What is Hall effect?

Short Answer

The Hall effect is the production of a small electric voltage across a conductor or semiconductor when a magnetic field is applied perpendicular to the direction of current. This voltage is called the Hall voltage. It appears because moving charges experience a sideways force in the magnetic field.

The Hall effect is used to find the type of charge carriers, measure magnetic field strength, and calculate the speed of electrons in materials. Hall sensors based on this effect are used in motors, vehicles, mobiles, and many electronic devices.

Detailed Explanation

Hall effect

The Hall effect is an important physical phenomenon that helps us understand the behavior of electric charges in the presence of a magnetic field. It was discovered by the American scientist Edwin Hall in 1879. The effect occurs when an electric current flows through a conductor or semiconductor and a magnetic field is applied at right angles to the direction of the current. Under these conditions, a small voltage is produced across the material in a direction perpendicular to both the magnetic field and the current. This voltage is known as the Hall voltage.

The Hall effect provides valuable information about the nature of charge carriers in a material—whether they are electrons (negative charges) or holes (positive charges). It also helps measure magnetic fields and understand the electrical properties of materials.

How the Hall effect occurs

To understand the Hall effect, consider a flat strip of conducting material. When electric current flows through this strip, charges move along its length. Now imagine applying a magnetic field perpendicular to the flow of current. According to the Lorentz force, the moving charges experience a sideways force due to the magnetic field.

  • If electrons are the main carriers, they will be pushed to one side of the strip.
  • If holes are the main carriers, they will move to the opposite side.

This sideways movement of charges creates an imbalance—one side becomes negatively charged and the other becomes positively charged. Because of this separation, an electric potential difference develops across the width of the material. This is the Hall voltage. The stronger the magnetic field or the higher the current, the larger the Hall voltage.

Mathematical expression

The Hall voltage  is given by:

Where:

  •  = magnetic field
  •  = current
  •  = number of charge carriers per unit volume
  •  = charge of an electron
  •  = thickness of the conductor

This formula helps in finding unknown properties of materials.

Significance of the Hall effect

The Hall effect is important for several reasons:

  1. Identifying charge carriers

The sign of the Hall voltage tells whether the current is carried by electrons or holes.

  • Negative Hall voltage → electrons
  • Positive Hall voltage → holes

This is extremely useful in semiconductor physics.

  1. Measuring magnetic fields

Hall probes based on the Hall effect are used to measure magnetic field strength accurately.

  1. Measuring carrier concentration

By using the Hall voltage formula, the number of charge carriers in a material can be calculated. This helps in designing semiconductor devices.

  1. Measuring mobility of carriers

Combining Hall effect with conductivity measurements helps determine how quickly electrons or holes move inside a material.

Applications of Hall effect

The Hall effect has many practical applications in science and technology:

  1. Hall sensors:
    Used in mobile phones, computers, and vehicles to detect magnetic fields.
  2. Speed detectors:
    Used in fans, motors, and electric vehicles to determine rotational speed.
  3. Position sensors:
    Used in printers, robotics, and industrial machines.
  4. Proximity sensors:
    Used to detect the presence of nearby magnetic objects.
  5. Automotive applications:
    Used in anti-lock braking systems (ABS), ignition systems, and fuel level sensors.
  6. Current measurement:
    Hall-effect current sensors are used in power systems to measure current without touching the conductor.
  7. Semiconductor studies:
    Used in laboratories to determine carrier concentration and type.

Factors affecting Hall voltage

Several factors affect the size of the Hall voltage:

  • Strength of the magnetic field
  • Amount of current flowing
  • Thickness of the conductor or semiconductor
  • Type and number of charge carriers

By controlling these factors, engineers design sensitive Hall sensors for specific applications.

Conclusion

The Hall effect is the generation of a voltage across a conductor or semiconductor when current flows through it in the presence of a perpendicular magnetic field. This happens because moving charges experience a sideways force, causing charge separation. The Hall effect helps identify charge carriers, measure magnetic fields, and study semiconductor properties. It also has wide applications in sensors, vehicles, robotics, and electronic devices, making it a highly useful and practical concept in physics and engineering.