Download class xii - kvszietmysorephysics

CLASS XII
CHAPTER 1 - ELECTRIC CHARGES AND FIELDS
1) Explain what is meant by quantization of charge and conservation of charge? Why charges are
quantized?
2) How is the force between two charges affected when dielectric constant of the medium in
which they are held increases?
3) Force of attraction between two point charges placed at a distance d is F. What distance apart
should they be kept in the same medium so that force between them is F/3?
4) Calculate the coulomb force between two α particles separated by a distance of 3.2 x 10-15 m in
air?
5) Derive an expression for electric field intensity at a point due to (i) A point charge (ii) A group of
charges (iii) Continuous charge distribution
6) Derive an expression for dipole field intensity at any point on (i) axial line of dipole (ii) equatorial
line of dipole.
7) Give two properties of electric lines of force. Sketch them for an isolated positive point charge.
8) Derive an expression for total work done in rotating an electric dipole through an angle θ in a
uniform electric field.
9) Is an electric dipole in stable equilibrium in uniform electric field?
10) Define electric field at a point. Give the S.I unit of electric moment of a dipole.
11) An electric dipole of length 2 cm is placed with its axis making an angle of 300 to a uniform
electric field of 105 NC-1. If it experiences a torque of 10√3 Nm, Calculate (i) magnitude of
charge on dipole, and (ii) potential energy of dipole.
12) Derive an expression for potential at a point (i) due to point charge (ii) due to a group of
charges (iii) due to continuous charge distribution (iv) due to an electric dipole.
13) Using Gauss’s theorem, derive an expression for electric field intensity at a point due to (i) a line
of charge (ii) a uniformly charged spherical cell (iii) a charged solid sphere (iv) an infinite sheet
of charge.
14) Electric charge is distributed uniformly on the surface of a spherical rubber ballon. Show how
the value of electric intensity and potential vary (i) on the surface (ii) inside and (iii) outside ?
15) What is the amount of work done in moving a 200 nC charge between two points 5 cm apart
on an equipotential surface?
16) Name the physical quantity which has its unit joule coloumb-1. Is it a scalar or vector?
17) Sketch a graph to show how charge Q given to a capacitor of capacity C varies with the
potential difference V.
18) Equipotential surfaces are perpendicular to field lines. Why?
19) Is electric flux a scalar or a vector? What are the units of electric flux?
20) What is the dielectric constant of a metal?
21) The electric field at a point due to a point charge is 30 N/C, and the electric potential at that
point is 15J/C. Calculate the distance of the point from the charge and the magnitude of the
charge.
22) Two point charges A and B of value +15µC and +9µC are kept 18cm apart in air. Calculate the
work done when charge B is moved by 3 cm towards A.
23) An infinite thin plane sheet of charge density 10-8 Cm-2 is held in air. How far apart are two
equipotential surfaces whose p.d is 5 volt?
24) A point charge causes an electric flux of -1.0 x 10-3 Nm2/C to pass through a spherical Gaussian
surface of 10.0 cm radius centered on the charge (a) If the radius of the Gaussian were doubled,
how much flux would pass through the surface? (b) What is the value of the point charge?
25) Explain the term electric field intensity. Electric field inside a conductor is zero. Explain.
26) What is a capacitor? Define capacitance. Discuss its units.
27) Explain the principle of capacitor. Derive an expression for the capacitance of a parallel plate
capacitor. Write two applications of capacitors in electric circuits.
28) Derive an expression for the energy stored in a capacitor. What is the form of this energy and
wherefrom it comes?
29) The battery remains connected to a parallel plate capacitor and a dielectric slab is inserted
between the plates. What will be the effect on its (i) capacity (ii) charge (iii) potential difference
(iv) electric field (v) energy stored?
30) What is meant by dielectric constant? Explain electrostatic shielding. Give one example.
31) Why does the electric conductivity of earth’s atmosphere increase with altitude?
32) A parallel plate capacitor has a capacity of 6µF in air and 60µF when dielectric medium is
introduced. What is the dielectric constant of medium?
33) Why does the electric field inside a dielectric decrease when it is placed in an external electric
field?
34) A parallel plate capacitor with air between its plates having area of 6 x 10-3 m2 and separation
between them 3mm is connected to a 100V supply. Calculate charge on each plate of the
capacitor. Explain what would happen when a 3mm thick mica sheet (K=6) is inserted between
the plates (a) while voltage supply remains connected (b) after the supply is disconnected.
35) Calculate the capacitance of the capacitor C in figure. The equivalent capacitance of the
combination between P and Q is 30µF.
36) Two capacitors of capacitances C1 = 3 µF and C2 = 6 µF arranged in series are connected in
parallel with a third capacitor C3 = 4 µF. The arrangement is connected to a 6.0 V battery.
Calculate the total energy stored in capacitors.
37) In the figure is a plot of lines of force due to two charges q1 and q2. Figure out the sign of the
charges.
a) Both positive b) Both negative c) Upper positive and lower negative d) Upper negative and
lower positive.
