Ohm\'s Law P- V=IR where V is voitage, I is current, and R is resistance Ohm\'s

Question

Ohm's Law P- V=IR where V is voitage, I is current, and R is resistance Ohm's Law Objective 1. Determine resistance by measuring voltage and current. Procedure: Set up a simple circuit with a power supply and a resistance box. Using an ammeter as part of the circuit loop to measure current. Using a voltmeter across the resistance e value. Change the voltage on the power box to measure voltage. Set the resistance to on supply and record the result the precision of the voltmeter and ammeter ing change in current. Repeat with two other resistances. Record Analysis Enter your data in the spreadsheet program, Excel. Use this program to create a graph of current on the horizontal axis and vottage on the vertical axis. Use the function, the y-intercept Use propagation of error to determine the precision of each of the three resistances based on the precision of the voltmeter and ammeter. Use the middle value for slope, in Excel to determine the slope of the curve. Use the function, "intercept, to determine voltage and current in the calculation. Do propagation of error only for Objective 1 For a linear (straight line) relationship such as Ohm's Law, the graph should show a curve following the math formula, y-mx+b where y is the vertical variable, x is the horizontal variable, m is the siope, and b is the y-intercept. The slope of the graph is simply rise divided by run, that is, the change in the vertical range divided by the change in horizontal range. For this Ohm's Law Objective 2. Determine current by measuring voltage and resistance. objective, the siope is the resistance. In this case the y-intercept should be zero according to Procedure: Use the same setup as you did in Objective 1. As the value of resistance in the resistance box is changed, adjust the voltage on the power supply to keep the current constant. Record the resulting resistances and voltages. Analysis: Again, enter your data in the spreadsheet program, Excel. Create a graph of voltage on the vertical axis and resistance on the horizontal axis. Determine the slope and y-intercept of the resulting curve. Objective 3. Determine voltage by measuring current and resistance. Procedure: Use the same setup as you did in Objective 1. Keep the voltage on the power supply constant. As the resistance in the resistance box is changed, record the resulting change in current Analysis: Once again, enter your data in the spreadsheet program, Excel. Make a graph of the data with the current on the vertical axis and 1/resistance on the horizontal axis. (You will need to create a third column of data in Excel where you convert resistance to 1/resistance.) Page 1

Explanation / Answer

Although the data for the experiment is not provided so all the questions cannot be answered but I'll try to answer the physics part of the problems which only requires understanding of the Ohm's law. I hope this helps.

Objective 1.

1. The value calculated from Ohm's law might differ from the value obtained in the experiment because in Ohm's law we treat the resistance as a proportionality constant. However resistance can vary with temperature. So as you increase the voltage the heat dissipated by the resistance increases and its resistance changes with the rise in temperature. Hence for higher values of both voltage and current the experimental curve will deviate from the theoretical straight line curve.

2. It depends upon the sensitivity of the voltmeter and ammeter used in the experiment. Say the minimum voltage the voltmeter can measure is 0.1v whereas the minimum current measured by the ammeter is 0.01 mA then if the voltage is less than 0.1v the voltmeter will show the reading of 0v however as the ammeter is sensitive enough to measure the current it will show a non zero reading.

3. If we use a larger resistance then the current through it will be lesser for the same value of voltage which will cause less rise in temperature hence the resistance would behave more like an ideal resistor. So for larger resistances the deviation from the straight line would be lesser compared to a smaller resistance.

Objective 2.

4. The slope might be different from the constant current that you tried to maintain because as you increase the voltage drop across the resistance its effective resistance will change and you will obtain a different value of current than you expect from Ohm's law.

6. The method from objective 1 is better way of verifying Ohm's law because here you control both the current and voltage parameters. Thus there is lesser chance of introducing an error in calculation of resistance. However in the second case we may obtain wrong values of current as the resistance may change with increase in voltage so it will introduce significant error.

Objective 3.

9. We can calculate the power using the relation P=V.I and then plot P against I2. This will give a straight line with the value of the slope giving resistance.

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