Lab 1 - Ohm's Law and DC Circuits

# Lab 1 Ohm's Law - Physics 8B Lab 1 Ohm's Law DC Circuits rev 4.0 Lab 1 Ohm's Law DC Circuits Part 1 Ohm's Law We will begin by measuring current I

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Physics 8B Lab 1 – Ohm’s Law & DC Circuits rev 4.0 Lab 1 – Ohm’s Law & DC Circuits Part 1: Ohm’s Law We will begin by measuring current, I, and voltage, V, for two devices and investigating whether they obey Ohm’s law, V=IR. We will use a DC power supply to provide a adjustable DC voltage and multimeters to make the measurements. Power Supply: This serves as the constant voltage source, much like a battery except we can adjust the voltage to different values. The red jack is like the “+” terminal of a battery, i.e. “positive” current flows out of this jack. The black jack is like the “-“ terminal of a battery where the current returns. Set the voltage switch to 15V and the current switch to 100mA. Turn the current limiter on the power supply to the highest setting of 1A. DC Ammeter: Set the dial on one of the multimeters to DC Amps (A with straight line next to it). To measure current, the ammeter will need to be placed such that the current flows through the meter, i.e. an ammeter must be placed in series where you want to measure the current. Current will flow into the 300 mA plug, through the meter and out the COM plug. The reading will be in milliamps, mA. DC Voltmeter: Set the dial on the other multimeter to DC Volts (V with straight line next to it). To measure a voltage difference, the voltmeter can be attached to any two points in the circuit. The voltmeter doesn’t have to be built into the circuit before hand, you can come along after and measure any voltage difference you want. A wire from the V plug is attached to the point with higher potential, a wire from the COM plug is attached to the point with lower potential. The reading is the potential difference between the two points. With the power supply off, build the circuit shown below attaching the resistor to the power supply. Attach the voltmeter across the resistor. A V DC Power Supply + - R

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Physics 8B Lab 1 – Ohm’s Law & DC Circuits rev 4.0 a) Predict what will happen to the voltage across the resistor as the current through it increases from zero? Turn the power supply on and record current values from the ammeter for given voltage values on the voltmeter (NOT the power supply setting). Plot the voltage versus current graph on the axis below. I (mA) V (V) 0 3 6 9 12 b) An Ohmic device is something which has a fixed resistance, R, and obeys Ohm’s law, V=IR, independent of the voltage across it. Based on your graph, is a resistor an Ohmic device? How do you know? c) What is the resistance of your resistor? V(V) I(mA)
Physics 8B Lab 1 – Ohm’s Law & DC Circuits rev 4.0 With the power supply off, replace the resistor in your circuit with the larger round bulb. Just unplug the wires from each end of the resistor and plug them into each end of the

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## This note was uploaded on 09/28/2009 for the course PHYSICS 8B taught by Professor Shapiro during the Spring '07 term at University of California, Berkeley.

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Lab 1 Ohm's Law - Physics 8B Lab 1 Ohm's Law DC Circuits rev 4.0 Lab 1 Ohm's Law DC Circuits Part 1 Ohm's Law We will begin by measuring current I

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