# Magnetic flux through the circular cross-sectional area of the solenoid

## Homework Statement

A solenoid 1.7 cm in diameter and 30 cm in length has 4000 turns and carries a current of 5 A. Calculate the magnetic flux(in Wb) through the circular cross-sectional area of the solenoid. Since this is a very long solenoid, you may use the simplified magnetic field formula for the infinite solenoid.

B = µ * N * I

## The Attempt at a Solution

B = (4 . π . 10^–7) . (4000 / 0.3) . 5 = 8.4 . 10^–2 T

My online homework is telling me this is incorrect. Im not sure what im doing wrong.

collinsmark
Homework Helper
Gold Member
Hello Kourtney0115,

It seems you've already calculated the magnetic field (measured in Teslas). Next step is to find the magnetic flux (measured in Webers).

Im not sure how to convert T into Wb. I tried to look it up on google and the only thing i found was T=Wb/m^2. But i am not given m^2.

collinsmark
Homework Helper
Gold Member
Im not sure how to convert T into Wb. I tried to look it up on google and the only thing i found was T=Wb/m^2. But i am not given m^2.

Magnetic flux is the magnetic field integrated over some surface (which has an area). For the special case where magnetic field is constant over a given area (surface), the the magnetic flux through that surface is the dot product of the magnetic field and the surface (the "surface" being something which has a surface area).

Hint: The problem statement says, "...through the circular cross-sectional area of the solenoid."