CBSE Physics Past year paper - 2014, Class 12 Class 12 Notes | EduRev

Physics Class 12

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Class 12 : CBSE Physics Past year paper - 2014, Class 12 Class 12 Notes | EduRev

 Page 1


  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
CBSE Board 
Class XII Physics (Theory) 
Board Question Paper 2014 – Set 3 
  
Time: 3 hrs Max. Marks: 70 
 
 
 
 
 
 
 
 
 
 
 
 
 
General Instructions: 
 
(i) All questions are compulsory. 
(ii) There are 30 questions in total. Questions No. I to 8 are very short answer type 
questions and carry one mark each. 
(iii) Questions No. 9 to 18 carry two marks each, questions 19 to 27 carry three marks each 
and questions 28 to 30 carry five marks each. 
(iv) One of the questions carrying three marks weightage is value based question. 
(v) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each weightage. You have to attempt only one of the choices in such questions. 
(vi) Use of calculators is not permitted. However, you may use log tables if necessary. 
(vii) You may use the following values of physical constants wherever necessary: 
 
c = 3 x 10
8
 m/s 
 
h = 6.63 x 10
-34
 Js 
 
e = 1.6 x 10
-19
 C 
 
µ 0 = 4 p x 10
-7 
T mA
-l
 
     1 
                 = 9 x 10
9
  Nm
2  
c
-2
 
   4 p? 0 
 
m e= 9.1x 10
-31
 kg 
 
? Please check that this question paper contains 15 printed pages. 
? Code number given on the right hand side of the question paper should be 
written on the title page of the answer-book by the candidate. 
? Please check that this question paper contains 30 questions. 
? Please write down the Serial Number of the question before attempting it. 
? 15 minutes time has been allotted to read this question paper. The question 
paper will be distributed at 10:15 a.m. From 10.15 a.m. to 10.30 a.m., the 
students will read the question paper only and will not write any answer on the 
answer-book during this period. 
 
Page 2


  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
CBSE Board 
Class XII Physics (Theory) 
Board Question Paper 2014 – Set 3 
  
Time: 3 hrs Max. Marks: 70 
 
 
 
 
 
 
 
 
 
 
 
 
 
General Instructions: 
 
(i) All questions are compulsory. 
(ii) There are 30 questions in total. Questions No. I to 8 are very short answer type 
questions and carry one mark each. 
(iii) Questions No. 9 to 18 carry two marks each, questions 19 to 27 carry three marks each 
and questions 28 to 30 carry five marks each. 
(iv) One of the questions carrying three marks weightage is value based question. 
(v) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each weightage. You have to attempt only one of the choices in such questions. 
(vi) Use of calculators is not permitted. However, you may use log tables if necessary. 
(vii) You may use the following values of physical constants wherever necessary: 
 
c = 3 x 10
8
 m/s 
 
h = 6.63 x 10
-34
 Js 
 
e = 1.6 x 10
-19
 C 
 
µ 0 = 4 p x 10
-7 
T mA
-l
 
     1 
                 = 9 x 10
9
  Nm
2  
c
-2
 
   4 p? 0 
 
m e= 9.1x 10
-31
 kg 
 
? Please check that this question paper contains 15 printed pages. 
? Code number given on the right hand side of the question paper should be 
written on the title page of the answer-book by the candidate. 
? Please check that this question paper contains 30 questions. 
? Please write down the Serial Number of the question before attempting it. 
? 15 minutes time has been allotted to read this question paper. The question 
paper will be distributed at 10:15 a.m. From 10.15 a.m. to 10.30 a.m., the 
students will read the question paper only and will not write any answer on the 
answer-book during this period. 
 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
1. A conducting loop is held below a current carrying wire PQ as shown. Predict the 
direction of the induced current in the loop when the current in the wire is constantly 
increasing.           (1) 
 
 
 
2. The graph shows variation of stopping potential V 0 versus frequency of incident 
radiation ? for two photosensitive metals A and B. Which of the two metals has higher 
threshold frequency and why?        (1) 
 
 
 
 
 
3. Using the concept of force between two infinitely long parallel current carrying 
conductors, define one ampere of current.        (1) 
 
