Faraday’s Law of Induction

 = -N  B /  t –  : induced potential (V) – N: # loops –  B : magnetic flux (Webers, Wb) – t: time (s)

Faraday’s Law of Induction  = -N  B /  t –  : induced potential (V) – N: # loops –  B : magnetic flux (Webers, Wb) – t: time (s)

A closer look …  = -  B /  t  = -  (BAcos  )/  t – To generate voltage Change B Change A Change 

Sample Problem A coil of radius 0.5 m consisting of 1000 loops is placed in a 500 mT magnetic field such that the flux is maximum. The field then drops to zero in 10 ms. What is the induced potential in the coil?

Sample Problem A single coil of radius 0.25 m is in a 100 mT magnetic field such that the flux is maximum. At time t = 1.0 seconds, field increases at a uniform rate so that at 11 seconds, it has a value of 600 mT. At time t = 11 seconds, the field stops increasing. What is the induced potential A) at t = 0.5 seconds? B) at t = 3.0 seconds? C) at t = 12 seconds?

Lenz’s Law The current will flow in a direction so as to oppose the change in flux. Use in combination with hand rule to predict current direction.

Sample Problem The magnetic field is increasing at a rate of 4.0 mT/s. What is the direction of the current in the wire loop?

Sample Problem The magnetic field is increasing at a rate of 4.0 mT/s. What is the direction of the current in the wire loop?

Sample Problem The magnetic field is decreasing at a rate of 4.0 mT/s. The radius of the loop is 3.0 m, and the resistance is 4 . What is the magnitude and direction of the current?