1. Concept Overview
Induced current is the current that flows in a conductor when the magnetic flux linked with it changes. No battery is needed — the changing magnetic environment itself produces the emf that drives the current. I always keep this thought in mind: changing flux creates emf, and emf creates current (if the circuit is closed).
Whenever flux increases or decreases, the conductor responds by producing its own current. This current is temporary and lasts only while the flux is changing.
1.1. Quick one-line idea
Changing magnetic flux → induced emf → induced current (in a closed loop).
2. What Induced Current Really Means
Induced current is simply the flow of charges caused by induced emf. The conductor behaves just like it is connected to a voltage source, but this voltage source is created by changing magnetic conditions instead of a chemical battery.
3. How Changing Flux Produces Induced Current
Since magnetic flux is \( \Phi_B = B A \cos\theta \), the flux changes whenever:
- the magnetic field strength changes,
- the area of the loop changes,
- the orientation of the loop changes.
In all these cases, the change in flux produces an induced emf, which gives rise to an induced current.
3.1. Examples of flux change
- Moving a magnet towards or away from a coil.
- Sliding a conductor in a magnetic field so the enclosed area changes.
- Rotating a loop in a magnetic field (basis of AC generation).
4. Direction of Induced Current
Finding the direction of induced current is important in understanding magnetic interactions. Two tools help me decide the direction:
- Lenz’s law (conceptual rule)
- Fleming’s right-hand rule (hand-rule method)
4.1. Using Lenz’s law
Lenz’s law says: the induced current flows in such a direction that its magnetic effect opposes the change in flux. So first I check whether flux is increasing or decreasing, then imagine what magnetic field the coil must produce to oppose it. That tells me the current direction (clockwise or anticlockwise).
4.2. Using Fleming’s right-hand rule
For a moving conductor, I stretch the right hand so that thumb, first finger and middle finger are at right angles:
- Thumb → direction of motion of conductor
- First finger → direction of magnetic field
- Middle finger → direction of induced current
5. Instantaneous vs. Average Induced Current
The induced current depends on the type of flux change.
5.1. Instantaneous induced current
When flux changes continuously or irregularly, the induced emf is given by:
\( \varepsilon = -\dfrac{d\Phi_B}{dt} \)
and the instantaneous current is:
\( I(t) = \dfrac{\varepsilon(t)}{R} \)
5.2. Average induced current
For uniform flux changes over a time interval:
\( I = \dfrac{1}{R} \left( -\dfrac{\Delta \Phi_B}{\Delta t} \right) \)
6. Opposition Created by Induced Current
Induced current isn’t passive — it produces a magnetic field that actively opposes the process that caused it. This opposition ensures energy conservation. I can feel this resistance physically when I move a magnet quickly near a coil.
6.1. Physical feel examples
- A magnet pushed into a coil feels resisted because the induced current creates a repelling field.
- A magnet falling through a copper tube slows down due to induced currents (eddy currents).
- Sliding a metal rod in a field becomes harder because induced current creates opposing magnetic forces.
7. Practical Situations Where Induced Current Appears
Induced current is everywhere — in machines, household devices and even simple classroom demonstrations. These examples help me connect the concept to real applications.
7.1. Generators
Rotating coils in a magnetic field changes flux continuously, producing alternating induced current.
7.2. Transformers
Rapidly changing flux in the primary coil induces current in the secondary coil.
7.3. Induction cookers and induction motors
Changing magnetic fields induce currents in metal surfaces, producing heating or rotation.