Question 787 of 949
In a closed loop of wire, if the magnetic field passing through the loop is increased at a constant rate, what will be the direction of the induced current according to Lenz's Law?
- It will flow in a direction to oppose the increase in magnetic flux through the loop.
- It will flow in the same direction as the increasing magnetic field.
- It will not flow at all, as there is no change in magnetic flux.
- It will alternate direction depending on the strength of the magnetic field.
Correct Answer:
A
Explanation
### Correct Option: A. It will flow in a direction to oppose the increase in magnetic flux through the loop.
### Detailed Explanation:
To understand why option A is correct, we need to delve into the principles of electromagnetism, specifically Faraday's Law of Electromagnetic Induction and Lenz's Law.
1. **Faraday's Law of Electromagnetic Induction** states that a change in magnetic flux through a closed loop induces an electromotive force (EMF) in the loop. The induced EMF generates an induced current if the circuit is closed. The formula for Faraday's Law is:
\[
\text{EMF} = -\frac{d\Phi_B}{dt}
\]
where \(\Phi_B\) is the magnetic flux through the loop.
2. **Magnetic Flux (\(\Phi_B\))** is defined as:
\[
\Phi_B = B \cdot A \cdot \cos(\theta)
\]
where:
- \(B\) is the magnetic field strength,
- \(A\) is the area of the loop,
- \(\theta\) is the angle between the magnetic field and the normal (perpendicular) to the surface of the loop.
3. **Lenz's Law** states that the direction of the induced current will be such that it opposes the change in magnetic flux that produced it. This is a consequence of the conservation of energy. If the induced current were to flow in the same direction as the change in magnetic flux, it would create additional magnetic flux in the same direction, leading to an increase in energy that violates conservation principles.
### Application to the Question:
In the scenario presented, the magnetic field passing through the loop is **increasing** at a constant rate. This means that the magnetic flux through the loop is also increasing. According to Lenz's Law, the induced current will flow in a direction that opposes this increase in magnetic flux.
- **Induced Current Direction**: If the magnetic field is increasing in a certain direction (let's say into the page), the induced current will flow in a direction that creates a magnetic field opposing this increase. For example, if the magnetic field is directed into the page, the induced current will flow in a counterclockwise direction (when viewed from above) to create a magnetic field that points out of the page.
### Why the Other Options Are Incorrect:
- **Option B**: "It will flow in the same direction as the increasing magnetic field."
- This option is incorrect because it contradicts Lenz's Law. If the induced current flowed in the same direction as the increasing magnetic field, it would reinforce the increase in magnetic flux, which is not allowed by the principle of conservation of energy.
- **Option C**: "It will not flow at all, as there is no change in magnetic flux."
- This option is incorrect because there **is** a change in magnetic flux. The problem states that the magnetic field is increasing, which means the magnetic flux is changing. An induced current will occur due to this change.
- **Option D**: "It will alternate direction depending on the strength of the magnetic field."
- This option is misleading. The induced current will not alternate direction as long as the magnetic field is increasing steadily. Alternating current (AC) would occur if the magnetic field were changing direction periodically, which is not the case here.
### Summary of Key Points:
- **Lenz's Law** states that induced currents oppose the change in magnetic flux.
- An **increasing magnetic field** through a loop induces a current that creates a magnetic field opposing the increase.
- The induced current flows in a direction that opposes the change, which is consistent with the conservation of energy.
- Understanding the relationship between magnetic fields and induced currents is crucial for solving problems in electromagnetism.
This thorough understanding of Lenz's Law and Faraday's Law will help you tackle similar questions in your physics studies effectively!