current electricity

Question 1

Why Nichrome, Constantan and Manganin are used as standard?

Answer 1

as thier resitivity does not vary with temprature they are called standard resistors

Question 2

.What do you mean by internal resistance of a cell

Answer 2

Resistance offered by the electrolytes to the flow of current through it is
called internal resistance of the cell

Question 3

.Write the limitations of Ohm’s Law

Answer 3

Some materials and devices used in electric circuits do not obey
Ohm’s law and are called Non – Ohmic conductors.
▪ V-I graps of non – ohmic conductors not linear.
▪ Eg:- Semi conductors, Diodes , Transistors.

Question 4

.What do you mean by relaxation time?

Answer 4

The average time interval between two successive collisions of free
electrons is called relaxation time

Question 5

What do you mean by resistivity of a conductor. Write its unit.

Answer 5

The resistance of a conductor is directly proportional to length 𝑙 of the
conductor and inversely proportional to the cross-sectional area, A.
Unit of resistivity is Ωm.
Resistivity depends on the material of the conductor but not on its
dimensions.

Question 6

Define conductance

Answer 6

reciprocal of resistance

Question 7

.What are the factors on which the resistance of a conductor depends?
i

Answer 7

)The material of the conductor
ii)Length of the conductor , R ∝ 𝑙
iii) The area of cross section of the conductor

Question 8

.Define mobility .

Answer 8

Mobility µ defined as the magnitude of the drift velocity per unit electric
field.

Question 9

23.Differentiate emf and terminal voltage of a cell

Answer 9

The emf ε is the potential difference between the positive and negative
electrodes of a cell in an open circuit, i.e., when no current is flowing
through the cell.
The terminal voltage (V) is the potential difference between the positive
and negative electrodes of a cell in a closed circuit, i.e., when current is
flowing through the cell.

Question 10

Define current density. Write its unit.

Answer 10

Current per unit area ,taken normal to the current is called current density.

Question 11

State Kirchhoff’s junction rule or current law.

Answer 11

At any junction, the sum of the currents entering the junction is equal to the
sum of currents leaving the junction . ∑ I =0

or the sum of all the current meeting at tthe junction is zero

Question 12

State Kirchhoff’s loop rule or voltage law.

Answer 12

The algebraic sum of changes in potential around any closed loop of resistor etc is
zero. ∑ ΔV = 0