Class 10 Ch 12 Magnetic Effects of Electric Current

• Hans Christian Oersted discovered that Electricity & Magnetism are linked.
• A compass needle is a small bar magnet. Its ends point towards North and South.
• Magnetic field is a quantity that has both Direction & Magnitude.

• Direction: Outside magnet $\to$ North to South. Inside magnet $\to$ South to North.
• They form closed curves.
• Relative strength is shown by the closeness of lines. (More crowded = Stronger field).
• IMP: No two field lines ever cross each other. If they did, the compass would point in two directions at once—Impossible!

• दक्षिण-हस्त अंगुष्ठ नियम: Used to find direction of field around a straight wire.
• Imagine holding a wire: Thumb $\to$ Current direction. Wrapped fingers $\to$ Magnetic Field lines.
• Field consists of concentric circles centered on the wire.

• At every point of the loop, field lines are concentric circles.
• At the center of the loop, the arcs appear as straight lines.
• Magnetic field $\propto$ Number of turns in the coil. (Each turn adds up).

• A coil of many circular turns of insulated copper wire wrapped in a cylinder shape.
• Inside the solenoid, field lines are parallel straight lines $\implies$ Field is Uniform.
• One end acts as North, other as South (like a bar magnet).

• A strong magnetic field inside a solenoid can magnetise a piece of Soft Iron placed inside.
• Difference!
  • Electromagnet: Temporary, very strong, polarity can be reversed.
  • Permanent Magnet: Fixed strength, cannot be easily demagnetised.

• André Marie Ampère suggested that the magnet also exerts an equal and opposite force on the conductor.
• The Displacement is largest when current is perpendicular to the magnetic field.

फ्लेमिंग का वाम-हस्त नियम: Stretch Forefinger, Middle finger & Thumb mutually perpendicular.

• Forefinger $\to$ Field (B).
• Middle finger $\to$ Current (I).
• Thumb $\to$ Force (F) or Motion.

• Discovered by Michael Faraday.
• The process by which a changing magnetic field in a conductor induces a Current in another conductor.
• वैद्युतचुंबकीय प्रेरण: जब चुंबक को कुंडली की ओर ले जाया जाता है, तो धारा उत्पन्न होती है।

• Used to find the direction of Induced Current.
• Thumb $\to$ Motion of conductor.
• Forefinger $\to$ Magnetic Field.
• Middle finger $\to$ Induced Current.

We receive power through mains supply (usually 220 V at 50 Hz in India).

• 1. Live Wire (Vidhyunmay): Red insulation. High potential.
• 2. Neutral Wire: Black insulation. Zero potential.
• 3. Earth Wire (Bhu-sampark): Green insulation. Connected to a metal plate deep in earth.

• Earth Wire: Provides a low-resistance path for leakage current. Prevents severe shocks from metallic appliances.
• Short Circuit: Occurs when Live and Neutral wires come in direct contact (insulation damage). Resistance becomes zero, current becomes huge!
• Overloading: Connecting too many appliances to a single socket. Excessive current draws can cause fire.
• Electric Fuse: Prevents damage from short-circuiting/overloading by melting and breaking the circuit.