# B field of a wire carrying AC current

• ShoesButtBack
In summary, the conversation discusses the calculation of magnetic field at a distance from a wire carrying a 495Hz signal, and the use of Ampere's law and Maxwell's correction in this scenario. The relationship between dE/dt and frequency is also mentioned, and it is noted that when dealing with AC currents, the electric and magnetic fields are coupled. For accurate results, all of Maxwell's equations must be solved simultaneously or transformed into non-homogenous wave equations and solved using Green functions.
ShoesButtBack
Hi. New to the forums so bear with me.

I am trying to calculate the magnetic field at a distance r from a wire carrying a 495Hz signal at 8Vpp and current 0.8mA. Initially I tried ampere's law, but fell into the trap of using the un-modified form (without maxwell's correction). I know that the field changes with the frequency, but I am unsure of exactly how they tie together, and I can't seem to find the relationship between dE/dt and frequency.

Any ideas?

you still would use amperes law . your current will be a function of time I(t)
You would only use maxwells correction if you had free charge and if it was changing as a function of time. Like charging up a capacitor. And i don't think you have any free charge.

Sorry, it's not that simple. When you have AC currents, you have changing fields, which means that the electric and magnetic fields are coupled. If the distance r you are interested in is very close to the wire compared to the wavelength of the signal, then you you can treat the problem as pseudo-static and just use Ampere's law. Otherwise you have to solve all of Maxwell's equations simultaneously because the fields are coupled. The best way to do this is to transform Maxwell's equations into non-homogenous wave equations and solve using Green functions. See http://faculty.uml.edu/cbaird/95.658%282011%29/Lecture6.pdf" , for example.

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## 1. What is the "B field" of a wire carrying AC current?

The "B field" refers to the magnetic field that is created around a wire when it carries an alternating current (AC). This field is perpendicular to the direction of the current and can be visualized as concentric circles around the wire.

## 2. How is the strength of the B field affected by the AC current?

The strength of the B field is directly proportional to the magnitude of the AC current. This means that as the current increases, the B field becomes stronger.

## 3. What factors can influence the B field of a wire carrying AC current?

The strength of the B field is influenced by several factors including the magnitude and direction of the current, the distance from the wire, and the material of the wire. Additionally, the frequency of the AC current can also affect the B field.

## 4. How can the B field be measured?

The B field can be measured using a magnetic field sensor such as a magnetometer. This device can detect the strength and direction of the B field and provide a numerical value for its magnitude.

## 5. What are some practical applications of the B field of a wire carrying AC current?

The B field of a wire carrying AC current is utilized in many everyday devices such as electric motors, generators, and transformers. It is also used in medical imaging techniques such as magnetic resonance imaging (MRI) to produce detailed images of the human body.

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