# A magnetic circuit has a 20 cm lenght core with a permeability of 0.005 Wb/(Atm). The coil has 250 turns, and draws 0.4 ampere. Determine the flux density.

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The magnetic flux density due to a coil is given by,

`B=mu*H`

`=(mu*N*I)/l` (Where mu is the permeability of the solenoid, N, the number of turns, I, the current strength and l, the path length)

Plugging in the values,

`B=(0.005*250*0.4)/(20*10^(-2))`

`=2.5` Wb/m^2

`=2.5 T`

Therefore, the flux density of the coil is **2.5 T**.

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