Identify conditions for magnetic force
Scenario
Jab tum ek electric motor dekhte ho jaise fan mein lagati hai, toh bina kisi cheez ko takraye wo tezi se ghumti hai.
Yeh push ya force kahan se aa rahi hai jo wire ko physical motion de rahi hai?
Mental model
Jab current wale wire ka apna chota field, aur bahar ke magnet ka bada field aapas mein takrate hain, toh dono mein ladai (repulsion/attraction) hoti hai jisse wire ko dhakka (force) lagta hai.
Magnetic field mein rakha hua current-carrying conductor (wire) ek force feel karta hai. French scientist Andre Marie Ampere ne yeh suggest kiya ki agar wire magnet par force lagata hai, toh Newton's third law ke hisab se magnet ko bhi wire par equal aur opposite force lagana chahiye.
Explanation
Ek current-carrying conductor (jaise ki taar) khud ek magnetic field produce karta hai. Jab is taar ko kisi external magnetic field (jaise horseshoe magnet ke beech) mein rakha jata hai, toh do magnetic fields ka interaction hota hai. Is interaction ki wajah se conductor par ek physical (mechanical) force lagta hai.
Yeh force sabse maximum tab hota hai jab electric current ki direction aur magnetic field ki direction ek dusre se perfectly perpendicular (90 degrees par) hoti hain. Agar current aur magnetic field exactly same direction ya opposite (parallel) direction mein travel kar rahe ho, toh conductor par koi force nahi lagta (zero force).
Yeh experiment usually ek aluminum rod ko stand par latka kar, aur uske crosswise ek strong horseshoe magnet rakh kar dikhaya jata hai. Jaise hi current on hota hai, rod physically side mein jhatke se displace ho jati hai. Current ki direction badalne se force ki direction (displacement) bhi reverse ho jati hai, aur magnet ke poles ko palat dene se bhi force palat jata hai.
Isi principle (magnetic force on current) ka hi use electric motors, loudspeakers, aur measuring instruments mein hota hai.
Worked example
Problem: A current-carrying straight wire is placed in a strong magnetic field. Under what condition will the force experienced by the wire be maximum?
- Force donon vectors (Current and Magnetic Field) ke angle par depend karti hai.
- Jab wo ek doosre ke directly perpendicular (90 degree) hote hain, tab fields strongly interact karti hain aur push sabse strong hota hai.
Answer: When the direction of the current is at right angles (90°) to the direction of the magnetic field.
Problem: An electron enters a magnetic field horizontally. If the electron travels exactly along the same line and direction as the magnetic field, what will be the magnetic force on it?
- Yahan electron aur magnetic field ki path ek dusre ke parallel hai (same direction).
- Parallel movement par magnetic field charged particles (ya current) pe bilkul koi force apply nahi kar pata.
Answer: The magnetic force will be zero because it is moving parallel to the field.
Key points
- Maximum Force: Felt when the direction of current is right angles (perpendicular) to the magnetic field.
- Zero Force: Felt when the conductor is placed perfectly parallel to the magnetic field lines.
Common mistakes
- Confusing magnetic force with electrostatic force: Bachhe sochte hain charge dekhte hi attraction/repulsion hoga. Lekin stationary charge par magnet koi force nahi dalta, aur parallel moving charge par bhi force zero hota hai. Force tab lagta hai jab charge crossed (perpendicular) move kare.
Recall questions
- When is the magnetic force on a current-carrying conductor placed in a magnetic field maximum?
- Which scientist suggested that the magnet must also exert an equal and opposite force on the current-carrying conductor?
- When does a current-carrying conductor experience maximum magnetic force?
Questions & answers
When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
The force is largest (maximum) when the direction of current is strictly at right angles to the direction of the magnetic field.
Approach: State the perpendicularity condition clearly.
An electron enters a magnetic field parallel to the field lines. What force does it experience?
Zero force.
Approach: Force is zero when the angle between velocity and magnetic field is 0 or 180 degrees.
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