# Electricity and Magnetism question

A solenoid 2.9 cm in diameter and 15 cm in length has 300 turns and carries a current of 5 A. Calculate the magnetic flux through the circular cross-sectional area of the solenoid.

-->> I tried using the equation B = u(0)NI/L to calculate magnetic field, and then putting this in the formula flux = BNA, where N is number of turns, and A is area (pi*r squared). This didn't work, though.

I'd appreciate some help!!! Thanks!

## Answers and Replies

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The field is indeed given by
$$B=\frac{\mu_{0}NI}{L}$$

and the total flux through the solenoid
$$\phi=NAB$$ is also right.

Maybe what they asked for is the flux through a single turn which would be your answer divided by N

Also keep in mind that
$$B=\frac{\mu_{0}NI}{L}$$
is valid only for a long solenoid. (When its length is large compared to its radius)

I feel your solenoid is long enough. I don;t see why you're not arriving at the answer.

yep, it was wanting it through one turn. thanks.

mukundpa
Homework Helper
matt85 said:
... Calculate the magnetic flux through the circular cross-sectional area of the solenoid....

I think NBA is the total flux linked with the solenoid, not the flux through the cross-section. It is BA only.

MP