# Magnetic Fields

1. Dec 2, 2007

### captainjack2000

1. Magnetic field inside a long solenoid with cross-sectional area A is given by B=(mu)nI where n is the number of turns per unit length and I is the current. Suppose that the current is given by I(t) = I(0)e^(a*t) where t is the time and a and I(0) are constants. What is the magnetic flux through the solenoid as a function of t? Hence find the induced emf outside the solenoid as a function of time

2. Relevant equations
Magnetic flux is the integral of B.dA
Faraday's Law: Emf = rate of change of magnetic flux through loop

2. Dec 3, 2007

### Gokul43201

Staff Emeritus
For a long solenoid, what is the direction of the B-field inside the solenoid? And is B a function of the position inside? What does this make $\int B\cdot dA~=~$ ?

3. Dec 5, 2007

### captainjack2000

Inside the solenoid the magnetic field B will be horizontal. But we know from the equation B=mu*n*I that it doesn't depend on the radius of the solenoid.