Why is the minus sign omitted in the voltage across the inductor?

In summary, according to Faraday's law, the equation for EMF is equal to the negative derivative of flux with respect to time. However, in practice, we write the voltage across an inductor as the derivative of flux with respect to time without the negative sign. This is because, in the case of an inductor in series with a battery and the switch is opened, the flux is decreasing but the voltage across the inductor will 'maintain' the current. This is explained by Lenz's law, which accounts for the choice of sign. Additionally, Kirchhoff's law states that the sum of voltage drops around a circuit must equal zero.
  • #1
ajith.mk91
30
0
According to faraday's law the governing equation is emf=-d(flux)/dt.But we usually write the voltage across the inductor as v=d(flux)/dt.What happened to the minus sign?
 
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  • #2
If there's an inductor in series with a battery and you open the switch, the flux will be decreasing yet the voltage that appears across the inductor in a sense that will 'maintain' the current. I think that (Lenz's law) accounts for the choice of sign.
 
  • #3
It is used to indicate that the induced emf OPPOSES the change producing it.
If you only need to calculate the magnitude is is common to drop the - sign
 
  • #4
Kirchhoff's law states the the sum of the voltage drops around the circuit must equal zero.
 
  • #5


The minus sign in Faraday's law represents the direction of the induced voltage, which is opposite to the change in magnetic flux. However, when we write the voltage across the inductor as v=d(flux)/dt, we are only interested in the magnitude of the induced voltage, not the direction. This is because in most practical applications, the direction of the induced voltage is already known based on the circuit configuration. Therefore, the minus sign is omitted for simplicity and convenience. However, it is important to remember the direction of the induced voltage when analyzing circuits and applying Faraday's law.
 

Related to Why is the minus sign omitted in the voltage across the inductor?

1. What is voltage across the inductor?

Voltage across the inductor refers to the potential difference between the two ends of the inductor in an electrical circuit. It is measured in volts and represents the amount of energy stored in the inductor.

2. How is voltage across the inductor calculated?

Voltage across the inductor can be calculated using Ohm's Law, which states that voltage (V) is equal to the product of current (I) and resistance (R). In the case of an inductor, the resistance is known as inductive reactance (XL) and is dependent on the frequency of the current passing through the inductor.

3. What is the relationship between voltage across the inductor and current?

The voltage across the inductor and the current through it are directly proportional. This means that as the current increases, the voltage across the inductor also increases. However, the rate at which the voltage increases is dependent on the inductor's inductance and the frequency of the current.

4. Why is voltage across the inductor important?

Voltage across the inductor is important because it affects the behavior of the inductor in an electrical circuit. It determines the amount of energy stored in the inductor and how it will respond to changes in the current passing through it. It is also a crucial factor in the design of electronic circuits.

5. How does voltage across the inductor change over time?

In an ideal inductor, the voltage across it remains constant over time. However, in a real-world circuit, the voltage across the inductor may change due to factors such as resistance in the circuit, changes in the frequency of the current, and the presence of other components. Additionally, when the current passing through the inductor changes, the voltage across it will also change as the inductor resists changes in current.

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