CBSE Board Paper 2020 (Marking Scheme and Solutions) | Physics Class 12 - NEET PDF Download

 Page 1


Page 1 of 18 
 
 
Strictly Confidential: (For Internal and Restricted use only) 
Senior School Certificate Examination-2020 
Marking Scheme – PHYSICS THEORY (042) 
(55/1/1) 
General Instructions: - 
 
1. You are aware that evaluation is the most important process in the actual and 
correct assessment of the candidates. A small mistake in evaluation may lead to 
serious problems which may affect the future of the candidates, education system 
and teaching profession. To avoid mistakes, it is requested that before starting 
evaluation, you must read and understand the spot evaluation guidelines 
carefully. Evaluation is a 10-12 days mission for all of us. Hence, it is 
necessary that you put in your best efforts in this process. 
2. Evaluation is to be done as per instructions provided in the Marking Scheme. It 
should not be done according to one’s own interpretation or any other 
consideration. Marking Scheme should be strictly adhered to and religiously 
followed. However, while evaluating, answers which are based on latest 
information or knowledge and/or are innovative, they may be assessed for 
their correctness otherwise and marks be awarded to them.  
3. The Head-Examiner must go through the first five answer books evaluated by 
each evaluator on the first day, to ensure that evaluation has been carried out as 
per the instructions given in the Marking Scheme. The remaining answer books 
meant for evaluation shall be given only after ensuring that there is no significant 
variation in the marking of individual evaluators. 
4. Evaluators will mark( v ) wherever answer is correct.  For wrong answer ‘X”be 
marked.  Evaluators will not put right kind of mark while evaluating which gives an 
impression that answer is correct and no marks are awarded.  This is most 
common mistake which evaluators are committing. 
5. If a question has parts, please award marks on the right-hand side for each part. 
Marks awarded for different parts of the question should then be totaled up and 
written in the left-hand margin and encircled.  This may be followed strictly. 
6. If a question does not have any parts, marks must be awarded in the left-hand 
margin and encircled. This may also be followed strictly. 
7. If a student has attempted an extra question, answer of the question deserving 
more marks should be retained and the other answer scored out. 
8. No marks to be deducted for the cumulative effect of an error. It should be 
penalized only once. 
10. Every examiner has to necessarily do evaluation work for full working hours i.e. 8 
hours every day and evaluate 20 answer books per day in main subjects and 25 
answer books per day in other subjects (Details are given in Spot Guidelines). 
11. Ensure that you do not make the following common types of errors committed by 
the Examiner in the past:- 
• Leaving answer or part thereof unassessed in an answer book. 
• Giving more marks for an answer than assigned to it. 
• Wrong totaling of marks awarded on a reply. 
• Wrong transfer of marks from the inside pages of the answer book to the title 
page. 
• Wrong question wise totaling on the title page. 
• Wrong totaling of marks of the two columns on the title page. 
• Wrong grand total. 
9. A full scale of marks 0-70 has to be used. Please do not hesitate to award full 
marks if the answer deserves it. 
Page 2


Page 1 of 18 
 
 
Strictly Confidential: (For Internal and Restricted use only) 
Senior School Certificate Examination-2020 
Marking Scheme – PHYSICS THEORY (042) 
(55/1/1) 
General Instructions: - 
 
