📘Class 10 Science – Chapter: Electricity Notes

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⚡ Electric Current and Circuit

What is Electric Current?

• The flow of electric charge is called electric current.

• It is carried by electrons in a conductor.

Formula:

• I = Q / t
  where,

  • I = Current (in amperes, A)

  • Q = Charge (in coulombs, C)

  • t = Time (in seconds, s)

Example:

• If 10 C of charge flows through a wire in 2 seconds, current = 10 / 2 = 5 A

Electric Circuit:

• A closed path in which electric current flows.

Circuit Symbols Table:

Component	Symbol
Cell	🔋
Battery	🔋🔋
Switch (Open)	⬛⬜
Switch (Closed)	⬛⬛
Resistor	zigzag line
Ammeter	A
Voltmeter	V
Connecting wires	straight line

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🔌 Potential Difference

• Work done to move a unit charge between two points.

Formula:

• V = W / Q
  where,

  • V = Potential difference (volt, V)

  • W = Work done (joule, J)

  • Q = Charge (coulomb, C)

Example:

• 10 J of work done in moving 2 C of charge: V = 10 / 2 = 5 V

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🔥 Ohm’s Law

• The current flowing through a conductor is directly proportional to the voltage across it at constant temperature.

Formula:

• V = I × R
  where,

  • V = Voltage (volt)

  • I = Current (ampere)

  • R = Resistance (ohm)

Graphical Representation:

• Straight line graph between V and I; slope = Resistance

Example:

• V = 10 V, I = 2 A → R = V/I = 10/2 = 5 Ω

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🧱 Resistance and Factors Affecting It

Resistance (R):

• The opposition offered by a conductor to the flow of electric current.

Factors Affecting Resistance:

Factor	Effect on Resistance
Length (L)	R ∝ L
Area (A)	R ∝ 1/A
Material	Depends on resistivity (ρ)
Temperature	Resistance increases with temp

Formula:

• R = ρ × (L / A)

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🔗 Resistors in Series and Parallel

Series Combination:

• Current is same, voltage divides.

Formula:

• R_total = R1 + R2 + R3 + …

Parallel Combination:

• Voltage is same, current divides.

Formula:

• 1 / R_total = 1 / R1 + 1 / R2 + 1 / R3 + …

Example Table:

Type	Formula	Effect on Resistance
Series	R_total = R1 + R2 + R3	Increases
Parallel	1/R_total = 1/R1 + 1/R2 + 1/R3	Decreases

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💡 Heating Effect of Electric Current

• When electric current flows through a conductor, it produces heat.

Joule’s Law of Heating:

• H = I² × R × t
  where,

  • H = Heat produced (joules)

  • I = Current (A)

  • R = Resistance (Ω)

  • t = Time (s)

Applications:

• Electric heater, iron, filament bulbs

Example:

• I = 2 A, R = 10 Ω, t = 5 s → H = 2² × 10 × 5 = 200 J

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🔋 Electric Power and Energy

Power:

• Rate at which electric work is done or energy is consumed.

Formula:

• P = V × I

• P = I² × R or P = V² / R

Commercial Unit of Energy:

• 1 kilowatt hour (kWh) = 1000 watt × 3600 seconds = 3.6 × 10⁶ J

Example:

• 1000 W heater used for 2 hours = 2 kWh

Table of Units:

Quantity	Unit	Symbol
Current	Ampere	A
Voltage	Volt	V
Resistance	Ohm	Ω
Power	Watt	W
Energy	Joule/kWh	J / kWh

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