Class 10 Science Electricity Notes

Introduction

• Electricity is the flow of electric charge (usually electrons) through a conductor.
• It powers many devices and is essential in everyday life.

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1. Electric Current

• Definition: The flow of electric charge through a conductor.
• SI unit of current: Ampere (A)
• Formula:
  $I = \frac{Q}{t}$I=tQ​
  Where:
  • $I$I = Current (in amperes, A)
  • $Q$Q = Charge (in coulombs, C)
  • $t$t = Time (in seconds, s)

Direction of Current

• Conventional Current: Flows from positive to negative (opposite to electron flow).

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2. Potential Difference (Voltage)

• Definition: The difference in electric potential energy between two points in a circuit.
• SI unit of voltage: Volt (V)
• Formula:
  $V = \frac{W}{Q}$V=QW​
  Where:
  • $V$V = Voltage (in volts, V)
  • $W$W = Work done (in joules, J)
  • $Q$Q = Charge (in coulombs, C)
• Potential Difference causes the flow of current in a circuit.

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3. Ohm’s Law

• Statement: The current flowing through a conductor is directly proportional to the potential difference across it and inversely proportional to its resistance.
• Formula:
  $V = I \times R$V=I×R
  Where:
  • $V$V = Voltage (in volts, V)
  • $I$I = Current (in amperes, A)
  • $R$R = Resistance (in ohms, Ω)
• Resistance: The opposition to the flow of current.
• SI unit of resistance: Ohm (Ω)

Factors Affecting Resistance

1. Material: Conductors have low resistance (e.g., copper), while insulators have high resistance.
2. Length: Longer conductors have higher resistance.
3. Area of Cross-Section: Wider conductors have lower resistance.
4. Temperature: Higher temperature increases resistance.

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4. Resistance in Series and Parallel Circuits

Series Circuit

• Current is the same through all components.
• Total resistance: $R_{total} = R_1 + R_2 + \dots$Rtotal​=R1​+R2​+…
• Total Voltage: $V_{total} = V_1 + V_2 + \dots$Vtotal​=V1​+V2​+…

Parallel Circuit

• Voltage is the same across all components.
• Total resistance:
  $\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \dots$Rtotal​1​=R1​1​+R2​1​+…
• Total Current: $I_{total} = I_1 + I_2 + \dots$Itotal​=I1​+I2​+…

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5. Electric Power

• Definition: The rate at which electrical energy is consumed or converted into other forms of energy.
• Formula:
  $P = V \times I$P=V×I
  Where:
  • $P$P = Power (in watts, W)
  • $V$V = Voltage (in volts, V)
  • $I$I = Current (in amperes, A)
• Unit of power: Watt (W)
• 1 kW = 1000 W
• Energy consumed (in kilowatt-hours):
  $E = P \times t$E=P×t
  Where:
  • $E$E = Energy (in kWh)
  • $P$P = Power (in kW)
  • $t$t = Time (in hours)

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6. Heating Effect of Electric Current

• When current flows through a conductor, it produces heat.
• Joule’s Law:
  $H = I^2 \times R \times t$H=I2×R×t
  Where:
  • $H$H = Heat produced (in joules)
  • $I$I = Current (in amperes, A)
  • $R$R = Resistance (in ohms, Ω)
  • $t$t = Time (in seconds, s)
• Applications of heating effect: Electric heaters, fuses, and electric bulbs.