1. You are aware that evaluation is the most important process in the actual and 
correct assessment of the candidates. A small mistake in evaluation may lead to 
serious problems which may affect the future of the candidates, education system 
and teaching profession. To avoid mistakes, it is requested that before starting 
evaluation, you must read and understand the spot evaluation guidelines 
carefully. Evaluation is a 10-12 days mission for all of us. Hence, it is 
necessary that you put in your best efforts in this process. 
2. Evaluation is to be done as per instructions provided in the Marking Scheme. It 
should not be done according to one’s own interpretation or any other 
consideration. Marking Scheme should be strictly adhered to and religiously 
followed. However, while evaluating, answers which are based on latest 
information or knowledge and/or are innovative, they may be assessed for 
their correctness otherwise and marks be awarded to them.  
3. The Head-Examiner must go through the first five answer books evaluated by 
each evaluator on the first day, to ensure that evaluation has been carried out as 
per the instructions given in the Marking Scheme. The remaining answer books 
meant for evaluation shall be given only after ensuring that there is no significant 
variation in the marking of individual evaluators. 
4. Evaluators will mark( v ) wherever answer is correct.  For wrong answer ‘X”be 
marked.  Evaluators will not put right kind of mark while evaluating which gives an 
impression that answer is correct and no marks are awarded.  This is most 
common mistake which evaluators are committing. 
5. If a question has parts, please award marks on the right-hand side for each part. 
Marks awarded for different parts of the question should then be totaled up and 
written in the left-hand margin and encircled.  This may be followed strictly. 
6. If a question does not have any parts, marks must be awarded in the left-hand 
margin and encircled. This may also be followed strictly. 
7. If a student has attempted an extra question, answer of the question deserving 
more marks should be retained and the other answer scored out. 
8. No marks to be deducted for the cumulative effect of an error. It should be 
penalized only once. 
10. Every examiner has to necessarily do evaluation work for full working hours i.e. 8 
hours every day and evaluate 20 answer books per day in main subjects and 25 
answer books per day in other subjects (Details are given in Spot Guidelines). 
11. Ensure that you do not make the following common types of errors committed by 
the Examiner in the past:- 
• Leaving answer or part thereof unassessed in an answer book. 
• Giving more marks for an answer than assigned to it. 
• Wrong totaling of marks awarded on a reply. 
• Wrong transfer of marks from the inside pages of the answer book to the title 
page. 
• Wrong question wise totaling on the title page. 
• Wrong totaling of marks of the two columns on the title page. 
• Wrong grand total. 
9. A full scale of marks 0-70 has to be used. Please do not hesitate to award full 
marks if the answer deserves it. 
Page 2 of 18 
 
• Marks in words and figures not tallying. 
• Wrong transfer of marks from the answer book to online award list. 
• Answers marked as correct, but marks not awarded. (Ensure that the right tick 
mark is correctly and clearly indicated. It should merely be a line. Same is with 
the X for incorrect answer.) 
• Half or a part of answer marked correct and the rest as wrong, but no marks 
awarded.  
 
12. While evaluating the answer books if the answer is found to be totally incorrect, it 
should be marked as cross (X) and awarded zero (0)Marks. 
  
13. Any unassessed portion, non-carrying over of marks to the title page, or totaling 
error detected by the candidate shall damage the prestige of all the personnel 
engaged in the evaluation work as also of the Board. Hence, in order to uphold 
the prestige of all concerned, it is again reiterated that the instructions be followed 
meticulously and judiciously. 
 
14. The Examiners should acquaint themselves with the guidelines given in the 
Guidelines for spot Evaluation before starting the actual evaluation. 
 
15. Every Examiner shall also ensure that all the answers are evaluated, marks 
carried over to the title page, correctly totaled and written in figures and words. 
 
16. The Board permits candidates to obtain photocopy of the Answer Book on request 
in an RTI application and also separately as a part of the re-evaluation process 
on payment of the processing charges.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 3


Page 1 of 18 
 
 
Strictly Confidential: (For Internal and Restricted use only) 
Senior School Certificate Examination-2020 
Marking Scheme – PHYSICS THEORY (042) 
(55/1/1) 
General Instructions: - 
 
