How Induced EMF and Current Work in Everyday Physics
Induced electromotive current is the induction of current in the loop just by changing the magnetic field. In Faraday’s law, there are some experiments which are based on this theory. In the first experiment, we have noticed that the ammeter shows zero current reading which generally means or proves that a stationary magnet does not induce a current in a coil. In the second experiment, we have noticed that the meter shows the induction the current which demonstrates that it is due to the change in the magnetic field as the magnet is moved towards or we can say away from the coil.
So it is very clear to us that a constant magnetic field generally does nothing to the coil while we can say that a changing field causes current to flow.
Hence we can gain an observation from the above experiments that we have discussed that only by changing a magnetic field we can make the current flow. To be more accurate we can say that if the magnetic flux through a coil is changed then a voltage will be produced. This voltage is called the induced emf.
Based on his understanding of electromagnets we can say that he expected that when current started to flow in one wire a sort of wave would travel through the ring and then cause some electrical effect on the opposite side. He plugged one wire that too into a galvanometer and then watched it as he connected the other wire to a battery as well. He saw a transient current which he for himself called as a "wave of electricity". when he connected the wire with the battery and another when he disconnected it. Within two months the scientist named Faraday found several other manifestations of electromagnetic induction.
Induced Electromotive Force
The Magnetic flux is generally linked with the surface area when it is held inside the magnetic field. We can say that when the direction of the magnetic field is perpendicular to the surface area then the flux of magnet or we can say that the magnetic flux on the surface is more. When the magnetic field is said to be parallel to the surface area, then the magnetic flux is on the surface which is less.
Have you ever wondered that when the coil completely remains inside the magnetic field that too during motion then why no current flows through it?
When the coil is said to be entirely inside the magnetic field, one of the two ends of the coil becomes positive and the other end of the coil becomes negative. The potential difference which is between the coils will be equal in each case. So when two cells that are having equivalent electromotive force are connected to each other then we can say that no current flows through the coil, and no net induced electromotive force exists in the coil.
The law of Lenz's describes the direction which is of the induced field.
Induced Electromotive Force and Current
Faraday's law that generally describes two different phenomena that is the motional EMF generated by a force which is the magnetic force on a moving wire and the transformer that is of the EMF this is generated by an electric force due to a changing magnetic field that too due to the differential form of the Maxwell–Faraday equation. In 1861, James Clerk Maxwell drew attention to this separate physical phenomena. This is believed or said to be a unique example in physics of where such a fundamental law is invoked to explain two such different phenomena.
Do You Know?
What happens when the string of the electric guitar which we use to play vibrates?
When the string of an electric guitar vibrates then we can say that an electromotive force is introduced in the coil. The induced magnetization which is present in the string is picked up from the vibration of the guitar. The input which is of an amplifier that is of the guitar is connected to the two ends of the coil which are connected to the speakers.
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FAQs on Induced Electromotive Force and Current: Key Concepts
1. What are induced electromotive force (EMF) and induced current?
An induced electromotive force (EMF) is the potential difference (voltage) generated in a conductor or a coil when it is subjected to a changing magnetic field. This phenomenon is known as electromagnetic induction. If the conductor forms a closed circuit, this induced EMF drives a flow of charge, which is called the induced current. Essentially, the changing magnetic field creates the EMF, and the EMF causes the current to flow in a complete circuit.
2. What is the fundamental difference between an induced EMF and an induced current?
The key difference lies in cause and effect. Induced EMF is the cause; it is the voltage produced due to the rate of change of magnetic flux, irrespective of whether the circuit is open or closed. Induced current is the effect; it is the flow of charge that results from the induced EMF, but it only exists if there is a complete, closed path for the current to flow. The magnitude of the induced current depends on both the induced EMF and the resistance of the circuit (I = ε/R).
3. How is induced EMF calculated according to Faraday's Law of Induction?
According to Faraday's Law of Induction, the magnitude of the induced EMF (ε) in any closed circuit is directly proportional to the rate of change of the magnetic flux (ΦB) through the circuit. The formula is given by:
ε = -N (dΦB / dt)
Where:
- ε is the induced EMF (in Volts).
- N is the number of turns in the coil.
- dΦB/dt is the rate of change of magnetic flux (in Weber/second).
- The negative sign indicates the direction of the induced EMF, as explained by Lenz's Law.
4. Why is there a negative sign in the formula for induced EMF (Faraday's Law)?
The negative sign in the formula ε = -dΦB/dt represents Lenz's Law, which is a consequence of the conservation of energy. It states that the direction of the induced current (and hence the induced EMF) is always such that it opposes the very change in magnetic flux that produced it. For example, if the magnetic flux through a coil is increasing, the induced current will create its own magnetic field in the opposite direction to counteract this increase.
5. How does an AC generator demonstrate the principle of electromagnetic induction?
An AC generator is a prime practical application of electromagnetic induction. It works by rotating a coil of wire (armature) within a uniform magnetic field. As the coil rotates, the angle between the coil's area vector and the magnetic field changes continuously. This continuous change in orientation causes the magnetic flux linked with the coil to change, which, according to Faraday's Law, induces an alternating EMF and hence an alternating current (AC) in the coil.
6. What would happen if a closed conducting loop moves through a uniform magnetic field without changing its orientation or shape?
If a closed conducting loop moves through a uniform magnetic field such that the magnetic flux passing through it remains constant, no EMF will be induced. An induced EMF is generated only when there is a *change* in magnetic flux (dΦB/dt ≠ 0). If the loop moves entirely within the uniform field without rotating or deforming, the amount of magnetic field passing through it does not change, and therefore, both the induced EMF and induced current will be zero.
7. What are eddy currents and how are they related to induced current?
Eddy currents are loops of electrical current induced within the bulk of a conductor when it is subjected to a changing magnetic field. They are essentially a form of induced current that flows in circular paths within the material, similar to eddies in a fluid. Because they flow through the resistance of the material, they dissipate energy as heat (I²R loss). This effect is utilised in applications like magnetic braking in trains and induction furnaces, but it is an undesirable cause of energy loss in transformer cores.
8. How do self-induction and mutual induction differ from each other?
Both are phenomena of electromagnetic induction, but they differ in the source and location of the induced EMF.
- Self-Induction: This occurs when the changing current in a coil induces an EMF *in the same coil*. This induced EMF, known as back EMF, opposes the change in the current that is causing it. A single inductor is an example.
- Mutual Induction: This occurs when a changing current in one coil induces an EMF *in a separate, nearby coil*. The magnetic flux produced by the first coil (primary) links with the second coil (secondary), and any change in this flux induces an EMF in the secondary coil. This is the working principle of a transformer.
