In this chapter, we study what happens when electric current flows through a conductor. You already know that electricity is used in our daily life, but here we will understand how electric current produces heat, magnetic effects, and mechanical motion. This chapter is very important for the SSC board exam because it includes laws, formulas, diagrams, and application-based questions. If you understand the concepts step by step, this chapter becomes very logical and scoring.
Table of Contents
Important Concepts of the Chapter
Energy Transfer in an Electric Circuit
When an electric cell is connected in a circuit, it provides energy to the charges (electrons) flowing through the circuit.
In simple words, the cell is the source of energy, and this energy is transferred to the components connected in the circuit.
For example, when current flows through a resistor, the electrical energy is converted into heat energy.
If a motor is connected instead of a resistor, electrical energy gets converted into mechanical energy.
Heating Effect of Electric Current
When current flows through a conductor having resistance, heat is produced in it.
This phenomenon is called the heating effect of electric current.
This happens because moving electrons collide with atoms of the conductor and transfer energy to them, increasing their temperature.
Daily life examples:
- Electric iron
- Electric heater
- Electric bulb
- Electric kettle
Joule’s Law of Heating
The amount of heat produced in a conductor depends on:
- Square of the current flowing (I²)
- Resistance of the conductor (R)
- Time for which current flows (t)
This relationship is known as Joule’s law of heating.
Electric Power
Electric power is the rate at which electrical energy is consumed or converted.
In simple words, it tells us how fast an appliance uses electrical energy.
High-power appliances consume more electricity in less time.
Unit of Electrical Energy
In daily life, electrical energy is measured in kilowatt-hour (kWh), also called one unit of electricity.
Electricity bills are calculated using this unit.
Important Laws / Formulae
Joule’s Law of Heating
Formula:
H = I²Rt
Where:
- H = Heat produced (joule)
- I = Current (ampere)
- R = Resistance (ohm)
- t = Time (second)
This formula is frequently used in numerical’s.
Electric Power Formula
P = VI
Where:
- P = Power (watt)
- V = Potential difference (volt)
- I = Current (ampere)
Other forms (from Ohm’s law):
- P = I²R
- P = V²/R
These formulas are used in numerical problems related to appliances.
Magnetic Effect of Electric Current
When electric current flows through a conductor, a magnetic field is produced around it.
This discovery showed that electricity and magnetism are closely related.
This effect was first observed by Hans Christian Oersted.
Magnetic Field around a Straight Current Carrying Conductor
When current flows through a straight wire:
- Magnetic field lines form concentric circles around the wire
- Strength of the magnetic field increases with current
- Strength decreases as distance from the wire increases
Right Hand Thumb Rule
This rule helps to find the direction of the magnetic field.
If you hold the conductor in your right hand with the thumb pointing in the direction of current, the curled fingers show the direction of the magnetic field.
Magnetic Field due to a Circular Loop
When current flows through a circular loop:
- Each part of the loop contributes to the magnetic field
- At the centre of the loop, the magnetic field is strong and almost straight
- More turns in the loop produce a stronger magnetic field
Solenoid and its Magnetic Field
A solenoid is a coil of many circular loops of insulated wire.
Magnetic field of a solenoid:
- Is uniform inside the solenoid
- Resembles the magnetic field of a bar magnet
- One end behaves as north pole, the other as south pole
Force on a Current Carrying Conductor in a Magnetic Field
When a current-carrying conductor is placed in a magnetic field, it experiences a force.
The direction of this force depends on:
- Direction of current
- Direction of magnetic field
This principle is used in electric motors.
Fleming’s Left Hand Rule
This rule helps to find the direction of force.
If:
- Index finger → magnetic field
- Middle finger → current
- Thumb → force
Then all three are mutually perpendicular.
This rule is used in electric motor questions.
Electric Motor
An electric motor is a device that converts electrical energy into mechanical energy.
It works on the principle that:
A current-carrying conductor placed in a magnetic field experiences a force.
Main parts:
- Rectangular coil
- Split ring (commutator)
- Carbon brushes
- Magnet
- Axle
Electric motor’s construction and working with diagram is very important for SSC exam.
Electromagnetic Induction
When a conductor moves in a magnetic field or when the magnetic field around a conductor changes, an electric current is induced.
This phenomenon is called electromagnetic induction.
It was discovered by Michael Faraday.
Faraday’s Law of Induction
Whenever the number of magnetic field lines linked with a conductor changes, an electric current is induced in it.
The produced current is called induced current.
Fleming’s Right Hand Rule
This rule helps to find the direction of induced current.
If:
- Thumb → motion of conductor
- Index finger → magnetic field
- Middle finger → induced current
This rule is used in generator-related questions.
Electric Generator
An electric generator converts mechanical energy into electrical energy.
There are two types:
- AC generator
- DC generator
AC generator produces alternating current, while DC generator produces direct current using a split ring.
Diagram and difference between AC and DC generator is frequently asked.
Important Definitions
- Heating Effect of Current – Production of heat when current flows through a conductor
- Electric Power – Rate of consumption of electrical energy
- Solenoid – Coil of many turns producing magnetic field
- Electromagnetic Induction – Production of current due to change in magnetic field
- AC – Current that changes direction periodically
- DC – Current flowing in one direction only
Numerical / Process Explanation
For numericals:
- Identify given values clearly
- Choose correct formula
- Convert units properly
- Write final answer with unit
Students should always check units before solving.
For diagrams:
- Practice neat, labelled diagrams
- Learn step-wise working of motor and generator
Important Points for SSC Board Exam
- Joule’s law numericals are common
- Diagrams carry good marks
- Differences between AC and DC are important
- Heating effect and its applications are important
- Fleming’s rules must be remembered clearly
- Short circuit and fuse-related questions are asked
Quick Revision Summary
- Electric current produces heat and magnetism
- Heat depends on I², R and time
- Electric power shows energy consumption rate
- Magnetic field forms around current-carrying wire
- Solenoid behaves like bar magnet
- Motor converts electrical to mechanical energy
- Generator converts mechanical to electrical energy
- Fleming’s rules help find directions