1. You are aware that evaluation is the most important process in the actual and 
correct assessment of the candidates. A small mistake in evaluation may lead to 
serious problems which may affect the future of the candidates, education system 
and teaching profession. To avoid mistakes, it is requested that before starting 
evaluation, you must read and understand the spot evaluation guidelines 
carefully. Evaluation is a 10-12 days mission for all of us. Hence, it is 
necessary that you put in your best efforts in this process. 
2. Evaluation is to be done as per instructions provided in the Marking Scheme. It 
should not be done according to one’s own interpretation or any other 
consideration. Marking Scheme should be strictly adhered to and religiously 
followed. However, while evaluating, answers which are based on latest 
information or knowledge and/or are innovative, they may be assessed for 
their correctness otherwise and marks be awarded to them.  
3. The Head-Examiner must go through the first five answer books evaluated by 
each evaluator on the first day, to ensure that evaluation has been carried out as 
per the instructions given in the Marking Scheme. The remaining answer books 
meant for evaluation shall be given only after ensuring that there is no significant 
variation in the marking of individual evaluators. 
4. Evaluators will mark( v ) wherever answer is correct.  For wrong answer ‘X”be 
marked.  Evaluators will not put right kind of mark while evaluating which gives an 
impression that answer is correct and no marks are awarded.  This is most 
common mistake which evaluators are committing. 
5. If a question has parts, please award marks on the right-hand side for each part. 
Marks awarded for different parts of the question should then be totaled up and 
written in the left-hand margin and encircled.  This may be followed strictly. 
6. If a question does not have any parts, marks must be awarded in the left-hand 
margin and encircled. This may also be followed strictly. 
7. If a student has attempted an extra question, answer of the question deserving 
more marks should be retained and the other answer scored out. 
8. No marks to be deducted for the cumulative effect of an error. It should be 
penalized only once. 
10. Every examiner has to necessarily do evaluation work for full working hours i.e. 8 
hours every day and evaluate 20 answer books per day in main subjects and 25 
answer books per day in other subjects (Details are given in Spot Guidelines). 
11. Ensure that you do not make the following common types of errors committed by 
the Examiner in the past:- 
• Leaving answer or part thereof unassessed in an answer book. 
• Giving more marks for an answer than assigned to it. 
• Wrong totaling of marks awarded on a reply. 
• Wrong transfer of marks from the inside pages of the answer book to the title 
page. 
• Wrong question wise totaling on the title page. 
• Wrong totaling of marks of the two columns on the title page. 
• Wrong grand total. 
9. A full scale of marks 0-70 has to be used. Please do not hesitate to award full 
marks if the answer deserves it. 
Page 2 of 18 
 
• Marks in words and figures not tallying. 
• Wrong transfer of marks from the answer book to online award list. 
• Answers marked as correct, but marks not awarded. (Ensure that the right tick 
mark is correctly and clearly indicated. It should merely be a line. Same is with 
the X for incorrect answer.) 
• Half or a part of answer marked correct and the rest as wrong, but no marks 
awarded.  
 
12. While evaluating the answer books if the answer is found to be totally incorrect, it 
should be marked as cross (X) and awarded zero (0)Marks. 
  
13. Any unassessed portion, non-carrying over of marks to the title page, or totaling 
error detected by the candidate shall damage the prestige of all the personnel 
engaged in the evaluation work as also of the Board. Hence, in order to uphold 
the prestige of all concerned, it is again reiterated that the instructions be followed 
meticulously and judiciously. 
 
14. The Examiners should acquaint themselves with the guidelines given in the 
Guidelines for spot Evaluation before starting the actual evaluation. 
 
15. Every Examiner shall also ensure that all the answers are evaluated, marks 
carried over to the title page, correctly totaled and written in figures and words. 
 
