# Need Help, Cant Figure Out

1. Mar 19, 2011

### imapeiceofwod

Transcranial magnetic stimulation (TMS) is a noninvasive technique used to stimulate regions of the human brain. In TMS, a small coil is placed on the scalp and a brief burst of current in the coil produces a rapidly changing magnetic field inside the brain. The induced emf can stimulate neuronal activity.
(a) One such device generates an upward magnetic field within the brain that rises from zero to 1.50 T in 125 ms. Determine the induced emf around a horizontal circle of tissue of radius 1.70 mm.
magnitude 109 µV

(b) The field next changes to 0.500 T downward in 95.0 ms. How does the emf induced in this process co

A long solenoid with 6.50 102 turns per meter and radius 2.00 cm carries an oscillating current I = 3.00 sin 90πt, where I is in amperes and t is in seconds.
(a) What is the electric field induced at a radius r = 1.00 cm from the axis of the solenoid? (Use the following as necessary: t. Let E be measured in millivolts/meter and t be measured in seconds.)
E=?

any help.

2. Mar 19, 2011

### v0id19

Well what have you tried so far to solve these?

Remember Maxwell's equations; they are the tools you'll need to solve most E&M problems at this level. Specifically, Faraday's Law will help with part (a).

3. Mar 19, 2011

### imapeiceofwod

can anyone help be out?

4. Mar 19, 2011

### v0id19

hmm apparently my hint wasn't help...

Faraday's law: $$E \cdot dl = -\frac{d\Phi}{dt}$$
You know dl, and can calculate the change in flux, so you can solve for E...

5. Mar 19, 2011

### imapeiceofwod

im sorry im still not getting it. can you show me with an example? like use different values or something then i could do it on my own. maybe its just me but that is how i learn.

6. Mar 19, 2011

### I like Serena

$$emf = - \frac {d\Phi} {dt}$$
$$V = - \frac {\Delta B \times A} {\Delta t} = - \frac {\Delta B \times \pi r^2} {\Delta t}$$