Electricity powers our homes, schools, hospitals, and industries.
Fans rotate, bulbs glow, heaters become hot, and mobiles charge because electric current flows through circuits.
This chapter explains:
- What electricity is
- How electric current flows
- Why some materials conduct electricity
- How current produces heat, light, and magnetism
- How electrical power is measured
Table of Contents
Static and Current Electricity
Electricity exists in two main forms:
- Static electricity
- Current electricity
Static Electricity
Static electricity refers to electric charges at rest.
It is produced due to transfer of electrons from one body to another.
Example:
When a plastic comb is rubbed with dry hair, it attracts small pieces of paper.
In static electricity:
- Charges remain stationary
- No continuous flow of charge
Current Electricity
Current electricity refers to electric charges in motion.
When charges flow through a conductor continuously, electric current is produced.
Example:
Electric current flowing through a wire in a bulb makes it glow.
Current electricity is used for practical purposes.
Conductors and Non-Conductors
Materials are classified based on their ability to allow electric current to pass.
Conductors
Conductors are materials that allow electric current to pass easily. They contain free electrons.
Examples:
Copper, aluminium, iron, silver
Metals are generally good conductors.
Non-Conductors (Insulators)
Non-conductors do not allow electric current to pass easily.
They lack free electrons.
Examples:
Rubber, plastic, glass, wood
Insulators are used for safety.
Electric Current
Electric current is the rate of flow of electric charge.
Current flows only when:
- There is a closed circuit
- A potential difference exists
Electric current always flows from higher potential to lower potential.
Ohm’s Law
Ohm’s Law explains the relationship between current, voltage, and resistance.
It states that:
At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across it.
This means:
- More voltage → more current
- Less resistance → more current
This law applies only when physical conditions remain unchanged.
Resistance
Resistance is the opposition offered by a conductor to the flow of electric current.
Resistance depends on:
- Length of conductor
- Thickness of conductor
- Nature of material
Thin and long wires have higher resistance.
Simple Electrical Circuits
An electric circuit is a closed conducting path through which current flows.
A simple circuit consists of:
- Cell or battery
- Connecting wires
- Switch
- Electrical appliance
If the circuit is broken, current stops flowing.
Open and Closed Circuits
- Closed circuit: current flows
- Open circuit: current does not flow
Switches are used to open or close circuits.
Heating Effect of Electric Current
When electric current flows through a conductor, it produces heat.
This happens because:
- Electrons collide with atoms
- Electrical energy converts into heat energy
Uses of Heating Effect
- Electric iron
- Heater
- Electric kettle
Heating effect is useful but sometimes undesirable.
Lighting Effect of Electric Current
Electric current can produce light.
This happens in:
- Electric bulbs
- Tube lights
In bulbs:
- Filament becomes hot and glows
In tube lights:
- Gas glows due to electric discharge
Magnetic Effect of Electric Current
Electric current produces a magnetic field around the conductor.
This was discovered by Oersted.
Applications of Magnetic Effect
- Electric bell
- Electric motor
- Electromagnets
Electric current and magnetism are closely related.
Measurement of Electrical Power
Electrical power is the rate at which electrical energy is consumed.
Power tells how fast an appliance uses electricity.
Units of Electrical Power
- SI unit: watt (W)
- Commercial unit: kilowatt (kW)
Higher power means more energy consumption per second.
Electrical Energy
Electrical energy consumed is measured in:
- kilowatt-hour (kWh)
This unit is commonly called one unit of electricity.
Importance of Current Electricity
This chapter helps us understand:
- Domestic wiring
- Safety devices
- Electric appliances
- Power consumption
It forms the base for advanced topics in physics.
CURRENT ELECTRICITY – FAQs
Can static electricity do useful work?
No, because charges do not flow continuously.
Why are metals good conductors?
Because they have free electrons.
Is electric current flow possible in an open circuit?
No.
Does current flow without voltage?
No.
Why does a bulb glow when current flows?
Due to heating effect.
What opposes current flow?
Resistance.
Does current produce magnetism?
Yes.
What happens if resistance increases?
Current decreases.
Which unit is used in electricity bills?
Kilowatt-hour.
Is heating effect always useful?
No, it causes power loss in wires.
Last-Moment Notes (Cheat Sheet)
CURRENT ELECTRICITY
- Static electricity → charges at rest
- Current electricity → charges in motion
- Conductors → allow current
- Insulators → block current
- Current flows only in closed circuit
- Voltage is required for current flow
- Ohm’s Law → current ∝ voltage
- Resistance opposes current
- Heating effect → current produces heat
- Used in heaters and irons
- Current produces magnetic field
- Basis of motors and electromagnets
- Power = rate of energy use
- SI unit → watt
- Electricity unit → kWh