Diagram: A diagram should show a straight wire with a current flowing upwards. An arrow representing the magnetic field B should point out of the page. An arrow representing the magnetic force F on the wire should be shown perpendicular to both the wire (upwards) and the magnetic field (out of the page). The direction of the force should be determined using Fleming's Left-Hand Rule.

Fleming's Left-Hand Rule: The direction of the magnetic force on a current-carrying conductor is determined by pointing your thumb in the direction of the current (I), your index finger in the direction of the magnetic field (B), and your middle finger will point in the direction of the force (F). This is represented by the mnemonic "Left Thumb, Index Finger, Middle Finger".

Explanation: The rule is used to determine the direction of the force by applying the three-finger rule. The thumb indicates the direction of the current, the index finger indicates the direction of the magnetic field, and the middle finger indicates the direction of the force. The force is always perpendicular to both the current and the magnetic field.

Apparatus:

• A rectangular bar magnet (or a solenoid to produce a uniform magnetic field)
• A conducting wire (e.g., copper) with a low resistance
• A battery to provide a constant voltage (e.g., 6V)
• A variable resistor to control the current
• A meter bridge or ammeter to measure the current
• A sensitive galvanometer or a compass to detect the deflection of the wire
• Connecting wires
• A ruler or measuring tape

Procedure:

1. Set up the apparatus as a Helmholtz coil configuration (or arrange the magnet and wire parallel to each other). Ensure the wire is positioned so that the magnetic field is perpendicular to the current direction.
2. Connect the battery, variable resistor, and conducting wire in a circuit.
3. Adjust the variable resistor to a low initial current.
4. Increase the current gradually using the variable resistor, noting the deflection of the galvanometer (or the compass needle).
5. Measure the current using the ammeter.
6. Record the current and the direction of the deflection.
7. Repeat the experiment for several different current values.

Collecting and Presenting Results:

For each current value, record the current (I) and the direction of the deflection. The direction of the deflection indicates the direction of the force. Plot a graph of force (deflection) against current. Alternatively, you could plot a graph of force against the magnetic field strength (if using a solenoid). The slope of the graph will represent the magnetic force per unit current.

Demonstrating the effect of reversing the current:

If the current is reversed, the direction of the force will also be reversed. This is because the force on a current-carrying conductor is given by F = BIlsinθ, where B is the magnetic field strength, I is the current, l is the length of the conductor in the magnetic field, and θ is the angle between the current and the magnetic field. If the current direction is reversed, sinθ becomes -sinθ, resulting in a force with the opposite direction.

Demonstrating the effect of reversing the direction of the magnetic field:

If the direction of the magnetic field is reversed, the direction of the force will also be reversed. This is because the force is proportional to the magnetic field strength (B). Reversing the field reverses the direction of the force. The magnitude of the force will remain the same if the magnetic field strength is constant.

When the velocity of a charged particle is parallel to the magnetic field, the magnetic force is zero. This is because sin(90°) = 1, and the force is proportional to sinθ. Therefore, F = qvBsinθ = qvBsin(90°) = qvB.

In this case, the velocity (v) is parallel to the magnetic field (B), so θ = 90 degrees and sin(90°) = 1.

Therefore, F = (-1.60 x 10^-19 C) * (2.0 x 10⁷ m/s) * (0.5 T)

F = -1.60 x 10^-18 N

The magnitude of the force is 1.60 x 10^-18 N, and the direction is parallel to the magnetic field (because the charge is negative).