Sp Unit 4.4

Practicals

Magnetic fields

Sp Unit 4.4

Practicals

Magnetic fields

Learners should be able to demonstrate and apply their knowledge and understanding of:
1. Investigation of the force on a current in a magnetic field
2. Investigation of magnetic flux density using a hall probe

  • 1.    Investigation of the force on a current in a magnetic field

  • ⇒ Objective:

  • To study the force experienced by a current-carrying conductor in a magnetic field and verify the relationship:
  • [math]F = BILsinθ[/math]
  • Where:
  • – F = Force (N)
  • – B = Magnetic flux density (T)
  • – I = Current (A)
  • – L = Length of conductor in the field (m)
  • – θ = Angle between the conductor and the magnetic field

  • ⇒   Apparatus Required:

  • – A U-shaped magnet
  • – A copper wire (thin, straight conductor)
  • – A digital balance
  • – A DC power supply
  • – A variable resistor
  • – A switch
  • – A ammeter
  • Figure 1 The force on a current in a magnetic field

  • ⇒   Procedure:

  • Step 1: Set Up the Circuit
    1. Place the U-shaped magnet on a digital balance.
    2. Suspend a straight copper wire horizontally between the poles of the magnet so that it is perpendicular to the magnetic field.
    3. Connect the wire in series with a power supply, an ammeter, and a variable resistor.
    4. Zero the balance before switching on the current.
  • Step 2: Measure the Force
    1. Switch on the power supply and set a small current.
    2. Observe the reading on the balance—it changes due to the force exerted on the conductor.
    3. Record the mass difference before and after switching on the current. Convert this mass change ([math]Δm[/math]) into force using

      [math]F = Δmg[/math]

    4. Repeat for different currents and record data.

  • ⇒  Precautions & Errors:

  • – Ensure the wire is perpendicular to the magnetic field for accurate results.
  • – Minimize external vibrations that can affect the balance reading.
  • – Use a precise digital balance for better accuracy.

  • ⇒  Conclusion:

  • The experiment confirms that the force on a current-carrying conductor in a magnetic field is directly proportional to the current, verifying the equation
  • [math]F = BILsinθ[/math]

  • 2.    Investigation of magnetic flux density using a hall probe

  • ⇒   Objective:

  • To measure the magnetic flux density (B) of a magnetic field using a Hall probe.

  • ⇒  Apparatus Required:

  • – Hall probe
  • – Electromagnet or permanent magnet
  • – Voltmeter
  • – Ammeter
  • – Variable power supply
  • – Gaussmeter (optional for verification)

  • ⇒  Theory:

  • The Hall effect states that when a current-carrying conductor is placed in a magnetic field, a voltage (Hall voltage) is produced perpendicular to both the current and the field:
  • [math]V_H = \frac{BI}{net}[/math]
  • Where:
  • – [math]V_H[/math] = Hall voltage (V)
  • – B = Magnetic flux density (T)
  • – I = Current in the conductor (A)
  • – n = Charge carrier density (m−3)
  • – e = Electron charge (C)
  • – t = Thickness of the conductor (m)
  • Figure 2 Magnetic flux density using a hall probe

  • ⇒  Procedure:

  • Step 1: Set Up the Circuit
    1. Connect the Hall probe to a voltmeter.
    2. Position the Hall probe between the poles of a magnet or inside an electromagnet.
    3. Connect the electromagnet to a variable power supply and ammeter.
  • Step 2: Measure the Hall Voltage
    1. Turn on the electromagnet and gradually increase the current.
    2. Measure and record the Hall voltage at different magnetic field strengths.
  • Step 3: Determine Magnetic Flux Density
    1. Plot a graph of Hall voltage ([math]V_H[/math]​) vs. magnetic field current (I).
    2. The slope of the graph is proportional to the magnetic flux density B.

  • ⇒  Precautions & Errors:

  • – Ensure the Hall probe is properly calibrated.
  • – Avoid external magnetic fields that may interfere with readings.
  • – Use stable power supply to prevent fluctuations.

  • ⇒   Conclusion:

  • This experiment verifies the Hall effect and allows measurement of the magnetic flux density (B) of a field.
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