PHYSICS EXPERIMENT 4

EXPERIMENT NO. 4

Object: -     To study the Hall Effect and to calculate:-

(i) The Hall Coefficient R_H

(ii) The concentration of charge carriers

Required Apparatus:-   Power supply for electromagnets, Gauss meter with hall probes, p type   Ge semiconductor on PCB, multimeter, electromagnets.

Theory:     A current carrying conductor (semiconductor/metal) is placed in the magnetic field perpendicular to the direction of current; a voltage is developed across the conductor in a direction perpendicular to both the current and magnetic field. The effect is known is as Hall Effect. This effect is very useful in   determining-  

> The nature of charge carries e.g. whether semiconductor is on n-type or p-type

> Carrier concentration or the no. density of charge carries

> Mobility of charge carriers

Formula used

                   Hall Coefficient  

                        Carrier Concentration  

                                                                                                                                                                                        Procedure:-       

(1) Connect one pair of contact of specimen on the opposite faces to the                                current source and other pair to the multimeter.

         (2) Switch on the power supply of electromagnet and measure the                                 magnetic flux density at the centre between the pole faces by placing       

(3)Place the specimen at the centre between the pole faces   such that the magnetic field is perpendicular to the strip.

(4) Pass the current (mA) from the current source through the specimen and measure the resulting hall voltage in the multimeter / milivoltmeter.

(5)Increase the current through the specimen gradually and measure the corresponding Hall voltages.

(6)The entire process can be repeated for different values of magnetic flux density. Find the mean of different R_H

Observation:-  Width of specimen, w = 4 mm = 4 × 10^-3 m

                             Thickness of the specimen, d = 0.5mm = 5 × 10^-4 m

                             Current through the specimen, I = ------

                             Magnetic flex density, B = --------- Gauss = ………..× 10^-4 Tesla

S.No.	Current  I [mA]	Voltage HV [mV]	Hall Coefficient [RH ]

Calculations:-   Hall Coefficient  

                               Mean R_H = ----------------

                              Carrier Concentration  

Result:-                            Hall Coefficient  R_H =………………….

                                      Carrier Concentration n=…………………….

Source of Error:-

(1) Before starting the experiment, check the gauss mete is showing zero value. For this put the prove in separate place and switch on the gauss meter, it will show zero meter.

(2)   Ensure that the specimen is located at the centre between   the pole faces and is exactly perpendicular to the magnetic field.

     (3)  To measure the magnetic flux the hall probe should placed at the center the pole faces, parallel to the crystal.

          (4)  Check the direction of electromagnet coils so that it generates the maximum magnetic field, this can be check by placing the soft iron near the generated magnetic field, if soft iron attracts forcefully the magnetic field produced is strong, otherwise magnetic field is weak.

Viva voce

Q.1 Define Hall Effect?

Ans. When a current carrying specimen is placed in a transverse magnetic field then a voltage is developed which is perpendicular to both, direction of current and magnetic field. This phenomenon is known Hall Effect.

Q.2 What causes Hall Effect?

Ans. Whenever a charge moves in a mutually perpendicular electric and magnetic field it experiences Lorentz force due to which it deflects from its path and Hall voltage is developed.

Q.3 What is Lorentz force?

Ans. If charge ‘q’ moves in a magnetic and electric field ‘B’ &’E’ respectively with velocity v then force on it is given by

 F= qE+ Bqv.sinө

Q.4 What is Hall Coefficient?

Ans. It is the electric field developed per unit current density per unit magnetic field

Q.5  What are the uses of Hall Effect?

Ans. To determine the sign of charge carrier and charge carrier concentration

Q.6 Define Charge carrier concentration.

Ans. No. of charge carriers per unit volume.

Q.7 why Hall voltage differ for different type of charge carrier?

Ans. Because direction of Lorentz force is different for different type of charge carrier.

Q.8 what is unit Hall coefficient?

Ans. Ohm-meter/Tesla.

Q.9 What is the unit of charge carrier concentration

Ans. Per Cubic-centimeter.

Q10 Which type of magnet is used in the experiment, temporary or permanent?

Ans. Temporary.