Download INDIAN SCHOOL, ALWADI ALKABIR DEPARTMENT OF SCIENCE

INDIAN SCHOOL, ALWADI ALKABIR
DEPARTMENT OF SCIENCE 2016 -17
CLASS – XII
PHYSICS
DATE- 03/04/2017
WS. NO. 1
UNIT1-ELECTROSTATICS
1. If the radius of the Gaussian surface enclosing a charge is halved, how does the electric flux through
the Gaussian surface change?
(1)
A. Electric flux is independent of the radius. Electric flux remains constant.
2. Define the term electric dipole moment of a dipole. State it’s S.I.Unit.
(1)
A. It is defined as the product of either charge and the length of electric dipole
P = q X 2a. It is a vector quantity whose direction from negative to positive charge.
3. Which orientation of an electric dipole in a uniform electric field would correspond to stable
equilibrium?
(1)
A. When the electric dipole is in the direction of the electric field
4. Two point charges 20 X 10-6 C and -4 X 10-6 C are separated by a distance of 50cm in air.
(i)
Find the point on the line joining the charges, where the electric potential is zero.?
(ii)
Also find the electrostatic potential energy of the system.
(2)
5. Two point charges 4Q, Q are separated by 1m in air. At what point on the line joining the charges is
the electric field intensity zero?
Also calculate the electrostatic potential energy of the system of charges, taking the value of
charge, Q = 2 X 10-7C.
(2)
6. Two point charges 4C and -2C are separated by a distance of 1m in air. Calculate at what point
on the line joining the two charges is the electric potential zero.
(2)
7. The electric field and electric potential at any point due to a point charge kept in air is 20N/C and 10
V respectively. Compute the magnitude of this charge.
(2)
8. The given graph shows the variation of charge q Vs potential difference V for two capacitors C 1 and
C2. The two capacitors have same plate separation but the plate area of C2 is double than that of C1.
Which of the lines in the graph correspond to C1 and C2 and why?
(2)
9. Two capacitors of capacitance 6F and 12F are connected in series with a battery. The voltage
across the 6F capacitor is 2V. Compute the total battery voltage.
(2)
10. A parallel capacitor with air between the plates has a capacitance of 8pF. 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.
(2)
11. A point charge ‘q’ is placed at O as shown in the figure. Is Vp-Vqpositive or negative when (i) q > 0
(ii) q <0? Justify your answer.
(2)
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12. Define electric flux. Write its S.I. units. A spherical rubber balloon carries a charge that is uniformly
distributed over its surface. As the balloon is blown up and increases in size, how does the total
electric flux coming out of the surface charge? Give reason.
(2)
13. State Gauss’s theorem in electrostatics. Apply this theorem to derive an expression for electric field
intensity at a point near an infinitely long straight charged wire.
(3)
14. Explain the underlying principle of working of a parallel plate capacitor. If two similar plates, each
of area A having surface charge densities + and - are separated by a distance d in air, write
expression for
(i)
the electric field at points between the two plates.
(ii)
The potential difference between the plates.
(iii)
The capacitance of the capacitor so formed.
(3)
15. Using Gauss’s theorem, show mathematically that for any point outside the shell, the field due to a
uniformly charged thin spherical shell is the same as if the entire charge of the shell is concentrated
at the centre. Why do you expect the electric field inside the shell to be zero according to this
theorem?
(3)
16. Deduce an expression for the electric potential due to an electric dipole at any point on its axis.
Mention one contrasting feature of electric potential of a dipole at a point as compared to that due
to a single charge.
(3)
17. What is electric flux? Write its SI units. Using Gauss’s theorem, deduce an expression for the
electric field at a point due to a uniformly charged infinite plane sheet.
(3)
18. State Gauss’s theorem in electrostatics. Apply this theorem to derive an expression for electric field
intensity at a point outside a uniformly charged thin spherical shell.
(3)
19. Derive an expression for the energy stored in a parallel plate capacitor.
On charging a parallel plate capacitor to a potential V, the spacing between the plates is halved, and
a dielectric medium of r= 10 is introduced between the plates, without disconnecting the d.c.
source. Explain, using suitable expressions, how the (i) capacitance, (ii) electric field and (iii) energy
density of the capacitor change.
(5)
20. (a)Define electric flux. Write its S.I.units
(b) The electric field components due to a charge inside the cube of side 0.1 m are as shown.
Ex = x,
where = 500 N/Cm Ey= 0,Ez=0.
Calculate (i) the flux through the cube, and (ii) the charge inside the cube.
(5)
Prepared by Manu J Yohannan
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