A metal sheet is placed in front of a strong magnetic pole. A force is needed to

Options

A. hold the sheet there if the metal is magnetic
B. hold the sheet there if the metal is nonmagnetic
C. move the sheet away from the pole with uniform velocity if the metal is nonmagnetic.
D. move the sheet away from the pole with uniform velocity if the metal is nonmegnetic. Neglect any effect of paramagnetism, diamagnetism and gravity.

Answer

To solve the problem, we need to analyze the situation of a metal sheet placed in front of a strong magnetic pole and determine the forces required under different conditions.

### Step-by-Step Solution:

1. **Understanding the Setup**:
- We have a metal sheet placed in front of a strong magnetic pole.
- The metal sheet can be either magnetic (like iron) or non-magnetic (like aluminum).

2. **Holding the Sheet in Place**:
- If the metal sheet is **magnetic**: When a magnetic material is placed in a magnetic field, it will generate its own magnetic field. This induced magnetic field will interact with the external magnetic field, leading to a repulsive or attractive force. To keep the sheet stationary in the magnetic field, an external force is required to counteract this interaction.
- If the metal sheet is **non-magnetic**: Non-magnetic materials do not generate their own magnetic field. Therefore, no external force is needed to hold the sheet in place since there is no interaction with the magnetic field.

3. **Moving the Sheet Away from the Magnetic Pole**:
- If the metal sheet is **non-magnetic**: When moving a conductor through a magnetic field, an electromotive force (EMF) is induced according to Faraday's law of electromagnetic induction. This induced EMF will create a current that generates its own magnetic field, which opposes the motion (Lenz's Law). Therefore, a force is required to move the sheet away at a uniform velocity.
- If the metal sheet is **magnetic**: The same principle applies. As the magnetic sheet moves away from the magnetic pole, it will also experience an induced EMF and a magnetic interaction that opposes the motion. Thus, an external force is also required in this case.

4. **Summary of Forces Required**:
- To **hold the sheet** in place:
- **Magnetic sheet**: Requires external force.
- **Non-magnetic sheet**: Does not require external force.
- To **move the sheet away**:
- **Magnetic sheet**: Requires external force.
- **Non-magnetic sheet**: Requires external force.

### Final Conclusion:
- An external force is required to hold a magnetic metal sheet in place, while no force is needed for a non-magnetic sheet. However, an external force is required to move the sheet away from the magnetic pole, regardless of whether the sheet is magnetic or non-magnetic.