16. The Board permits candidates to obtain photocopy of the Answer Book on request 
in an RTI application and also separately as a part of the re-evaluation process 
on payment of the processing charges.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 3 of 18 
 
MARKING SCHEME: PHYSICS 
QUESTION PAPER CODE: 55/1/1 
Q.No. Value Points/Expected Answer Marks  Total 
Marks 
SECTION A 
1 (A)  
 
no net charge is enclosed by the surface 
1 1 
2 (C)  
 
-?????? 
1 1 
3 (C) 
 
No current flows in the potentiometer wire at balance 
1 1 
4 (B) 
 
3:2 
1 1 
5 (D) 
 
material of the turns of the coil 
1 1 
6 (A)  
 
increases the resolving power of telescope 
1 1 
7 (A)  
 
1.47 
1 1 
8 (A) 
 
red colour 
1 1 
9 (D) 
 
The stability of atom was established by the model 
1 1 
10 (C) 
 
1:3 
1 1 
11 0.15G 1 1 
12 Eddy 1 1 
13 Four times    1 1 
14 Integral  
OR 
Nucleons 
1 1 
15 
v3 
1 1 
16 
??? .???? = ?? 0
(?? ?? + ?? ?? ) 
1 1 
17 Decreases or reduce 1 1 
18 4.8 fermi       
OR  
 
1
1836
 
1 1 
19 M2  1 1 
20 Si & Ge  cannot be used for fabrication of  visible LED because 
their energy gap is less 1.8eV 
 
 
1 1 
Page 4


Page 1 of 18 
 
 
Strictly Confidential: (For Internal and Restricted use only) 
Senior School Certificate Examination-2020 
Marking Scheme – PHYSICS THEORY (042) 
(55/1/1) 
General Instructions: - 
 
1. You are aware that evaluation is the most important process in the actual and 
correct assessment of the candidates. A small mistake in evaluation may lead to 
serious problems which may affect the future of the candidates, education system 
and teaching profession. To avoid mistakes, it is requested that before starting 
evaluation, you must read and understand the spot evaluation guidelines 
carefully. Evaluation is a 10-12 days mission for all of us. Hence, it is 
necessary that you put in your best efforts in this process. 
2. Evaluation is to be done as per instructions provided in the Marking Scheme. It 
should not be done according to one’s own interpretation or any other 
consideration. Marking Scheme should be strictly adhered to and religiously 
followed. However, while evaluating, answers which are based on latest 
information or knowledge and/or are innovative, they may be assessed for 
their correctness otherwise and marks be awarded to them.  
3. The Head-Examiner must go through the first five answer books evaluated by 
each evaluator on the first day, to ensure that evaluation has been carried out as 
per the instructions given in the Marking Scheme. The remaining answer books 
meant for evaluation shall be given only after ensuring that there is no significant 
variation in the marking of individual evaluators. 
4. Evaluators will mark( v ) wherever answer is correct.  For wrong answer ‘X”be 
marked.  Evaluators will not put right kind of mark while evaluating which gives an 
impression that answer is correct and no marks are awarded.  This is most 
common mistake which evaluators are committing. 
5. If a question has parts, please award marks on the right-hand side for each part. 
Marks awarded for different parts of the question should then be totaled up and 
written in the left-hand margin and encircled.  This may be followed strictly. 
6. If a question does not have any parts, marks must be awarded in the left-hand 
margin and encircled. This may also be followed strictly. 
7. If a student has attempted an extra question, answer of the question deserving 
more marks should be retained and the other answer scored out. 
8. No marks to be deducted for the cumulative effect of an error. It should be 
penalized only once. 
10. Every examiner has to necessarily do evaluation work for full working hours i.e. 8 
hours every day and evaluate 20 answer books per day in main subjects and 25 
answer books per day in other subjects (Details are given in Spot Guidelines). 
11. Ensure that you do not make the following common types of errors committed by 
the Examiner in the past:- 
• Leaving answer or part thereof unassessed in an answer book. 
• Giving more marks for an answer than assigned to it. 
• Wrong totaling of marks awarded on a reply. 
• Wrong transfer of marks from the inside pages of the answer book to the title 
page. 
• Wrong question wise totaling on the title page. 
• Wrong totaling of marks of the two columns on the title page. 
• Wrong grand total. 
9. A full scale of marks 0-70 has to be used. Please do not hesitate to award full 
marks if the answer deserves it. 
Page 2 of 18 
 
• Marks in words and figures not tallying. 
• Wrong transfer of marks from the answer book to online award list. 
• Answers marked as correct, but marks not awarded. (Ensure that the right tick 
mark is correctly and clearly indicated. It should merely be a line. Same is with 
the X for incorrect answer.) 
• Half or a part of answer marked correct and the rest as wrong, but no marks 
awarded.  
 
