# Mutual Inductance and wire coils

• edlin
In summary, the conversation is about a problem with mutual inductance involving two coils. The first coil carries a time-varying current and at t=0.800s, the voltage measured across the second coil is -3.60V. The equation used is emf2=-M dI1/dt, where M is the mutual inductance. The user's answer, 80 V*s/A, is not correct and they have tried other answers. Another user suggests that the correct answer may be 472 V*s/A and explains that the units of inductance are named after Joseph Henry. There is some confusion about the units, with one user thinking it is mHz instead of mH.

#### edlin

Hi..I am new here and I am really thankful for any help that I may get

I am stuck in a problem of mutual inductance. It seems fairly simple, yet I cannot get the correct answer.

Two coils are close to each other. The first coil carries a time-varying current given by I(t) = (4.60 A) e-0.0250tsin(377 t). At t = 0.800 s, the voltage measured across the second coil is -3.60 V. What is the mutual inductance of the coils?

So, the equation I have used is: emf2 = -M dI1/dt ...which is the voltage of the second coil equals the mutual inductance times the current with respect to time. I solved for M, but the answer is not right.

My answer was: 80 V*s/A and I got various other answers but they are incorrect.

I really, really would appreciate any help! Thankyou so much!

edlin said:
Hi..I am new here and I am really thankful for any help that I may get

I am stuck in a problem of mutual inductance. It seems fairly simple, yet I cannot get the correct answer.

Two coils are close to each other. The first coil carries a time-varying current given by I(t) = (4.60 A) e-0.0250tsin(377 t). At t = 0.800 s, the voltage measured across the second coil is -3.60 V. What is the mutual inductance of the coils?

So, the equation I have used is: emf2 = -M dI1/dt ...which is the voltage of the second coil equals the mutual inductance times the current with respect to time. I solved for M, but the answer is not right.

My answer was: 80 V*s/A and I got various other answers but they are incorrect.

I really, really would appreciate any help! Thankyou so much!
Is it by any chance more like 472 V*s/A?.

Well, I actually did get answers in the hundreds, but when I put my answer in, it tells me it has the wrong magnitude. And since they provide me with the units, it says mHz...so the answer is multiplied by 1/10^3... and I really don't understand why. I get no answer near that.

edlin said:
Well, I actually did get answers in the hundreds, but when I put my answer in, it tells me it has the wrong magnitude. And since they provide me with the units, it says mHz...so the answer is multiplied by 1/10^3... and I really don't understand why. I get no answer near that.
Are you sure it is mHz and not just mH? The units of inductance are named after Joseph Henry.

H = V·s/A

## 1. What is mutual inductance?

Mutual inductance is the phenomenon in which a changing current in one wire induces a voltage in another wire that is in close proximity. This is due to the magnetic field created by the changing current.

## 2. How is mutual inductance measured?

Mutual inductance is measured in units called henrys (H), which represents the amount of voltage induced in the secondary coil per unit of current change in the primary coil.

## 3. What is the relationship between mutual inductance and the number of turns in a coil?

The mutual inductance between two coils is directly proportional to the number of turns in each coil. This means that if the number of turns in one coil is increased, the mutual inductance will also increase.

## 4. How can mutual inductance be increased?

Mutual inductance can be increased by increasing the number of turns in the coils, increasing the current in the primary coil, or by decreasing the distance between the two coils.

## 5. What are some practical applications of mutual inductance?

Mutual inductance is used in various electrical devices such as transformers, generators, and motors. It is also used in wireless power transfer systems, where the primary and secondary coils are not physically connected but are still able to transfer energy through mutual inductance.