Wednesday, 30 July 2014
Monday, 28 July 2014
Saturday, 26 July 2014
CLASS 12 PHYSICS TEST PRACTICE 4
Practice Test Paper 4
Physics
(Theory) – XII
Time
allowed: 3 hours Maximum
marks: 70
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Q. 1.
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An
electrostatic field line cannot be discontinuous. Why?
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1
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Q. 2.
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The
force
 experienced by a
particle of charge q moving with a velocity  in a magnetic field  is given by = q(x). Which pairs out of these vectors are always at right
angles to each other?
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1
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Q. 3.
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Why
does the electric field inside a dielectric decrease when it is placed in an
external electric field?
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1
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Q. 4.
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Electrons are emitted from a photosensitive surface when
it is illuminated by green light but electron emission does not take place by
yellow light. Will the electrons be emitted when the surface is illuminated
by (a) red light, and (b) blue light?
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1
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Q. 5.
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Name
the process by which exact reproduction of a document at a distant place can
be received.
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1
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Q. 6.
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Define the term ‘temperature
coefficient of resistivity’. Show graphically the variation of resistivity
with temperature for nichrome.
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2
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Q. 7.
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Define
‘electric line of force’ and give its two important properties.
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2
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Q. 8.
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The
image of a candle is formed by a convex lens on a screen. The lower half of
the lens is painted black to make it completely opaque. Draw the ray diagram
to show the image formation. How will this image be different from the one
obtained when the lens is not painted black?
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2
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Q. 9.
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Write two characteristic properties to distinguish
between diamagnetic and paramagnetic materials.
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2
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Q. 10.
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A
circular coil of radius 8 cm and 20 turns rotates about its vertical diameter
with an angular speed of 50 s-1 in a uniform horizontal magnetic
field of magnitude 3x10-2T. Find the maximum and average value of
the emf induced in the coil.
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2
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Q. 11.
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Write
two conditions necessary for total internal reflection to take place.
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2
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Q. 12.
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Draw a
labelled circuit diagram to show the use of zener diode as a voltage
regulator.
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2
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Q. 13.
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A galvanometer
with a coil of resistance 120 ohm shows full scale deflection for a current
of 2.5 mA. How will you convert the galvanometer into an ammeter of range 0
to 7.5 A? Determine the net resistance of the ammeter. When an ammeter is put
in a circuit, does it read slightly less or more than the actual current in
the original circuit? Justify your answer.
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3
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Q. 14.
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Give reasons for the following:
(a) Long
distance radio broadcasts use short-wave bands.
(b) The
small ozone layer on top of the stratosphere is crucial for human survival.
(c) Satellites
are used for long distance TV transmission.
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3
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Q. 15.
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Deduce
an expression for the capacitance of a parallel plate capacitor with air as
the medium between the plates.
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3
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Q. 16.
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With
the help of a circuit diagram explain in brief the use of a potentiometer for
comparison of emf of two cells.
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3
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Q. 17.
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For a common emitter transistor amplifier, the audio
signal voltage across the collector resistance of 2 kΩ is 2 V. If the current
amplification factor of the transistor is 100, calculate
(a) input
signal voltage,
(b) base
current, and
(c) power
gain. Given that the value of the base resistance is 1 kΩ.
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3
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Q. 18.
|
Using Huygen’s principle,
explain the refraction of a plane wavefront at a plane surface. Hence prove
Snell’s law.
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3
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Q. 19.
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Write the nuclear reactions for the following:
(a) a-deacy
of
(b) b-
- decay of
(c) b+ -
decay of
 |
3
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Q. 20.
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A converging lens has a focal length of 20 cm in air. It
is made of material of refractive index 1.6. If it is immersed in a liquid of
refractive index 1.3, what will be its new focal length?
How
does the nature of the lens change if this lens is immersed in a liquid of
refractive index 1.8?
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3
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Q. 21.
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Write two applications each of
(a) microwaves,
(b) infra-red
waves, and
(c) radio
waves.
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3
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Q. 22.
|
Mention the significance of
Davisson-Germer experiment. An a-particle and a proton are accelerated from rest
through the same potential difference V. Find the ratio of de-Broglie
wavelengths associated with them.
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3
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Q. 23.
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(a)
Draw a labelled ray diagram to show the formation of
an image by a compound microscope. Write the expression for its magnifying
power.
