#Lesson Overview
(Electricity and Magnetism)
Electricity and magnetism are interlinked physical phenomena that govern how electric currents create magnetic fields and how magnetic fields produce electric currents. Understanding these concepts helps explain motors, generators, transformers, and many devices used in daily life.
1. Direct Current (DC) and Alternating Current (AC)
Direct Current (DC)
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Flows in one direction only.
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Produced by battery, solar cells, and DC generators.
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Used in: mobile phones, laptops, flashlights, and electric vehicles.
Alternating Current (AC)
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Changes direction periodically.
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Produced by AC generators/power stations.
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Used in: home appliances, electric heaters, refrigerators.
Difference Between DC and AC
| Feature | DC | AC |
|---|---|---|
| Direction | One direction | Alternates direction |
| Source | Battery, DC generator | Power station |
| Transmission | Inefficient for long distances | Efficient for long distances |
| Uses | Electronics | Household wiring |
2. Magnetic Field Around a Straight Wire and Solenoid
When an electric current passes through a conductor, it creates a magnetic field around it.
a. Magnetic Field Around a Straight Wire
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Magnetic field lines form concentric circles around the wire.
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Direction is given by Right-Hand Thumb Rule:
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Thumb → direction of current
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Fingers → direction of magnetic field
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Diagram (Text Format)
b. Magnetic Field Around a Solenoid
A solenoid is a long coil of wire with many turns.
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Produces a strong magnetic field similar to a bar magnet.
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One end acts as the North pole, the other the South pole.
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Inside the solenoid, magnetic field lines are parallel and uniform.
Diagram (Text Format)
3. Magnetic Lines of Force and Magnetic Flux
#Magnetic Lines of Force#
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Imaginary lines representing the magnetic field.
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Direction: from the North Pole to the South Pole.
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Properties:
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Never intersect.
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Denser lines = stronger magnetic field.
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Form closed loops.
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#Magnetic Flux (Φ)#
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Total number of magnetic field lines passing through a surface.
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Symbol: Φ (phi)
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Unit: Weber (Wb)
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Φ = B × A × cosθ
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B = magnetic field strength
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A = area
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θ = angle between field and surface normal
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4. Motor Effect and Its Daily Uses
When a current-carrying conductor is placed in a magnetic field, it experiences a force.
This is known as the Motor Effect.
Applications in Daily Life
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Electric fan
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Mixer grinder
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Water pump
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Electric vehicle motors
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Hard disk drive motors
Principle of Electric Motor:
Current + Magnetic field → Force → Rotation of coil
5. Faraday’s Law of Electromagnetic Induction, Dynamo & Generator
Faraday’s Law of Electromagnetic Induction
When the magnetic flux linked with a coil changes, an induced emf is produced inside the coil.
The magnitude of the induced emf is proportional to the rate of change of the magnetic flux.
Formula:
e = − dΦ/dt
(Negative sign = Lenz’s Law)
a. Working of Dynamo
A dynamo converts mechanical energy → electrical energy (usually DC).
Working Process
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A coil rotates in a magnetic field.
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Magnetic flux through the coil changes.
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Induced emf is generated.
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A commutator converts alternating emf into a DC output.
b. Working of Generator
A generator converts mechanical energy → electrical energy (AC).
Working Process
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The coil rotates between the magnetic poles.
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Flux linking the coil changes continuously.
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Alternating current is produced.
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Slip rings deliver AC to the external circuit.
6. Transformer – Structure, Working & Importance
A transformer changes voltage levels (AC only).
Structure of a Transformer
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Core: Soft iron core
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Primary Coil: Connected to the input AC
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Secondary Coil: Connected to output
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Coils are insulated and wound on opposite sides of the core.
Diagram (Text Format)
Working Principle
Based on Faraday’s law and mutual induction.
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AC flows through the primary coil.
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Creates a changing magnetic flux in the iron core.
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The same flux links the secondary coil.
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Induced emf is produced in the secondary coil.
Types
Step-up Transformer
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Increases voltage
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Secondary turns > Primary turns
Step-down Transformer
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Decreases voltage
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Secondary turns < Primary turns
Transformer Formula (for numericals)
Voltage Ratio:
Vs / Vp = Ns / Np
(V = Voltage, N = Number of turns)
Current Ratio:
Is / Ip = Np / Ns
Importance
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Power transmission
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Mobile chargers
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Inverters
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Distribution lines
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Microwave ovens
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TV, computers, and electronic devices
Summary of Lesson
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DC flows in one direction; AC changes direction periodically.
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Magnetic fields form around straight wires and solenoids; solenoids act like bar magnets.
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Magnetic lines of force show the field direction; magnetic flux measures the total field lines.
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The motor effect is responsible for electric motors used in daily life machines.
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Faraday’s law explains induction; generators and dynamos work based on it.
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Transformers change AC voltage using mutual induction and are essential in power systems.
- Practice : ✅ MCQ Set (25 Questions) Electricity & Magnetism