Why is the induced EMF on an inductor equal to -L (di/dt)?

In summary: L di/dt we need Ldi/dt; don't we not need a greater value? The induced emf is Ldi/dt; the negative sign just indicates it opposes the battery's emf. The electrons pushed through the inductor must overcome a voltage of Ldi/dt (that is, they must overcome an increase in potential of magnitude Ldi/dt), so they gain Lidi/dt of potential energy per unit time. This gain in potential is what the energy stored in the inductor really is.
  • #1
zero_kilo
10
0
so the amount of work done to drive the current through the inductor is given by

dw=Eidt where E is the emf of the variable voltage source.We put E=+L (di/dt).

can you please tell me why we put that value?? (i know the induced e.m.f on the inductor is - L (di/dt)

thanks :smile:
 
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  • #2
while calculating the amount of work done we have to take the integration. For that we have to reduce the expression of dw in single variable
So dw = Eidt = L*i*di/dt*dt = L*i*di.
Now take integrations to get the energy stored in the inductor.
 
  • #3
rl.bhat said:
while calculating the amount of work done we have to take the integration. For that we have to reduce the expression of dw in single variable
So dw = Eidt = L*i*di/dt*dt = L*i*di.
Now take integrations to get the energy stored in the inductor.

thanks but this is what i actually asked

zero_kilo said:
We put E=+L (di/dt).
can you please tell me why we put that value??
thanks :smile:

why we put E=+L dI/dt for the applied e.mf:confused:
 
  • #4
zero_kilo said:
why we put E=+L dI/dt for the applied e.mf:confused:

Consider the equation E = -L di/dt. The minus sign in the equation indicates that the induced EMF has an orientation that opposes the the change in current.

The reason why it's positive for your given equation, is because positive work must be done to induce the current. We need only the magnitude of E then.
 
  • #5
buffordboy23 said:
Consider the equation E = -L di/dt. The minus sign in the equation indicates that the induced EMF has an orientation that opposes the the change in current.

The reason why it's positive for your given equation, is because positive work must be done to induce the current. We need only the magnitude of E then.

thanks :smile: but why to drive the current through the circuit so as to defeat the induced e.m.f -L di/dt we need Ldi/dt; don't we not need a greater value??

thanks again.
 
  • #6
The induced emf is Ldi/dt; the negative sign just indicates it opposes the battery's emf. The electrons pushed through the inductor must overcome a voltage of Ldi/dt (that is, they must overcome an increase in potential of magnitude Ldi/dt), so they gain Lidi/dt of potential energy per unit time. This gain in potential is what the energy stored in the inductor really is.
 
  • #7
ideasrule said:
The induced emf is Ldi/dt; the negative sign just indicates it opposes the battery's emf.

I don't think that this is quite correct.

Consider a circuit with an applied emf, resistor, and inductor, where the current varies with time. If the current is increasing (di/dt > 0 ), then the self-induced emf opposes the direction of the applied emf. If the current is decreasing (di/dt < 0), the self-induced emf is actually oriented in the same direction as the applied emf.

In both cases, the self-induced emf has orientation that always opposes the "change in current", not the "applied emf."
 
  • #8
thanks :-)
 

1. What is an inductor?

An inductor is a passive electronic component that is designed to store energy in the form of a magnetic field. It is typically made of a coil of wire and is used in many electronic devices.

2. How does an inductor store energy?

An inductor stores energy by creating a magnetic field when an electric current flows through it. This magnetic field stores the energy in the form of potential energy.

3. What is the unit of measurement for energy stored in an inductor?

The unit of measurement for energy stored in an inductor is joules (J). This is the same unit used to measure other forms of energy, such as kinetic energy and potential energy.

4. How is the energy stored in an inductor calculated?

The energy stored in an inductor can be calculated using the formula E = 1/2 * L * I^2, where E is the energy in joules, L is the inductance in henrys, and I is the current in amperes.

5. How does the energy stored in an inductor affect the performance of an electronic device?

The energy stored in an inductor can affect the performance of an electronic device in various ways. For example, it can cause delays in signal transmission, regulate power supply, and affect the overall efficiency of the device.

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