(b)
How does the resolving power of a compound microscope
change, when
(i)
refractive index of the medium between the object and
the objective lens increases, and
(ii)
wavelength of the radiation used is increased?
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3
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Q. 24.
|
Distinguish between analog and
digital communication. Write any two modulation techniques employed for the
digital data. Describe briefly one of the techniques used.
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3
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Q. 25.
|
A dielectric slab of thickness ‘t’ is kept
in between the plates, each of area ‘A’, of a parallel plate capacitor
separated by a distance ‘d’. Derive an expression for the capacitance of this
capacitor for t<<d.
Or
(a) Explain
briefly how a capacitor stores energy of charging. Obtain an expression for
the energy thus stored.
(b) A
battery of 10 V is connected to a capacitor of 0.1 F. The battery is now
removed and the capacitor is then connected to a second uncharged capacitor
of same capacitance. Calculate the total energy stored in the system.
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5
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Q. 26.
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(a)
How is a wavefront different from a ray? Draw the
geometrical shape of the wavefronts when
(i)
light diverges from a point source, and
(ii)
light emerges out of a convex lens when a point
source is placed at its focus
(b)
State Huygen’s principle. With the help of a suitable
diagram, prove Snell’s law of refraction using Huygen’s principle.
Or
(a)
In Young’s double slit experiment, deduce the
conditions for
(i)
constructive, and
(ii)
destructive interference at a point on the screen.
Draw a graph showing variation of the resultant intensity in the interference
pattern against position ‘x’ on the screen.
(b)
Compare and contrast the pattern which is seen with
two coherently illuminated narrow slits in Young’s experiment with that seen
for a coherently illuminated single slit producing diffraction.
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5
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Q. 27.
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(a) With
the help of a circuit diagram explain the working of transistor as
oscillator.
(b) Draw
a circuit diagram for a two input OR gate and explain its working with the
help of input, output waveforms.
Or
(a) Explain
briefly with the help of a circuit diagram how V-I characteristics of a p-n
junction diode are obtained in
(i)
Forward bias, and
(ii)
Reverse bias. Draw the shape of the curves obtained.
(b) A
photodiode is fabricated from a semiconductor with a band gap of 2.8 eV. Can
it detect wavelength of 6000 nm? Justify.
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5
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CLASS 12 PHYSICS TEST PRACTICE 3
Practice Test Paper 3
Physics
(Theory) – XII
Time
allowed: 3 hours Maximum
marks: 70
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Q. 1.
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An
electron and a proton, moving parallel to each other in the same direction
with equal momenta, enter into a uniform magnetic field which is at right
angles to their velocities. Trace their trajectories in the magnetic
field.
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1
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Q. 2.
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Two
identical loops, one of copper and another of constantan are removed from a
magnetic field within the same time interval. In which loop will the induced
current be greater?
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1
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Q. 3.
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The
power factor of an a.c. circuit is 0.5. What will be the phase difference
between voltage and current in this circuit?
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1
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Q. 4.
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Does
the ‘stopping potential’ in photoelectric emission depend upon
(a) the
intensity of the incident radiation in a photocell?
(b) The
frequency of the incident radiation?
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1
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Q. 5.
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What
is the function of ‘cladding’ in a typical optical fibre?
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1
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Q. 6.
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(a)
Draw the graphs showing variation of inductive
reactance and capacitive reactance with frequency of applied a.c. source.
(b)
Can the voltage drop across the inductor or the
capacitor in a series LCR circuit be greater than the applied voltage of the
a.c. source? Justify your answer.
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2
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Q. 7.
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Define
electric field intensity. Write its S.I. unit. Write the magnitude and
direction of electric field intensity due to an electric dipole of length 2a
at the mid-point of the line joining the two charges.
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2
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Q. 8.
|
State
the underlying principle of a transformer. Write two causes of power loss in
it.
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2
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Q. 9.
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Two dielectric slabs of dielectric constant K1
and K2 are filled in between the two plates, each of area A, of
the parallel plate capacitor as shown in the figure. Find the net capacitance
of the capacitor.
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2
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Q. 10.
|
Explain
the term remote sensing in communication. Name the satellite used for this
purpose.
|
2
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Q. 11.
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With
the help of diagrams distinguish between forward biasing and reverse biasing
of a p-n junction diode.
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2
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Q. 12.
|
Monochromatic
light is refracted from air into glass of refractive index n. Find the ratio
of wavelengths of the incident and refracted light.
|
2
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Q. 13.
