iii Question number 1 to 5 are very short answer questions, carrying 1 mark each.. iv Question number 6 to 12 are short answer questions, carrying 2 marks each.. v Question number 13 to
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Sample Question Paper – III
General Instructions
(i) All questions are compulsory
(ii) There is no overall choice However, an internal choice has been provided in one question of two marks, one question of three marks and one question of five marks You have to attempt only one of the choices in such questions
(iii) Question number 1 to 5 are very short answer questions, carrying 1 mark each
(iv) Question number 6 to 12 are short answer questions, carrying 2 marks each
(v) Question number 13 to 24 are also short answer questions, carrying 3 marks each
(vi) Question number 25 to 27 are long answer questions, carrying 5 marks each
(vii) Use of calculators is not permitted However, you may use Log Tables, if necessary
(viii) You may use the following physical constants wherever necessary:
c = 3 × 108 ms–1
h = 6.6 × 10–34 Js
e = 1.6 × 10–19 C
µ0 = 4π × 10–7 T mA–1
2. Why are infrared waves preferred for optical fibre communication? 1
3. Two electric bulbs are rated as 220V-100W & 220V-60W Which one of these has greater
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4. In which direction will a freely suspended magnet allign itself when placed at the magnetic pole
5. A graph is plotted between the maximum K.E of emitted photoelectrons & the frequency of incident radiations Which physical constant can be determined from the slope of this graph? 1
6. Define the term resistivity Write an expression for the resistivity of a conductor in terms of
7. An ac generator has a coil of N turns each of area A, rotating with angular speed ω in a uniform magnetic field B.
(i) What is the maximum emf between its slip rings?
(ii) What is the flux associated with the coil when the emf across it is zero? 2
8. Draw the energy level diagrams for (i) n-type & (ii) p-type semiconductors Mark the donor and
9. The refractive index of water is 4/3 Obtain the value of the semi vertical angle of the cone within which the entire outside view would be confined for a fish under water Draw an
10. When an uncharged body B is charged by induction, using a charged body A, the charge on A does not change Explain how this fact is in accordance with the principle of conservation of
11. A coil of n turns and radius R carries a current I It is unwound and rewound to make another coil of radius R/2, current remaining the same Calculate the ratio of the magnetic moments of
12. What will be the effect on the interference fringes in Young’s double slit experiment when,
(i) the monochromatic source is replaced by another monochromatic source of shorter
wave-length
(ii) monochromatic source is replaced by a source of white light Justify your answer in each
case
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OR
The polarisation of a beam of light by reflection is best achieved when the reflected and re-fracted rays are at right angles to each other Show that the polarising angle of incidence is then
13. State any two properties of the electric lines of force Draw the lines of force in each of the following
(b) Between the plates of a charged parallel plate capacitor. 3
14. A bar magnet is placed in a unifrom magnetic field with its magnetic moment making an angle
θ witht he field
(i) Write an expression for the torque acting on the magnet and hence define its magnetic
(ii) Write an expression for the potential energy of the magnet in this orientation Hence obtain
15. Define the term binding energy of a nucleus Which of the two, 235
92 Uor 144
56Ba,has a higher value
of B.E./nucleon? Give the formula for B.E./nucleon for a nucleus of mass number A and atomic number Z.
Name the nucleus of low atomic number that is much more stable than its immediate neighbours
3
16. Two charges of magnitude +25 nC and –9nC are located at points A(1,2) and B(5,2) respec-tively Find the magnitude of electric field due to these charges at the point C(5,5) All distances
17. How does one remove the defect of polarisation in a
(i) Daniel cell (ii) Leclanche cell
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Write the chemical equation for charging in
(i) Lead accumulator (ii) Alkali accumulator.
18. A small town with a demand of electric power 800 kW at 220 V is situated 15 km away from an electric generating station The resistance of the two wire line carrying power is 0.5 Ω/km The town gets power from the line through a 4000 V – 220 V step down transformer at a substation
in the town
(i) Estimate the line power losses in the form of heat.
