🧲 Magnetic Field of Straight Wire Calculator
Calculate magnetic field around a straight current-carrying wire
Perpendicular distance from the wire
How to Use This Calculator
Enter Current
Input the current flowing through the straight wire in Amperes. This is the current that creates the magnetic field.
Enter Distance
Input the perpendicular distance from the wire to the point where you want to calculate the magnetic field, in meters. This distance must be perpendicular to the wire.
Calculate
Click the "Calculate Magnetic Field" button to get the magnetic field strength in Tesla at the specified distance from the wire.
Formula
B = (μ₀ × I) / (2π × r)
Where:
- B = Magnetic Field (Tesla, T)
- μ₀ = Permeability of Free Space = 4π × 10⁻⁷ T⋅m/A
- I = Current (Amperes, A)
- r = Perpendicular Distance from Wire (meters, m)
Example Calculation:
For a wire with I = 10 A, r = 0.05 m (5 cm):
B = (4π×10⁻⁷ × 10) / (2π × 0.05)
B = (1.257×10⁻⁵) / (0.314) = 4×10⁻⁵ T
Note: The magnetic field forms concentric circles around the wire. Direction follows the right-hand rule: point thumb in current direction, fingers curl in B direction. Field strength decreases as 1/r (inversely proportional to distance).
About Magnetic Field of Straight Wire Calculator
The Magnetic Field of a Straight Current-Carrying Wire Calculator determines the magnetic field strength around a long, straight wire carrying an electric current. This fundamental relationship, discovered by Biot and Savart, shows that the magnetic field is inversely proportional to distance and directly proportional to current. The field forms concentric circles around the wire, following the right-hand rule.
When to Use This Calculator
- Electrical Engineering: Calculate magnetic fields around power lines and conductors
- Physics Education: Solve problems involving magnetic fields from current-carrying wires
- Safety Analysis: Determine magnetic field exposure near electrical systems
- Electromagnetic Design: Design systems with controlled magnetic fields
- Power Systems: Analyze magnetic fields in power distribution systems
Why Use Our Calculator?
- ✅ Quick Calculation: Instantly determine magnetic field from current and distance
- ✅ Biot-Savart Law: Based on fundamental electromagnetic principles
- ✅ Safety Applications: Important for assessing magnetic field exposure
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Learn about magnetic fields around conductors
Common Applications
Power Line Safety: Calculate magnetic fields around high-voltage power lines to assess exposure levels. Understanding field strength at various distances helps evaluate safety and compliance with exposure limits. This is important for both workers and the general public near power transmission infrastructure.
Electromagnetic Interference (EMI): Determine magnetic field strength around wires to assess potential interference with sensitive electronics. Strong magnetic fields can induce currents in nearby conductors, causing interference. This calculator helps design systems with appropriate spacing to minimize EMI.
Magnetic Sensor Design: Calculate the magnetic field that sensors will detect when placed near current-carrying wires. This is essential for designing current sensors, Hall effect devices, and other magnetic field detection systems used in power monitoring and protection circuits.
Tips for Best Results
- Formula applies to long, straight wires (length much greater than distance r)
- Distance must be measured perpendicular to the wire
- Field strength decreases as 1/r (doubling distance halves the field)
- Magnetic field direction follows right-hand rule
- For multiple wires, calculate each separately and add vectorially
Frequently Asked Questions
What is the right-hand rule for magnetic field direction?
Point your right thumb in the direction of current flow. Your curled fingers indicate the direction of the magnetic field (counterclockwise around the wire). The magnetic field forms concentric circles perpendicular to the wire.
Does this formula work for any wire length?
This formula is exact for an infinitely long straight wire. For practical purposes, it's accurate when the wire length is much greater than the distance r (typically > 10×). For short wires, you need the complete Biot-Savart law integration.
Why does the field decrease as 1/r?
The magnetic field strength is inversely proportional to distance because the field lines spread out in circular patterns. As you move farther from the wire, the same total magnetic flux is distributed over a larger circumference (2πr), so field strength decreases proportionally.
How do I calculate the field for multiple parallel wires?
Calculate the magnetic field from each wire separately at the point of interest, then add them vectorially (considering direction). For parallel wires with current in the same direction, fields add; with opposite currents, they subtract. Use vector addition for fields at angles.
What happens inside the wire?
Inside the wire, the magnetic field depends on current distribution. For uniform current density, B = (μ₀Ir)/(2πR²) where R is wire radius and r is distance from center. The field increases linearly from center to surface, then decreases as 1/r outside.
Is this related to Ampere's law?
Yes! This formula can be derived from Ampere's law: ∮B·dl = μ₀I. For a circular path around a straight wire, the integral simplifies to B × 2πr = μ₀I, giving B = μ₀I/(2πr). Ampere's law is a powerful tool for calculating magnetic fields with symmetry.