Apply Fleming's Left-Hand Rule
Scenario
Tumne padha ki magnet current wale wire ko dhakka marta hai.
Lekin theek-theek kaise pata chale ki dhakka upar lagega, neeche, left ya right?
Mental model
FBI trick: F = Force (Thumb), B = Magnetic field (Forefinger), I = Current (Middle finger). Apne left hand ko in teeno ko perpendicular karke stretch karo.
Jab humara thumb, forefinger, aur middle finger left hand ki ek dusre se 90-degrees (mutually perpendicular) par stretch ki jati hain, toh wo ek 3D coordinate system banati hain. Ye teen ungliyan force, magnetic field aur current ke relation ko represent karti hain.
Explanation
Fleming's Left-Hand Rule ek practical rule hai jo predict karta hai ki current-carrying conductor kis taraf move karega (force kis taraf lagega) jab usay kisi magnetic field mein perpendicular rakha jaye.
Is rule ko use karne ke liye, apne Left Hand ke Thumb (anguthe), Forefinger (index finger), aur Middle finger ko aise stretch karo ki wo teeno ek dusre par right angles (90 degrees) banayein. Ab unhe set karo is order mein:
1. Forefinger ko Magnetic Field ki direction mein point karo (North se South).
2. Middle finger ko Current ki direction mein point karo (Positive to Negative).
3. Jis disha mein aapka Thumb (angutha) point kar raha hoga, wahi disha conductor pe lagne wali Force (motion) ki hogi.
Questions mein aksar alpha particles (positive charge) ya electrons (negative charge) ka movement diya hota hai. Dhyan rakhna, current ki direction hamesha alpha particles (positive) ke movement ki direction mein hi li jati hai, par electrons ke movement ke theek opposite direction mein. Agar electrons east ja rahe hain, toh current ko west consider karke apna middle finger point karna hota hai. Tabhi thumb sahi force batayega.
Worked example
Problem: An electron beam enters a magnetic field at right angles to it. The magnetic field is pointing downwards, and the electrons are moving from left to right. In which direction will the force act?
- Electrons left se right ja rahe hain, iska matlab conventional current right se left mana jayega.
- Field clearly downwards hai, toh humari forefinger neeche point karegi. Apne left hand ki forefinger ko neeche aur middle finger ko left point karo.
- Is haalat mein, tumhara thumb exactly paper ke ander ki taraf, yani aapse door point kar raha hoga.
Answer: Into the page
Problem: A positively charged particle (alpha particle) projected towards the West is deflected towards the North by a magnetic field. Find the direction of the magnetic field.
- Alpha particle positive hota hai, isliye current ki direction seedhi west hogi.
- Particle north ki taraf mud gaya, matlab force north direction mein lagi hai.
- Apne left hand ke thumb ko North aur middle finger ko West mein set karo. Tumhari forefinger seedhe upar aasmaan ki taraf point karegi.
Answer: Upwards
Key points
- Forefinger: Represents the direction of the Magnetic Field (B).
- Middle Finger: Represents the direction of the Electric Current (I).
- Thumb: Points to the direction of Force (F) or motion of the conductor.
Common mistakes
- Using right hand instead of left hand: Bachhe Fleming ka naam padh ke bhool jate hain left lagana tha ya right (generator). Force nikalne ke liye hamesha LEFT hand use hota hai (motors ke liye).
- Ignoring electron charge rule: Log electrons ki direction ko hi current ki direction maan lete hain. Electrons jahan jayein, uske ulta current manna zaroori hai.
Recall questions
- In Fleming's Left-Hand rule, what does the middle finger represent?
- What rule gives the direction of magnetic force on a current-carrying wire?
- Which finger represents the magnetic field in Fleming's Left Hand Rule?
Questions & answers
An electron enters a magnetic field at right angles to it, as shown. The direction of force acting on the electron will be?
Into the page. (Because current is taken opposite to electron flow, applying Left-Hand Rule points thumb into the page)
Approach: Reverse electron direction to get current, then apply FBI rule with left hand.
If a positively charged alpha particle moves west and experiences an upward force, what is the direction of the magnetic field?
North
Approach: Apply Fleming's Left-Hand Rule.
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