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An
electric dipole is held in a uniform electric field. (a) using suitable
diagram, show that it does not undergo any translatory motion, and (b) derive
an expression for the torque acting on it and specify its direction.
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3
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Q. 14.
|
Explain,
with the help of diagram, the principle and working of an a.c. generator.
Write the expression for the e.m.f. generated in the coil in terms of its
speed of rotation.
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3
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Q. 15.
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Define
the term ‘temperature coefficient of resistivity’. Write its SI unit. Plot a
graph showing the variation of resistivity of copper with temperature.
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3
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Q. 16.
|
Draw a
labelled diagram of a moving coil galvanometer. Explain its working
principle. Can this galvanometer be used to detect an a.c. in a circuit? Give
reason.
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3
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Q. 17.
|
A battery of emf 10 V and internal resistance 3Ω is
connected to a resistor R.
(a) If
the current in the circuit is 0.5 A, calculate the value of R.
(b) What
is the terminal voltage of the battery when the circuit is closed?
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3
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Q. 18.
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Draw a labelled diagram of
experimental setup of Rutherford’s alpha particle scattering experiment.
Write two important inferences drawn from this experiment.
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3
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Q. 19.
|
With
the help of a labeled diagram explain in brief the working of a
cyclotron.
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3
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Q. 20.
|
Calculate
the binding energy per nucleon (in MeV) for
 and  . Comment on the difference of these binding energies and
its significance in relation to a-decay of the nuclei. Given: mass of = 1.00783 u, mass of = 1.00867 u, mass of
= 3.01664 u, mass of = 4.00387 u.
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3
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Q. 21.
|
A ground receiver station is receiving a signal at (a) 5
MHz and (b) 100 MHz, transmitted from a ground transmitter at a height of 300
m located at a distance of 100 km. Identify whether it is coming via space
wave or sky wave propagation or satellite transponder. (Given the value of
radius of the earth is 6400 km and maximum electron density, Nmax
= 1012 m-3)
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3
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Q. 22.
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(a)
Draw the energy level diagram showing the emission of
b-particles
followed by g-rays
by a
.
(b)
Plot the distribution of kinetic energy of b-particles
and state why the energy spectrum is continuous.
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3
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Q. 23.
|
Name the constituent radiation of electromagnetic spectrum
which
(a) is
used in satellite communication.
(b) is
used for studying crystal structure.
(c) is
similar to the radiations emitted during decay of radioactive nuclei.
(d) has
its wavelength range between 390 nm and 770 nm.
(e) is
absorbed from sunlight by ozone layer.
(f) produces
intense heating effect.
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3
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Q. 24.
|
Explain, with the help of a circuit diagram, how the
thickness of depleteion layer in a p-n junction diode changes when it is
forward biased. In the following circuits which one of the two diodes is
forward biased and which is reverse biased?
   -10V    (a)
 (b)
-10
V
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3
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Q. 25.
|
Draw a level diagram of a Van de Graaff generator. Give
its principle and explain its working.
Or
Define
capacitance of a capacitor. Give its S.I. unit. Prove that the total
electrostatic energy stored in a parallel plate capacitor is
 CV2 and hence find the expression for the energy
density of the capacitor. |
5
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Q. 26.
|
(a)
Define the term ‘impedance of series LCR circuit’.
Derive a mathematical expression for it using Phasor diagram.
(b)
Obtain the resonant frequency of a series LCR circuit
with L = 2.0 H, C = 32 mF and R = 10 Ω
Or
(a) Distinguish
between the terms resistance, reactance and impedance of an a.c. circuit.
(b) A
100 mF
capacitor in series with a 40 Ω resistance is connected to a 100 V, 60 Hz
supply. Calculate (i) the reactance, (ii) impedance, and (iii) maximum
current in the circuit.
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5
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Q. 27.
|
Using Huygen’s principle, draw a diagram to show
propagation of a wavefront originating from a monochromatic point source.
Describe diffraction of light due to a single slit.
Explain formation of a pattern of fringes obtained on the screen and plot
showing variation of intensity with angle q in single slit
diffraction.
Or
What is meant by a linearly
polarized light? Which type of waves can be polarized? Briefly explain a
method for producing polarized light.
Two polaroids are placed at 90o to each other
and the intensity of transmitted light is zero. What will be the intensity of
transmitted light when one more polaroid is placed between these two
bisecting the angle between them? Take intensity of unpolarised light as I.
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5
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