Physics expriment

Physics lab

 

 

Experiment1

aimrify Ohm`s law and calculate the value of resistance using V-I curve.

Materials Required
resistor , voltmeter, ammeter, battery, rheostat,connecting wires and key

THEORY: - Ohm's Law deals with the relationship between voltage and current in an ideal conductor.

This relationship states that:

The potential difference (voltage) across an ideal conductor is proportional to the current through it. The

constant of proportionality is called the "resistance", R. Ohm's Law is given by:

V = I R

Where V is the potential difference between two points which include a resistance R. I is the current

flowing through the resistance.

Or

Ohm’s law states that the current through a conductor between two points is directly proportional to the

voltage

across the two points, and inversely proportional to the resistance between them. V, I, and R, the

parameters of Ohm's law.

I = V / R

Ohm's law is among the most fundamental relationships in electrical engineering. It relates the current,

voltage, and resistance for a circuit element so that if we know two of the three quantities we can

determine the third. Thus, if we measure the current flowing in a resistor of known value, we can deduce

the voltage across the resistance according to V = IR. Similarly, if we measure the voltage across a

resistor and the current through it, we calculate the resistance of the element to be R = V/I. Not only does

this reduce the number of measurements that must be made, it also provides a way to check the results

of several different measurement methods.

Observations

VIcharacteristics	Of ohm's law
	Resistor Used	1KΩ
	Readings Obtained
	Voltage (V)	Current (mA)
	0	0
	1	1
	2	2
	3	3
	4	4
	5	5
	6	6
	7	7
	8	8
	9	9
	10	10
	11	11
	12	12

PROCEDURE

Note : Connection of battery are important as per polarity.

1. Connect 6V battery/ DC power supply (external) across red & black

terminals as shown in the printed circuit diagram.

2. Switch ON the piano type switch provided on the front panel.

3. Vary the resistance of Potentiometer & note down the corresponding

current & voltage.

 

 

 

 

 

Expriment2

Aim: To study V-I characteristics of p-n diode.

(a)    in forward bias (b) in reverse bias

 

 

Apparatus
A p-n junction (semi-conductor) diode, a  volt battery, a high resistance rheostat, one  volt voltmeter, one 0-100 mA ammeter, one way key, connecting wires and pieces of sand paper ,Multisim software, resistors, multimeter, DC power source

THEORY

If a region of n-type semiconductor is in intimate contact with a region of p-type semiconductor, they

form p-n junction.A PN junction is formed at the interface between the indium saturated p-region and the n-type

semiconductor. The holes from the p-zone cross over to n-zone and electrons from n-zone cross over to pzone.This flow continues- until there are positive and negative layers on both sides of the junction to stop the

flow.We call it the depletion layer or the potential barrier. It exists at the junction before any external field is

applied.

FORWARD BIASING : When the positive terminal of the battery is connected to p-type and negative terminal

to n-type region of a PN junction as shown in Fig. (1a). The PN Juntion is said to be forward biased. This applied potential difference

provides the necessary energy for the holes

and electrons to diffuse through the junction

on barrier. The holes in the p-region are

pushed forward towards the n-region and

electrons from the n-region because of

negative applied potential cross over to pregion. Hence the diode starts conducting.

As the potential is increased, there is gradual increase in the current initial but then current shoots up. This

happens because at this applied potential almost all the majority carriers (i.e. holes and electrons) cross over.

 

               

 

 

 

 

 

 

 

 

REVERSE BIASING : In this case the

negative terminal of the battery is connected

to the p-region and positive terminal is

connected to the n-region as shown in

(2a).The holes of p-region move towards the

-ve terminal and electrons towards the

positive terminal of the battery or the

deflection layer becomes thick or we can

say that the junction barriers gets strengthened. Practically there should be no flow of current but in fact a very

small current flows which is called reverse current.

This current is due to the thermally generated electron-hole pairs within both p and n type materials.

As the reverse bias is increased to sufficient high value, the covalent bonds near the junction break down and

as a result of this large number of electron holes pairs are liberated.Thus the current rises abruptly as shown

in Fig. (2b). The voltage at which the current rises abruptly is called breakdown voltage.

 PROCEDURE

Forward Bias Characteristics :

1.              Make all the connections as shown in Connections Diagram Fig. (1) using patchcords by connecting Series Resistance in circuit.

2.              Keep 3V/ 30 switch at 3V side & 100 A/ 10mA at 10mA side.

3.              Keep Set Volts 3V/ 30V Switch at 3V DC.

4.              Keep Potentiometer Knob’s (Set Volts) at extreme left side.

5.              Switch ON the instrument using ON/ OFF Indicator switch provided on the front panel.

6.              Set the voltage at 0.2V and note down the corresponding current reading in the Table No. (1b).

7.              Keep on increasing voltage in the steps of 0.2V & note down corresponding current in the Table No.

(1b).     

 

Reverse Bias Characteristics :

1.              Make all the connections as shown in Connections Diagram Fig. (2) using patchcords by connecting Series Resistance in circuit.

2.              Keep 3V/ 30 switch at 30V side & 100 A/ 10mA at 100 A side.

3.              Keep Set Volts 3V/ 30V Switch at 30V DC.

4.              Keep Potentiometer Knob’s (Set Volts) at extreme left side.

5.              Switch ON the instrument using ON/ OFF Indicator switch provided on the front panel.

6.              Set the voltage at 0.2V and note down the corresponding current reading in the Table No. (2b).

7.              Keep on increasing voltage in the steps of 0.2V & note down corresponding current in the Table No.

(2b).