Electricity

Question 1

Atomic Structure

Answer 1

An atom has a positively charged nucleus and negatively charged electrons revolving
around it.

Valence electrons in metals are free to move within the conductor and constitute an
electric current

Question 2

Charge

Answer 2

The charge is an intrinsic property of matter by virtue of which it can exert electromagnetic force

Question 3

Conductors and Insulators

Answer 3

A substance which offers comparatively less opposition to the flow of current is known as
conductors and substances which offer larger opposition are insulators.

Question 4

Electric Potential and Potential Difference

Answer 4

The electric potential at a point is defined as work done in bringing a unit positive charge
from infinity to that point. The potential difference between two points is defined as the
difference in electric potentials at the two given points

Question 5

Models of Electric Current

Answer 5

Electric Current(I)
Flow of electric charges is called electric current, i.e, I = Q/t

Electron sea model
Electric current in a solid conductor is due to drift of a ‘sea’ of free electrons, which are free
to jump onto any neighbouring atom.

Question 6

Drift velocity of Electron

Answer 6

Average velocity which an electron attains inside a metallic conductor due to the application of an electric field due to the potential difference.

Question 7

Battery and its working

Answer 7

A cell is a source of potential difference, which is created inside it due to internal chemical
reactions.

At anode: Cu(s) ⇌ Cu2+(aq) + 2e−
At cathode: Ag(aq) + 2e− ⇌ 2Ag(s)

A combination of cells is called a battery

Question 8

Electric Circuit

Answer 8

A closed-loop path which a current take is called an electric circuit.
Representation of an electric circuit through symbols is called a circuit diagram.

Question 9

Resistance and Ohm’s Law

Answer 9

Ohm’s law
The current flowing through an ohmic conductor is directly proportional to the applied
potential difference between the two ends of the conductor

Resistance
Resistance is a measure of the opposition offered to the current flow in an electric circuit.

Question 10

Factors affecting Resistance & How they affect

Answer 10

Resistance is:

*directly proportional to the length of the conductor.
*directly proportional to nature of the conductor.
*directly proportional to the temperature of the conductor.
*inversely proportional to the cross-sectional area of the conductor.

Question 11

Resistivity

Answer 11

The electrical resistance offered by a substance of unit length and unit cross-sectional area
is called resistivity.

Question 12

Ohmic and Non-Ohmic resistors

Answer 12

Resistors which follow Ohm’s Law are called Ohmic resistors, and those which do not follow it are called Non-Ohmic resistors.

Question 13

Superconductors

Answer 13

Conductors which offer zero resistance to the flow of current are called superconductors

Question 14

Combination of resistors

Answer 14

Two resistors are said to be combined in series if they carry the same current.
Two resistors are said to be combined in parallel if the same potential difference is
applied to them.

Question 15

Equivalent Resistance of a system of resistors

Answer 15

The equivalent resistance of two resistors is given as:
In series, Req = R1 + R2
In parallel, 1/Req= 1/R1 + 1/R2

Question 16

EMF and Terminal Voltage

Answer 16

EMF: The potential difference between the two terminals of a cell, when there is no
current flowing through the circuit.
Terminal voltage: The potential difference between the two terminals of a cell, when
current is flowing through the circuit.
EMF and Terminal voltage

Question 17

Electric Power and AC
Heating Effect of Current
Joule’s Law:

Answer 17

Heat (H) ∝ square of the current (I).
H ∝ Resistance of the given circuit.
H ∝ Time (t) for which current flows through the conductor.

When a potential difference is established, it causes electrons to move i.e. flow of current.

Question 18

Electric Power

Answer 18

The rate of doing work or rate of consumption of electrical energy is called Electric Power. If W is work done in time t, then P = .w/t
S.I unit is Watt(W). One watt of power is consumed when 1 A of current flows at a potential difference of 1(2) V.

The commercial unit of electrical energy is kilowatt-hour (kWh).

1kWh = 3, 600, 000J = 3.6 × 106J
Represented as
P = I R and P = v2/R

*One kilowatt-hour is defined as the amount of energy consumed when 1kW of power is used for 1 hour.