## Magnetic Field and Electric field outside a long solenoid

Hello,

The question goes like this:

A long solenoid has n turns per unit length and carries a current given by I=I₀sinωt. The solenoid has a circular cross section of radius R. Find the induced electric field at a radios r from the axis of the solenoid for (a) r<R (b) r>R

Well, i got the first part as E=μRēNēωI₀cos(ωt)/(2Rl). Does this looks like it?

For the second bit, i found it as zero. But i am not really sure. And if it is zero, What should i say?
 PhysOrg.com science news on PhysOrg.com >> City-life changes blackbird personalities, study shows>> Origins of 'The Hoff' crab revealed (w/ Video)>> Older males make better fathers: Mature male beetles work harder, care less about female infidelity
 Hello there, You'll have to excuse me because I'm not using the greek symbols. (a) rR, outside You are confusing with the case when magnetic field is zero outside long solenoid due to cancellations between field due to currents in successive & opposite loops. In this case, (r>R...remember loop is longer) E*2*pi*r = -pi*(R^2)*mu*n*I*omega*cos(omega*t) (remember flux is over an area defined by pi*(R^2)) E = -(mu*n*I*omega*(R^2)*cos(omega*t))/ (2*r) is the induced electric field outside. Hope that helps, Rama
 Mentor Are you sure they are asking about Electric fields? That doesn't make much sense. More often, you will be asked to solve for the magnetic field as a function of radius for the solenoid....

## Magnetic Field and Electric field outside a long solenoid

Yea, i m asked to find electric field. And i just found out this is one of the question found from the textbook. And yes, thats the correct answers! but i am still not sure why it is not zero. isnt that when theres no magnetic field, theres no electric field as well?
 Recognitions: Gold Member Homework Help Science Advisor darkar, To understand why there is an electric field outside the solenoid, just think about Faraday's Law. If you draw a loop around the solenoid, the magnetic flux through the loop is changing as a function of time, right? Even though there is no magnetic field outside the solenoid there is still a changing magnetic flux (from the field inside the solenoid). What does this tell you about the electric field?
 Yea, thats amaze me. Why can there be magnetic flux but no magnetic field. So lif theres magnetic field, the magnetic flux is constant?

 Similar discussions for: Magnetic Field and Electric field outside a long solenoid Thread Forum Replies General Physics 4 Introductory Physics Homework 6 General Engineering 0 Introductory Physics Homework 6 Electrical Engineering 2