Static Electricity

Question 1

What is meant by “Electrostatics:?

Answer 1

It is the branch of Physics, that deals with the forces between the charges at rest. ( Electric fields/ Potentials due to charges at rest)

Question 2

What is the origin of electricity/ electric force/ electric charge?

Answer 2

Electrum ( Greek name for amber) . It is the origin for may familiar words like: electricity/ electric force/ electric charge

Question 3

Define Frictional Electricity?

Answer 3

An object is rubbed by another object, and the objects are charged by this rubbing process. It is said to possess frictional or static electricity.

Question 4

What are the methods of producing charge on a body?

Answer 4

1. By Friction : Rubbing process( both bodies acquire equal but opposite charges)
2. By Induction: Acquiring charge without physical contact ( Opposite kind of charge produced)
3. By Conduction: Acquiring charge by physical contact ( similar type of charge produced on bodies)

Question 5

What are the basic properties of Electric charges ?

Answer 5

i) Additive in nature
ii) Quantized
iii) Conserved

Question 6

State Coulomb’s law in Electrostatics.

Answer 6

It states that, the force of attraction / repulsion between two stationary point charges is directly proportional to the product of the magnitude of the charges and inversely proportional to the square of the distance between them.

Question 7

Define the term “ Relative permittivity”

Answer 7

The ratio of the force between two charges placed at a certain distance apart in air ( vacuum) to the force between the same two charges placed the same distance apart in that medium. ( dimensionless quantity)

Question 8

State Principle of superposition of electric forces.

Answer 8

The net force acting on a given charge due to a number of all other charges around it is the vector sum of individual forces acting on it due to all the charges.

Question 9

Define Electric field and its Intensity?

Answer 9

Electric field: The space / region/ vicinity around a charge in which its electrostatic influence can be felt .
Field intensity: The force experienced on a unit positive test charge at that point.

Question 10

Define Electric field line?

Answer 10

An imaginary line of force ( smooth curve / straight line) through which a unit positive test charge feel free to do so (move) . And the tangent drawn( on a smooth curve) indicates the direction of force acting on it placed at that point.

Question 11

What are the properties of electric lines of force?

Answer 11

1. It is a continuous / smooth curve originating fro +ve charge and ending at a -ve charge.
2. The tangent to the line of force at any point gives the direction of electric field intensity at that point.
3. No two electric field lines can cross each other.
4. Electric lines of force do not pass through a charged conductor.
5. The lines of force always originates and terminates normally to the surface of a charged conductor.
6. Have tendency to contract lengthwise ( shows attraction) and expands laterally (shows repulsion) .

Question 12

Define Electric Potential at a point.

Answer 12

It is defined as the amount of work done in moving a unit positive charge from infinity to that point without accelerating it.

Question 13

Define Electric potential difference.

Answer 13

It is the amount of work done in moving a unit positive charge from one point to another point without accelerating it.

Question 14

What is meant by Potential gradient?

Answer 14

It is the rate of charge of potential with distance at a point .

Question 15

What is meant by Potential gradient?

Answer 15

It is the rate of charge of potential with distance at a point .

Question 16

Define “Equipotential surface” and mention its properties.

Answer 16

The potential is same every point on its surface or potential difference between any two points is zero.
Properties: No work is done in moving charge over an equipotential surface. Electric field is normal to the surface. No two equipotential surfaces can intersect each other.

Question 17

Define “ Capacitance “ of a conductor

Answer 17

It is defined as the measure of its ability to hold electric charge.

Question 18

What are the dependent factors for the capacitance of a conductor

Answer 18

(i) Size and shape
(ii) Nature of the surrounding medium
(iii) Presence of other conductors in its neighbourhood

Question 19

Define Capacitor.

Answer 19

It is an assembly of two conductors separated by an insulating medium and it is used to store electrical energy by accumulating charge on the conductors.

Question 20

What is the effect of dielectric , when the battery is disconnected from the capacitor?

Answer 20

(i) Charge: remains same.
(ii) Electric Field: Decreases (reduces)
(iii) Potential difference: Decreases
(iv) Capacitance: Increases
(v) Energy Stored: Decreases.

Question 21

What is the effect of dielectric , when the battery is remains connected from the capacitor?

Answer 21

(i) Charge: Increases.
(ii) Electric Field: Un-changed
(iii) Potential difference: Remains same.
(iv) Capacitance: Increases
(v) Energy Stored: Increases.

Question 22

Define Dielectrics

Answer 22

A non conducting substance

May be non-polar or polar

Question 23

Define Polar and Nonpolar dielectrics with Examples.

Answer 23

(i) Polar : Polar molecules are those molecules in which the centers of +ve and -ve charges are separated, even when there is no electric field. (Having permanent dipole moment) EX: water..etc
(ii) Non-Polar: Non-Polar molecules are those molecules in which the centers of +ve and -ve charges are coincieded . (Having no permanent dipole moment) EX: Oxygen, Hydrogen ..etc

Question 24

Define (i) Dielectric constant (ii) Polarisation density (iii) Electrostatic shielding

Answer 24

(i) Dielectric constant : The ratio of strength of the applied electric field to the strength of the reduced value of the electric field on placing it between the plates of the capacitor.
(ii) Polarisation density: It is the induced dipole moment developed per unit volume.
(iii) Electrostatic shielding : The Phenomenon of protecting a certain region from the external electric field .