# Class XII Physics Assignment

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PHYSICS ASSIGNMENT

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Electric Charges and Fields

Q.1 (i) Can two equipotential surfaces intersect each other?(ii) Two chargesq and +q are located at points A (0, 0, -1) and B (0, 0, +1) respectively. How

much work is done in moving a test charge from p (7, 0, 0) to Q (-3, 0, 0)? (2 marks)Q.2 Can two equipotential surfaces intersect each other?

Q.3 Deduce an expression for electric potential due to dipole at a point in general? (3 marks)

Q.4 What is the work done in moving a test charge q through a distance of 1cm along the equatorial axesof dipole? (1 mark)

Q.5 The graph shows the variation of voltages V across the plates of two capacitors A & B versusincreases of charge, Q stored on them. Which of the two capacitors has HIGHERCAPACITANCE? (2 marks)

Q.6 Use gausss law to deduce an expression for electric field due to uniformly charged plate/sheet?(3 marks)

Q.7 Force of attraction b/w two point charges placed at distance d apart in a medium is F. Whatshould be the distance apart in the same medium so that the force of attraction b/w them becomes

9F? (2 marks)

Q.8 Two rectangular metal plates, each of area A are kept parallel to each other at a distance d apart toform a parallel plate capacitor. If the area of each of the plates is doubled and their distance ofseparation decreases to 1/2 of its initial value. Calculate the ratio of their capacitance in the twocases? (2 marks)

Q.9 Show that the electric field is always perpendicular to an equipotential surface? (2 marks)

Q.10 Two parallel plate capacitors X and Y, have the same area of plates and same separation b/w them.

X has air between the plates while Y contains a dielectric of medium r= 4. Calculate (3 marks)(a) capacitance of each capacitor if equivalent capacitance of the combination is 4 F.?(b) Calculate the potential difference b/w plates of X and Y?

(c) what is the ratio of electrostatic energy Y stored in X and Y?

Q.11 Define the term potential energy of charge q at a distance r in an external electric field? (1 mark)

Q.12 Two fixed point charges +4e and +e units are separated by a distance a. Where should the thirdpoint charge be placed for it to be in equilibrium? (2 marks)

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Q.13 Define the electric flux. Write its S.I. units. A charge 8.85 C is enclosed in a spherical surface ofradius R. Estimate the number of field lines emerging out from the point charge. If radius of sphere

is reduced to half, how would the flux through the surface change? (3 marks)

Q.14 Define electric field intensity. Write its S.I. unit. Write the magnitude and direction of electric fieldintensity due to an electric dipole of length ''2a'' at the midpoint of the line joining the two

charges? (2 marks)

Q.15 Two point charges 3 x 10-8

C and -2 x 10-8

C are located 15 cm apart in air. Find at what point on the

line joining these charges the electric potential is zero? (2 marks)

Q.16 Show that the electric field is always perpendicular to an equipotential surface?

Q.17 (a) Derive an expression for energy stored per unit volume in parallel plate Capacitor.

(b) A 10 F Capacitor is charged by a 30 v d.c. Supply and then connected t across an uncharged 50F Capacitor. Calculate the final potential difference across the combination and loss of energy inthe process? (5 marks)

Q.18 Derive expressions for the electric field due to a uniformly charges spherical shell at a point (I)INSIDE and (II) OUTSIDE the shell? (2 marks)

Q.19 S1and S2are two hollow concentric spheres enclosing charges q and 2q respectively.

(i) What is the ratio of electric flux through S1and S2?

(ii) How will the electric flux through sphere S1change is a medium of dielectric constant 5 isintroduced in the sphere S1in place of air ? (2 marks)

Q.20 Sketch a graph to show how the charge Q acquired by a capacitor of capacitance C varies withincrease in potential difference between the plates? (1 mark)

Q.21 An electric dipole is placed in uniform electric field translatory motion (5 marks)

(i) Show that dipole does not has translator motion.(ii) Also find out an expression for torque on dipole.(iii) State conditions for stable and unstable equilibrium.

Q.22 Define the term electric dipole moment of a dipole. State its S. I. unit ? (1 mark)

Q.23 A parallel plate capacitor is charged to a potential difference V by a source. The capacitor is thendisconnected from the source. If the distance b/w the plates are doubled stale with reason how willfollowing change. (3 marks)(i) electric field between the plates.?