4. A biconcave lens made of a transparent material of refractive index 1.25 is immersed in 
water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? 
Give reason.           (1) 
 
5. Why do the electric field lines never cross each other?     (1) 
 
6. To which part of the electromagnetic spectrum does a wave of frequency 5 x 10
11 
Hz 
belong?            (1) 
 
7. Why is it found experimentally difficult to detect neutrinos in nuclear ß-decay? (1) 
Page 3


  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
CBSE Board 
Class XII Physics (Theory) 
Board Question Paper 2014 – Set 3 
  
Time: 3 hrs Max. Marks: 70 
 
 
 
 
 
 
 
 
 
 
 
 
 
General Instructions: 
 
(i) All questions are compulsory. 
(ii) There are 30 questions in total. Questions No. I to 8 are very short answer type 
questions and carry one mark each. 
(iii) Questions No. 9 to 18 carry two marks each, questions 19 to 27 carry three marks each 
and questions 28 to 30 carry five marks each. 
(iv) One of the questions carrying three marks weightage is value based question. 
(v) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each weightage. You have to attempt only one of the choices in such questions. 
(vi) Use of calculators is not permitted. However, you may use log tables if necessary. 
(vii) You may use the following values of physical constants wherever necessary: 
 
c = 3 x 10
8
 m/s 
 
h = 6.63 x 10
-34
 Js 
 
e = 1.6 x 10
-19
 C 
 
µ 0 = 4 p x 10
-7 
T mA
-l
 
     1 
                 = 9 x 10
9
  Nm
2  
c
-2
 
   4 p? 0 
 
m e= 9.1x 10
-31
 kg 
 
? Please check that this question paper contains 15 printed pages. 
? Code number given on the right hand side of the question paper should be 
written on the title page of the answer-book by the candidate. 
? Please check that this question paper contains 30 questions. 
? Please write down the Serial Number of the question before attempting it. 
? 15 minutes time has been allotted to read this question paper. The question 
paper will be distributed at 10:15 a.m. From 10.15 a.m. to 10.30 a.m., the 
students will read the question paper only and will not write any answer on the 
answer-book during this period. 
 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
1. A conducting loop is held below a current carrying wire PQ as shown. Predict the 
direction of the induced current in the loop when the current in the wire is constantly 
increasing.           (1) 
 
 
 
2. The graph shows variation of stopping potential V 0 versus frequency of incident 
radiation ? for two photosensitive metals A and B. Which of the two metals has higher 
threshold frequency and why?        (1) 
 
 
 
 
 
3. Using the concept of force between two infinitely long parallel current carrying 
conductors, define one ampere of current.        (1) 
 
4. A biconcave lens made of a transparent material of refractive index 1.25 is immersed in 
water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? 
Give reason.           (1) 
 
5. Why do the electric field lines never cross each other?     (1) 
 
6. To which part of the electromagnetic spectrum does a wave of frequency 5 x 10
11 
Hz 
belong?            (1) 
 
7. Why is it found experimentally difficult to detect neutrinos in nuclear ß-decay? (1) 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
8. Why is the use of a.c. voltage preferred over d.c. voltage? Give two reasons.        (1) 
 
9. Considering the case of a parallel plate capacitor being charged, show how one is 
required to generalize Ampere's circuital law to include the term due to displacement 
current.                  (2) 
 
10. Estimate the average drift speed of conduction electrons in a copper wire of cross-
sectional area 2.5 x 10
-7
 m
2
 carrying a current of 2.7 A. Assume the density of 
conduction electrons to be 9 x 10
28
 m
-3
.             (2) 
 
11. A cell of emf 'E' and internal resistance ‘r’ is connected across a variable resistor 'R'. Plot 
a graph showing variation of terminal voltage 'V' of the cell versus the current 'I'. Using 
the plot, show how the emf of the cell and its internal resistance can be determined.  (2) 
 
12. A parallel plate capacitor of capacitance C is charged to a potential V. It is then 
connected to another uncharged capacitor having the same capacitance. Find out the 
ratio of the energy stored in the combined system to that stored initially in the single 
capacitor.                  (2) 
 
