Ohm's Law Lab
Purpose:
You will build circuits using variable and fixed resistors.
You will measure current when resistance is changed.
You will measure and graph change in voltage when current is changed.
You will use your data and graph to determine the relationship between voltage, current and resistance.
Background:
When working with circuits, you may need to know how much voltage will light a particular light bulb, or how much current will be in a circuit so you can choose the correct size wire to use. German physicist Georg S. Ohm (1787-1854) experimented with circuits to find out how voltage, current, and resistance are related mathematically. The relationship he discovered is called Ohm’s law.
Materials: Multimeter, bulbs, bulb holder, wires, battery, resistors, potentiometer(variable resistor)
You will build circuits using variable and fixed resistors.
You will measure current when resistance is changed.
You will measure and graph change in voltage when current is changed.
You will use your data and graph to determine the relationship between voltage, current and resistance.
Background:
When working with circuits, you may need to know how much voltage will light a particular light bulb, or how much current will be in a circuit so you can choose the correct size wire to use. German physicist Georg S. Ohm (1787-1854) experimented with circuits to find out how voltage, current, and resistance are related mathematically. The relationship he discovered is called Ohm’s law.
Materials: Multimeter, bulbs, bulb holder, wires, battery, resistors, potentiometer(variable resistor)
Draw these two tables in your notebook.
Procedure: Part 1: How does changing resistance affect current?
A resistor is used in a circuit to provide resistance. In this part of the Investigation you will use a variable resistor. As you turn the dial of the variable resistor, its resistance goes up. A variable resistor is also called a potentiometer. Many dials you use everyday, like dimmer switches, are potentiometers.
A resistor is used in a circuit to provide resistance. In this part of the Investigation you will use a variable resistor. As you turn the dial of the variable resistor, its resistance goes up. A variable resistor is also called a potentiometer. Many dials you use everyday, like dimmer switches, are potentiometers.
- Build a circuit with the battery, bulb and bulb holder, a switch, and your potentiometer like the diagram on the right.
- Turn the potentiometer until the bulb is very dim.
- Measure the current (remember to open your circuit to measure current and that the meter is set up correctly) at point indicated in the diagram and record the value.
- Reconnect the circuit so it is complete again.
- Turn the circuit off using the switch and measure resistance across the potentiometer (be careful not to touch the dial as you do this.) Remember "across" means from one side to the other. Record the value in data table 1.
- Close the switch and make the bulb a little bit brighter and repeat steps 3, 4 & 5. Continue until you have completed FIVE settings of the potentiometer. Record all values in data table 1.
Procedure: Part 2: How does changing voltage affect current?
In this part of the Investigation you will use a fixed resistor (one with a rubber covering). This component adds resistance to a circuit, but its resistance does not change.
In this part of the Investigation you will use a fixed resistor (one with a rubber covering). This component adds resistance to a circuit, but its resistance does not change.
- 1. Measure the resistance of ONLY your fixed resistor with rubber cover (place each lead on each end of the resistor). Record this value in the entire column titled "Resistance" in data table 2.
- 2. Build the circuit on the left. Turn the potentiometer all the way to one side (as though it was all the way off). This will be your Setting 1 where you will collect current and voltage.
- Measure the current through the circuit after the fixed resistor. Record in data table 2.
- Reconnect the circuit and measure voltage across the fixed resistor. Record in data table 2.
- Turn the potentiometer knob and change the setting slightly.
- Repeat steps 3 & 4 for your new setting. Do FIVE settings of the potentiometer. Record all values in data table 2.
Analysis: (Complete in notebook, then upload photos of your work on Edmodo. Be sure to write clearly and that your photo(s) are clear.)
- How does changing the resistance (with the potentiometer) affect the current? (Part 1)
- How does changing voltage affect current? (Part 2)
- Graph the data from part 2. Put voltage on the y-axis and current on the x-axis. (Remember to label axes and title your graph.)
- Calculate the slope of the graph. (Use your line of best fit)
- What does your slope mean? (HINT: look at your Ohm's Law equation.)
- Compare the slope you calculate to your data. What kind of similarities or patterns or patterns do you see?
- Most circuits use fixed voltage sources. Different values of current are needed to run different devices and appliances. With this information, explain the importance of resistors in a circuit.