Discussion:In this experiment, the students have been using the 100-microampere meter movement. Its use as a voltage multiplier (high resistance) if placed in series with the moving meter. For low-voltage instruments, this resistance is physically mounted inside the meter case with the meter movement. The students keep in mind that the meter movement uses current flow to produce a magnetic field that is proportional to the current. The meter movement is, therefore, an indicator of current flow rather than voltage. The addition of the series resistance is what allows the meter to be calibrated in terms of voltage; that is, the meter movement of a voltmeter operates because of the current flow through the meter, In extending the Voltmeter ranges the value of series resistance is determined by the current required for full-scale deflection and by the range of the voltages to be measured. Since the current through the meter circuit is directly proportional to the applied voltage, the meter scale can be calibrated directly in volts for a fixed value of series resistance.

The resistance (R meter) required to limit the total current in the circuit to 100 microamperes can be found by using the ff. formula:

Multi range voltmeters use one meter movement. The required resistances are connected in series with the meter by a switching arrangement

Conclusion:The students found out the influence of a voltmeter in a circuit. The purpose of a voltmeter is to indicate the potential difference between two points in a circuit. When a voltmeter is connected across a circuit, it shunts the circuit. If the voltmeter has a low resistance, it will draw a substantial amount of current. In this case this action lowers the effective resistance of the circuit and changes the voltage reading. The students observe that when making voltage measurements in high-resistance circuits; use a high-resistance voltmeter in order to prevent the shunting action of the voltmeter. But the effect is less noticeable in low-resistance circuits because the shunting effect is less like in the experiment.In addition to that the students encounter a difficulty in performing the ff. experiment because the value of the resistance needed to create the volt meter is not exact or rather difficult to find.

Computation:Meter Movement DataR1 = 8.04 KE(mv) = 59.8 mVI = 59.8 mV/8.04 KI = 3.3 A

Rm = R2 2R1Rm = 17.75 K 2(8.04 K)Rm1 = 1.65 K

Rm 2 = 1.831 KRm 3 = 1.769 K

Rm(ave) = Rm(ave) =

Rm(ave) = 1.75 K

Percentage ErrorE1E2PercentageError%

1.25 V

1.28 V

%e = 2.40%

2.5 V

2.55 V

%e = 2.00%

6.2 V

6.35 V

%e = 2.42%

12.5 V

12.94 V

%e = 3.52 %

26.7 V

26.2 V

%e = 1.87%

Reference:http://www.navymars.org/national/training/nmo_courses/nmoc/module16/14188_ch3.pdf

http://en.wikibooks.org/wiki/Circuit_Theory/Circuit_Basics

http://www.allaboutcircuits.com/worksheets/meters1.html