# Physics challenge

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16 years ago
#21
Yeah, regarding my post about a "spinning magnetic disc" in the first question of the exam, sorry, it should be "spinning *metal* disc", as it does not matter whether or not it is magnetic. (Thanks Rob)
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16 years ago
#22
The answer to the question is actually 0.0157Volts and can be easier calculated using V=ð*r^2*B*f, where V is the induced voltage required, B is the magnetic flux density r is the radius of rotating disk and f is the frequence of oscillations. Substituting...
V=ð*(0.1)^2*0.01*50=0.0157Volts approximately=0.016(2 d.c).
I think this way is much easier.
Btw did you find 0.0157 or 0.016 exactly?
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16 years ago
#23
Well Done. Thank you.
I found 0.0157 but I rounded it off.
You are right that you can do it both ways, whichever is easier is personal choice I guess..... I just like the neat way that it relates to the rate of change of flux, but is subtly different.
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