Ohm's law lab report answers

Borough of Manhattan Community College Science Department General Physics (PHY 109 and PHY 110) Laboratory Experiment #9 Ohm’s Law OBJECTIVES: To study the relationship among potential difference (voltage), current and resistance in a simple electric circuit. EQUIPMENT NEEDED: 100 Ω Resistor /nominal resistance Rnominal 100 Ω/ (1), 200 Ω Resistor /nominal resistance Rnominal 200 Ω/ (1), Ammeter (100 mA) (1), Cables - black (4) and red (2), Power Supply (1), Tap Key (1), Voltmeter (15 V) (1) THEORY: When a potential difference (voltage) V is applied at the ends of a resistor it results in the flow of a current, I, through the resistor and the resistance is defined as R V I (1) or V  RI (2) Ohm's Law states that in a large class of resistors, R is independent of V or I. In such a case, because of (2), the graph of V versus I is a straight line passing through the origin of the coordinate system. The slope of this line (V/I) is by definition equal to the resistance R. PROCEDURE: Measurements: (Ask your instructor to check the circuit before turning on the power supply.) 1. Set up the following circuit (Figure 1), using a power supply, an ammeter, a voltmeter and one 200 Ω Resistor (R). A digital multimeter may be used instead of an ammeter. Note: It is very important that the Ammeter is connected in series with the resistor R. Connect with a red cable the red outlet of the power supply with the red input on the ammeter. Color code: (+) red (-) black 55 Figure 1. A simple electric circuit to study the relationship among voltage, current and resistance. 2. Set the voltage to 2 V by turning the voltage knob of the power source gradually until you read 2 V on the voltmeter. (Disregard the numbers on the instruments of the DC power supply). 3. Record the voltage V and the current I on the ammeter in Table 1. Note: The ammeter scale is in milliampere (1 A = 1,000 mA; e.g. 15 mA = 0.015 A). 4. Increase the voltage and record voltage and current in Table 1 for 2 V, 4 V, 6 V, 8 V, 10 V and 11 V. 5. Set the voltage to 0 V by turning the voltage knob of the power supply. Turn off the power supply and replace a 200 Ω Resistor by a 100 Ω Resistor.