7/28/2019 Elecrostatics Part 1

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WORKSHEET

CLASS: XII MONTH:SUBJECT: PHYSICS TOPIC: ELECTRIC

CHARGES & FIELD1. If two charges are located 10 cm apart, it feels an attractive force of 12 units. What will

be the force between them when they are placed 5 cm apart?

2. The dielectric constant of pure water is 81. What will be the absolute permittivity of

water?3. Which physical quantity has unit NC

-1? It is a scalar or a vector quantity?

4. What is the direction of the electric field due to an electric dipole at a point on its

(i) axial line (ii) equatorial line?5. If the electric field is given by 6i + 3j + 4k. Calculate the electric flux through a surface

of area 20 units lying in YZ plane?6. A hollow conducting sphere of radius 8 cm is given a charge of 16 C. What is the

electric field intensity (i) at the center of the sphere (ii) on the outer surface of the

sphere.7. An electric dipole when held at 30

0w.r.t a uniform electric field of 10

4NC

-1

experiences a torque of 8 x 10-26

Nm. Calculate the dipole moment of the dipole.

8. An electric dipole is held in a uniform electric field.(i) Show that no translatory force acts on it.(ii) Derive an expression for the torque acting on it.(iii) The dipole is aligned parallel to the field. Calculate the work done in rotating

it through 1800.

9. A system has two charges qA = 2.5 x 10-7

C & qB = -2.5 x 10-7

C located at pointsA : (0,0,-15 cm) & B : (0,0,+15 cm), resp. What are the total charge & electric dipole

moment of the system.10. (a) Give two properties of electric lines of force.

(b) Sketch the electric lines of force when (i) q1q2 < 0 (ii) q > 0.

11. Two point charges of +5 x 10-19

C & +20 x 10-19

C are separated by a distance of2 m. Find the point on the line joining them at which electric field intensity is zero.

12. Define electric field at a point. Two point charges +q & -q are placed at a distance

2a apart. Calculate the electric field at a point P situated at a distance r along the

perpendicular bisector of the line joining the charges. What is the field when r>>a?13. State Gausss theorem in electrostatics and express it mathematically. Using it, derive

an expression for electric field at a point near a thin infinite plane sheet of electriccharge. How does this electric field change for a uniformly thick sheet of charge?

14. Two opposite corners of a square carry Q charge each & the other two oppositecorners of the square carry q charge each. If the resultant force on Q is zero, how

are Q & q related?

15. Two charges q1 = +20 x 10-6

C & q2 = -20 x 10-6

C are placed 20 cm apart at pointsA & B resp. Calculate the electric field strength at point C, 20 cm away from both A

& B.