Lab Experiment # 7

Series type Ohmmeter using Galvanometer

Objective:

How to design a series type ohmmeter using Galvanometer.

Apparatus:

Galvanometer

Bread board

Digital multi meter

Connecting wires

Resistance of different values

Dc power supply

Theory:

Voltage source is connected in series with the galvanometer that’s why we call

this type of ohmmeter as series type ohmmeter. A Known resistance is

connected to bring the pointer at 15 degree then unknown resistance can be

found as:

Obtain Rx=∞ for open circuit.

Obtain Rx=0 for short circuit.

To find R2

R2=ℑRmRhv−ImRm

To find R1

R1=Rh−ℑ RmR hV

Circuit Diagram:

Procedure:

Calculate Rm and Vm, for full scale deflection and then calculate Im =Vm /Rm

connect Rx=3KΩ so that needle moved to 15 degree that is half of full scale.

Remove the 3KΩ resistance and insert replace 1kΩ, 2KΩ, and 3KΩ resistances.

Calibrate the scale for these resistances.

Calculate the value of the resistance for the Rh=0 for short circuit.

Calculate the value of the resistance for Rh=∞ for open circuit.

Observations and calculation:

Rm=2.45KΩ Vm=0.69V Im =0.2816 mA

Sr.No. Resistances(Ω) Deflection(Ѳ)

1

2

3

4

5

6

Lab Experiment # 8

Shunt type Ohmmeter using Galvanometer

Objective:

How to design a shunt type ohmmeter using Galvanometer.

Apparatus:

Galvanometer

Bread board

Digital multi-meter

Connecting wires

Resistance of different values

Dc power supply

Theory:

Series ohm meter is called to this name because voltage source is connected in

shunt with galvanometer. A shunt type ohmmeter includes an internal resistor in

parallel with the galvanometer and internally connected DC power supply. A Known

resistance is connected to bring the pointer at 15 degree then unknown resistance can

be found as:

Obtain Rx=∞ for short circuit

Obtain Rx=0 for open circuit

To calculate R1:

R1= Rh RmRm+Rh

( 2VImRm

−1)

Circuit Diagram:

Procedure:

Calculate Rm and Vm, for full scale deflection and then find the Im by the formula

Im= Vm/ Rm

Insert Rx=3KΩ and move the needle to 15 degree for the half scale deflection.

Remove the 3KΩ resistance and insert replace 1kΩ, 2KΩ, and 470Ω resistances

and calibrate the scale for these resistances.

Find the value of the resistance for the Rh=0 open circuit.

Find the value of the resistance for Rh=∞ for short circuit.

Observations and calculation:

Rm= Vm= Im =_________

Sr.No. Resistances(Ω) Deflection(Ѳ)

1

2

3

4

5

6

Lab Experiment No 9

DC Bridge to measure Unknown Resistance

Objective:

In this experiment, we can find the value of unknown resistance by using the

Wheatstone bridge.

Apparatus: Breadboard Dc power supply Galvanometer Resistances Connecting wires Digital multi meter Variable resistor

Diagram:

Theory:

To determine the value of unknown resistance, the bridge is maintained at the balanced condition. The bridge is said to be balanced when the potential difference between the point ‘A’ and ‘B’ is 0 V so no current flowing through galvanometer.R2 is the unknown resistance whose value is to be find. So by given formula:

R2=R3R4

∗R1

Procedure:

Connect the four resistances in the form of bridge. Connect the galvanometer between point A and C. Connect the Dc power supply between point ‘B’ and ‘D’. Balanced the bridge by varying the resistance R1. Measure the value of R1 by using ohmmeter at which galvanometer shows 0 V. Using formula calculate the resistance of unknown resistance.

Observation and calculation: