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# Non Linear Resistance.

Extracts from this document...

Introduction

NON LINEAR RESISTANCE

Name of Instructor: Mr. A. R. Ilangakoon

Name                :         Perera K.N.S.

Index No        :                  020287

Field                :                 ENTC

Date of Per.        :            03/12/2003

Date of Sub.:           10/12/2003

CALCULATION

Measurement of filament lamp

RL = (V/I) × 1000 Ω

 I (mA) VL (V) RL (Ω) 30 2.0 66.67 40 3.0 75.00 50 4.4 88.00 60 6.4 106.67 70 8.8 125.71 80 13.4 167.50 90 18.6 206.67 100 25.2 252.00 110 35.0 318.18 120 43.0 358.33 130 53.0 407.69 140 61.0 435.71 150 72.0 480.00 160 83.3 520.63

Measurement of standard resistor

Middle

150

9.6

64.00

160

10.2

63.75

Measurement of standard resistor-filament lamp series combination

RL = (VL/I) × 1000 Ω

RS = 1000 × (VS - VL)/I Ω

Total Resistance = R = (RL + RS) Ω

 I (mA) VS (V) VL (V) RS (Ω) RL (Ω) R(Ω) 30 4.4 2.6 60.00 86.67 146.67 40 6.0 3.6 60.00 90.00 150.00 50 8.2 5.0 64.00 100.00 164.00 60 10.4 6.6 63.33 110.00 173.33 70 13.8 9.4 62.86 134.29 197.14 80 18.8 14.0 60.00 175.00 235.00 90 24.6 19.0 62.22 211.11 273.33 100 31.0 25.6 54.00 256.00 310.00 110 40.0 30.8 83.64 280.00 363.64 120 49.0 40.4 71.67 336.67 408.33 130 60.0 50.3 74.62 386.92 461.54 140 70.0 60.2 70.00 430.00 500.00 150 80.0 70.1 66.00 467.33 533.33 160 90.0 80.0 62.50 500.00 562.50

Conclusion

When the current changes from I = 50 mA to 150 mA the standard resistor had a 6.67 % increase in resistance and the filament resistance a 445.45 % and the series combination a 225.2 %. This clearly confirms the theory discussed above.

We got some practical errors in this experiment. The cold resistance 58.0 Ω was not the one obtained from calculation at initial current. This maybe due to the voltmeter finite resistance (ideally this should be ∞ Ω) and the ammter internal resistance (ideally this should be 0 Ω) and also the resistances associated with connecting wires, etc.

The standard resistor we used was a 100 Ω / 2 A rheostat adjusted to 58 Ω. Here the rated current 2 A is very much greater than the maximum current we allowed to flow in the experiment which is 160 mA. The meaning of the rated current is the maximum current the resistor can follow up to, without considerable heat generation i.e. maintaining resistance nearly a constant. So if we used a 150 mA rated rheostat which is even below the 160 mA, that resistor might not behave as a standard resistor. Instead it will show a higher degree of increasing resistance than before due to the considerable heating effect. Of course this might not be large as the filament resistance.

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