38) A hollow metal sphere of radius 10cm is charged such that the potential on its surface is 80
volt. The potential at the center of the sphere is
a) Zero b) 80 volt c) 800 volt d) 8 volt
39) A 4µF condenser is charged to 400 volts and then its plates are joined through a resistance of 1
KΩ . The heat produced in the resistance is
a) 1.28 J b) 0.64J c) 0.32J d) 0.16J
40) There is an electric flud E in X direction. If work done in moving a charge 0.2C through a
distance of 2m along a line making an angle of 60 degree with X axis is4.0 joule, what is the
value of E?
a) √3 newton per coloumb b) 4 newton per coloumb c) 5 newton per coloumb d) None of
these.
41) Two metallic spheres of radii 1 cm and 2cm are given charges of 10-2C and 5 x 10-2C
respectively. If these are connected by a conducting wire, the final charge on the smaller sphere
is
a) 3 x 10-2C
b) 1 x 10-2C
c) 4 x 10-2C
d) 2 x 10-2C
42) A point Q lies on perpendicular bisector of an electric dipole of moment p. If the distance of Q
from the dipole is r (much larger than size of dipole). Then the electric field at Q is proportional
to
a) P-1 and r-2
b) p and r-2
c) p2 and r-3
d) p and r-3
43) A parallel plate condenser with oil between the plates (dielectric constant of oil K =2) has a
capacitance C. If the oil is removed, then capacitance of the capacitor becomes
a)
𝐶
2
b)
𝐶
√2
c) 2C
d) √2C
44) In bringing an electron towards another electron, the electrostatic potential energy of the
system
a)
Remains same
b) becomes zero
c) increases
d) decreases
45) When air is replaced by dielectric medium of constant K, the maximum force of attraction
between two charges separated by a distance
a) Becomes K-1 times b) increases K times c) remains unchanged d) decreases K times.
46) A charge Q is placed at the corner of a cube. The electric flux through all the six faces of the
cube is
a) Q/6έ0
b) Q/8 έ0
c) Q/ έ0
d) Q/3 έ0
47) A capacitor is charged to store an energy U. The charging battery is disconnected. An identical
capacitor is now connected to the first capacitor in parallel. The energy in each of the capacitor
is
a)
𝜆
2𝜋𝜖0𝑎2
𝜆
b) 4𝜋𝜖
c)
0𝑎
𝜆2
2𝜋𝜖0𝑎
𝜆
d) 2𝜋𝜖
0𝑎
48) In a non-uniform electric field, electric dipole experiences
a) Torque only b) torque as well as net force c) force only d) none of these.
b)
49) An α particle and a proton are accelerated at same potential difference from rest. Find the
ratio of their final velocity
a) √2 : 1
b) 1 : 1
c) 1 : √2
d) 1 : 2
50) A charge Q µC is placed at the center of a cube, the flux coming from any surface will be
a)
𝑄
6𝜖0
x 10-6
b)
𝑄
6𝜖0
x 10-3
c)
𝑄
24𝜖0
d)
𝑄
8𝜖0
51) Two charges of magnitudes +4Q and -Q are located att points (a,0) and (-3a,0) respectively.
What is the electric flux due to these charges through a sphere of radius ‘2a’ with its centre at
the origin?
52) A capacitor, made of two parallel plates each of plate area A and separation d, is being
charged by an external ac source. Show that the displacement current inside the capacitor is
the same as the current charging the capacitor.
53) Define electric dipole moment. Is it scalar or a vector? Derive the expression for the electric
field of a dipole at a point on the equatorial plane of the dipole.
54) Draw the equipotential surfaces due to an electric dipole. Locate the points where the potential
due to the dipole is zero.
55) Using Gauss’s law deduce the expression for the electric field due to a uniformly charged
spherical conducting shell of radius R at a point (i) outside and (ii) inside the shell.
CURRENT ELECTRICITY
1) Define resistance of a conductor. What is its cause? Explain the factors on which the resistance
of a conductor depends.
2) Explain current density, conductance and electrical conductivity. State their S.I. units.
3) Define resistivity of the material. State its S.I unit and discuss its variation with temperature in
case of (i) metals (ii) semiconductors and (iii) insulators.
4) What are the factors on which the resistance of a conductor depends? Give the corresponding
relation.
5) A metallic wire of length 1m is stretched to double its length. Calculate the ratio of its initial and
final resistance assuming that there is no change in its density on stretching.
6) A car has a fresh storage battery of e.m.f 12 V and internal resistance 5.0 x 10-2Ω. If the starter
motor draws a current of 90A, what is the terminal voltage of the battery when the starter is on?
7) After long use of car, as given in the above question the internal resistance of the storage battery
increases to 500 Ω. What maximum current can be drawn from the battery? Assume the emf of
the battery to remain unchanged.
8) In the above question, if the discharged battery is charged by an external emf source, is the
terminal voltage of the battery during charging greater or less than its emf 12V/
9) Why constantan or manganin are chosen for the construction of standard resistances?
