4:Photoelectric Effect - Class 11 PDF Download

 Page 1


CBSE TEST PAPER-04 
CLASS - XI CHEMISTRY (Structure of Atom) 
Topic:-Photoelectric Effect 
Marks: 20 
1. Define photoelectric effect. [1] 
2. How does the intensity of light effect photoelectrons?
3. What is threshold frequency? [1] 
4. Name the scientist who demonstrated photoelectric effect experiment.   [1]
5. What did Einstein explain about photoelectric effect? [1] 
6. What is the relation between kinetic energy and frequency of the
photoelectrons? [2] 
7. Calculate energy of 2mole of photons of radiation whose frequency
is 
14
5 10 . Hz × [1] 
8. What is emission and absorption spectra? [2] 
9. What transition in the hydrogen spectrum would have the same
wavelength as the Balmer transition, n = 4 to n = 2 of He
+
 spectrum?   [2] 
10. Spectral lines are regarded as the finger prints of the elements. Why?   [2]
25
Page 2


CBSE TEST PAPER-04 
CLASS - XI CHEMISTRY (Structure of Atom) 
Topic:-Photoelectric Effect 
Marks: 20 
1. Define photoelectric effect. [1] 
2. How does the intensity of light effect photoelectrons?
3. What is threshold frequency? [1] 
4. Name the scientist who demonstrated photoelectric effect experiment.   [1]
5. What did Einstein explain about photoelectric effect? [1] 
6. What is the relation between kinetic energy and frequency of the
photoelectrons? [2] 
7. Calculate energy of 2mole of photons of radiation whose frequency
is 
14
5 10 . Hz × [1] 
8. What is emission and absorption spectra? [2] 
9. What transition in the hydrogen spectrum would have the same
wavelength as the Balmer transition, n = 4 to n = 2 of He
+
 spectrum?   [2] 
10. Spectral lines are regarded as the finger prints of the elements. Why?   [2]
25
CBSE TEST PAPER-04 
CLASS - XI CHEMISTRY  [ANSWERS] 
Topic: - Photoelectric Effect 
Ans1:  It is the phenomenon in which the surface of alkali metals like potassium and 
calcium emit electrons when a beam of light with high frequency is made to fall on 
them.  
Ans2:    The number of electron ejected and kinetic energy associated with them depend on 
the brightness of light.  
Ans3:  The minimum frequency below which photo electric effect is not observed is called 
threshold frequency (v o) 
Ans4: In 1887, H. Hertz demonstrated photo electric effect. 
Ans5: Einstein in 1905 was able to explain the photoelectric effect using Planck’s quantum 
theory of electromagnetic radiation. 
Ans6: Kinetic energy of the ejected electron is proportional to the frequency of the 
electromagnetic radiation.  
Ans7: Energy (E) of one photon = E = hv 
Where 
34
6.626 10 h Js
- = ×
14 1
5 10 v s
- = ×
( )
34 14
19
6.626 10 5 10
3.313 10
E
J
- - ? = × × ×
= ×
Energy of 2 mole of photon 
( ) ( )
19 23 1
3.313 10 2 6.022 10 J mol
- - = × × × ×
1
3990.2kJmol
- =
26
Page 3


CBSE TEST PAPER-04 
CLASS - XI CHEMISTRY (Structure of Atom) 
Topic:-Photoelectric Effect 
Marks: 20 
1. Define photoelectric effect. [1] 
2. How does the intensity of light effect photoelectrons?
3. What is threshold frequency? [1] 
4. Name the scientist who demonstrated photoelectric effect experiment.   [1]
5. What did Einstein explain about photoelectric effect? [1] 
6. What is the relation between kinetic energy and frequency of the
photoelectrons? [2] 
7. Calculate energy of 2mole of photons of radiation whose frequency
is 
14
5 10 . Hz × [1] 
8. What is emission and absorption spectra? [2] 
9. What transition in the hydrogen spectrum would have the same
wavelength as the Balmer transition, n = 4 to n = 2 of He
+
 spectrum?   [2] 
10. Spectral lines are regarded as the finger prints of the elements. Why?   [2]
25
CBSE TEST PAPER-04 
CLASS - XI CHEMISTRY  [ANSWERS] 
Topic: - Photoelectric Effect 
Ans1:  It is the phenomenon in which the surface of alkali metals like potassium and 
calcium emit electrons when a beam of light with high frequency is made to fall on 
them.  
Ans2:    The number of electron ejected and kinetic energy associated with them depend on 
the brightness of light.  
Ans3:  The minimum frequency below which photo electric effect is not observed is called 
threshold frequency (v o) 
Ans4: In 1887, H. Hertz demonstrated photo electric effect. 
Ans5: Einstein in 1905 was able to explain the photoelectric effect using Planck’s quantum 
theory of electromagnetic radiation. 
Ans6: Kinetic energy of the ejected electron is proportional to the frequency of the 
electromagnetic radiation.  
Ans7: Energy (E) of one photon = E = hv 
Where 
34
6.626 10 h Js
- = ×
14 1
5 10 v s
- = ×
( )
34 14
19
6.626 10 5 10
3.313 10
E
J
- - ? = × × ×
= ×
Energy of 2 mole of photon 
( ) ( )
19 23 1
3.313 10 2 6.022 10 J mol
- - = × × × ×
1
3990.2kJmol
- =
26
Ans8: The spectrum of radiation emitted by a substance that has absorbed energy is called 
an emission spectrum.  
When a sample of atomic vapors is placed in the path of white light from an arc 
lamp, it absorbs light of certain characteristic wave length and the light of other 
wavelength get transmitted. This produces a series of dark lines on a white 
background.  
Ans9: For the Balmer transition, n = 4, to n = 2 in a He
+
 ion, we can write. 
2
2 2
1 2
1 1 1
H
Z R
n n ?
? ?
= - ? ?
? ?
2
2 2
1 1
2 4
3
( )
4
H
H
Z R
R i
? ?
= - ? ?
? ?
= - - - - - - - For a hydrogen atom 
2 2
1 2
1 1 1
( )
H
R ii
n n ?
? ?
= - - - - - - - ? ?
? ?
Equating equation (ii) and (i), we get 
2 2
1 2
1 1 3
4 n n
- =
This equation gives n 1 = 1 and n = 2. Thus the transition n = 2 to n = 1 in hydrogen 
atom will have same wavelength as transition, n = 4 to n = 2 in He
+
 
Ans10: Spectral lines are regarded as the finger prints of the elements because the elements 
can be identified from these lines. Just like finger prints, the spectral lines of no two 
elements resemble each other.  
27