# Straight Wire Magnetic Field Formula

A long straight wire carrying a current has a magnetic field due to moving charges which will depend on the right-hand rule. For the case of a long straight wire carrying a current I, the magnetic field lines wrap around the wire and depends on the distance to the wire.

Magnetic field = magnetic permeability * current / (2 π distance from the wire)

The equation is:

B = μ I /2 π r

Where:

μ: permeability

B: magnetic field

I: current intensity flowing in the cable

r: distance to the wire (perpendicular to the wire)

Straight wire Formula Questions:

1) A wire of 30 cm length carries a current I= 2 A. what is the magnetic field at 50 cm from the wire?

Answer:

From the formula of the magnetic field of the straight we substitute the values,

B = μ I/2 π r = 4π *10^{(-7)} T*m/A * 2 A /(2 π *0.5 m)

= 8 *10^{(-7)} T

2) A wire of 30 cm length carries a current I= 2 A. At which distance is the magnetic field is of 4*10^{(-3)} T?

Answer:

From the formula of the magnetic field of the wire we find the distance r,

r= μ I/2 π B = (4π *10^{(-7)} T*m/A* 2A)/(2 π 4*10^{(-3)}T)

r= 0.5 *10^{(-4)} m = 0.05 mm

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