### Breaking News # BSc II Modern Physics CH 01

## BSc II MOdern Physics CH 01

### light and Quantum mechanics.

Class: BSc Part II
Subject: Physics
Modern Physics
Light & QM
Date: 21-05-2020
Marks: 25 , CH 1

Short Questions:                                    5x3 = 15

1) What is Stephon Boltzmann law. Define spectral radiancy (3)
2) Explain Wien’s displacement law. Write down the value of its constant (3)
3) What is plank’s  radiations law. Give physical significance of Plank. (3)
4) What is photo electric effect. Write down the experimental result of photo electric effect. (3)
5) Explain Einstein’s photo electric equation (3)

Long Question:                             6+2+2 = 10

1) What is Compton effect? Why classical theory fails and how quantum theory explained Compton effect. Explain in detail (6)
2) Find the frequency, energy and momentum of a photon having wavelength of 46 pm. (2)

3) If work function for a metal is 1.85 eV . What should be the stopping potential for light having wavelength 410 nm. (2)

1) When a material is hotter than its surroundings, then emission rate is ---- than absorption rate
..
Smaller
Equal
Larger
All of them

..
Shape of material
Temperature
Nature
Medium

3) Which one is black body
..
🌍 earth
💡  bulb
☀   sun
None of them

4) A black body is that which
..
None of them

5) Platinum wire become orange at what temperature
..
900 degree
1600 degree
1100 degree
1250 degree

6) At what temperature the polished flat surface of tungsten has radiation intensity 23.5 w/cm^2
..
T = 1250 degree
T = 2000 degree
T = 1000 degree
T = 900 degree

7) With the increase in temperature ------ of emitted radiations decreases
..
Wavelength
Energy
Frequency
Intensity

8) In stephan Boltzmann law equation. If temperature is doubled. What will be the effects on intensity
..
Decreases 4 times
Increases 4 times
Increases 16 times
Decreases 16 times

9) Emissivity of all objects is
..
Equal to 1
Less than 1
Greater than 1

10) Which photon, red, green or blue carries the most energy
..
Red
Blue
Green
All have same energy

11) The radiation intensity per unit wavelength at a given temperature is called
..
Emissivity
All of them

12) A beam of red light and a beam of blue light have exactly the same energy. Which beam contains the greater number of photons
..
Blue
Red
Both have same
None

13) Value of Wiens's constant "b" is
..
2800 micro meter - Kelvin
2000 micro meter - Kelvin
2600 micro meter - Kelvin
2898 micro meter - Kelvin

14) According to plancks constant energy is
..
Discreet
Quantized
Both a and b
None of these

15) Wien's formula explains only
..
Shorter wavelength
Longer wavelength
Longer energy
Both a and c

16) Value of planck's constant is
..
6.63 x 10^-33 Js
1.38 x 10^-34 Js
6.63 x 10^-34 Js
5.88 x 10^-34 Js

17) With great accuracy, photo electric effect is explained by
..
Classical theory
Quantum theory
Einstein's theory
Both b and c

18) For the occurrence of photo electric effect the frequency must be
..
Less than threshold frequency
Equal to threshold frequency
Greater than threshold frequency
Both b and c

19) At constant intensity, by increasing frequency the no. of electron from metal surface
..
Decreases
Increases
Remains constant
None of them

20) If frequency is equal to threshold frequency (f = fo) , the K.E(max) is equal to
..
2 times its original value
Half of its original value
Remains constant
Zero

21) Maximum kinetic energy depends upon
..
Frequency of light
Intensity of light
No of emitted electrons
All of above

22) According to Classical theory K.E of electrons is directly proportional to
..
Frequency of light
Energy
Intensity of light
None of them

23) Compton effects proves
..
Wave nature of particle
Dual nature of particle

24) The work function of a metal is Xev when light of energy 2X is made incident on it. Maximum K.E of emitted photo electrons will be
..
Zero
Xev
2Xev
X/2 ev

25) Compton shift is maximum at an angle
..
0 degree
45 degree
90 degree
180 degree

26) The process of photo electric depends on
..
Wavelength of incident light
Work function of surface
Nature of surface
All of above

27) In compton effect, the wavelength of the scattered photon as compared to the wavelength of incident X-rays is
..
Smaller
Larger
same
None of these

28) At what angle, the compton shift equals to the Compton wavelength
..
0 degree
45 degree
90 degree
180 degree

29) Dimensions of plancks constant are same as that of
..
Energy density
Surface energy
Gravitational constant
Angular constant

30) Compton effects shows that
..
Photon have momentum
X-rays are wave
X-ray can penetrate matter
X-ray have high energy

Note;

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