“Electricity” is one of the important chapters in SSLC Science. This chapter explains electric current, electric circuit, electric potential, resistance, Ohm’s law, Joule’s law of heating, series and parallel circuits, thermal effects of electric current and their practical applications. This article is prepared based on the uploaded English LBA document.
Learning Points
This chapter mainly includes:
- Electric current, electric circuit, electric potential, potential difference, electric charge and their SI units
- Electric circuit and circuit symbols
- Ohm’s law and Joule’s law of heating
- Resistance of conductor
- Series and parallel combination of resistors
- Advantages and disadvantages of series and parallel circuits
- Thermal effects of electric current and applications
These learning points are listed in the LBA document.
Electric Current
The rate of flow of electric charges through a conductor is called Electric Current.
Formula:
$$I = \frac{Q}{t}$$
Where:
- I = Electric current
- Q = Electric charge
- t = Time
SI Unit:
Ampere (A)
Electric Charge
Electric charge is the quantity of electricity flowing through a conductor.
SI Unit:
Coulomb (C)
1 Coulomb = Charge carried by approximately:
$$6.25 * 10^{18} electrons$$
Electric Potential and Potential Difference
Electric Potential
Work done in bringing a unit positive charge from infinity to a point is called Electric Potential.
Potential Difference
The work done in moving unit charge from one point to another is called Potential Difference.
Formula:
$$V = \frac{W}{Q}$$
SI Unit:
Volt (V)
Electric Circuit
A closed conducting path through which electric current flows is called an Electric Circuit.
Basic components:
- Electric cell
- Bulb
- Switch (Key)
- Connecting wires
- Ammeter
- Voltmeter
Resistance of a Conductor
The property of a conductor that opposes the flow of electric charges is called Resistance.
Formula:
$$R = \frac{V}{I}$$
SI Unit:
Ohm (Ω)
Ohm’s Law
Ohm’s law states that:
At constant temperature, current flowing through a conductor is directly proportional to the potential difference across it.
Formula:
V = IR
Ohm’s law gives relation between:
- Potential difference (V)
- Current (I)
- Resistance (R)
Factors Affecting Resistance
Resistance depends on:
- Length of conductor
$$R \propto l$$
- Area of cross-section
$$R \propto \frac{l}{A}$$
- Nature of material
- Temperature
Combined relation:
$$R = \rho \frac{l}{A}$$
Where:
- ρ = Resistivity
- l = Length
- A = Area of cross-section
Resistivity
Resistivity is the resistance offered by a conductor of unit length and unit cross-sectional area.
SI Unit:
Ohm-metre (Ωm)
Silver has very low resistivity and is a good conductor.
Nichrome has high resistivity and is used in heating devices.
Series Combination of Resistors
When resistors are connected one after another in same path, it is called Series Connection.
Equivalent resistance:
$$R_S = R_1 + R_2 + R_3$$
Characteristics:
- Same current flows through all resistors
- Total resistance increases
Parallel Combination of Resistors
When resistors are connected across the same potential difference, it is called Parallel Connection.
Equivalent resistance:
$$\frac{1}{R_P} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$$
Characteristics:
- Same potential difference across each resistor
- Total resistance decreases
Joule’s Law of Heating
Joule’s law states that heat produced in a conductor is:
- Directly proportional to square of current
- Directly proportional to resistance
- Directly proportional to time
Formula:
$$H = I^2 Rt$$
Applications:
- Electric iron
- Heater
- Toaster
- Electric kettle
Electric Power
Electric power is the rate of consumption of electrical energy.
Formula:
P = VI
Other formulas:
$$P = I^2 R$$
$$P = \frac{V^2}{R}$$
SI Unit:
Watt (W)
Electric Energy
Electrical energy consumed:
E = Pt
Commercial Unit:
1 kWh (Unit)
Relation:
$$1kWh = 3.6 * 10^6 J$$
Fuse
Fuse is a safety device used to protect electrical appliances from overload and short circuit.
Functions:
- Prevents damage to appliances
- Protects circuits from excessive current
Fuse is connected in series in domestic circuits.
Electric Bulb
Tungsten is used as filament in electric bulb because:
- High melting point
- High resistivity
- Produces more heat without melting
Bulbs are filled with nitrogen or argon gas to prevent oxidation of filament.
Important Exam Questions
One Mark Questions
- What is electric current?
- Define 1 ohm.
- What is resistivity?
- Name SI unit of power.
Two Mark Questions
- State Ohm’s law.
- Explain Joule’s law of heating.
- Differentiate series and parallel circuits.
Three Mark Questions
- Explain the working of electric bulbs.
- Explain function of fuse.
- Explain electric resistance and resistivity.
Four Mark Questions
- Derive Ohm’s law.
- Explain series and parallel combinations.
- Solve numerical problems on electric power and energy.
These questions are repeatedly asked in examinations.
Preparation Tips for Students
- Learn all formulas carefully
- Practice numerical problems regularly
- Revise circuit symbols and diagrams
- Study series and parallel circuits clearly
- Practice Joule’s law and power calculations
Conclusion
“Electricity” is an important scoring chapter in SSLC Science. Understanding current, resistance, circuits, Ohm’s law and electric power helps students score better marks in examinations.
