practical engineering science

用戶173198

2007-03-15 7:07 am

the magnetic flux passing through a coil haveing 150 turns drops from .01Wb to .025 Wb in 2 second.The coil connected to light bulb of resistance 5 ohms .Calculate the emf induced and the current delivered to the light bulb

thx~~

回答 (1)

Mr. Ding

2007-03-15 7:39 am

✔ 最佳答案

Ok. This question is about electromagnetic induction.

Step One
Assuming the flux is dropping linearly, the average rate of change of flux is given by:

(0.01 - 0.025) / 2 = -0.0075 (Wb/s)

Since we are not interested in the direction of induced emf/current, we can just take the magnitude of this value, i.e. 0.0075(Wb/s)

Step Two
By Faraday's Law, the induced emf is given by the rate of change of flux linkage.

that is to say, induced emf = (No. of turns) x (rate of change of flux)

induced emf = 150 x (0.0075) = 1.125V which is generated across the resistance

Step Three
By Ohm's law, V=IR

the induced current I = V/R = 1.125 / 5 = 0.225A

Thank you for reading

參考: myself

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