12. While evaluating the answer books if the answer is found to be totally incorrect, it 
should be marked as cross (X) and awarded zero (0)Marks. 
  
13. Any unassessed portion, non-carrying over of marks to the title page, or totaling 
error detected by the candidate shall damage the prestige of all the personnel 
engaged in the evaluation work as also of the Board. Hence, in order to uphold 
the prestige of all concerned, it is again reiterated that the instructions be followed 
meticulously and judiciously. 
 
14. The Examiners should acquaint themselves with the guidelines given in the 
Guidelines for spot Evaluation before starting the actual evaluation. 
 
15. Every Examiner shall also ensure that all the answers are evaluated, marks 
carried over to the title page, correctly totaled and written in figures and words. 
 
16. The Board permits candidates to obtain photocopy of the Answer Book on request 
in an RTI application and also separately as a part of the re-evaluation process 
on payment of the processing charges.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 3 of 18 
 
MARKING SCHEME: PHYSICS 
QUESTION PAPER CODE: 55/1/1 
Q.No. Value Points/Expected Answer Marks  Total 
Marks 
SECTION A 
1 (A)  
 
no net charge is enclosed by the surface 
1 1 
2 (C)  
 
-?????? 
1 1 
3 (C) 
 
No current flows in the potentiometer wire at balance 
1 1 
4 (B) 
 
3:2 
1 1 
5 (D) 
 
material of the turns of the coil 
1 1 
6 (A)  
 
increases the resolving power of telescope 
1 1 
7 (A)  
 
1.47 
1 1 
8 (A) 
 
red colour 
1 1 
9 (D) 
 
The stability of atom was established by the model 
1 1 
10 (C) 
 
1:3 
1 1 
11 0.15G 1 1 
12 Eddy 1 1 
13 Four times    1 1 
14 Integral  
OR 
Nucleons 
1 1 
15 
v3 
1 1 
16 
??? .???? = ?? 0
(?? ?? + ?? ?? ) 
1 1 
17 Decreases or reduce 1 1 
18 4.8 fermi       
OR  
 
1
1836
 
1 1 
19 M2  1 1 
20 Si & Ge  cannot be used for fabrication of  visible LED because 
their energy gap is less 1.8eV 
 
 
1 1 
Page 4 of 18 
 
SECTION B 
21 
 
 
Meter bridge works on the principle of  a balanced wheatstone 
bridge. 
 
?? 1
?? 2
=
?? 3
?? 4
 at null point when Ig=0  
                                                               (unknown) 
 
 
 
 
 
 
 
 
 
 
 
½  
 
 
 
 
 
 
 
½  
 
 
 
 
1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 
22 
 
?? 1
=
????
?? ?? ?? 
Capacitor are connected in series 
?? 2
=
?? '
?? ''
?? '
+ ?? ''
= (
2?? 1
?? 2
?? 1
+ ?? 2
)
?
?? ?? ?? 
 
C1=C2 
 
?? =
2?? 1
?? 2
?? 1
+ ?? 2
 
 
 
 
 
 
 
 
 
 
 
½ 
 
 
1  
 
 
 
 
½  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 
 
 
 
 
 
 
 
(a) Principle      1 mark 
(b) Circuit diagram for determining unknown resistance 
of meter bridge    1 mark 
Formula for parallel plate   ½ mark 
Calculation of effective capacitance of the combination 
      1 mark 
Relation K, K1 and K2    ½ mark 
Page 5


Page 1 of 18 
 
 
Strictly Confidential: (For Internal and Restricted use only) 
Senior School Certificate Examination-2020 
Marking Scheme – PHYSICS THEORY (042) 
(55/1/1) 
General Instructions: - 
 
