-4}Tesla is applied parallel to the metal surface , find the radius of the largest circular path followed by the emitted photo electrons.

Ans. 4.82 x10

^{16}, 4.0 cm

**Q 4.**Calculate the wavelength of the wave associated with :

(a) 1 MeV photon

(b) 1 MeV proton

Ans. 1.242 x 10

^{-10}cm, 2.84 x 10

^{-12}cm

**Q 5.**The molecules of a certain gas at 320 K have a rms speed of .499 Km/sec. Calculate the De Brogli wavelength of these molecules. What is the gas?

Ans. 0.25Å , O

^{16}

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