# Lenz's Law and Induced Magnetic Fields

• jaydnul
In summary: The primary winding then sees a lower resistance than it would normally and more current flows through it. This increased current creates a stronger magnetic field which induces a higher voltage in the secondary coil. In summary, in a transformer, the primary coil creates a magnetic field which induces a current in the secondary coil. This induced current creates a magnetic field that opposes the inducing field, but does not completely cancel it out. This effect can be managed in electrical shielding circuits by placing wires carrying current away from sensitive electronics.
jaydnul
In a transformer, the primary coil has a current running through it which creates a magnetic field. Then this field induces a current in the secondary coil. That induced current creates a magnetic field exactly opposite the inducing magnetic field.

This might be an obvious question, but that means there is effectively zero magnetic field around the second coil, correct? What about the wires that are carrying that current away? Do they now have an associated magnetic field because they are not submerged in the primary coils initial magnetic field to cancel it out?

The reason I ask this is I'm curious how this is managed in electrical shielding circuits. Only part of the shielding is submerged in the EM noise at a given moment. So that part of the shielding will cancel the field, but the wires carrying that current off to ground will still have a magnetic field. Are those wires just put in places furthest from any sensitive electronics?

Thanks

davenn
jaydnul said:
That induced current creates a magnetic field exactly opposite the inducing magnetic field.
Yes, that's right.
jaydnul said:
This might be an obvious question, but that means there is effectively zero magnetic field around the second coil, correct?
No. It does not perfectly cancel out. This is because the reverse magnetic field acts to appose the current in the primary coil. When a load is attached to the secondary coil, the resistance of the load is reflected back onto the primary winding through this effect.

## 1. What is Lenz's Law?

Lenz's Law is a fundamental law in electromagnetism that states that the direction of an induced current in a conductor will always be such that it opposes the change that caused it.

## 2. How does Lenz's Law relate to induced magnetic fields?

Lenz's Law is directly related to induced magnetic fields because the induced current in a conductor creates its own magnetic field that opposes the change in the original magnetic field that caused it.

## 3. What is the formula for calculating the direction of an induced current according to Lenz's Law?

The formula is: I = −ΔΦ/Δt where I is the induced current, ΔΦ is the change in magnetic flux, and Δt is the change in time.

## 4. How is Lenz's Law applied in everyday life?

Lenz's Law is used in many everyday devices, such as generators and transformers, to produce and control the flow of electricity. It is also used in electromagnetic brakes, which use induced currents to slow down moving objects.

## 5. Are there any exceptions to Lenz's Law?

While Lenz's Law holds true in most cases, there are some exceptions, such as in superconductors where there is no resistance to oppose the induced current, or in certain cases of alternating current where the direction of the induced current may not always oppose the change in magnetic field.

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