Physics Ohm’s Law Lab
To be completed in your lab notebook
Pre Lab:
· On a fresh piece of paper in your lab notebook write today’s date and the title of the lab.
· Don’t forget to continue the page numbers in your lab notebook.
· Don’t forget to add this lab and its page number to your Table of Contents.
1. Define Ohm’s Law.
2. Draw a circuit diagram that has one resistor, one ammeter, one voltmeter, one switch and a voltage generator. Label each of these parts of your drawing.
Objective: During this investigation you will determine the values of resistors by applying Ohm’s Law.
Materials:
Voltage Source 1 Voltmeter
4 Banana-Banana leads Switch
2 Banana-Alligator leads 1 Ammeter
4 different Resistors (<30Ω)
Procedure:
1. Glue your two data tables into your lab notebook beneath your drawing.
2. Connect the source of current, the switch (opened), an ammeter, and any of your resistors in series. Connect a voltmeter in parallel around your resistor. This should look like your circuit diagram from the pre-lab.
3. Turn the voltage source on and adjust it until the voltmeter reads 3 V across the resistor. Be sure to use the 1-5V plug and scale on the voltmeter. Turn your circuit off and on using the switch.
4. NOTE Leave the switch open until your teacher has checked your circuit and told you to close the switch. The meters you are using are expensive and can be ruined with improper use.
5. Close the switch and quickly read the two meters. Open the switch as soon as you are done recording the readings. Record your readings in Data Table #1 in your lab notebook.
6. Repeat this procedure for three more different resistors until your first data table is completely filled in except for the last column. You will have to change the voltage each time so that the voltmeter reads 3 V across the resistor.
7. Reset the voltage source to 6 volts across the resistor. Be sure to use the 1-15V plug and scale on the voltmeter.
8. Again measure the current and voltage for each of your four different resistors but this time record the data into Data Table #2. You will have to change the voltage each time so that the voltmeter reads 6 V across the resistor.
9. You should have two different voltage readings for each of the four different resistors.
Analyzing:
?Underneath your Data Tables and Observations, write “Analyzing” and you will answer the questions below in complete sentences. Don’t forget to number your answers!
1. State the relationship between the current flowing through a circuit and the voltage and resistance in the circuit that your observed in your lab.
2. Describe the proper placement of a voltmeter in a circuit and why it must be that way to measure voltage.
3. Describe the proper placement of an ammeter in a circuit and why it must be that way to measure current.
4. Compare the printed values of the resistors you used with your calculated values. Specifically focus on your largest and smallest resistors. What could have affected a difference between your calculated value and the printed value on the resistors? (Answer hypothetically if you got the same value.)
5. Notice that next to your two tables is a space labeled “Resistance” and “Current.” Rank your resistors in order from the least to the greatest resistance. Rank the current you found for each resistor at 3 V from the greatest to the least current. What do you notice about these two lists?
Applying:
?Underneath your Analyzing questions, write “Applying” and you will answer the questions below in complete sentences. Don’t forget to number your answers!
6. Your voltage sources could have gone as high as 15 V although you will not have it that high. If your voltage source was set to 15 V, calculate the current you would expect for each of your four resistors. Show each GUESS calculation.
7. A friend calls you because they know you’re smart and in Physics. They tell you that they have an unlabeled resistor and they have to find out how big it is. Describe, step-by-step, how they could determine the value of that resistor.
If you are unsure if a 9 V battery can still supply a voltage you can test it by touching both of the terminals to your tongue. You will feel a small shock, not usually painful. Repeat the experiment against your arm and you will feel no shock.
8. What would such an experience tell about the level of resistance of your tongue compared to your arm? What properties of your anatomy cause this?
9. If humans generally don’t “feel” a shock unless it is over 4 mA, calculate the resistance of your tongue assuming that was the current going through it. Show GUESS.
10. Prominent signs and labels warning of electrical shock often accompany hair dryers, curling irons, etc. Other electric devices used in your house may not have such prominent labels. Discuss why prominent warning signs are so important in those particular electric devices.