Important Equations and Definitions: Electricity | Science Class 10 PDF Download

Electric Current

• Definition: The flow of electric charge is known as Electric Current. It is carried by moving electrons through a conductor.
• Direction: By convention, electric current flows in the opposite direction to the movement of electrons.
• Electric Circuit: A continuous and closed path of electric current.

Expression of Electric Current

• Symbol: Electric current is denoted by the letter ‘I’.
• Formula: If a net electric charge (Q) flows through a conductor in time t, then

S.I. Units

• Electric Charge: Coulomb (C). 1 C=6×10¹⁸ electrons.
• Electric Current: Ampere (A). 1 A=1 C/s.

Small Quantities

• Milliampere (mA): 1 mA=10⁻³ A
• Microampere (μA): 1 μA=10⁻⁶ A

Instruments

• Ammeter: Measures electric current in a circuit.

Ammeter

Electric Charge and Potential

• Charge: Fundamental property of matter. Two types: Positive and Negative.
• Properties of Electric Charge:
  • Unlike charges attract, like charges repel.
  • Force between charges varies with the product of charges and inversely with the square of the distance.

Electric Potential and Potential Difference

• Electric Potential: Amount of electric potential energy at a point.
• Potential Difference (Voltage): Difference in electric potential energy between two points.
  V=W/Q
• S.I. Unit: Volt (V).

Instruments

• Voltmeter: Measures potential difference.

Voltmeter

• Galvanometer: Detects current in a circuit.

Galvanometer

Ohm’s Law

• Statement: Potential difference is directly proportional to electric current at constant temperature.
• 
• Resistance: Property resisting electric current. Unit: Ohm (ΩΩ).

Factors Affecting Resistance

• Nature: Good conductors vs. insulators.
• Length:R ∝ l
• Area of Cross Section: R ∝ 1/A
• Specific Resistance (Resistivity):. Unit: Ω⋅m

Combination of Resistors

Series Combination

• Total Resistance (R_s):R_s=R₁+R₂+R₃.

Parallel Combination

• Inverse of Total Resistance
  

Heating Effect of Electric Current

• Joule’s Law: H=I²Rt
• Applications: Electric bulb, electric iron, electric heater.

Electric Power

• Definition: Work done per unit time. P=VI.
• S.I. Unit: Watt (W). 1 W=1 V×1 A.
• Kilowatt: 1 kW=1000 W.

Electric Energy

• Definition: Amount of work done to maintain continuous electric current.
• Unit: Joule (J).

Electric Power Consumption

• Unit: Kilowatt-hour (kWh). 1 kWh=3.6×10⁶ J.

Conductors and Insulators

• Conductor: Allows flow of electrons. Low opposition to current.
• Insulator: Doesn't allow flow of electrons. High opposition to current.

Current Rating

• Definition: Maximum current without damaging the appliance.