**Ohm's law**

background [prelab assignment (15 points) due at the begining of lab]

1. what is Ohm's law ?

2. what is a potentiometer (or voltage divider) ?

3. sketch a circuit diagram to reflect the experimental setup to get the appropriate experimental measurements to confirm / refute ohm' law.

purpose

1. use of a multimeter's ohm meter feature: (i) to compare resistor's color code & its resistance based on the ohm meter's reading; and (ii) to explore a potentimeter's behavior

2. use of a multimeter's voltmeter feature to collect appropriate measurments to (i) describe resistor and / or diode current - voltage behavior, (ii) determine the battery's internal resistance, and (iii) explore the potentiometer's behavior in regards to the design / development of a (crude / nonideal) variable voltage source.

3. use multimeter's voltmeter / ammeter features in simple circuit consisting of the preceding "variable voltage source" and a single ___ to illustrate Ohm's law.

a. resistor

b. diode

materials

battery, resistors, diodes (tentative), potentiometer, 7 different "color" wires with alligator clips

2 groups: use a pair of multimeter - use as a ± 200 mA ammeter & voltmeter with 100 Ω resistor

4 groups: use a single multmeter as volt meter and a ± 500 µA ammeter with a 3.3 kΩ resistor

methods / data analysis

student design

to avoid drawing a lot of current; i.e. to not damage the ammeter

especially for a diode, start at 0 V, since there might be a sharp rise in current as a function of voltage

estimate / calculate expected current, then select appropriate current range in the ammeter. if in doubt, start at highest current range, then work to a lower current range

**content of lab report** [20 points]

resistor: graph of current versus voltage (have both positive and negative values) to estimate the resistance of resistors; compare to multimeter's ohm meter value

1N4727A zener diode: graph of current versus voltage (have both positive and negative values)

determine the battery's internal resistance; show your work, include circuit diagram and value of corresponding measurements

does Ohm's law describe the behavior of the resistor and diodes ? support your response based on your experimental results

**resources**

resistor color code

example of an Ohm's law lab handout

remarks

multimeter / ammeter lead / connection convention: red = high V; black = low V. not heeding this convention will give the "wrong" sign (i.e. positive vs negative) of the volt / current

the rationale / motivation of multi color wires to aid in building the circuit; real circuits don't use as much different colored wires. suggestion: in your prelab schematic circuit diagram, label wire colors

measuring a current > ammeter range may damage it, so calculate expected current beforehand, then use appropriate current range and / or start from highest current range, then goto lower current range if there's no current "detected"

don't lose the multimeter connection guards