1. You are aware that evaluation is the most important process in the actual and 
correct assessment of the candidates. A small mistake in evaluation may lead to 
serious problems which may affect the future of the candidates, education system 
and teaching profession. To avoid mistakes, it is requested that before starting 
evaluation, you must read and understand the spot evaluation guidelines 
carefully. Evaluation is a 10-12 days mission for all of us. Hence, it is 
necessary that you put in your best efforts in this process. 
2. Evaluation is to be done as per instructions provided in the Marking Scheme. It 
should not be done according to one’s own interpretation or any other 
consideration. Marking Scheme should be strictly adhered to and religiously 
followed. However, while evaluating, answers which are based on latest 
information or knowledge and/or are innovative, they may be assessed for 
their correctness otherwise and marks be awarded to them.  
3. The Head-Examiner must go through the first five answer books evaluated by 
each evaluator on the first day, to ensure that evaluation has been carried out as 
per the instructions given in the Marking Scheme. The remaining answer books 
meant for evaluation shall be given only after ensuring that there is no significant 
variation in the marking of individual evaluators. 
4. Evaluators will mark( v ) wherever answer is correct.  For wrong answer ‘X”be 
marked.  Evaluators will not put right kind of mark while evaluating which gives an 
impression that answer is correct and no marks are awarded.  This is most 
common mistake which evaluators are committing. 
5. If a question has parts, please award marks on the right-hand side for each part. 
Marks awarded for different parts of the question should then be totaled up and 
written in the left-hand margin and encircled.  This may be followed strictly. 
6. If a question does not have any parts, marks must be awarded in the left-hand 
margin and encircled. This may also be followed strictly. 
7. If a student has attempted an extra question, answer of the question deserving 
more marks should be retained and the other answer scored out. 
8. No marks to be deducted for the cumulative effect of an error. It should be 
penalized only once. 
10. Every examiner has to necessarily do evaluation work for full working hours i.e. 8 
hours every day and evaluate 20 answer books per day in main subjects and 25 
answer books per day in other subjects (Details are given in Spot Guidelines). 
11. Ensure that you do not make the following common types of errors committed by 
the Examiner in the past:- 
• Leaving answer or part thereof unassessed in an answer book. 
• Giving more marks for an answer than assigned to it. 
• Wrong totaling of marks awarded on a reply. 
• Wrong transfer of marks from the inside pages of the answer book to the title 
page. 
• Wrong question wise totaling on the title page. 
• Wrong totaling of marks of the two columns on the title page. 
• Wrong grand total. 
9. A full scale of marks 0-70 has to be used. Please do not hesitate to award full 
marks if the answer deserves it. 
Page 2 of 18 
 
• Marks in words and figures not tallying. 
• Wrong transfer of marks from the answer book to online award list. 
• Answers marked as correct, but marks not awarded. (Ensure that the right tick 
mark is correctly and clearly indicated. It should merely be a line. Same is with 
the X for incorrect answer.) 
• Half or a part of answer marked correct and the rest as wrong, but no marks 
awarded.  
 
12. While evaluating the answer books if the answer is found to be totally incorrect, it 
should be marked as cross (X) and awarded zero (0)Marks. 
  
13. Any unassessed portion, non-carrying over of marks to the title page, or totaling 
error detected by the candidate shall damage the prestige of all the personnel 
engaged in the evaluation work as also of the Board. Hence, in order to uphold 
the prestige of all concerned, it is again reiterated that the instructions be followed 
meticulously and judiciously. 
 
14. The Examiners should acquaint themselves with the guidelines given in the 
Guidelines for spot Evaluation before starting the actual evaluation. 
 
15. Every Examiner shall also ensure that all the answers are evaluated, marks 
carried over to the title page, correctly totaled and written in figures and words. 
 
