The induced e.m.f in a circuit

Options

A. Decreases the magnetic flux through the circuit
B. increases the magnetic flux through the circuit
C. May increase or decrease the magnetic flux through the circuit
D. Leaves the magnetic flux through the circuit unchanged

Answer

To solve the question regarding the induced electromotive force (e.m.f) in a circuit, we will analyze the options provided and apply the principles of electromagnetic induction.

### Step-by-Step Solution:

1. **Understand the Concept of Induced EMF**:
- According to Faraday's Law of Electromagnetic Induction, an electromotive force is induced in a circuit when there is a change in magnetic flux through the circuit. The induced e.m.f. is directly proportional to the rate of change of magnetic flux.

2. **Analyze the Options**:
- The options provided are:
1. Decrease the magnetic flux through the circuit.
2. Increase the magnetic flux through the circuit.
3. May increase or decrease the magnetic flux through the circuit.
4. Lift the magnetic flux through the circuit.

3. **Evaluate Each Option**:
- **Option 1**: Decrease the magnetic flux through the circuit.
- This is correct. If the magnetic flux decreases, an induced e.m.f. will be generated to oppose this change (Lenz's Law).
- **Option 2**: Increase the magnetic flux through the circuit.
- This is also correct. If the magnetic flux increases, an induced e.m.f. will be generated to oppose the increase.
- **Option 3**: May increase or decrease the magnetic flux through the circuit.
- This is correct as well. The induced e.m.f. can occur with either an increase or a decrease in magnetic flux.
- **Option 4**: Lift the magnetic flux through the circuit.
- This option is not correctly stated in terms of electromagnetic induction principles. "Lifting" does not accurately describe a change in magnetic flux.

4. **Conclusion**:
- The correct options regarding induced e.m.f. in a circuit are Options 1, 2, and 3. Option 4 is incorrect.

### Final Answer:
- The induced e.m.f. in a circuit can occur when there is a decrease in magnetic flux, an increase in magnetic flux, or it may vary depending on the situation. However, "lifting" the magnetic flux is not a valid description.