Prove that emf from E equals emf from dB/dt

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In summary, the conversation is about proving that two equations, e1 and e2, are equal. Both equations involve integrals and have different variables and conditions. The conversation also discusses the tricky part of integrating a vector over a surface and how to approach it.
  • #1
Addez123
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Exercise:
I'm suppose to prove that e1 = e2
e1 = ∫E*dl
e2 = ∫dB/dt*dS

where S is the surface encircled by the conture c.
c is a box with with a length (in x axis) and b height (in y axis).
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for an electromagnetic wave:
E = E0*sin(kx - wt) (in y axis)

I'm ASSUMING this means that
B = B0*sin(kx - wt) (in z axis)

Pathetic Attempt:
e1 calculated on the outside of c becomes
b*E(x + a,t) - b*E(x,t) =
E0*sin(kx + ka - wt) + E0*sin(kx - wt)
This expression is confusing and doesn't lead to any simplification at all.

e2 = ∫dB/dt*dS
dB/dt = B0*-w*cos(kx - wt)

Now here's the tricky part, how do I integrate this infinitly thing vector over a surface?
The wave has no thickness, shouldn't the integral be zero?!
 
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  • #2
I'm also suppose to prove this explicitly, I DONT EVEN KNOW WHAT THAT MEANS!
 
  • #3
Addez123 said:
e1 calculated on the outside of c becomes
b*E(x + a,t) - b*E(x,t) =
E0*sin(kx + ka - wt) + E0*sin(kx - wt)
What happened to the factor of b in going to the last line. Also, what happened to the negative sign between the two terms?

This expression is confusing and doesn't lead to any simplification at all.
You've made a good start once you make the corrections above.

e2 = ∫dB/dt*dS
dB/dt = B0*-w*cos(kx - wt)
OK

Now here's the tricky part, how do I integrate this infinitly thing vector over a surface?
The wave has no thickness, shouldn't the integral be zero?!
Not sure what you mean by "this infinitly thing vector".
##\frac{\partial B}{\partial t}## is a function of ##x## and ##t##. ##t## is some fixed but arbitrary time. So, you can think of ##\frac{\partial B}{\partial t}## as a function of ##x## that you need to integrate over the rectangular area. What would be a good way to break up the area into infinitesimal elements ##dS##? Recall how you did similar integrals in your calculus course.
 

Related to Prove that emf from E equals emf from dB/dt

1. What is the equation for emf from E and emf from dB/dt?

The equation for emf from E and emf from dB/dt is given by:
emf = - (dΦ/dt), where Φ is the magnetic flux through a closed loop.

2. How does emf from E and emf from dB/dt relate to each other?

The emf from E and emf from dB/dt are equal in magnitude but have opposite signs. This means that they cancel each other out and result in a net emf of zero.

3. Why is the equation for emf from E and emf from dB/dt important?

This equation is important because it helps us understand how changing magnetic fields can induce an emf in a closed loop. It also forms the basis for Faraday's law of induction.

4. Can you give an example of how this equation is used in real life?

One example is the functioning of generators, where mechanical energy is used to rotate a coil in a magnetic field, producing an emf according to the equation.

5. How is the concept of emf from E and emf from dB/dt related to electromagnetic waves?

In electromagnetic waves, the changing electric and magnetic fields are perpendicular to each other and constantly changing. This results in an oscillating emf that propagates as the wave. However, the equation for emf from E and emf from dB/dt still holds true for each individual point in the wave.

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