(ii) Assuming negligible power losses due to leakage, find the power that must be supplied by
19. State Huygens’ principle and use it to construct refracted wave-front for refraction of a plane wavefront at a plane refracting surface Hence derive Snell’s Law 3
20. Compare the energy of an electron of de Broglie wavelength 1Å with that of an X-ray photon of
21. Differentiate between absolute magnitude and apparent magnitude of brightness of a star The apparent and absolute magnitudes of stars A and B are as under:
star Apparent Absolute
magnitude magnitude
Which of the stars is nearer to earth? Give reason for your answer 3
22. Explain the working of a typical fibre optic communication link using a block diagram 3
23. A 50W - 100 V electric bulb is to be used on a 200V-50Hz ac supply Calculate the inductance
of the lamp so that it may glow with its normal brightness (Take π ≈ 3) 3
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24. What will be the required height of a TV tower which can cover the population of 60.3 lakhs if average population density around the tower is 1000 km–2
OR
24. How do we make the choice of a communication channel? A message signal has a bandwidth of
5 MHz Suggest a possible communication channel for its transmission 3
25. Explain the function of the (i) collimator (ii) telescope in a spectrometer With the help of an
appropriate ray diagram discuss how we use a spectrometer for finding the refracting angle of a prism Write the formula used for determination of refractive index of the material of the prism
26. Define the term potential gradiant Using this concept, explain the method for comparison of emfs of two primary cells using a potentiometer Establish the relation used Write two possible causes of potentiometer giving only one sided deflection in this method 5
27. With the help of a block diagram, explain the concept of feedback used in an oscillator Explain
by drawing a circuit diagram, the working of a transistor as an oscillator 5
OR
Draw a circuit diagram of a common emitter amplifier using npn transistor Write an expression
for the current gain Show input and output voltages graphically and explain the phase relation
ANSWERS
or Any two other properties
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=V , Hence for a given voltage
4. It will align itself normal (vertical) to the surface of the earth 1
5. Planck’s constant (h) can be determined from the slope of this graph. 1
6. Resistance offered by unit length and unit area of cross section is resistivity 1
2
m ne
ρ = τ
7. (i) Emax = NBAω
(ii) flux = NBA
8. n type = Conduction band
Donor level Valence band
p type = Conduction band
Acceptor level Valence band
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9. Diagram
q ic
c
1
sin i
c
c
4 1
3 sin
3
sin
4
i
i
=
=
10. During charging of B by induction, the charged object A simply helps B to share charges with the earth
It is, therefore, the earth that provides/takes away charge from B and there is no violation of the
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11. = 2 = 2
2
R
M = =
n π I n π I
′ ′
1 2
M
M
′
12. (i) The fringe width decreases as D
d
λ
β =
(ii) Central fringe will be white surrounded by coloured fringes on both side of the central
fringe This is because the fringe width depends on the wavelength of light ½ + ½
OR
12. Ray diagram
angle of reflection + angle of refraction = 90°
∴ angle of refraction = 90º – angle of reflection
= 90º – angle of incidence (∠ i = ∠ r)
= 90º – ip
p p
sin sin
sin sin(90 )
i i
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∴ µ = tan ip
13. Any two properties
q < 0
q > 0
14. (i) →τ =M→×→B
τ = MB sin θ
sin
M
B
τ
=
θ if B = 1 tesla and sin θ = 1, M = τ ½ Hence the magnetic moment is the torque experienced by the magnet when it is placed normally
in a magnetic field of uniform unit strength, i.e, 1 tesla
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(ii) U= −M B→ →. orU= −MBcosθ
P.E will be minimum when
θ = 0, (Umax = – M B)
Hence the P.E is minimum when the magnetic moment of the magnet is aligned parallel to the
15. Definition of B.E
144
Formula
2
p ( ) n
A
Name – 4
16.
