22%20-%20Electron%20and%20Photons

22%20-%20Electron%20and%20Photons - 22 - ELECTRON AND...

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- ELECTRON AND PHOTONS Page 1 ( Answers at the end of all questions ) 1 ) A photocell is illuminated by a small source placed 1 m away. When the same source of light is placed 1 / 2 m away, the number of electrons emitted by photocathode would ( a ) increase by a factor of 4 ( b ) decrease by a factor of 4 ( c ) increase by a factor of 2 ( d ) decrease by a factor of 2 [ AIEEE 2005 ] 2 ) The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The band gap in ( eV ) for the semi-conductor is ( a ) 2.5 eV ( b ) 1.1 eV ( c ) 0.7 eV ( d ) 0.5 eV [ AIEEE 2005 ] 3 ) According to Einstein’s photoelectric equation, the plot of the kinetic energy of the emitted photoelectrons from a metal vs. the frequency of the incident radiation gives a straight line whose slope ( a ) depends on the nature of the metal used ( b ) depends on the intensity of the radiation ( c ) depends both on the intensity of the radiation and the metal used ( d ) is the same for all metals and independent of the intensity of radiation [ AIEEE 2004 ] 4 ) The work function of a substance is 4.0 eV. The longest wavelength of light that can cause photoelectron emission from this substance is approximately ( a ) 540 nm ( b ) 400 nm ( c ) 310 nm ( d ) 220 nm [ AIEEE 2004 ] 5 ) A charged oil-drop is suspended in uniform field of 3 × 10 4 V / m so that it neither falls nor rises. The charge on the drop will be ( take the mass of charge = 9.9 × 10 - 15 kg and g = 10 m / s 2 ) ( a ) 3.3 × 10 - 18 C ( b ) 3.2 × 10 - 18 C ( c ) 1.6 × 10 - 18 C ( d ) 4.8 × 10 - 18 C [ AIEEE 2004 ] 6 ) Two identical photocells receive light of frequencies ν 1 and ν 2 . If the velocities of the photo-electrons ( of mass m ) coming out are v 1 and v 2 respectively, then ( a ) v 1 - v 2 = [ m h 2 ( v 1 - v 2 ) ] 1 / 2 ( b ) v 1 2 - v 2 2 = m h 2 ( v 1 - v 2 ) ( c ) v 1 + v 2 = [ m h 2 ( v 1 - v 2 ) ] 1 / 2 ( d ) v 1 2 + v 2 2 = m h 2 ( v 1 - v 2 ) [ AIEEE 2003 ] 7 ) The photoelectric threshold wavelength for potassium ( work function being 2 eV ) is ( Take h = 6.6 × 10 34 Js ). ( a ) 310 nm ( b ) 620 nm ( c ) 1200 nm ( d ) 2100 nm [ AIEEE 2003 ] 8 ) A particle of charge - 16 × 10 - 18 C moving with velocity 10 ms - 1 along the x - axis enters a region where a magnetic field of induction B is along the y - axis, and an electric field of magnitude 10 4 V / m is along the negative z - axis. If the charged particle continues moving along the x - axis, the magnitude of B is ( a ) 10 - 3 Wb / m 2 ( b ) 10 3 Wb / m 2 ( c ) 10 5 Wb / m 2 ( d ) 10 16 Wb / m 2 [ AIEEE 2003 ] 9 ) The potential difference between the cathode and the target in a Coolidge tube is 100 kilovolt. What can be the minimum wavelength of the X-rays emitted by the tube ? ( a )
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This note was uploaded on 11/28/2011 for the course PHYSICS 300 taught by Professor Smith during the Spring '06 term at ITT Tech Flint.

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22%20-%20Electron%20and%20Photons - 22 - ELECTRON AND...

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