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xii sample paper

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Explain the meaning of the statement ‘electric charge of a body is
quantised’.
Why can one ignore quantisation of electric charge when dealing with
macroscopic i.e., large scale charges?
An infinite line charge produces a field of 9 × 104 N/C at a distance of
2 cm. Calculate the linear charge density.
When does the path traced by a moving charged particle in a
magnetic field is helix?
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State Ampere’s circuital Law.
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Justify that the tangential component of electrostatic field is
continuous from one side of a charged surface to another.
Which physical quantity has its SI unit as (i) C – m (ii) Vm
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Draw a graph to show a variation of resistance of a metal wire as a
function of its diameter keeping its length and material constant.
Figure shows tracks of three charged particles in a uniform
electrostatic field. Which particle has the highest charge to mass
ratio?
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10 A regular hexagon of side 10 cm has a charge 5 μC at each of its
vertices. Calculate the potential at the centre of the hexagon.
11 An electron and a proton, having equal momenta, enter a uniform
magnetic field at right angles to the field lines. What will be the ratio
of the radii of curvature of their trajectories?
12 Alloys usually have much (lower/higher) temperature coefficients of
resistance than pure metals. Which is correct?
13 What is the nature of the force between two long straight parallel
conductors when they carry currents in the (i) same direction? (ii)
opposite direction?
14 compare the magnitudes of the magnetic field of the coil at its centre
and at an axial point for which z = 3 .
15 Does the charge given to a metallic sphere depend on whether it is
hollow or solid ? Give reason for Your answer.
16 Define 1A of current.
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17 The storage battery of a car has an emf of 12 V. If the internal
resistance of the battery is 0.4 Ω, what is the maximum current that
can be drawn from the battery?
18 With circuit diagram only explain how can a galvanometer be
converted into a voltmeter?
19 A wire whose cross-sectional area is increasing linearly from its one
end to the other, is connected across a battery of V volts. Which of the
following quantities remain constant in the wire ? (a) drift speed
(b) current density?
20 A low voltage supply from which one needs high currents must have
very low internal resistance. Why?
21 An oil drop of 12 excess electrons is held stationary under a constant
electric field of 2.55 × 104 NC–1 in Millikan’s oil drop experiment. The
density of the oil is 1.26 g cm–3. Estimate the radius of the drop. (g =
9.81 m s–2; e = 1.60 × 10–19 C).
22 Two wires A and B of the same material and having same length,
have their cross sectional areas in the ratio 1:6. What would be the
ratio of heat produced in these wires when same voltage is applied
across each?
23 Two identical capacitors of 12 pF each are connected in series across a
battery of 50 V. How much electrostatic energy is stored in the
combination ? If these were connected in parallel across the same
battery, how much energy will be stored in the combination now ?
24 A hollow charged conductor has a tiny hole cut into its surface. Show
that the electric field in the hole is (σ/2ε0) ˆn , where ˆn is the unit
vector in the outward normal direction, and σ is the surface charge
density near the hole.
25 State the principle of an moving coil galvanometer. Write an
expression for the current sensitivity.
26 Two charged conducting spheres of radii a and b are connected to
each other by a wire. What is the ratio of electric fields at the surfaces
of the two spheres? Use the result obtained to explain why charge
density on the sharp and pointed ends of a conductor is higher than
on its flatter portions.
27 Derive the expression for the electric field at a point on the equatorial
line of the ideal electric dipole.
28 A proton and an alpha particle enter at right angles into a uniform
magnetic field of intensity B. Calculate the radii of their paths when
they enter the field with the same a) momentum and b) kinetic energy
29 Using Biot-Savart’s law, derive the expression for the magnetic field
at a point along the axis of a circular current loop.
30 Determine the current in each branch of the network shown in Fig.
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31 Describe the concept used for the selection of velocity of a charged
particle. Explain the principle of the device with the help of a diagram
where the same concept is used. What is the resonating condition for
the said device?
32 A point charge of +2µC is kept fixed at the origin. Another point
charge of +4µC is brought from a far off point to a point distant 50 cm
from the origin. Calculate the electrostatic potential energy of this two
charge system. Another charge of +1µC is brought to a point distant
100 cm from each of these two charges (assumed to be kept fixed).
What is the work done?
33 Derive the expression for the time period of oscillation of the bar
magnet in the magnetic field.
34 For the potentiometer circuit, shown in the given figure, points X and
Y represent the two terminals of an unknown emf E. A student
observed that when the jockey is moved from the end A to the end B
of the potentiometer wire, the deflection in the galvanometer remains
in the same direction. What are the two possible faults in the circuit
that could result in this observation ? If the galvanometer deflection at
the end B is (i) more (ii) less than that at the end A, which of the two
faults, listed above, would be there in the circuit? Give reasons in
support of your answer in each case.
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35 How will a dia–, para – and a ferromagnetic material behave when
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kept in a non-uniform external magnetic field? Give two examples of
each of these materials. Name two main characteristics of a
ferromagnetic material which help us to decide its suitability for
making (i) a permanent magnet (ii) an electromagnet. Which of these
two characteristics should have high or low values for each of these
two types of magnets?
36 (a) In a metre bridge , the balance point is found to be at 39.5 cm from 5
the end left end A, when the resistor Y in the right gap is of 12.5 Ω.
Determine the resistance of X in the left gap. Why are the connections
between resistors in a Wheatstone or meter bridge made of thick
copper strips?
(b) Determine the balance point of the bridge above if X and Y are
interchanged.
(c) What happens if the galvanometer and cell are interchanged at the
balance point of the bridge? Would the galvanometer show any
current?
37 Find the expression for the energy density of the capacitor. Also find
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the energy lost when the charged capacitor is disconnected from the
source and connected in parallel with the uncharged capacitor. Where
does this loss of energy appear?
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