What Is the Formula for Solenoid Magnetising Current?

[Suyash Singh]

Homework Statement

Part d of attached question

Homework Equations

Solenoid equations
B=uo n i

The Attempt at a Solution

B (absence)=B (presence)
Uo n (i+im)=u n i
im=798A
But answer is 794A.[/B]

 

[mfb]

I don't understand what you calculated, but such a small difference looks like a rounding error.

 

[rude man]

Homework Statement

Part d of attached question

Homework Equations

Solenoid equations
B=uo n i

The Attempt at a Solution

B (absence)=B (presence)
Uo n (i+im)=u n i
im=798A
But answer is 794A.[/B]

The answer should be M/H x 2A.

 

[Suyash Singh]

Can you guys give a formula for magnetising current for solenoid?Every book gives for transformer but not for solenoid

 

[rude man]

Can you guys give a formula for magnetising current for solenoid? Every book gives for transformer but not for solenoid

I just did, in post 3.

But you raise a good point: magnetizing current in a transformer is fundamentally different from magnetizing current in a solenoid. The latter term is actually rarely encountered. Why? Because it's a fictitious current whereas for a transformer it's very real.

For a solenoid, magnetizing current is defined to be the extra current that would be needed to restore the flux if the high-permeability core were removed.

For a transformer it's the actual primary current with the secondary open. It's the current needed to establish the flux given by Faraday's emf = -N d phi/dt. Note that emf = applied voltage - primary losses voltage drops.