Current electricity

Question 1

Define Drift Velocity

Answer 1

avg velocity with which free electrons get drifted towards +ve end of the conductor under the influence of an external electric field applied.

Question 2

Define mobility

Answer 2

the magnitudr of the drift velocity acquired by it in a unit electric field.

Question 3

electrical conductivity

Answer 3

reciprocal of resistivity

Question 4

conductance

Answer 4

reciprocal of resistance

Question 5

factors affecting electrical conductivity

Answer 5

number density, nature of material, relaxation time and temperature.

Question 6

alpha sign for metals, alloys, semi conductors

Answer 6

++-

Question 7

criteria for greater accuracy of potentiometer

Answer 7

The potential gradient (slope) V/l must be as small as possible.

Question 8

behavior of Hg near 4K.

Answer 8

• super conductor.
• the resistance of Hg becomes 0.

Question 9

relaxation time

Answer 9

relaxation time of free electrons drifting in a conductor is the average time elapsed between two successive collisions.

Question 10

Why are alloys used for making standard resistance coils?

Answer 10

• Low value of temperature coefficient and the resistance of the alloy does not vary much with rise in temperature.
• High resistivity, so even a smaller length of the material is sufficient to design high standard resistance.

Question 11

Ohm’s law

Answer 11

It states that the current fluid in a conductor is directly proportional to the potential difference applied across the conductor provided physical conditions example temperature pressure etc remain the same.
- it is only applicable to those conducting material for which the vi graph is linear.

Question 12

Joule’s law of heating

Answer 12

Mathematically, amount of heat produced is proportional to the square of amount of current flowing through conductor electrical resistance of wire and time of current flow through it.

Question 13

Power

Answer 13

Rate of energy dissipation in a resistor is called power.

Question 14

Resistivity

Answer 14

Resistivity of a substance is defined as the resistance offered by a wire of the substance of one meter length and one square meter cross sectional area.

Question 15

Temperature dependence of resistance

Answer 15

• The resistance of a metallic conductor increases with increase in temperature.
• The resistance of a semiconductor decreases with increase in temperature

Question 16

Electric cell

Answer 16

It is a device which converts chemical energy into electrical energy.

Question 17

Terminal potential difference

Answer 17

The potential difference when current is being delivered to external load resistance.

Question 18

EMF of a cell

Answer 18

the maximum potential difference when no current is being drawn from the cell.

Question 19

Internal resistance

Answer 19

Internal resistance offers cell is the hindrance offered by the electrolyte of cell to the flow of current.

Question 20

factors affecting internal resistance

Answer 20

• Separation between electrodes.
• Area of immersed part of Electrodes.
• Concentration and nature of electrolyte.

Question 21

Kirchoff’s junction law

Answer 21

The algebraic sum of currents meeting at any junction in an electrical network is zero
- This law is based on conservation of charge.

Question 22

Kirchoff’s loop law

Answer 22

The algebraic sum of potential differences of different circuit elements of a closed circuit is zero.

Question 23

Wheatstone’s bridge

Answer 23

It is an arrangement of four Resistances pqrs forming a closed circuit. A potential difference is applied across terminals a and C. A galvanometer is connected across B and D.
the condition of null point is: -
P/Q = R/S