CLASS 10 SCIENCE
ELECTRICITY — COMPLETE NOTES
Concepts • Formula Sheet • Solved Numericals • MCQs • Important Questions
1. Electric Current
Electric current is the rate of flow of electric charge through a conductor.
Formula: I = Q/t
I = current, Q = charge, t = time. SI unit of current is ampere (A). 1 A means 1 coulomb of charge flows through
a point in 1 second.
2. Electric Potential Difference
Potential difference between two points is the work done in moving a unit charge from one point to another.
Formula: V = W/Q
SI unit: volt (V). 1 volt = 1 joule/coulomb.
3. Circuit and Measuring Instruments
A closed conducting path is called an electric circuit. An ammeter measures current and is connected in
series. A voltmeter measures potential difference and is connected in parallel across a component.
4. Ohm’s Law
At constant temperature, the potential difference across a conductor is directly proportional to the current
through it.
V ∝ I → V = IR
R is resistance. SI unit: ohm (Ω). Therefore, R = V/I.
The V-I graph for an ohmic conductor is a straight line passing through the origin.
5. Resistance and Resistivity
Resistance is the opposition offered by a conductor to the flow of current. It depends on length, cross-sectional
area, nature of material and temperature.
R = ρl/A
ρ (rho) is resistivity, l is length and A is cross-sectional area. SI unit of resistivity: Ω m.
For the same material and temperature: longer wire → greater resistance; thicker wire → smaller resistance.
, 6. Combination of Resistors
Series combination
In series, the same current flows through every resistor.
R = R■ + R■ + R■
The potential difference is divided among the resistors. If one resistor breaks, the circuit is interrupted.
Parallel combination
In parallel, the potential difference across each branch is the same.
1/R = 1/R■ + 1/R■ + 1/R■
Current divides among branches. Domestic circuits generally use parallel connections so appliances can work
independently.
7. Heating Effect of Electric Current
When current passes through a resistance, electrical energy is converted into heat energy.
Joule’s law: H = I²Rt
Using V = IR, the equivalent forms are: H = VIt and H = (V²t)/R. SI unit of heat energy: joule (J).
Applications include electric heater, iron, toaster, kettle and fuse.
8. Electric Power
Electric power is the rate at which electrical energy is consumed.
P = VI = I²R = V²/R
SI unit: watt (W). 1 kW = 1000 W.
9. Electrical Energy and Commercial Unit
E = Pt
The commercial unit of electrical energy is kilowatt-hour (kWh).
1 kWh = 3.6 × 10■ J
10. Fuse and Electrical Safety
A fuse is a safety device connected in series with the live wire. It contains a wire with a relatively low melting
point. If excessive current flows, the fuse melts and breaks the circuit.
Overloading and short circuiting can cause excessive current and heating. Proper earthing and suitable
fuse/MCB help protect users and appliances.
ELECTRICITY — COMPLETE NOTES
Concepts • Formula Sheet • Solved Numericals • MCQs • Important Questions
1. Electric Current
Electric current is the rate of flow of electric charge through a conductor.
Formula: I = Q/t
I = current, Q = charge, t = time. SI unit of current is ampere (A). 1 A means 1 coulomb of charge flows through
a point in 1 second.
2. Electric Potential Difference
Potential difference between two points is the work done in moving a unit charge from one point to another.
Formula: V = W/Q
SI unit: volt (V). 1 volt = 1 joule/coulomb.
3. Circuit and Measuring Instruments
A closed conducting path is called an electric circuit. An ammeter measures current and is connected in
series. A voltmeter measures potential difference and is connected in parallel across a component.
4. Ohm’s Law
At constant temperature, the potential difference across a conductor is directly proportional to the current
through it.
V ∝ I → V = IR
R is resistance. SI unit: ohm (Ω). Therefore, R = V/I.
The V-I graph for an ohmic conductor is a straight line passing through the origin.
5. Resistance and Resistivity
Resistance is the opposition offered by a conductor to the flow of current. It depends on length, cross-sectional
area, nature of material and temperature.
R = ρl/A
ρ (rho) is resistivity, l is length and A is cross-sectional area. SI unit of resistivity: Ω m.
For the same material and temperature: longer wire → greater resistance; thicker wire → smaller resistance.
, 6. Combination of Resistors
Series combination
In series, the same current flows through every resistor.
R = R■ + R■ + R■
The potential difference is divided among the resistors. If one resistor breaks, the circuit is interrupted.
Parallel combination
In parallel, the potential difference across each branch is the same.
1/R = 1/R■ + 1/R■ + 1/R■
Current divides among branches. Domestic circuits generally use parallel connections so appliances can work
independently.
7. Heating Effect of Electric Current
When current passes through a resistance, electrical energy is converted into heat energy.
Joule’s law: H = I²Rt
Using V = IR, the equivalent forms are: H = VIt and H = (V²t)/R. SI unit of heat energy: joule (J).
Applications include electric heater, iron, toaster, kettle and fuse.
8. Electric Power
Electric power is the rate at which electrical energy is consumed.
P = VI = I²R = V²/R
SI unit: watt (W). 1 kW = 1000 W.
9. Electrical Energy and Commercial Unit
E = Pt
The commercial unit of electrical energy is kilowatt-hour (kWh).
1 kWh = 3.6 × 10■ J
10. Fuse and Electrical Safety
A fuse is a safety device connected in series with the live wire. It contains a wire with a relatively low melting
point. If excessive current flows, the fuse melts and breaks the circuit.
Overloading and short circuiting can cause excessive current and heating. Proper earthing and suitable
fuse/MCB help protect users and appliances.
