Download File

First Pre Board 2016-2017
Physics
Time 3 Hrs.
class-XII
M.M. 70
Section A
1.
A cell of emf E and internal resistance r is connected across a variable
resistor R. Plot a graph showing the variation of terminal potential V
with resistance R.
2.
Why no two magnetic field lines intersect with each other ?
3.
Why the core of a transformer is laminated ?
4.
Define stopping potential.
5.
Give one point of difference between a metal and a semi conductor
based an band theory.
Section B
6.
Derive an expression for force and torque acting on an electric dipole
in a uniform electric field. In which situation, torque on the dipole is
(i)
Maximum and
(ii) minimum.
OR
Write two properties of electric lines of force. Sketch them for an
isolated positive point charge and electric dipole.
7.
The horizontal component of earth's magnetic field at a
place is
0.4 x 10-4 T. If angle of dip is 450, what are the values of vertical
component and total field strength of earth's field ?
8.
State Fara day's laws of electromagnetic induction. How is Lenz's law
in accordance with the law of conservation of energy.
9.
State Huygen's principle. Using it prove laws of refraction.
10.
In the given block diagram of a receiver, identify the boxes labelled as
X and Y and, write their functions.
Section - C
11.
State and prove Gauss's theorem. Using the theorem, derive an
expression for electric field intensity at a point due to a line of charge
with proper labelled diagram.
12.
Find the expression for capacitance of a parallel plate capacitor when
(i) a thin dielectric slab is inserted in between the plates (ii) a dielectric
slab fills the entire space between the plates.
13.
State the working principle of potentiometer with the help of a circuit
diagram, explain how a potentiometer is used to compare the emf's of
two primary cells. Obtain the required expression used for comparing
the emf's.
Write two possible causes for one sided deflection in a potentiometer
experiment.
OR
State wheat stone bridge principle with appropriate diagram. Discuss
the determination of unknown resistance with the help of proper circuit
diagram of meter bridge. Obtain the required expression.
Why thick copper strips are fitted on meter bridge instead of copper
wires.
14.
State Kirchoff's rules. The wheat stone bridge circuit have the
resistances in various arms as shown in figure. Calculate the current
through the galvanometer.
15.
Name the parts of the electromagnetic spectrum which is
a. Suitable for radar system used in air craft navigation.
b. Used to treat muscular strain.
c. Used as a diagnostic tool in medicine.
Write how these waves can be produced.
16.
Draw course of rays through a compound microscope. Deduce an
expression for its magnifying power. How can the magnifying power
be increased ?
17.
Describe Davisson and Germer experiment to establish the wave nature
of electrons. Draw a labelled diagram of the apparatus used.
18.
a. The energy levels of an atom are shown in the figure. Which of
them will result in the emission of a photon of wave length 275 nm?
b. Which transition corresponds to emission of radiation of maximum
wavelength ?
19.
What is nuclear binding energy ? Draw a curve between mass number
and average binding energy per nucleon. Explain the energy release in
the processes of nuclear fission and nuclear fusion from this plot.
20.
a) Which of the two diodes in forward biased and which is reverse
biased.
b) Draw a circuit diagram of a full wave rectifier. Draw the input and
output waveforms indicating clearly the functions of the two diodes
used.
21.
Identify the gate symbol given below. Sketch the output Y using the
gate shown and write its truth table.
22.
a) What is ionospheric propagation ? Draw a labelled diagram of
ionospheric propagation.
b) A transmitting antenna at the top of a tower has a height 32m and
that of the receiving antenna is 50 m. What is the maximum
distance between them for satisfactory communication in line of
sight mode ? Given radius of earth is 6.4 x 106 m.
Section D
23.
Rashmi's grandfather was old. Due to some reasons doctor suggested
him to go through an endoscopic tests. Grandfather had never gone
through any such test ever before. So, he was afraid. He thought that
these tests will cause negative effect to his body organs. Therefore, he
was not ready for endoscopy. Everyone tried to let him understand and
convince him. But he got ready only when his granddaughter Rashmi
convinced him and explained that it is nothing but just a test in which
light wave is involved and possessing total internal reflection, which is
used to view and observe the internal parts of the body.
i.
What are the values of grandfather and the grand daughter's
relation displayed here ?
ii.
What is the basic principle used in optical fibre ?
iii.
Explain total internal reflection with a suitable diagram.
Section E
24.
a) Draw a neat and labelled diagram of a cyclotron. State the
underlying principle and explain how a positively charged particle
gets accelerated in this machine. Show mathematically that the
cyclotron frequency does not depend upon the speed of the particle.
b) The magnetic flux density applied in cyclotron is 3.5 T. What will
be the frequency of electric field that must be applied between the
dees in order (a) to accelerate protons (b) ∝ - Particles ?
OR
a) Draw a labelled diagram of a moving coil galvanometer. State and
explain the principle on which it works. Define current sensitivity
and voltage sensitivity.
b) In the circuit shown, the current is to be measured. What is the
value of current if the ammeter shown.
i.
is a galvanometer with resistance RG = 60 ohms
ii.
is a galvanometer described in (i) but converted to an
ammeter by a shunt resistance rs = 0.02ohms.
25.
a) Derive an expression for the average power in LCR series circuit
connected to ac supply. Hence define power factor. Show that the
average power consumed per cycle in an ac circuit containing an
ideal capacitor is zero.
b) A series LCR circuit with R = 10 ohm, L = 2H and C = 25 micro
Farad is connected to a variable frequency 200 V ac supply. when the
frequency of the supply equals the natural frequency of the circuit,
what is the average power transferred to the circuit in one complete
cycle ?
OR
a) An ac supply E = Eo sin wt is connected to a series combination of
L, C and R. Using phasor diagram calculate impedance of the
circuit.
Calculate frequency of series resonance circuit. Define Q factor of
this circuit.
b) A charged 30 micro farad capacitor is connected to a 27 milli henry
inductor. What is the frequency of free oscillation of the circuit.
26 What is meant by interference of light ? Derive the conditions for
constructive and destructive interference In young's double slit
experiment, explain with reason in each case, how the interference
pattern changes when
i.
Width of the slits is doubled.
ii.
Separation between the slits is increased and.
iii.
Screen is moved away from the plane of slits ?
OR
c)
a) What do you understand by polarization of light ? Explain
polarization of light by reflection and hence prove Brewster's law.
d)
b) Light posses through two Polaroid's P1 and P2 with pass axis of P2
making an angle, θ with the pass axis of P1. For what value of θ is
the intensity of emergent light zero ?