Calculate The average EMF induced in the loop (1 Viewer)

[Jouma47]

Hi, i have no idea how to do this, i missed the lesson, so plz help or just tell me what equation to use plz. thx

A single loop of wire shaped in a circle is located in a 0.25T magnetic field. The plane of the loop is at right angles to the magnetic field and the loop has raduis 7.5cm. The loop is rotated through 90degrees in 0.15s so that the plane of the loop is now parallel to the magnetic field.
Calculate the average emf induced in the loop.

 

[Mountain.Dew]

EMF = -(change in flux) / time, where:

t = 0.15, flux = B*A, B = magnetic field strength, A = area.

so, change in flux = 0.25 * (0.075)²*pi. note that 7.5cm = 0.075m

so EMF = 0.25 * (0.075)²*pi / 0.15 = -3pi/320V

hopefully that is right...

 

[Dragie]

1st find the area:
A=πr^2
A=π x 0.075^2
A=0.0176

2nd, find the magnetic flux:
φ=BA
φ=0.25x0.0176
φ=0.0044

3rd, find the EMF induced:
E=-n(Δφ/Δt)
E=-1(0.0044/0.15)
E=-0.0333 (the minus indicates the EMF)

When you do it in these three steps using the three different formulas, you'll find that it is much easier to understand and to actually answer the question!

 

[Mountain.Dew]

mmmmmmm i got a different answer, -0.0294...

1st find the area:
A=πr^2
A=π x 0.075^2
A=0.0176

i personally wouldnt round off values HERE, since the round of error will carry on to the 2nd and 3rd formulae.

personally, i suggest leaving ur answer as accurately as possible (e.g. retaining the pi's) unti the very end.

that said, Dragie's mathematical method looks good. explained it much more clearly than i did! XD. cheers, Dragie!

 

[Dragie]

Woops I tend to round off to much Haha thanks mountaindew!

 

[Riviet]

I would highly recommend you keep those exact values stored in your memory and use them later for the next equation or part of the question.
You can write it as 0.12345.... for example, store it in your calculator, and use this in your next substitution. You should only round when you get to your final answer.

 

[Dragie]

Haha so true - last physics exam I got told off about rounding off too early and then I did it again in maths lol I never learn