# 12th Physics Unit 20 Atomic Spectra Past Papers MCQs

12th Physics Unit 20 solved MCQs from past papers of Fsc. Chapter-wise past papers of Fsc 2nd year Physics from Punjab Boards. Download in pdf.

## 12th Physics Unit 20 Atomic Spectra:

The speed of an electron in nth orbit is given as:
(A) x dành
B 2 Ke Kenth

Laser is a beam of light which is:
(A) Monochromatic
(1) Coherent

Radius of first orbit of an atom is 0.053 nm. Radius of second orbitr, will be:
(A) 0.106 nm
B 0.212 nm
(C) 0.053 nm

If electron jumps from second orbit to first orbit in hydrogen atom it emits Photon of:
(SWL GI, 2014) (SWL 2018)
(A) 3.40 eV
(B) 10.20 eV
C 13.6 eV

The velocity of electron in 1″ orbit of H-atom is:
(A) 2.09×109 m/sec
B) 2.19x106m/sec
(C) 2.18*10m/sec

### Physics 2nd Year Past Papers MCQs:

In the meta stable the atoms can reside for:
(A) !O’s
DT 10’s
(C) 10-es

Speed of the electron in the first Bohr’s orbit is: (RWP. GI, 2014)
A 2.19-10 m/sec
(B) 2.19x10m/sec
(C) 2.19x106cm’s
(D) 2.19 10-6cm/sec

The first laser (Ruby Laser) was built by: (AJK. GI, 2014)
(A) Arthurs Schawlow
(B) T.H Maiman
(C) Peter Sorokin
(D) C.H Townes

The radius of first shell of hydrogen atom was quantized which is: (MLN. GI, 2014)
(A) 0.0053 nm
(B) 0.0053 nm
(C) 0.53 nm
(D) 0.053 nm

Which is not characteristic of LASER: (FBD. GI, 2016)
(A) Monochromatic
(B) Coherent
(C) Intense
(D) Multi direction

For Holography we use: (DGK. GI, 2017)
(A) X-rays
(B) Laser
(C) Y-rays
(D) B-rays

The unit of Rydberg’s constant is: (GRW. GI, 2016)
(A)m
(B) K
C) m-

_has the largest de Broglie wavelength at same speed: (MLN. GI, 2016)
(A) Proton
(B) a particle
(C) Carbon atom
(D) Electron

Laser is a beam of light which is:
(A) Monochromatic
(B) Coherent
(C) Unidirectional
(D) All of these

The longest wavelength of Paschen series is: (LHR. GI, 2018)
(A) 656 nm
(B) 1094nm
C) 1875 nm
(D) 2000 nm

The mass spectrum of naturally occurring neon shows the most abundant isotope has
atomic mass: (LHR. GI, 2018)
(A) 19
B20
(C) 21
(D) 22

Paschen series lie in the (GRW.2018)
(A) far-ultraviolet region
(B) visible region
C infrared region
(D) ultraviolet regionRadiation produced from TV picture tube is:

ture to:-
(B) B-rays

Metastable state of Neon is
A) 20.66 eV
(B) 20.61 eV
(C) 18.70 eV
(D) 1.60 eV

(C) Infrared light
Al Y-rays
(C) a-rays
(D) Cathode rays