Magneto, determine magnet strength and voltage at rpm

[Jakefreese]

Homework Statement

A small engine flywheel rotates at 2000rpm and has 4 permanent magnents pressed into the flywheel at a radius of 10cm spaced 90deg apart 1.2cm diameter magnets. A 1.2cm diameter pickup coil with 500 turns is at the edge of the flywheel. Max voltage detected is .76 volts

What is the strength of the magnets and what would the max voltage be at 1000rpm

Homework Equations

[tex]\Phi[/tex]b=NBA[tex]\varpi[/tex]

The Attempt at a Solution

.076=(500)(.011304)(800/3[tex]\pi[/tex] )


B=[tex]\Phi[/tex]/[tex]\varpi[/tex]NA

B=.76/(500)(.011304)(800/3[tex]\pi[/tex]) = .00016 for magnetic strength but I know that Is not right, I am so twisted up on this problem, I think I need to just start back over. any guidance to get me pointed in a better direction would be appreciated. I know I need to factor in the flywheel size, but I am having an issue figuring out what to do to find that.

TIA

Jake

 

[AvroArrow]

The magnetic field strength B can be calculated from the equation B = V/(N*A*ω), where V is the maximum voltage detected, N is the number of turns in the pickup coil, A is the area of the magnet, and ω is the angular velocity in rad/s. Therefore, B = .76/(500*(.011304)*(800/3*π)) = 0.00016 T. At 1000 rpm, the maximum voltage detected would be 0.38V (half of the original voltage since the angular velocity is halved).