CLASS – XII
SUBJECT-PHYSICS
[TIME: 3 hrs] [M.M.:70]
GENERAL INSTRUCTIONS:
1. All questions are compulsory.
2. Ques. No. 1 to 5 carry one mark each.
3. Ques. No. 6 to 10 carry 2 marks each.
4. Ques. No. 11 to 22 carry 3 marks each.
5. Ques. No. 11 to 22 carry 3 marks each.
6. Ques. No. 23 is value based question carrying 4 marks.
7. Ques. No. 24 to 26 carry 5 marks each.
8. Calculator is not allowed. Use log table is necessary.
Q 1 Define the SI unit of capacitance?
Q 2 Write the formula which connects electric current and drift velocity of electrons?
Q 3 How does the mutual inductance of a pair of coils change when –
(a) Distance between coils is increased and
(b)Number of turns in each coil is decreased?
Q 4 An object is place at the centre of curvature of a concave mirror. Draw a ray diagram to find nature and position of image?
Q 5 Define (a) atomic mass unit and (b) isotones.
Q 6 Two point changes +10µc and -10µc are separated by a distance of 40 cm in air calculate the electrostatic potential energy of the system, assuming 0 potential energy at infinity.
Q 7 What are Faraday’s laws of electromagnetic induction?
OR
derive the formula of induced e.m.f. produced in a conductor which moves in a perependicular magnetic field.
Q 8 Two straight narrow parallel slits 3mm apart are illuminated with monochromatic of wavelength 5900 X 10-8 cm. fringes are obtained at a distance of 3 m from the slits. Find the width of the fringes.
Q 9 Inputs A and B are applied to the logic gate set up as shown below. Write the truth table of the gate.
Q 10 A carrier wave of peak voltage 12V is used to transmit message signal. What should be the peak Voltage of the modulating signal in order to have a modulation index of 75%?
Q 11 The three resistances R1, R2 and R3 are connected in parallel. Derive an expression of equivalent resistance.
Q 12 Use Kirchhoff’s laws to determine value of current l1 in the given electrical circuit.
Q 13 Use biot-savart law to derive an expression for magnetic field intensity at the centre of current carrying circular coil.
Q 14 An A.C. voltage of 100V, 50Hz is connected across a 20ohm resistor and 2mH inductor in series. Calculate (a) impendence and (b) runs current in the circuit.
Q 15 Describe principle and working of transformer. Write its losses also.
OR
define self inductance. Show mathematically that an ideal inductor does not consume any power in an A.C. circuit.
Q 16 Write the method of production and use of each of the following.
(a)infrared (b) gamma rays (c)microwaves
Q 17 Draw labeled ray diagram of compound microscope.
Q 18 What is Huyghen’s principle? Deduce law of reflection of the basis of it?
Q 19 What is photoelectric effect? Calculate kinetic energy of a photoelectron (in eV) emitted on a shining light of wavelength 6.2 X 10-6 m on a metal surface of work function 0.1 ev .
Q 20 Define half life period of a radioactive substance. A radioactive substance decays to 1/32 of its initial activity on 25 days. Calculate its half life period
Q 21 Derive an expression for the total energy of an electron in the nth orbit of hydrogen using Bohr’s postulate.
Q 22 Write the three important factors which justify the need of modulating a message signal. Show diagrammatically how an amplitude modulated wave is obtained when a modulating signal is superimposed on carrier wave.
Q 23 Ankit’s mother had put a lot of clothes in the washing machine but the machine did not start and indicator shows that the lid did not close. Ankit seeks his mother in trouble tried closing the lid by fore but realized that the mechanism was different. It was a magnetic system. In his effort he damaged the lid of the machine.
(a)What were the values developed by Ankit.
(b)What values did his mother impart to Ankit?
(c)What could have Ankit done to avoid the damage.
Q 24 What is Gauss’ theorem? Use it to derive an expression for electric field intensity due to a spherical shell of charge?
OR
what is electric potential energy? Derive and expression for electric potential energy for a system of three point charges.
Q 25 Derive lens maker’s formula. An object is placed at a distance of 30cm from a convex lens of focal length 20cm. find the position and nature of image formed.
OR
define (a) coherent sources (b) superposition principle(c) Breuster’s angle(d) polarization of light(e) diffraction.
Q 26 What is pn-junction material? Explain its uses as (a) half wave rectifier & (b) full wave rectifier drawing necessary diagrams.
OR
what is transistor? Explain its input and output characteristics drawing necessary circuit diagram.
CLASS – XII
SUBJECT-PHYSICS
[TIME: 3 hrs] [M.M.:70]
MARKING SCHEME
1. A conductor is said to have 1 faraday when 1 C charge raises its potential by 1 V . …..1mark
2. I=Avne …..1mark
3. (a) decrease …..1mark
(b) decrease …..1mark
4. Image is formed at C of equal height …..1mark
image is real and inverted …..1mark
5. Correct definitions …..1mark
6. PE=-2.2J …..2mark
7. Correct definition …..2mark
OR
Correct derivation …..1mark
e=Blv …..1mark
8. W=9X10-5m …..2mark
9. Y= A+B …..1mark
=A+B=AB
Y B C …..1mark
0 0 0
0 1 0
1 0 0
1 1 1
10. Em=75/100X12=9V …..2mark
11. Correct derivation
1/R = 1/R1 + 1/R2 + 1/R3 …..3mark
12. I1=-1.2A …..3mark
13. Correct derivation …..3mark
14. Z=70ohm …..2mark
Irms=5A …..1mark
15. Principle + working …..2mark
losses …..1mark
OR
Correct definition …..2mark
power consumption …..1mark
16. Correct description …..3mark
17. Correct ray diagram …..2mark
labeling …..1mark
18. Hugghen’s Priciple …..1mark
deduction of law of reflection …..2mark
19. Photoelectric effect …..1mark
KE = 0.1eV …..2mark
20. Definition …..1mark
T =5 years …..2mark
21. En=-13.6/n2 eV …..3mark
22. Correct factors …..2mark
amplitude modulation …..1mark
23. (a) sympathy, responsibility etc. …..1mark
(b)appreciation, thankfulness etc. …..1mark
(c)to wash clothes in two parts …..2mark
magnetic door
24. Gauss’ theorem …..1mark
correct derivation …..4mark
OR
correct definition …..1mark
correct derivation …..4mark
25. Correct derivation …..3mark
V=60cm …..2mark
OR
correct definitions …..5mark
26. Definition …..1mark
half wave rectifier …..2mark
Full wave rectifier …..2mark
Or
transistor …..1mark
input characteristics …..2mark
output Characteristics …..2mark