13. Using Rutherford model of the atom, derive the expression for the total energy of the 
electron in hydrogen atom. What is the significance of total negative energy possessed 
by the electron?                  (2) 
OR 
Using Bohr's postulates of the atomic model derive the expression for radius of nth 
electron orbit. Hence obtain the expression for Bohr’s radius.          (2) 
 
14. Show diagrammatically the behaviour of magnetic field lines in the presence of  
(i) paramagnetic and 
 
(ii) diamagnetic substances. How does one explain this distinguishing feature?           (2) 
 
15. Explain, with the help of a circuit diagram, the working of a p-n junction diode as a half-
wave rectifier.                 (2) 
 
16. Two monochromatic rays of light are incident normally on the face AB of an isosceles 
right-angled prism ABC. The refractive indices of the glass prism for the two rays '1' and 
'2' are respectively 1.38 and 1.52. Trace the path of these rays after entering through 
the prism.                  (2) 
 
Page 4


  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
CBSE Board 
Class XII Physics (Theory) 
Board Question Paper 2014 – Set 3 
  
Time: 3 hrs Max. Marks: 70 
 
 
 
 
 
 
 
 
 
 
 
 
 
General Instructions: 
 
(i) All questions are compulsory. 
(ii) There are 30 questions in total. Questions No. I to 8 are very short answer type 
questions and carry one mark each. 
(iii) Questions No. 9 to 18 carry two marks each, questions 19 to 27 carry three marks each 
and questions 28 to 30 carry five marks each. 
(iv) One of the questions carrying three marks weightage is value based question. 
(v) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each weightage. You have to attempt only one of the choices in such questions. 
(vi) Use of calculators is not permitted. However, you may use log tables if necessary. 
(vii) You may use the following values of physical constants wherever necessary: 
 
c = 3 x 10
8
 m/s 
 
h = 6.63 x 10
-34
 Js 
 
e = 1.6 x 10
-19
 C 
 
µ 0 = 4 p x 10
-7 
T mA
-l
 
     1 
                 = 9 x 10
9
  Nm
2  
c
-2
 
   4 p? 0 
 
m e= 9.1x 10
-31
 kg 
 
? Please check that this question paper contains 15 printed pages. 
? Code number given on the right hand side of the question paper should be 
written on the title page of the answer-book by the candidate. 
? Please check that this question paper contains 30 questions. 
? Please write down the Serial Number of the question before attempting it. 
? 15 minutes time has been allotted to read this question paper. The question 
paper will be distributed at 10:15 a.m. From 10.15 a.m. to 10.30 a.m., the 
students will read the question paper only and will not write any answer on the 
answer-book during this period. 
 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
1. A conducting loop is held below a current carrying wire PQ as shown. Predict the 
direction of the induced current in the loop when the current in the wire is constantly 
increasing.           (1) 
 
 
 
2. The graph shows variation of stopping potential V 0 versus frequency of incident 
radiation ? for two photosensitive metals A and B. Which of the two metals has higher 
threshold frequency and why?        (1) 
 
 
 
 
 
3. Using the concept of force between two infinitely long parallel current carrying 
conductors, define one ampere of current.        (1) 
 
4. A biconcave lens made of a transparent material of refractive index 1.25 is immersed in 
water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? 
Give reason.           (1) 
 
5. Why do the electric field lines never cross each other?     (1) 
 
6. To which part of the electromagnetic spectrum does a wave of frequency 5 x 10
11 
Hz 
belong?            (1) 
 
7. Why is it found experimentally difficult to detect neutrinos in nuclear ß-decay? (1) 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
8. Why is the use of a.c. voltage preferred over d.c. voltage? Give two reasons.        (1) 
 
9. Considering the case of a parallel plate capacitor being charged, show how one is 
required to generalize Ampere's circuital law to include the term due to displacement 
current.                  (2) 
 
10. Estimate the average drift speed of conduction electrons in a copper wire of cross-
sectional area 2.5 x 10
-7
 m
2
 carrying a current of 2.7 A. Assume the density of 
conduction electrons to be 9 x 10
28
 m
-3
.             (2) 
 
11. A cell of emf 'E' and internal resistance ‘r’ is connected across a variable resistor 'R'. Plot 
a graph showing variation of terminal voltage 'V' of the cell versus the current 'I'. Using 
the plot, show how the emf of the cell and its internal resistance can be determined.  (2) 
 
