ROSHAN MUJEEB
Last Activity: 5 Years ago
To find the magnetic field due to an infinitely long current-carrying wire in the direction of a vector î + ĵ + k̂ passing through the origin, we’ll use the vector form of the Biot–Savart Law for a straight infinite wire and a bit of vector geometry.
Step-by-step Approach
1. Direction Vector of the Wire
The wire lies along the direction of the vector:
𝐥̂ = (î + ĵ + k̂) / √3
This is the unit vector of the wire’s direction.
2. Point Where We Need Magnetic Field
The observation point is at (1, 0, 0).
3. Use of Formula for Infinite Wire
The magnetic field **B** at a perpendicular distance **r⊥** from an infinite wire is:
B = (μ₀ I) / (2π r⊥)
But B is a vector
Its direction is given by the cross product:
𝐁 ∝ (𝐥̂ × 𝐫̂)
4. Find Perpendicular Distance (r⊥)
We calculate the perpendicular distance from the point (1,0,0) to the line passing through origin along 𝐥̂.
Let 𝐫 = (1,0,0), and 𝐥̂ = (1,1,1)/√3
Perpendicular distance formula from point to a line:
r⊥ = |𝐥̂ × 𝐫| / |𝐥̂|
𝐥̂ × 𝐫 = (1,1,1) × (1,0,0) = (0,1,–1)
|𝐥̂ × 𝐫| = √(0² + 1² + (–1)²) = √2
|𝐥̂| = √(1² + 1² + 1²) = √3
So, r⊥ = √2 / √3 = √(2/3)
5. Compute Magnitude of Magnetic Field
B = (μ₀ I) / (2π r⊥) = (μ₀ I) / (2π √(2/3)) = (μ₀ I √3) / (2π √2)
6. Direction of Magnetic Field
Direction is given by 𝐥̂ × 𝐫̂. We already found 𝐥̂ × 𝐫 = (0,1,–1), which is in the direction of **ĵ – k̂**
Final Answer:
Magnitude: (μ₀ I √3) / (2π √2)
Direction: Along the vector (ĵ – k̂), or more precisely,
𝐁 = [(μ₀ I √3) / (2π √2)] × (ĵ – k̂) / √2 = (μ₀ I √3) / (4π) × (ĵ – k̂)