Y
X
A (1,2) B (5,2)
4m
3m
C (5,5) E1
E2
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1
0
1
4 (5)
q
E =
π ε
→
9
9 25 10
9 10
25
−
×
N
9
C
2
0
1 9 10 (9) 10
q E
−
π ε
→
N
9
C
+
= 81 + 81 + 2 (+81) (–sinα)
= 162 – 162 × 3/5
= 162 – 97.2
= 64.8
1
64.8 8.05 NC
→
17. Daniel cell — copper sulphate acts as the depolariser/H+ ions interact with CuSo4 and
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Leclanche cell —Manganese dioxide acts as the depolariser / 2H++ MnO2→
Lead accumulator :
At the cathode Pb So4 + 2H+ + 2e–→ Pb + H2So4
At the anode Pb So4 + 2H2O → PbO2 + 2H2SO4 + 2e– ½ + ½ Alkali accumulator:
At the cathode Fe (OH)2 + 2K+ + 2e–→ Fe + 2KOH
18. Length of wire = 15 × 2 = 30 km
Resistance of wire 1 30 15
2
P = Erms × Irms
5 rms
rms
4000
P
I
E
×
(a) Line power loss = I2
= 1400 kW
19. Statement of Huygens’ principle Diagram with complete idea of formation of
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20. for the electron, h or p=h
p
λ =
2
Also K.E
2
p m
=
2
Electron energy
2
h
m 2
λ
For the X-Ray photon, energy= νh = hc
2
Electron energy X-ray Photon energy
h hc
m 2
λ
2 λ h
m c
=
2 λ
34
6.6 10
1 10 2 9.1 10 3 10
−
×
=
21 Absolute Magnitude: It is the magnitude of brightness of a star observed from a distance of 10
Apparent magnitude: It is magnitude of brigthness of a star as observed from the earth Star
B is nearer because it is less bright but appears brighter than A
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22 Working: The input analog signal is first sampled and modulated using PCM which
pro-duces discrete pulses & gives coded stream of bit (0´S & 1´S) representing the signal Corresponding to this stream of bits, the optical beam from a source is modulated This modu-lated signal is propagated in medium called optical fibre At the receiver, an optical detector detects the signal which in turn, is converted back to electrical signal This is decoded and
Transmitter
Input Signal Modulation Optical
source
Receiver
Demodulation Output Signal
Optical Detector
23. rms 50 1
= = A
100 2
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voltage across L
eff
( ) ( )
100 3 V
=
rms
100 3
1 2
= 2π
2 3
=
2π 3
1.154 H
L
L
L
L
V
X
I
X
L
f
=
=
24. πr2 × density = Population covered
2
5 3
5
9 2 2
6
r
π ×1000 = 60.3×10
10
60.3×10
π
= 1.92 ×10 m
= 2
1.92 ×10
2 2 × 6.4 ×10
= 150 m
r
r
h
R
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OR
24. The communication channel is determined both by the nature of the signal and the nature of
(ii) For unguided media, frequency band of signal is important ½
Co-axial cable, AM radio
25 Function of collimator: To obtain a parallel beam of light coming from a source. ½
Function of telescope: To obtain image from rays refracted from the prism. ½ Ray diagram
FROM COLLIMATOR
TELES CO PE
E
PRISM 2A A
Explanation with relevant formula for finding the angle of prism 2
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26. Definition of potential gradient
Explanation of comparison of emf’s using potentiometer with formula 2 Causes
(i) All the positive terminals may not be connected to the same terminal of the potentiometer (ii) Emf of main supply producing the potential gradient may be less than the emf of cells.
½ + ½
Amp
Feedback Network
OR
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RL Vo
E
C B Ib
Ic
Ie Input signal
Vbe
Vcc
Ic
Output signal Vi
V1
V0
t
t
Explanation:
Output voltage differs by a phase angle of π with respect to the input voltage
Vo = Vcc – IC RL During the half of cycle of input voltage emitter current Ie increases and thus Ic increases
Vo decreases (according to the above equation)
Increase in input signal voltage decreases output voltage Vo
Output collector voltage and input signal voltage are out of phase in common emitter amplifier