10) Two identical cells, each of emf E, having negligible internal resistance, are connected in parallel
with each other across an external resistance R. What is the current through this resistance?
11) Explain the term ‘drift velocity’ of electrons in a conductor. Hence obtain the expression for the
current through a conductor in terms of ‘drift velocity’.
12) Explain in brief with the help of a circuit diagram, how a potentiometer is used to determine the
internal resistance of a cell.
13) A light bulb is rated at 125 W for a 250 V a.c. supply. Calculate the resistance of the bulb.
14) Define current sensitivity of a galvanometer. Write its S.I unit.
15) In the following two circuits each having a galvanometer and a battery of 3V. When the
galvanometers in each arrangement do not show any deflection, obtain the ratio R1/R2.
16) A wire of resistivity is stretched to three times to length. What will be its new resistivity?
17) A carbon resistor of 47 K Ω is to be marked with rings of different colours for its identification.
Write the sequence of colours.
18) A wire of resistance 4R is bent in the form of a circle. What is the effective resistance between
the ends of a diameter?
19) A carbon resistance is marked in red green and orange bands. What is the approximate
resistance of the resistor?
20) If the temperature of a good conductor decreases, how does the relaxation time of electrons in
the conductor change?
21) A current flowing in a copper wire is passed through another copper wire of the same length but
of double the radius of the first one. How would the drift velocity of free electrons change?
22) A carbon resistor is marked in coloured bands in the sequence blue, green, orange and gold.
What is the resistance and tolerance value of resistance?
23) Find the resistance between (i) A and B and (ii) A and C of the network shown in figure.
24) Calculate the current shown by the ammeter A in the circuit diagram.
.
25) Derive an expression for the resistivity of a good conductor, in terms of the relaxation time of
electrons.
26) (i)Calculate the equivalent resistence of the given electrical network between points A and B.
(ii) Also calculate the current through CD and ACB, if a 10V d.c. source is conntected between A
and B, and the value of R is assumed as 2 Ω.
27) A battery of emf E, and internal resistance r gives a current of 0.4 A with an external resistor of
12 ohm, and a current of 0.25 A with an external resistor of 20 ohm. Calculate (i) internal
resistance and (ii) emf of the battery.
28) You are given several identical resistances each of value R = 10 Ω and each capable of carrying a
maximum current of one ampere. It is required to make a suitable combination of these
resistances of 5 ohm which can carry a current of 4 ampere. Find the minimum number of
resistances of the type R that will be required for the job.
29) Explain with necessary theory the determination of internal resistance of a cell by potentiometer
method.
30) Give the principle of Wheatstone bridge. How do you use it to measure the unknown resistance?
Explain with necessary theory.
31) With a circuit diagram, briefly explain how a metre bridge can be used to find the unknown
resistance of a given wire. State the formula used.
32) The following circuit shows use of potentiometer to measure the internal resistance of a cell.
(i)
When the key K is open, how does the balance point change, if the current from the driver
cell decreases?
(ii)
When the key K is closed, how does the balance point change if R is increased, keeping the
current from the driver cell constant?
33) ABCDEF is a regular hexagon formed by six equal wires, each of resistance r ohm. The corners
have been joined at the centre of hexagon by wires of the same resistance. Find the equivalent
resistance between the corners A and D using Kirchhoff’s laws.
34) Two cells of emfs 4.5V and 6.0 V and internal resistance 6 ohm and 3 ohm respectively have
their negative terminals joined by a wire of 18 ohm and positive terminals by a wire of 12 ohm
resistance. A third resistance wire of 24 ohm connects middle points of these wires. Draw the
circuit diagram. Using Kirchhoff’s laws, find the potential difference at the end of this third wire.
35) Two cells of emf E1 and E2 (E1>E2) are connected as shown in the figure. When a potentiometer
is connected between A and B, the balancing length of the potentiometer wire is 300 cm. On
connecting the same potentiometer between A and C the balancing length is 100 cm. Calculate
the ratio of E1 and E2.
36) The length of a potentiometer wire is 1200 cm and it carries a current of 80mA. For a cell of emf
4.0 V and internal resistance 20 ohm, the null point is found to be at 1000cm. If a voltmeter is
connected across the cell, the balancing length is decreased by 20 cm. Find (i) the resistance of
the whole wire (ii) reading of the voltmeter, and (iii) resistance of voltmeter.
37) Write two special characteristics of an electric heater.
38) Two electric bulbs A and B are marked 220 V, 40 W and 220 V , 60W respectively. Which one of
these bulbs has higher resistance?
39) Name the physical quantity which has its unit joule coloumb-1. Is it a scalar or vector quantity?
40) A heater coil is rated 100W, 200V. It is cut into two identical parts. Both parts are connected
together in parallel, to the same source of 200V. Calculate the energy liberated per second in
the new combination.
41) What is the effect of temperature on the conductivity of an electrolyte?
42)