Laboratory 1-Kirchoff's Law's Overview The pupose of this experiment is to review the properties of resistors and batteries and to use them to investigate Ohm's Law, Kirchoff's Laws and Thevenin's theorem. 1. Ohm's Law In this experiment I hooked up the variable power supply, a digital multimeter (DMM) and a resitor in a circuit. This same circuit was then tested on a lamp to see when the filament would begin to glow and see if it would obey Ohm's Law and finally it was tested on a 1.5 V battery to see if it to would follow Ohm's Law. Part I. 1 kilo-ohn resistor Current (mA) Voltage (V) 0.16 mA 0.20 V 0.45 mA 0.50 V 0.93 mA 1.00 V 1.89 mA 2.00 V 5.09 mA 5.00 V Part II. Lamp Current (mA) Voltage (V) 18.1 mA 0.20 V 33.6 mA 0.50 V 39.8 mA 0.80 V 50.1 mA 1.00 V 72.6 mA 2.00 V 126.1 mA 5.00 V This data shows that the lamp seemed to follow a linear relation until it began to glow which i recorded at about 0.80 V and from then on it didn't follow a nice linear relation. This i believe is caused by the increasing resistance of the filament as it continued to glow and get brighter and expel more heat. Part III. 1.5 V Battery Current (A) Voltage (V) 0.95 A 2.0 V 1.98 A 2.5 V 3.01 A 3.0 V 3.18 A 3.5 V 3.32 A 4.0 V 3.38 A 4.5 V 3.38 A 5.0 V The batterry obeys Ohm's law but has a changing internal resitance as the voltage is increased and when the voltage was in the 4 volt range the battery began to be drained of it's energy and began to feel a little warm. 2. Kirchoff's Law In this experiment a circuit was built with a 10 kilo-ohm resistor in parallel with a second 10 kilo-ohm resistor and a load resistor rated at 10 kilo-ohms. Current (mA) Voltage (V) I1=0.33 mA V1=3.38 V I2=0.167 mA V2=1.67 V IL=0.167 mA VL=1.67 V R1=R2=RL=10 kilo-ohms I --> I2 --> l---------/\/\/\---------------------------------l l R1 l I1 l -------- < \/ > V=5V ---- > < RL l < R2 > l l l l------------------------l---------------------- l Loop equations -I2RL+I1R2=0 I1=I2 5 V=-I1R2-IR1 Junction Equation I= I1+I2 5 V= -I2 (10 k)-(I1+I2)(10 k) 5 V= (30 k) I1 I1=I2=0.167 mA I= 0.33 mA Based on Kirchoff's Laws my measurements were very accurate with what was predicted and were within the accepatble measurement error. 3. Thevenin' Theorem In this experiment I removed the load resistor then measured the open circuit voltage and the short circuit to compute the equivalent voltage and resistance. Open circuit=2.52 V Short circuit current=0.50 mA Rth=Vth/Isc 2.52 V/ 0.50=5.0 kilo-ohm I set the variable power supply to Vth and got a resistor equal to the Rth and measured the current and voltage across RL Voltage across RL=1.7 V Current through RL=0.17 mA so RL=1.7 V / 0.17 mA= 10 kilo ohms In this part the power supply and resistors were replaced with a 1.5 V battery and a 10 ohm resistor in series The open circuit voltage =0.192 V and the short circuit element was 21 mA so the Rth =9.14 ohms so the reistance of the battery is 10-9.14=o.86 ohms. In the last part I set the voltage to 1.000 V with a 1 Mega-ohm resistor for the RL. I replaced the RL and put in a 100 ohm resistor and measured the voltage.I measured the voltages of both resistances and i took these values to estimate the resitance of the power supply. Req=(0.003/0.997)*100=0.300 ohms