Unit – 1 ELECTROSTATICS 2022-2023
Q.1 Give the SI units of (i) electric moment of a dipole. (ii) Electric field intensity (2003)
Q.2 Two point charges q1 = 3 C and q2 = -3 C are located 20 cm apart in vacuum
(i) Find the electric field at the midpoint of the line AB joining the two charges.
(ii) If a –ve test charge of magnitude 1.5 x 10 –9 C is placed at the centre find the force
experienced by the test charge. (2003)
Q.3 Obtain the expression for the capacitance of a parallel plate capacitor. Three capacitors of
capacitance c1, c2, c3 are connected (i) in series (ii) in parallel show that the energy stored in
the series combination is the same as that in the parallel combination.
Q.4 Two similarly and equally charged identical metal spheres A & B repel each other with a
force of 2x10–5 N. A third identical uncharged sphere is touched with A & then placed at the
midpoint between A & B. Calculate the net electric force on C. (2003)
Q.5 An electric dipole of length 4 cm, when placed with its axis making an angle of 600
with a
uniform electric field experiences a torque of 4 3 Nm. Calculate the (i) magnitude of the
electric field, (ii) potential energy of the dipole, if the dipole has charges of 8 nC. (2004)
Q.6 State Gauss’ theorem in electrostatics. Using this theorem, derive an expression for the
electric field intensity due to an infinite plane sheet of charge of charge of charge density
C/m2
.
Q.7 A 10 F capacitor is charged by a 30 V d.c. supply and then connected across an
uncharged 50 F capacitor. Calculate (i) the final potential difference across the
combination, and (ii) the initial and final energies. How will you account for the difference in
energy? 2004
Q.8 An electrostatic field line cannot be discontinuous. Why? 2005
Q.9 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.
Q.10 State Gauss’ theorem. Apply this theorem to obtain the expression for the electric field
intensity at a point due to an infinitely long, thin, uniformly charged straight wire.
Q.11 A parallel plate capacitor is to be designed with a voltage rating 1 kV using a material of
dielectric constant 3 and dielectric strength about 107Vm–1. For safety we would like the field
never to exceed say, 10% of the dipole strength. What minimum area of the plates is
required to have a capacitance of 50 pF?
Q.12 A 4 F capacitor is charged by a 200 V supply. The supply is then disconnected and the
charged capacitor is connected to another uncharged 2 F capacitor. How much
electrostatic energy of the first capacitor is lost in the process of attainting the steady
situation?
Q.13 Two fixed point charges +4e and +e units are separated by a distance a where should the
third point charge be placed for it to be equilibrium.
Q.14 Define the term electric dipole moment. Is it a scalar or vector quantity? 2006
Q.15 A point charge ‘q’ is placed at O as shown in the figure.
O P Q
Is Vp – Vq positive or negative when (i) q> 0, (ii) q <0 ? Justify your answer. 2006
Q.16 Two capacitors of capacitance 6 F and 12 F are connected in series with a battery.
The voltage across the 6 F capacitor is 2 V. Compute the total battery voltage.
Q.17 A parallel plated capacitor with air between the plates has a capacitance of 8 pF. The
separation between the plates is now reduced by half and the space between them is filled
with a medium of dielectric constant 5. Calculate the value of capacitance of the capacitor in
the second case.
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