Question
Consider a magnet surrounded by a wire with an on/off switch S (Fig). If the switch is thrown from the off position (open circuit) to the on position (closed circuit), will a current flow in the circuit? Explain.
Consider a magnet surrounded by a wire with an on/off switch S (Fig). If the switch is thrown from the off position (open circuit) to the on position (closed circuit), will a current flow in the circuit? Explain.
✓
Answer
Key concept: The total number of magenetic lines of force passing notmally through an area placed in a magnetic field is equal to the magnetic flux linked with that area.
$\phi_\text{m}=\vec{\text{B}}.\vec{\text{A}}=\text{BA}\cos\theta$
($\theta$ is the angle between area vector and magnetic field vector)
Whenever the number fo magnetic lines of force (magnetic flux) passing through a circuit changes an emf is produced in the circuit called induced emf.
The induced emf persists only as long as there is a change or cutting of flux.
The induced emf is given by rate of change of magnetic flux linked with the circuit i.e, $\text{e}=-\frac{\text{d}\phi}{\text{dt}}$. so flux linked will change when either magnetic field, area or the angle between B and A changes.
If the switch is closed, the circuit will complete. But to induce emf in the circuit, we need:
$\phi_\text{m}=\vec{\text{B}}.\vec{\text{A}}=\text{BA}\cos\theta$
($\theta$ is the angle between area vector and magnetic field vector)
Whenever the number fo magnetic lines of force (magnetic flux) passing through a circuit changes an emf is produced in the circuit called induced emf.
The induced emf persists only as long as there is a change or cutting of flux.
The induced emf is given by rate of change of magnetic flux linked with the circuit i.e, $\text{e}=-\frac{\text{d}\phi}{\text{dt}}$. so flux linked will change when either magnetic field, area or the angle between B and A changes.
If the switch is closed, the circuit will complete. But to induce emf in the circuit, we need:
- A changing magnetic field, but the bar magnet is stationary so it is not possible in this situation.
- A changing area, which is also not possible because area is also constant as coil is not expanding or compressed.
- Angle between B bar and A bar changes, which is also not possible in this situation because orientation of bar magnet and coil is fixed.
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