12. A parallel plate capacitor of capacitance C is charged to a potential V. It is then 
connected to another uncharged capacitor having the same capacitance. Find out the 
ratio of the energy stored in the combined system to that stored initially in the single 
capacitor.                  (2) 
 
13. Using Rutherford model of the atom, derive the expression for the total energy of the 
electron in hydrogen atom. What is the significance of total negative energy possessed 
by the electron?                  (2) 
OR 
Using Bohr's postulates of the atomic model derive the expression for radius of nth 
electron orbit. Hence obtain the expression for Bohr’s radius.          (2) 
 
14. Show diagrammatically the behaviour of magnetic field lines in the presence of  
(i) paramagnetic and 
 
(ii) diamagnetic substances. How does one explain this distinguishing feature?           (2) 
 
15. Explain, with the help of a circuit diagram, the working of a p-n junction diode as a half-
wave rectifier.                 (2) 
 
16. Two monochromatic rays of light are incident normally on the face AB of an isosceles 
right-angled prism ABC. The refractive indices of the glass prism for the two rays '1' and 
'2' are respectively 1.38 and 1.52. Trace the path of these rays after entering through 
the prism.                  (2) 
 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
 
17. Draw a circuit diagram of n-p-n transistor amplifier in CE configuration. Under what 
condition does the transistor act as an amplifier?             (2) 
 
18. Write the functions of the following in communication systems:           (2) 
(i) Receiver 
(ii) Demodulator 
 
19. A convex lens of focal length 20 cm is placed coaxially with a convex mirror of radius of 
curvature 20 cm. The two are kept 15 cm apart. A point object is placed 40 cm in front 
of the convex lens. Find the position of the image formed by this combination. Draw the 
ray diagram showing the image formation.              (3) 
 
20. An electron microscope uses electrons accelerated by a voltage of 50 kV. Determine the 
de-Broglie wavelength associated with the electrons. Taking other factors, such as 
numerical aperture etc. to be same, how does the resolving power of an electron 
microscope compare with that of an optical microscope which uses yellow light?         (3) 
 
21. Write any two distinguishing features between conductors, semiconductors and 
insulators on the basis of energy band diagrams.            (3) 
 
22. Write two basic modes of communication. Explain the process of amplitude modulation. 
Draw a schematic sketch showing how amplitude modulated signal is obtained by 
superposing a modulating signal over a sinusoidal carrier wave.           (3) 
 
23. Answer the following  :                 (3) 
(a)  Why are the connections between the resistors in a meter bridge made of thick 
copper strips? 
(b) Why is it generally preferred to obtain the balance point in the middle of the meter 
bridge wire? 
(c) Which material is used for the meter bridge wire and why? 
OR 
A resistance of R ? draws current from a potentiometer as shown in the figure. The 
potentiometer has a total resistance R 0 ?. A voltage V is supplied to the potentiometer. 
Derive an expression for the voltage across R when the sliding contact is in the middle 
of the potentiometer.                 (3) 
 
 
 
 
Page 5


  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
CBSE Board 
Class XII Physics (Theory) 
Board Question Paper 2014 – Set 3 
  
Time: 3 hrs Max. Marks: 70 
 
 
 
 
 
 
 
 
 
 
 
 
 
General Instructions: 
 
(i) All questions are compulsory. 
(ii) There are 30 questions in total. Questions No. I to 8 are very short answer type 
questions and carry one mark each. 
(iii) Questions No. 9 to 18 carry two marks each, questions 19 to 27 carry three marks each 
and questions 28 to 30 carry five marks each. 
(iv) One of the questions carrying three marks weightage is value based question. 
(v) There is no overall choice. However, an internal choice has been provided in one 
question of two marks, one question of three marks and all three questions of five 
marks each weightage. You have to attempt only one of the choices in such questions. 
(vi) Use of calculators is not permitted. However, you may use log tables if necessary. 
(vii) You may use the following values of physical constants wherever necessary: 
 
