What is the Hall effect?

Short Answer:

The Hall effect is the generation of a voltage across a conductor or semiconductor when it carries electric current and is placed in a magnetic field perpendicular to the current. This voltage, called the Hall voltage, appears at right angles to both the current and the magnetic field.

The Hall effect is used to measure magnetic field strength, identify the type of charge carriers (electrons or holes), and determine the mobility and concentration of carriers in semiconductors. It is the basic working principle behind Hall sensors used in various electronic devices.

Detailed Explanation:

Hall Effect

The Hall effect is a physical phenomenon discovered by Edwin H. Hall in 1879. It occurs when a magnetic field is applied perpendicular to the direction of electric current flowing through a conductor or semiconductor. Due to this setup, the charge carriers (electrons or holes) experience a force that pushes them sideways, resulting in the buildup of electric charge on one side of the material.

This buildup creates a voltage known as the Hall voltage (V_H). It is measurable and provides valuable information about the material and the surrounding magnetic field.

How Hall Effect Works

Consider a thin flat strip of a conducting or semiconducting material with:

  • Electric current (I) flowing along the x-axis
  • Magnetic field (B) applied in the z-axis (perpendicular to the strip)
  • Resulting Hall voltage (V_H) develops along the y-axis

As the current flows, the magnetic field exerts a Lorentz force on the moving charge carriers. This force pushes them to one side, creating a potential difference. When the electric field from this potential balances the magnetic force, a steady Hall voltage is established.

VH=IBnetV_H = \frac{IB}{net}VH​=netIB​

Where:

  • V_H = Hall voltage
  • I = Current
  • B = Magnetic field strength
  • n = Charge carrier concentration
  • e = Charge of an electron
  • t = Thickness of the material

Key Uses and Applications

  1. Magnetic Field Measurement
    • Hall sensors detect the strength and direction of magnetic fields.
  2. Current Measurement
    • Hall-effect sensors are used in contactless current sensors in power systems.
  3. Speed Detection
    • Used in automotive applications for sensing wheel speed and crankshaft position.
  4. Position Sensing
    • In joysticks, brushless motors, and robotics for tracking movement.
  5. Semiconductor Research
    • Used to determine carrier type (n-type or p-type)
    • Measures carrier density and mobility
  6. Digital Devices
    • Found in mobile phones, laptops, and tablets for detecting open/close positions (e.g., flip covers).

Characteristics of Hall Effect

  • Works in both conductors and semiconductors (more sensitive in semiconductors)
  • Direction of Hall voltage depends on the type of charge carrier
  • The effect is directly proportional to current and magnetic field
  • Highly reliable and has no moving parts

Factors Affecting Hall Voltage

  • Material type: Semiconductor materials show higher Hall voltage
  • Temperature: Can affect carrier mobility
  • Magnetic field strength and current: Directly impact the output voltage
  • Thickness of the material: Thinner materials give higher Hall voltage
Conclusion:

The Hall effect is the development of a transverse voltage when current-carrying material is placed in a perpendicular magnetic field. This simple yet powerful principle is used in magnetic field sensors, current measurement tools, and electronic switching systems. It plays a crucial role in modern electronics, especially in non-contact sensing and semiconductor characterization