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Physics

B
oard
Q
uestion
P
aper:
M
arch 2013
P
hysics
Time: 3 Hours Total Marks: 70
Note:
i.All questions are compulsoryii.Neat diagrams must be drawn wherever necessary.iii.Figure to the right indicate full marks.iv.Use of logarithmic table is allowed. v.All symbols have their usual meaning unless otherwise stated.
SECTION – I
Q.1. Select and write the most appropriate answer from the given alternatives for eachsub-question: [7]
i.The moment of inertia of a thin uniform rod of mass M and length L, about an axis passingthrough a point, midway between the centre and one end, perpendicular to its length is ______.(A)
487
ML
2
(B)
748
ML
2
(C)
148
ML
2
(D)
116
ML
2
ii.‘n’ droplets of equal size of radius r coalesce to form a bigger drop of radius R. The energyliberated is equal to _______. (T = Surface tension of water)(A)4
π
R
2
T[
13
n 1
−
](B)4
π
r
2
T[
13
n 1
−
](C)4
π
R
2
T[
23
n 1
−
](D)4
π
r
2
T[
23
n 1
−
]iii.The buckling of a beam is found to be more if _______.(A)the breadth of the beam is large.(B)the beam material has large value of Young’s modulus.(C)the length of the beam is small.(D)the depth of the beam is small.iv.When a transverse wave on a string is reflected from the free end, the phase change producedis _______.(A)zero rad(B)
2
π
rad (C)
34
π
rad (D)
π
rad v.The number of degrees of freedom for a rigid diatomic molecule is _______.(A)3(B)5(C)6(D)7 vi.Two particles perform linear simple harmonic motion along the same path of length 2A andperiod T as shown in the graph below. The phase difference between them is _______.(A)zero rad(B)
4
π
rad (C)
2
π
rad (D)
34
π
rad
T4
D i s p l a c e m e n t
→
O A A X
T2
3T4
T
A 2
(Time)
→
vii.The light from the Sun is found to have a maximum intensity near the wavelength of 470 nm.Assuming the surface of the Sun as a black body, the temperature of the Sun is _______.(Wien’s constant b = 2.898
×
10
−
3
mK)(A)5800 K(B)6050 K(C)6166 K(D)6500 K
Q.2. Attempt any SIX:[12]
i.State Kepler’s law of orbit and law of equal areas.
ii.A car of mass 1500 kg rounds a curve of radius 250m at 90 km/hour. Calculate the centripetalforce acting on it.iii.Draw a neat labelled diagram for Ferry’s perfectly black body.iv.A mass M attached to a spring oscillates with a period of 2 seconds. If the mass is increasedby 2 kg, the period increases by 1 second. Find the initial mass, assuming that Hooke’s law isobeyed. v.Differentiate between free and forced vibrations. vi.The surface tension of water at 0
°
C is 75.5 dyne/cm. Find surface tension of water at 25
°
C.(
α
for water = 0.0021/
°
C) vii.Derive the relation between surface tension and surface energy per unit area.
viii.A wheel of moment of inertia 1 kgm
2
is rotating at a speed of 40 rad/s. Due to friction on theaxis, the wheel comes to rest in 10 minutes. Calculate the angular momentum of the wheel,two minutes before it comes to rest.
Q.3. Attempt any THREE:[9]
i.A particle of mass m, just completes the vertical circular motion. Derive the expression forthe difference in tensions at the highest and the lowest points.ii.The Earth is rotating with angular velocity
ω
about its own axis. R is the radius of the Earth.If R
ω
2
= 0.03386m/s
2
, calculate the weight of a body of mass 100 gram at latitude 25
°
.(g = 9.8 m/s
2
)iii.Derive an expression for kinetic energy, when a rigid body is rolling on a horizontal surfacewithout slipping. Hence find kinetic energy for a solid sphere.iv.A steel wire of diameter 1
×
10
−
3
m is stretched by a force of 20 N. Calculate the strainenergy per unit volume. (Y steel = 2
×
10
11
N/m
2
)
Q.4.
Define an ideal simple pendulum. Show that, under certain conditions, simple pendulum performslinear simple harmonic motion. A train blows a whistle of frequency 640 Hz in air. Find the difference in apparent frequencies of the whistle for a stationary observer, when the train moves towards and away from the observer with the speed of 72 km/hour. (Speed of sound in air = 340 m/s)
[7] OR Q.4.
