Electricity

Notes

1. Electricity

Electricity is the flow of electric charge through a conductor.

Electric Charge (Q)

SI Unit: Coulomb (C)

Symbol: Q

Charge on one electron = 1.6 × 10⁻¹⁹ C

2. Electric Current (I)

Current is the rate of flow of electric charge through a conductor.

Formula

I=

t

Q

​

Where,

I = Current (Ampere)

Q = Charge (Coulomb)

t = Time (Second)

SI Unit

Ampere (A)

Instrument

Ammeter

Remember

Ammeter is connected in series.

It has very low resistance.

3. Electric Potential Difference (V)

Work done to move one unit charge from one point to another.

Formula

V=

Q

W

​

Unit:

Volt (V)

Instrument:

Voltmeter

Connected:

Parallel

High resistance.

4. Electric Circuit

A closed conducting path through which current flows.

Types

Open Circuit → Current does not flow.

Closed Circuit → Current flows.

5. Ohm's Law

At constant temperature,

Current is directly proportional to potential difference.

V∝I

or

V=IR

Where

V = Voltage

I = Current

R = Resistance

V-I Graph

Straight line passing through origin.

6. Resistance (R)

Resistance opposes the flow of current.

Unit:

Ohm (Ω)

1 Ohm

If 1 Volt produces 1 Ampere current,

Resistance = 1 Ohm.

7. Factors Affecting Resistance

Resistance depends upon

Length (L)

Area of cross-section (A)

Nature of material

Temperature

Formula

R=ρ

A

L

​

Where

ρ = Resistivity

Unit of resistivity

Ω m

8. Resistivity

Property of material.

Copper → Low resistivity

Nichrome → High resistivity

9. Combination of Resistors

(A) Series Combination

Current remains same.

Voltage divides.

Equivalent resistance

R=R

1

​

+R

2

​

+R

3

​

Applications

Decorative lights (older type)

Simple circuits

(B) Parallel Combination

Voltage remains same.

Current divides.

Formula

R

1

​

=

R

1

​

1

​

+

R

2

​

1

​

+

R

3

​

1

​

Advantages

Independent working

Equal voltage

Used in homes

10. Heating Effect of Electric Current

When current flows,

Electrical energy converts into…