c = 3 x 10
8
 m/s 
 
h = 6.63 x 10
-34
 Js 
 
e = 1.6 x 10
-19
 C 
 
µ 0 = 4 p x 10
-7 
T mA
-l
 
     1 
                 = 9 x 10
9
  Nm
2  
c
-2
 
   4 p? 0 
 
m e= 9.1x 10
-31
 kg 
 
? Please check that this question paper contains 15 printed pages. 
? Code number given on the right hand side of the question paper should be 
written on the title page of the answer-book by the candidate. 
? Please check that this question paper contains 30 questions. 
? Please write down the Serial Number of the question before attempting it. 
? 15 minutes time has been allotted to read this question paper. The question 
paper will be distributed at 10:15 a.m. From 10.15 a.m. to 10.30 a.m., the 
students will read the question paper only and will not write any answer on the 
answer-book during this period. 
 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
1. A conducting loop is held below a current carrying wire PQ as shown. Predict the 
direction of the induced current in the loop when the current in the wire is constantly 
increasing.           (1) 
 
 
 
2. The graph shows variation of stopping potential V 0 versus frequency of incident 
radiation ? for two photosensitive metals A and B. Which of the two metals has higher 
threshold frequency and why?        (1) 
 
 
 
 
 
3. Using the concept of force between two infinitely long parallel current carrying 
conductors, define one ampere of current.        (1) 
 
4. A biconcave lens made of a transparent material of refractive index 1.25 is immersed in 
water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? 
Give reason.           (1) 
 
5. Why do the electric field lines never cross each other?     (1) 
 
6. To which part of the electromagnetic spectrum does a wave of frequency 5 x 10
11 
Hz 
belong?            (1) 
 
7. Why is it found experimentally difficult to detect neutrinos in nuclear ß-decay? (1) 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
8. Why is the use of a.c. voltage preferred over d.c. voltage? Give two reasons.        (1) 
 
9. Considering the case of a parallel plate capacitor being charged, show how one is 
required to generalize Ampere's circuital law to include the term due to displacement 
current.                  (2) 
 
10. Estimate the average drift speed of conduction electrons in a copper wire of cross-
sectional area 2.5 x 10
-7
 m
2
 carrying a current of 2.7 A. Assume the density of 
conduction electrons to be 9 x 10
28
 m
-3
.             (2) 
 
11. A cell of emf 'E' and internal resistance ‘r’ is connected across a variable resistor 'R'. Plot 
a graph showing variation of terminal voltage 'V' of the cell versus the current 'I'. Using 
the plot, show how the emf of the cell and its internal resistance can be determined.  (2) 
 
12. A parallel plate capacitor of capacitance C is charged to a potential V. It is then 
connected to another uncharged capacitor having the same capacitance. Find out the 
ratio of the energy stored in the combined system to that stored initially in the single 
capacitor.                  (2) 
 
13. Using Rutherford model of the atom, derive the expression for the total energy of the 
electron in hydrogen atom. What is the significance of total negative energy possessed 
by the electron?                  (2) 
OR 
Using Bohr's postulates of the atomic model derive the expression for radius of nth 
electron orbit. Hence obtain the expression for Bohr’s radius.          (2) 
 
14. Show diagrammatically the behaviour of magnetic field lines in the presence of  
(i) paramagnetic and 
 
(ii) diamagnetic substances. How does one explain this distinguishing feature?           (2) 
 
15. Explain, with the help of a circuit diagram, the working of a p-n junction diode as a half-
wave rectifier.                 (2) 
 
16. Two monochromatic rays of light are incident normally on the face AB of an isosceles 
right-angled prism ABC. The refractive indices of the glass prism for the two rays '1' and 
'2' are respectively 1.38 and 1.52. Trace the path of these rays after entering through 
the prism.                  (2) 
 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
 
17. Draw a circuit diagram of n-p-n transistor amplifier in CE configuration. Under what 
condition does the transistor act as an amplifier?             (2) 
 
18. Write the functions of the following in communication systems:           (2) 
(i) Receiver 
(ii) Demodulator 
 
19. A convex lens of focal length 20 cm is placed coaxially with a convex mirror of radius of 
curvature 20 cm. The two are kept 15 cm apart. A point object is placed 40 cm in front 
of the convex lens. Find the position of the image formed by this combination. Draw the 
ray diagram showing the image formation.              (3) 
 
