Question

1. What is the Hall effect?
2. Describe the Hall effect apparatus and what are the precautions measures taken during the experiment.

Answer 1

Hall effect is defined as the production of a voltage difference across an electrical conductor which is transverse to an electric current and with respect to an applied magnetic field it is perpendicular to the current. Edwin Hall discovered this effect in the year 1879.

The effect is widely used in magnetic field sensors. It is associated with several well-known systematic errors, some of which can be eliminated by special measurement techniques.

BRIEF DESCRIPTION OF THE APPARATUS

1. (a) Hall Probe (Ge Crystal)-Ge single crystal with four spring type pressure contacts is mounted on a sunmica - deecorated bakelite strip Four leads are provided for connections with measuring devices. This type of probes are specially designed and recommended for Hall Effect experiment. (b)Hall Probe (InAs)-Indium Arsenide crystal (rectangular) is mounted on a phenolic strip with four soldered contacts for connections with measuring devices. The crystal is covered by a protective layer of paint. The whole system is mounted in a pen type case for further protection.These are essentially meant to be used as transducers.
2. OVEN -It is a small oven which could be easily mounted over the crystal or removed if required.
3. TEMPERATURE SENSOR -Temperature is measured with Cromel-Alumel thermocouple.

4. HALL EFFECT SETUP -The set-up consists of an electronic digital millivoltmeter and a constant current power supply. The Hall Voltage and probe current can be read on the same digital panel meter through the selector switch.

   Measurement of Probe Current & Hall Voltage

   This unit consists of a digital millivoltmeter and constant current power supply. The Hall voltage and probe current can be read on the same digital panel meter through a selector switch.(a) Digital Millivoltmeter-Since the use of internal reference causes the degradation in performance due to internal heating an external reference have been used. Digital voltmeter is much more convenient to use in Hall Experiment, because the input voltage of either polarity can be measured.(b) Constant Current Power Supply- This power supply, specially designed for Hall Probe, provides protection against crystal burn-out due to excessive current. The supply is a highly regulated and practically ripple free dc source.

   Measurement of Thermo emf and Heater current The unit consists of a digital millivoltmeter and constant current power supply. The thermo emf of thermocouple and heater current can be read on the same display through a selector switch.(a) Digital Millivoltmeter-. Digital Voltmeter is much more convenient to use, because the input voltage of either polarity can be measured.(b) Constant Current Power Supply-The supply is highly regulated and practical ripple free source.

5. ELECTROMAGNET-The present constant current power supply was designed to be used with the electromagnet

6. DIGITAL GAUSSMETER-The Gaussmeter operates on the principle of Hall Effect in semiconductors. A semiconductor material carrying current develops an electro-motive force, when placed in a magnetic field, in a direction perpendicular to the direction of both electric current www.sestechno.com and magnetic field. The magnitude of this e.m.f. is proportional to the field intensity if the current is kept constant, this e.m.f. is called the Hall Voltage. This small Hall Voltage is amplified through a high stability amplifier so that a millivoltmeter connected at the output of the amplifier can be calibrated directly in magnetic field unit (gauss)

Precautions

• The magnet power supply can furnish large currents at dangerous voltage levels; do not touch exposed magnet coil contacts.
• Never suddenly interrupt or apply power to a large magnet. Large inductive voltage surges may damage the insulation. Start with controls set for zero current and gradually increase current. When turning off, smoothly decrease current to zero and then turn off.
• Do not exceed magnet current of 10 A.
• The gaussmeter zero needs to be monitored and adjusted as needed. To do this, remove the gaussmeter probe well away from the magnet and check the zero for the scale that is in current use. The zero may shift when the scale is changed. To detect the effect of a stray field, observe the zero as the probe orientation is change by about 90 degrees.
• During the experiment investigate the geometry of the set-up. Note the direction of the magnetic field, probe current, and Hall voltage – this will help in the analysis. The extra probe is available to help with this