In: Physics
A solenoid of radius 3.5 cm has 800 turns and a length of 25 cm.
(a) Find its inductance.
mH
(b) Find the rate at which current must change through it to
produce an emf of 90 mV. (Enter the magnitude.)
A/s
a)
The magnetic flux is produced by the solenoid is given by

the magnetic flux through a single turn is given by

In a length 'l', there are 'nl' such turns, so the total flux is given by

we know that from the definition of the inductance

where
n=no of turns
l=length of solenoid
R=radius of solenoid
I=current through the solenoid
L=inductance of the solenoid
comparing equation (1) and equation (2) we get

Given
n=800
l=25cm=0.25m
R=3.5cm=0.35m
so

or,

b)
the emf is given by

or,

or,

the rate of change of current is

Given,

so,

