• JosephF
In summary, the conversation discusses a homework problem involving a rotating rectangular coil in a magnetic field. The value of theta at which the magnetic flux through the coil is a minimum is 0, and the maximum flux linkage occurs when theta is 90 degrees. The correct calculations for the problem are provided and confirmed by the other person in the conversation.

#### JosephF

Apologies for numerous posts today, I'm trying to catch up from work I missed last term, and my uni is on holiday at the moment so can't get help from lecturers.

I've been set the following which I think I've got correct, but not 100%. Am I right in calculating the area in m2?

## Homework Statement

2. A rectangular coil measuring 20mm by 35mm and having 650 turns is rotating about a horizontal axis which is at right angles to a uniform magnetic field of flux density 2.5x10-3T. The plane of the coil makes an angle θ with the vertical, as shown in the diagrams.

(i) State the value of θ when the magnetic flux through the coil is a minimum.
(ii) Calculate the magnetic flux passing through the coil when θ is 30o.
(iii) What is the maximum flux linkage through the coil as it rotates?

ΔΦ=NBAsinθ

## The Attempt at a Solution

i) Φ is at a minimum when θ=0

ii) ΔΦ=650x(2.5x10-3)x(0.002x0.0035)sin30

=1.365x10-5sin30

=5.6875x10-6Wb

iii) Flux linkage is maximum when θ=90

ΔΦ=1.375x10-5sin90

=1.375x10-5Wb

Thanks,

Almost, 1 m = 1000 mm, so 20 mm =20*10^-3m=0.02m. So you're a factor 100 off regarding the area.

3. The Attempt at a Solution

i) Φ is at a minimum when θ=0

ii) ΔΦ=650x(2.5x10-3)x(0.02x0.035)sin30

=1.1375x10-3sin30

=5.6875x10-4Wb

iii) Flux linkage is maximum when θ=90

ΔΦ=1.1375x10-3sin90

=1.1375x10-3Wb

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Ah, that was careless of me! Thanks for pointing it out. Is everything now correct. Am I right with my assumptions of min when θ=0 and max when θ=90?

Thanks,

Yes everything seems to be correct now. Your assumptions are easy to check. When theta is 0 the coil is parallel to the magnetic field so no field lines pass through the coil. When theta is 90 degrees the coil is perpendicular to the magnetic field and a maximum amount of field lines go through the coil.

That brilliant. Thanks again.