With a neat labelled diagram, show that all harmonics are present in an air column contained in apipe open at both the ends. Define end correction. Calculate the kinetic energy of 10 gram of Argon molecules at 127
°
C. (Universal gas constant R = 8320 J/k mole K, Atomic weight of Argon = 40)
[7]
SECTION – II
Q.5. Select and write the most appropriate answer from the given alternatives for eachsub-question:
[7]
i.In the diffraction pattern due to a single slit of width ‘d’ with incident light of wavelength ‘
λ
’,at an angle of diffraction ‘
θ
’, the condition for first minimum is _______.(A)
λ
sin
θ
= d(B)d cos
θ
=
λ
(C)d sin
θ
=
λ
(D)
λ
cos
θ
= dii.Kirchhoff’s junction law is equivalent to _______.(A)conservation of energy(B)conservation of charge(C)conservation of electric potential(D)conservation of electric fluxiii.let ‘p’ and ‘E’ denote the linear momentum and energy of emitted photon respectively. If thewavelength of incident radiation is increased _______.(A)both p and E increase(B)p increases and E decreases(C)p decreases and E increases(D)both p and E decreaseiv.The nuclei having same number of protons but different number of neutrons are called _______.(A)isobars(B)
α
- particles(C)isotopes(D)
γ
- particles v.In case of transistor oscillator, to obtain sustained oscillations, the product of voltage gainwithout feedback and feedback factor should be _______.(A)zero(B)less than 1(C)one(D)infinity vi.The process of regaining of information from carrier wave at the receiver is called _____.(A)modulation(B)transmission(C)propagation(D)demodulation vii.Reactance of a coil is 157
Ω
. On connecting the coil across a source of frequency 100 Hz, thecurrent lags behind e.m.f. by 45
°
. The inductance of the coil is _______.(A)0.25 H(B)0.5 H(C)4 H(D)314 H
Q.6. Attempt any SIX:[12]
i.Draw a neat labelled diagram of a parallel plate capacitor completely filled with dielectric.ii.A point is situated at 7 cm and 7.2 cm from two coherent sources. Find the nature of illumination at the point if wavelength of light is 4000 Å.iii.Obtain the expression for current sensitivity of moving coil galvanometer.iv.In a cyclotron, magnetic field of 3.5 Wb/m
2
is used to accelerate protons. What should be thetime interval in which the electric field between the dees be reversed?(Mass of proton = 1.67
×
10
−
27
kg, Charge on proton = 1.6
×
10
−
19
C). v.Define magnetization. State its formula and S.I. unit.
vi.Electrostatic energy of 3.5
×
10
−
4
J is stored in a capacitor at 700 V. What is the charge on thecapacitor? vii.What is space wave propagation? State its three components. viii.Find the value of energy of electron in eV in the third Bohr orbit of hydrogen atom.(Rydberg’s constant (R) = 1.097
×
10
7
m
−
1
,Planck’s constant (h) = 6.63
×
10
−
34
J – s,Velocity of light in air (c) = 3
×
10
8
m/s.)
Q.7. Attempt any THREE:[9]
i.With the help of neat labelled circuit diagram explain the working of half wave rectifier usingsemiconductor diode. Draw the input and output waveforms.ii.A cell balances against a length of 200 cm on a potentiometer wire, when it is shunted by aresistance of 8
Ω
. The balancing length reduces by 40 cm, when it is shunted by a resistanceof 4
Ω
. Calculate the balancing length when the cell is in open circuit. Also calculate theinternal resistance of the cell.iii.State the law of radioactive decay. Hence derive the expression N = N
o
e
−λ
t
where symbolshave their usual meanings.iv.The photoelectric work function for a metal is 4.2 eV. If the stopping potential is 3 V, find thethreshold wavelength and maximum kinetic energy of emitted electrons.(Velocity of light in air = 3
×
10
8
m/s,Planck’s constant = 6.63
×
10
−
34
J - s,Charge on electron = 1.6
×
10
−
19
C)
Q.8.
State Faraday’s laws of electromagnetic induction and Lenz’s law.Prove theoretically, the relation between e.m.f. induced and rate of change of magnetic flux in a coil moving in a uniform magnetic field. A circular coil of 250 turns and diameter 18 cm carries a current of 12 A. What is the magnitude of magnetic moment moment associated with the coil?
[7]
OR Q.8.
On the basis of Huygens’ wave theory of light prove that velocity of light in a rarer medium isgreater than velocity of light in a denser medium. In Young’s experiment the ratio of intensity at the maxima and minima in the interference pattern is 36:16. What is the ratio of the widths of the two slits?
[7]

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