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Four Probe Experiment for Physics Lab for High School Science Kits Lab Manufacturers, Suppliers & Exporters in India
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Naugra Export, are top Four Probe Experiment for Physics Lab for High School Science Kits Lab manufactures in India, along with our full range for High School Science Kits. Ideal for industrial training, classroom demonstrations, curriculum-based experiments, and laboratory practical, it combines rugged construction with reliable performance, built for bulk tender supply worldwide. Manufacturers of Four Probe Experiment for Physics Lab for High School Science Kits Lab in India and Trusted Supplier for OEM Suppliers around the globe. Full specifications are listed below.
Full specifications for the lab product:
Four Probe Experiment for Physics Lab - Resistivity of Semiconductors by
Four Probe Method at Different Temperatures and Determination of the
Band-gap
The Four Probe Method is one of the standard and most widely used method
for the measurement of resistivity of semiconductors. The experimental
arrangement is illustrated. In its useful form, the four probes are
collinear. The error due to contact resistance, which is specially
serious in the electrical measurement on semiconductors, is avoided by
the use of two extra contacts (probes) between the current contacts. In
this arrangement the contact resistance may all be high compare to the
sample resistance, but as long as the resistance of the sample and
contact resistances are small compared with the effective resistance of
the voltage measuring device (potentiometer, electrometer or electronic
voltmeter),the measured value will remain unaffected. Because of
pressure contacts, the arrangement is also specially useful for quick
measurement on different samples or sampling different parts of the same
sample.
Description of the experimental setup
1. Probes Arrangement
It has four individually spring loaded probes. The probes are collinear
and equally spaced. The probes are mounted in a teflon bush, which
ensure a good electrical insulation between the probes. A teflon spacer
near the tips is also provided to keep the probes at equal distance. The
whole –arrangement is mounted on a suitable stand and leads are
provided for the voltage measurement.
2. Sample
Germanium crystal in the form of a chip
3. Oven
It is a small oven for the variation of temperature of the crystal from
the room temperature to about 200°C (max.)
4. Four Probe Set-up,
The set-up consists of three units in the same cabinet.
(i) Multirange Digital Voltmeter
In this unit, intersil 3½ digit single chip A/D Converter ICL 7107 has
been used. It has high accuracy like auto zero to less than 10mV, zero
drift of less than 1mV/°C, input bias current of 10pA max. and roll-over
error of less than one count. Since the use of internal reference
causes the degradation in performance due to internal heating, an
external reference has been used.
Specifications
Range X1 (0-200mV) & X10 (0-2V)
Resolution 100mV at X1 range
Accuracy ±0.1% of reading ±1 digit
Stability Within ±1 digit
Input Impedance 1MW
Display 3½ digit, 7 segment LED (12.5mm height) with auto polarity and
decimal indication
Overload Indicator Sign of 1 on the left & blanking of other digits
(ii) Constant Current Generator
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
principle 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 ripple free d.c. source. The current is measured by the
digital panel meter.
Specifications
Open Circuit Voltage 18V
Current Range 0-20mA
Resolution 10mA
Accuracy ±0.25% or ±1 digit
Stability Within ±1 digit
Load regulation 0.03% for 0 to full load
Line regulation 0.05% for 10% chang
(iii) Oven Power Supply
Suitable voltage for the oven is obtained through a step down
transformer with a provision for low and high rates of heating. A
glowing LED indicates, when the oven power supply is ‘ON’.
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