NCERT Class 12 Physics | Chapter 4 Q4.4 solution | Magnetic Field Due to Current Carrying Wire

📘 Question 4.4 (NCERT Class 12 Physics – Chapter 4: Moving Charge and Magnetism):
A horizontal overhead power line carries a current of 90 A in the east to west direction.
Find the magnitude and direction of the magnetic field due to this current 1.5 m below the line.


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⚡ Concepts Covered in This Video:

1️⃣ Magnetic Field due to Long Straight Current-Carrying Wire
2️⃣ Formula – B = (μ₀ I) / (2πr)
3️⃣ Right-Hand Thumb Rule (Direction of Magnetic Field)
4️⃣ Real-Life Application – Power Lines & Magnetic Field
5️⃣ Important Concept for Board Exams + JEE + NEET


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📘 Given Data:

I = 90 \, A, \quad r = 1.5 \, m


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🧮 Formula Used:

B = \frac{μ₀ I}{2πr}

Where

μ₀ = 4π × 10^{-7} \, Tm/A


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🔢 Step-by-Step Solution:

B = \frac{4π × 10^{-7} × 90}{2π × 1.5}

B = 1.2 × 10^{-5} , T 

✅ Final Answer:
Magnetic Field = 1.2 × 10⁻⁵ T

👉 Direction:
Using the Right-Hand Thumb Rule,
Since current flows east to west, the magnetic field at the point below the wire is directed towards the south.


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💡 Concept in Simple Words:

Magnetic field lines form concentric circles around a current-carrying wire.
Use your right-hand thumb rule to find the direction:
👉 Thumb = current direction, Fingers = magnetic field direction.


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🎯 You Will Learn:
✔️ Concept of magnetic field around wire
✔️ How to use right-hand thumb rule
✔️ Real-life link with electric transmission lines
✔️ Quick tricks for solving similar NCERT numericals

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