20. An electron microscope uses electrons accelerated by a voltage of 50 kV. Determine the 
de-Broglie wavelength associated with the electrons. Taking other factors, such as 
numerical aperture etc. to be same, how does the resolving power of an electron 
microscope compare with that of an optical microscope which uses yellow light?         (3) 
 
21. Write any two distinguishing features between conductors, semiconductors and 
insulators on the basis of energy band diagrams.            (3) 
 
22. Write two basic modes of communication. Explain the process of amplitude modulation. 
Draw a schematic sketch showing how amplitude modulated signal is obtained by 
superposing a modulating signal over a sinusoidal carrier wave.           (3) 
 
23. Answer the following  :                 (3) 
(a)  Why are the connections between the resistors in a meter bridge made of thick 
copper strips? 
(b) Why is it generally preferred to obtain the balance point in the middle of the meter 
bridge wire? 
(c) Which material is used for the meter bridge wire and why? 
OR 
A resistance of R ? draws current from a potentiometer as shown in the figure. The 
potentiometer has a total resistance R 0 ?. A voltage V is supplied to the potentiometer. 
Derive an expression for the voltage across R when the sliding contact is in the middle 
of the potentiometer.                 (3) 
 
 
 
 
  
 
CBSE  XII  | Physics 
Board Paper ? 2014 
 
     
 
24. For the past some time, Aarti had been observing some erratic body movement, 
unsteadiness and lack of coordination in the activities of her sister Radha, who also 
used to complain of severe headache occasionally. Aarti suggested to her parents to get 
a medical check-up of Radha. The doctor thoroughly examined Radha and diagnosed 
that she has a brain tumour. 
(a) What, according to you, are the values displayed by Aarti? 
(b) How can radioisotopes help a doctor to diagnose brain tumour?         (3) 
 
25. (a) A rod of length l is moved horizontally with a uniform velocity 'v' in a direction 
perpendicular to its length through a region in which a uniform magnetic field is acting 
vertically downward. Derive the expression for the emf induced across the ends of the 
rod. 
(b) How does one understand this motional emf by invoking the Lorentz force acting on 
the free charge carriers of the conductor? Explain.             (3) 
 
26. (a)  Show, giving a suitable diagram, how unpolarized light can be polarised by 
reflection. 
(b) Two polaroids P 1 and P 2 are placed with their pass axes perpendicular to each other. 
Unpolarized light of intensity I 0 is incident on P 1. A third polaroid P 3 is kept in between 
P 1 and P 2 such that its pass axis makes an angle of 60° with that of P 1. 
Determine the intensity of light transmitted through P 1, P 2 and P 3.           (3) 
 
27. A voltage V=V 0 sin ?t is applied to a series LCR circuit. Derive the expression for the 
average power dissipated over a cycle. 
 
Under what condition is (i) no power dissipated even though the current flows through 
the circuit, (ii) maximum power dissipated in the circuit?            (3) 
 
28. (a) In Young's double slit experiment, describe briefly how bright and dark fringes are 
obtained on the screen kept in front of a double slit. Hence obtain the expression for the 
fringe width. 
(b) The ratio of the intensities at minima to the maxima in the Young's double slit 
experiment is 9 : 25. Find the ratio of the widths of the two slits.          (5) 
OR 
(a) Describe briefly how a diffraction pattern is obtained on a screen due to a single 
narrow slit illuminated by a monochromatic source of light. Hence obtain the conditions 
for the angular width of secondary maxima and secondary minima. 
(b) Two wavelengths of sodium light of 590 nm and 596 nm are used in turn to study 
the diffraction taking place at a single slit of aperture 2 x 10
-6 
m. The distance between 
the slit and the screen is 1.5 m. Calculate the separation between the positions of first 
maxima of the diffraction pattern obtained in the two cases.           (5) 
 
29. (a) Deduce an expression for the frequency of revolution of a charged particle in a 
magnetic field and show that it is independent of velocity or energy of the particle. 
(b) Draw a schematic sketch of a cyclotron. Explain, giving the essential details of its 
construction, how it is used to accelerate the charged particles.           (5) 
OR 
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