16. The Board permits candidates to obtain photocopy of the Answer Book on request 
in an RTI application and also separately as a part of the re-evaluation process 
on payment of the processing charges.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 3 of 18 
 
MARKING SCHEME: PHYSICS 
QUESTION PAPER CODE: 55/1/1 
Q.No. Value Points/Expected Answer Marks  Total 
Marks 
SECTION A 
1 (A)  
 
no net charge is enclosed by the surface 
1 1 
2 (C)  
 
-?????? 
1 1 
3 (C) 
 
No current flows in the potentiometer wire at balance 
1 1 
4 (B) 
 
3:2 
1 1 
5 (D) 
 
material of the turns of the coil 
1 1 
6 (A)  
 
increases the resolving power of telescope 
1 1 
7 (A)  
 
1.47 
1 1 
8 (A) 
 
red colour 
1 1 
9 (D) 
 
The stability of atom was established by the model 
1 1 
10 (C) 
 
1:3 
1 1 
11 0.15G 1 1 
12 Eddy 1 1 
13 Four times    1 1 
14 Integral  
OR 
Nucleons 
1 1 
15 
v3 
1 1 
16 
??? .???? = ?? 0
(?? ?? + ?? ?? ) 
1 1 
17 Decreases or reduce 1 1 
18 4.8 fermi       
OR  
 
1
1836
 
1 1 
19 M2  1 1 
20 Si & Ge  cannot be used for fabrication of  visible LED because 
their energy gap is less 1.8eV 
 
 
1 1 
Page 4 of 18 
 
SECTION B 
21 
 
 
Meter bridge works on the principle of  a balanced wheatstone 
bridge. 
 
?? 1
?? 2
=
?? 3
?? 4
 at null point when Ig=0  
                                                               (unknown) 
 
 
 
 
 
 
 
 
 
 
 
½  
 
 
 
 
 
 
 
½  
 
 
 
 
1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 
22 
 
?? 1
=
????
?? ?? ?? 
Capacitor are connected in series 
?? 2
=
?? '
?? ''
?? '
+ ?? ''
= (
2?? 1
?? 2
?? 1
+ ?? 2
)
?
?? ?? ?? 
 
C1=C2 
 
?? =
2?? 1
?? 2
?? 1
+ ?? 2
 
 
 
 
 
 
 
 
 
 
 
½ 
 
 
1  
 
 
 
 
½  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 
 
 
 
 
 
 
 
(a) Principle      1 mark 
(b) Circuit diagram for determining unknown resistance 
of meter bridge    1 mark 
Formula for parallel plate   ½ mark 
Calculation of effective capacitance of the combination 
      1 mark 
Relation K, K1 and K2    ½ mark 
Page 5 of 18 
 
23 
 
The time interval in which the number of radioactive nuclei 
reduced / disintegrated to half of initial value 
 
Let R1 and R2 be their activities then 
 
?? 1
= ?? 1
?? 1
 
 
?? 2
= ?? 2
?? 2
 
 
?? 1
?? 2
=
?? 1
?? 1
?? 2
?? 2
=
?? 1
?? 1
?? 2
?? 2
=
?? 1
?? 2
?? 2
?? 1
 
 
 
 
 
 
 
 
 
1 
 
 
 
 
½  
 
 
 
½  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 
24 
 
Wavefront is defined as the surface of constant phase; 
Alternatively 
It is a locus of all the points in the same phase of disturbance 
 
 
 
sin?? =
????
????
=
?? 1
?? ????
 
 
sin?? =
????
????
=
?? 2
?? ????
 
 
sin?? sin?? 
= 
?? 1
?? 2
 
 
OR 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
½ 
 
 
 
 
 
½  
 
 
 
 
½  
 
 
 
 
 
½ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 
 
 
 
 
 
 
 
 
 
Definition of half life     1 mark 
Determination of  ratio R1 and R2   1  mark 
Definition of wavefront    ½ mark 
Figure       ½ mark 
Derivation of law of refraction   1 mark