Electricity Class 10 || Science|| Chapter 11 Notes

Electricity Class 10 ||Science|| Chapter 11 Notes

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Introduction to Electricity

Electricity plays a vital role in our daily lives, powering everything from household appliances to industrial machinery. This chapter explores the concepts of electric charge, current, potential difference, and the laws governing electric circuits.

1. Electric Charge and Current

• Electric Charge (Q):
  Electric charge is a fundamental property of matter. There are two types of charges: positive and negative. Like charges repel, and opposite charges attract each other.

• Electric Current (I):
  The rate of flow of electric charge through a conductor is called electric current. It is given by the formula:

  $$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">I</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>\frac{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">Q</span></span>}}{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">t</span></span>}}$$

  where:

  • $I$ = Electric current (in amperes)
  • $Q$ = Charge (in coulombs)
  • $t$ = Time (in seconds)

  The unit of current is the ampere (A), and 1 ampere is equal to 1 coulomb of charge passing through a conductor in 1 second.

• Conventional Current:
  Electric current is conventionally considered to flow from the positive terminal to the negative terminal of a battery, though the actual flow of electrons is in the opposite direction.

2. Electric Potential and Potential Difference

• Electric Potential:
  Electric potential at a point is the amount of work done in bringing a unit positive charge from infinity to that point.

• Potential Difference (V):
  The potential difference between two points in a circuit is the work done to move a unit positive charge from one point to the other.
  It is given by the formula:

  $$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">V</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>\frac{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">W</span></span>}}{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">Q</span></span>}}$$

  where:

  • $V$ = Potential difference (in volts)
  • $W$ = Work done (in joules)
  • $Q$ = Charge (in coulombs)

  The unit of potential difference is volt (V). One volt is defined as 1 joule of work done to move 1 coulomb of charge.

• Voltmeter:
  A voltmeter is used to measure the potential difference across a component in a circuit. It is always connected in parallel.

3. Ohm’s Law

Ohm’s Law defines the relationship between potential difference (V), current (I), and resistance (R) in an electrical circuit. According to Ohm’s law:

$$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">V</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">I</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\times </span></span>\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}$$

where:

• $V$ = Potential difference (in volts)
• $I$ = Current (in amperes)
• $R$ = Resistance (in ohms)

4. Resistance and Resistivity

• Resistance (R):
  Resistance is a property of a material that opposes the flow of electric current through it. The unit of resistance is the ohm (Ω).

• Factors Affecting Resistance:

  1. Length of the conductor: Resistance is directly proportional to the length of the conductor.$$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\propto </span></span>\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">L</span></span>}$$
  2. Cross-sectional area: Resistance is inversely proportional to the cross-sectional area of the conductor.$$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\propto </span></span>\frac{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">1</span></span>}}{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">A</span></span>}}$$
  3. Nature of material: Different materials have different resistivities.
  4. Temperature: Resistance generally increases with an increase in temperature.

• Resistivity (ρ):
  Resistivity is the inherent property of a material and is given by the formula:

  $$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\rho </span></span>}\frac{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">L</span></span>}}{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">A</span></span>}}$$

  where:

  • $\rho$ = Resistivity of the material
  • $L$ = Length of the conductor
  • $A$ = Area of cross-section

  The unit of resistivity is ohm meter (Ωm).

5. Series and Parallel Circuits

• Series Circuit:
  In a series circuit, resistors are connected end-to-end, and the current flows through each resistor one after the other.

  • The current is the same through all resistors.
  • The total resistance is the sum of the individual resistances:$${\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}_{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">total</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">1</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">3</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span><span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\dots </span></span>$$
  • The potential difference across the circuit is the sum of the potential differences across each resistor.

• Parallel Circuit:
  In a parallel circuit, resistors are connected across the same two points, providing multiple pathways for the current.

  • The potential difference across each resistor is the same.
  • The total current is the sum of the currents through each resistor.
  • The total resistance in a parallel circuit is given by:$$\frac{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">1</span></span>}}{{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}_{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">total</span></span>}}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>\frac{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">1</span></span>}}{{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">1</span></span>}}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>\frac{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">1</span></span>}}{{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>\frac{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">1</span></span>}}{{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">3</span></span>}}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span><span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\dots </span></span>$$

6. Heating Effect of Electric Current

When an electric current flows through a conductor with resistance, electrical energy is converted into heat. This is called the heating effect of electric current. It is the basis for appliances like electric heaters, toasters, and irons.

• The heat produced in a conductor is given by Joule’s Law of Heating:$$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">H</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">I</span></span>}}^{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">t</span></span>}$$where:
  • $H$ = Heat energy (in joules)
  • $I$ = Current (in amperes)
  • $R$ = Resistance (in ohms)
  • $t$ = Time (in seconds)

7. Electric Power

Electric power is the rate at which electrical energy is consumed or converted into other forms of energy, such as heat, light, or mechanical energy.

• The formula for electric power is:

  $$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">P</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">V</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\times </span></span>\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">I</span></span>}$$

  where:

  • $P$ = Power (in watts)
  • $V$ = Potential difference (in volts)
  • $I$ = Current (in amperes)

  Alternatively, using Ohm's law:

  $$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">P</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">I</span></span>}}^{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">or</span></span>}\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">P</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">=</span></span>\frac{{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">V</span></span>}}^{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}}{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">R</span></span>}}$$

  The unit of power is the watt (W). One watt is defined as the power consumed when 1 ampere of current flows across a potential difference of 1 volt.

• Commercial Unit of Electrical Energy:
  The commercial unit of electrical energy is the kilowatt-hour (kWh), also known as a unit of electricity.
  1 kilowatt-hour (kWh) = 1000 watt-hours = 3.6 × 10⁶ joules

Conclusion

This chapter gives a comprehensive overview of the basics of electricity, including the flow of electric current, the relationship between current, voltage, and resistance (Ohm’s Law), the heating effect of electric current, and how electrical circuits are arranged. Understanding these fundamental principles is essential for both theoretical knowledge and practical applications.