Introduction  

When a current-carrying conductor is placed in a magnetic field perpendicular to the current direction, a voltage develops transverse to the cuurent. This voltage was first observed in 1879 by Edwin Hall and the effect is called Hall Effect.

The Hall effect has since led to a deeper understanding of the details of the conduction process. It can yield the density of the charge carriers as well as their sign.

Theory

As you are aware, a static magnetic field has no effect on charges unless they are in motion. When the charges flow, a magnetic field directed perpendicular to the direction of flow produces a mutually perpendicular force on the charges. When this happens, electrons and holes will be separated by opposite forces. They will in turn produce an electric field ( E̅h ) which depends on the cross product of the magnetic intensity, H̅ , and the current density, J̅.

h=RJ̅ X H̅

where R is called the Hall Coefficient

Now, let us consider a bar of a semiconductor, having dimensions, x, y and z. Let J̅ be directed along X and H̅ along Z, then E̅h will be along Y.

Then we could write

 

 

where Vh is the Hall voltage appearing between the two surfaces perpendicular to y and I=J̅yz.

Hall Effect experiment consists of the following:

      1. Hall Probe: Bismuth
      2. Constant Current Source, CCS-01
      3. Digital Microvoltmeter, DMV-001
      4. Electromagnet, EMU-75 (Specifications as per datasheet attached)
      5. Constant Current Power Supply, DPS-175 (Specifications as per datasheet          attached)
      6. Digital Gaussmeter, DGM-102 (Specifications as per datasheet attached)

Hall Probe

Bismuth Hall Probe

Bismuth strip with four spring-type pressure contacts is mounted on a sunmica-decorated bakelite strip. Seperate leads are provided for connections with measuring devices.

TECHNICAL DETAILS

Material Bismuth
Resistivity 1.29 x 10-4Ω.cm
Contacts Spring type (solid silver)
Zero-field potential <1mV (adjustable)
Hall Voltage 25-35mV/10mA/KG

It is designed to give a clear idea to the students about Hall Probe and is recommended for class room experiment. A minor drawback of this probe is that it may require zero adjustment.

Current Source

Constant Current Source, CCS-01

It is an IC regulated current generator to provide a constant current to the outer probes irrespective of the changing resistance of the sample due to change in temperatures. The basic scheme is to use the feedback principal to limit the load current of the supply to preset maximum value. Variations in the current are achieved by a potentiometer included for that purpose. The supply is a highly regulated and practically ripples free d.c source. The constant current source is suitable for the resistivity measurement of this films of metals/alloys and semiconductors like germanium

SPECIFICATIONS

Range 0-20mA, 0-200mA
Resolution 10µA
Accuracy ±0.25% of reading ±1 digit
Display 3½ digit, 7 segment LED with autopolarity and decimal indication


Voltage Meter

Digital Microvoltmeter, DMV-001

It is a very versatile multipurpose instrument for the measurement of low dc voltage. It has 5 decade ranges from 1mV to 10mv with 100% over-ranging. For better accuracy and convenience, readings are directly obtained on 31/2 digit DPM (Digital Panel Meter).

Range 1mV, 10mV, 100mV, 1V & 10V with 100% over-ranging.
Resolution 1µV
Accuracy ±0.2% ±1 digit
Stability Within ±1 digit
Input Impedance >1000MΩ (10MΩ on 10V range)
Display 3½ digit, 7 segment LED with autopolarity and decimal indication
 

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