# Find the Magnitude of Emf Induced in a Circular Loop After 6.00s

• Charanjit
In summary, the conversation discusses a homework problem involving a circular loop of flexible iron wire in a magnetic field. The loop's circumference is decreasing at a constant rate due to a tangential pull on the wire, and the problem asks to find the induced emf after 6.00 seconds. The attempted solution uses equations for flux and emf, but the feedback suggests that the decrease in circumference also affects the area and therefore the magnetic flux. The person is asking for clarification and help with entering mathematical symbols in their response.

#### Charanjit

1. Homework Statement :
A circular loop of flexible iron wire has an initial circumference of 166cm , but its circumference is decreasing at a constant rate of 13.0cm/s due to a tangential pull on the wire. The loop is in a constant uniform magnetic field of magnitude 1.00 T, which is oriented perpendicular to the plane of the loop.

Question: Find the (magnitude of the) emf induced in the loop after exactly time 6.00 s has passed since the circumference of the loop started to decrease.

2. Homework Equations :
Flux= Close integral(B*dA)
e=(d/dt)Flux

3. The Attempt at a Solution :
C(t)=C0-at = 1.66-0.13(6.00)=0.88m
0.88=2pi*r --> pi*r=0.44
e=pi*rdrB = 0.44(1)(0.130m/s)/2pi = 0.00190V

Since I am using web assign, it said this was incorrect. and gave me feedback which stated: A decrease in the circumference of the loop will also cause a decrease in the area and hence the magnetic flux. This will induce an emf in the loop.

Hmm... seems like two things are chaning the circumference and the area. So where am I wrong, and what should I do?

Edit: Also are there ways to enter integral sign and other things here?

Last edited:
Anyone help on this?

Hello?