Remember these things: 1. Batteries (or power supplies) are sources of constant potential. For current to flow in a circuit, there must be a closed loop. 3. When the current reaches device, it can either charge that device (like a capacitor), or it must go through the device. No current is ever lost (charge is conserved) 4. Asyou go around a circuit loop with devices there will be drops in electrical potential (voltage) across the two sides of the device if current passes through them. Examine the circuit shown below. A variable DC power supply is like a variable battery. When you turn the dial, you change the voltage (potential difference) between its terminals. owerSupply 106hm - The item labeled \"A\" is a current meter - it measures the current with a very, very small drop in potential (it does not affect the circuit). Current meters are always placed in series. The item labeled \"V\" is a potential meter (volt-meter) - these measure the potential difference across the two sides of the device across which the voltmeter is connected. Volt meters are always placed in parallel and they do not allow current to flow through them (it does not affect the circuit). In the circuit above the current meter measures the current in the circuit (there is only one path and therefore only one current) and the volt meter measures the voltage across the device. Prediction 1: What will happen to the potential difference across the resistor as the dial on the power supply is turned to higher and higher potential? Prediction 2: What will happen to the current through the resistor as you turn the dial on the power supply and increase the applied voltage from zero? Test your prediction. Ask your instructor for a resistor and connect the circuit above. Set the power supply to zero voltage and slowly turn the dial to 0.5V and record the current measured by the ammeter. Continue increasing the voltage slowly to about 3.5 volts in steps of 0.5 V. Record your data in the table below. Make sure to include the uncertainty of the measurements! Prediction 1: As the voltage applied by the power supply increases, the potential difference across the resistor will also increase, Prediction 2: As the voltage applied by the power supply increases, the current through the resistor will also increase. Explanation: (For the resistor, | shall assume the same 10-ohm resistor in the diagram was used in this experiment. A typical 10-ohm resistor has a color code of brown-black-black-gold. If your instructor gave you a different colored resistor, please inform me as the following results will change.) Resistance of resistor from color code: 10 ochms + 5%. (For the table below, | used the circuit simulation software Multisim to obtain the pertinent data, assuming + 0.01 volt and + 0.001 amp uncertainty for the voltage and current, respectively.) Potential Difference (volts) | 0.5 + 01 1001 1501 20+x01 25+01 30+01 35+01 Current (amps) 005+001 01+x001 015+x001 02x001 025+0.01 03+001 035001 Question 1: Based on the table above, both the potential difference across and the current through the resistor increased as a result of subsequent increases in the power supply voltage. Hence, the above predictions were correct. Question 2: Voltage vs. Current 4.00 3.00 2.50 2.00 Volts 1.50 1.00 0.50 0.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 Amps Question 3: Based on the voltage vs. current graph, the potential difference across and the current through the resistor exhibits a linear relationship. Question 4: Since R is the slope of the voltage vs. current graph, its value is constant as the graph is linear. This is because the resistor obeys Ohm's Law, which states that the voltage is directly proportional to the current with the constant of proportionality being the resistance R. Question 5: _ Ay (3.5+0.1)(0.5+0.1) 340.2 3+6.67% _ 0 R Ar [0.3520.01)(0.06=0.01) _ 0.3%0.02 0.3::6.67373 = 109 13.34% Thus, the calculated resistance agrees with the resistance value obtained from the color code of the resistor. Resistance of resistor from color code: Potential Difference (volts) Current (Amps) Question 1: Were your predictions correct? Question 2: In Excel make a plot of Voltage vs. Current and turn in that graph in the next class along with your group work on this worksheet. Don't forget to add uncertainty (error) bars to each of the data points in your graph. Question 3: What is the mathematical relationship between potential difference and current for a resistor? Explain based on your graphs. Comment: The relationship between potential difference and current that you have observed for a resistor is known as Ohm's Law. To put this law in its normal form, we must now define the quantity known as resistance. Resistance is defined as the slope of the voltage vs. current graph. The unit of resistance is the ohm (1Volt/Amp). Question 4: Based on your graph, what can you say about the value of R for the resistor is it constant or does it change as the current through the resistor changes? Explain. Question 5: Use the results of the experiment to determine the resistance of your resistor in ohms? How does this agree with the color-coded value written on the resistor do a percent error? Note: Many circuit elements do not obey Ohm's Law. The definition for resistance is still the same, but the resistance changes as the current changes. Circuit elements that follow Ohm's law like resistorsare said to be ohmic