(ii) Capacitance and

(iii) energy stored in the capacitor.?Q.24 Two chargesq and +q are located at points A (0, 0, -a) and B (0, 0, +a) respectively. How much

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work is done in moving a test charge from p (7, 0, 0) to Q (-3, 0, 0)?

Q.25 A charge q is enclosed by a spherical surface of radius R. If the radius is reduced to half, how wouldthe electric flux through the surface change? (1 mark)

Q.26 A 500 c charge is at the centre of square of side 10 cm. find the work done in moving a charge of

10 c b/w two diagonally opposite points on the square? (1 mark)Q.27 Define ideal dipole. Deduce an expression for electric field intensity due to electric dipole at a point

on perpendicular bisector.? (3 marks)

Q.28 An electric field is uniform and has direction in the +ve x direction for +ve x and uniform with the

same magnitude but in theve x direction forve x. N/C for x > 0 andN/C, [x< 0]. A right circular cylinder of length 20 cm and radius 5 cm has its centre at the origin andits axis along x axis so that one face is at x = +10cm and other face is at x = -10cm. Find the netcharge within the cylinder? (3 marks)

Q.29 A charge Q is placed on a large spherical conducting shell of radius R another small conductingsphere of radius r carrying charge q is introduced inside the large shell and is placed at its centre.

Show that Charge will How from inner sphere to shell . when connected together Name the devicewhich works on this fact mention its application? (5 marks)

Q.30 Which orientation of an electric dipole in a uniform electric field would correspond to a stableequilibrium? (1 mark)

Q.31 Derive an expression for the energy stored in a parallel plate capacitor. (3 marks)

Q.32 Three identical capacitors c1, c2and c3of capacitance 6 F each are connected to a battery of 12v.Find : (3 marks)(a) charge on each capacitor?(b) equivalent capacitance of network?(c) energy stored in the network?

Q.33 Draw the electric field lines due to charge system such that q1 + q2 = 0? (1 mark)

Electrostatic Potential and Capacitance

Q.1 What would be the work done if a point charge +q is taken from a point A to the point B on thecircumference of a circle with another point charge +q? (1 mark)

Q.2 What will be effect of dielectric slab on capacitance when space b/w the plates of capacitor is filled

with diaelectric slab? (1 mark)

Q.3 Deduce an expression for potential due to electric dipole at a point lying on its Bisector. (2 marks)

Q.4 Three point charges of +2c; and -3c are Kept at the vertices A, B and C respectively of anequilateral triangle of side 20cm. what should be the sign and magnitude of the charge to be placedat the mid-point M of side BC. So that charge at a remains in equilibrium. (3 marks)

Q.5 Deduce an expression for energy density of a parallel plate capacitor. (3 marks)

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Q.6 A10F capacitor is charged by a 30V d.c and then connected across the uncharged 50F capacitor.Calculate (i) the final potential difference across the combination and initial & final energies. (3

marks)

Q.7 The electric field and potential at any point due to a point charge kept in air is 20NC- and 10JC-

respectively . Calculate the magnitude of charge. (2 marks)

Q.8 Show that electric field is always perpendicular to an equipotential surface. (2 marks)

Q.9 (i) Explain the principle of working of a parallel plate capacitor.

(ii) Deduce an expression for equivalent capacitance when two capacitors are connected inparallel. (5 marks)

Q.10 Show that energy stored in a parallel plate capacitor is 1/2CV2. (2 marks)

Q.11 The graph shows the variation of potential difference V across the plates of two capacitor A and Bverses charge Q stored . Which of the two has higher capacitance? (2 marks)

Q.12 Two chargesq and +q are located at A(0,0,-a) and B(0,0,+a) respectively . How much work is done

in moving a test charge from P(7,0,0) to Q (-3,0,0)? (2 marks)

Q.13 Derive an expression for capacitance of a parallel plate capacitor. (2 marks)

Q.14 What is the physical importance of the line integral of an electric field? (1 mark)

Q.15 Can two equipotential surfaces intersect each other. (1 mark)

Q.16 With the help of labeled diagram, describe the construction and working of Van de graphgenerator. (5 marks)

Q.17 An electric dipole of length 2cm is placed with its axis making an angle of 60owith respect to a

uniform electric field of 105N/C. If it exists a torque of 8 , Calculate (3 marks)

(i) Magnitude of charge

(ii) Potential energy of the dipoleQ.18 How much energy will be started in a capacitor? (1 mark)

Q.19 Draw the equipotential surfaces due to charge q > 0. (1 mark)

Q.20 A point charge q is placed at 0 is VPVQpositive or

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