# Radiation from a Square Loop of Current

• STosh9
In summary, a loop of steady current, regardless of its shape, does not radiate as the static field of the charges is always normal to the wire. Radiation only occurs when there is a changing dipole moment, which can be seen in AC or switch-on currents. However, in vacuum tubes where electrons can travel at high speeds, cyclotron radiation can be observed. The radiated power can be calculated using Larmor's formula, taking into account the radial acceleration.

#### STosh9

It is well known that a circular loop of steady current does not radiate, even though each individual charge is undergoing centripetal acceleration.

How about a loop of steady current that is shaped in a square? Does this structure radiate?

How about a loop of steady current that is shaped in a square? Does this structure radiate?
Imagine the static field of the charges in the wire. The lines of force point radially outwards everywhere, and are always normal to the wire. Even when it goes round a corner they are normal to the wire. To have radiation, they need to be not normal but pushed to one side a bit. In this way a transverse component of field is created, the radiated E-field. This only occurs if the current is varied, as with AC or at switch-on.

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You get radiation when you have a changing dipole (or higher) moment. So nothing with a steady current will radiate.

Further to my reply, if the electrons can move fast enough with a steady current it is possible to obtain cyclotron radiation. But electrons in a wire are only traveling at, say, 1 mm an hour. In a vacuum tube it is possible for them to go round millions of times a second, and then cyclotron radiation can be seen at the rotation frequency.

debajyoti datta
tech99 said:
Further to my reply, if the electrons can move fast enough with a steady current it is possible to obtain cyclotron radiation. But electrons in a wire are only traveling at, say, 1 mm an hour. In a vacuum tube it is possible for them to go round millions of times a second, and then cyclotron radiation can be seen at the rotation frequency.
and i guess radiated power will be given by Larmor's formula ?

debajyoti datta said:
and i guess radiated power will be given by Larmor's formula ?

## 1. What is a square loop of current?

A square loop of current is a circuit in which a current flows in a square-shaped loop or path. It is commonly used in electromagnetism experiments and devices.

## 2. How does radiation occur in a square loop of current?

Radiation occurs in a square loop of current due to the changing electric and magnetic fields created by the flowing current. These changing fields create electromagnetic waves that radiate outwards from the loop.

## 3. What factors affect the amount of radiation emitted from a square loop of current?

The amount of radiation emitted from a square loop of current is affected by the frequency of the current, the size of the loop, and the strength of the current. Higher frequencies, larger loops, and stronger currents will result in more radiation.

## 4. Is radiation from a square loop of current harmful?

The amount of radiation emitted from a square loop of current is generally very low and is not harmful to humans. However, if the loop is very large or the current is extremely strong, it may pose a potential hazard and appropriate safety precautions should be taken.

## 5. Can radiation from a square loop of current be used for any practical applications?

Yes, radiation from a square loop of current has practical applications in devices such as antennas, wireless charging pads, and magnetic resonance imaging machines. It is also used in various forms of electromagnetic communication, such as radio and television broadcasting.