31. The spectrum obtained from a sodium vapour lamp is an example of

1. 1. band spectrum

   
   
   

   2. continuous spectrum

   
   
   

   3. emission spectrum

   
   
   

   4. absorption spectrum

   
   
   

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1. View Hint View Answer Discuss in Forum

   A spectrum is observed, when light coming directly from a source is examined with a spectroscope. Therefore spectrum obtained from a sodium vapour lamp is emission spectrum.

   Correct Option: C

   A spectrum is observed, when light coming directly from a source is examined with a spectroscope. Therefore spectrum obtained from a sodium vapour lamp is emission spectrum.

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32. When hydrogen atom is in its first excited level, its radius is

1. 1. four times its ground state radius

   
   
   

   2. twice

   
   
   

   3. same

   
   
   

   4. half

   
   
   

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1. View Hint View Answer Discuss in Forum

   R =	R0 n2
   	Z

   
   Radius in ground state
   

   =	R0
   	Z

   
   Radius in first excited state
   

   =	R0 × 4
   	Z

   
   (∴ n = 2)
   Hence, radius of first excited state is four times the radius in ground state.

   Correct Option: A

   R =	R0 n2
   	Z

   
   Radius in ground state
   

   =	R0
   	Z

   
   Radius in first excited state
   

   =	R0 × 4
   	Z

   
   (∴ n = 2)
   Hence, radius of first excited state is four times the radius in ground state.

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33. In the Bohr model of a hydrogen atom, the centripetal force is furnished by the coulomb attraction between the proton and the electron. If a₀ is the radius of the ground state orbit, m is the mass, e is the charge on the electron and ε₀ is the vacuum permittivity, the speed of the electron is

1. 1. 0

   
   
   

   2. 

   
   
   

   3. 

   
   
   

   4. 

   
   
   

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1. View Hint View Answer Discuss in Forum

   Centripetal force = Coulombian force
   

   	mv2	=	1	.	e × e
   	α0		4πε0		α20

   
   

   Correct Option: C

   Centripetal force = Coulombian force
   

   	mv2	=	1	.	e × e
   	α0		4πε0		α20

   
   

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34. The ionisation energy of hydrogen atom is 13.6 eV, the ionisation energy of helium atom would be

1. 1. 13.6 eV

   
   
   

   2. 27.2 eV

   
   
   

   3. 6.8 eV

   
   
   

   4. 54.4 eV

   
   
   

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1. View Hint View Answer Discuss in Forum

   E ∝ Z² and Z for helium = 2
   ∴ (E)_He = 4 × 13.6 = 54.4 eV

   Correct Option: D

   E ∝ Z² and Z for helium = 2
   ∴ (E)_He = 4 × 13.6 = 54.4 eV

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35. When an electron jumps from the fourth orbit to the second orbit, one gets the​

1. 1. second line of Lyman series

   
   
   

   2. ​second line of Paschen series

   
   
   

   3. ​second line of Balmer series

   
   
   

   4. ​first line of Pfund series

   
   
   

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1. View Hint View Answer Discuss in Forum

   When the electron drops from any orbit to second orbit, then wavelength of line obtained belongs to Balmer series.

   Correct Option: C

   When the electron drops from any orbit to second orbit, then wavelength of line obtained belongs to Balmer series.

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