Resistance Lab
Purpose:
You will learn how to measure resistance across a resistor
You will build circuits using variable and fixed resistors.
You will measure current when resistance is changed.
Materials differ in their ability to allow current to flow through them. This is a good thing! It means that we can build circuits out of metals that easily carry current. We can block the flow of current using air, glass, or plastic. Resistance is the quantity that describes how much an object will prevent (resist) the flow of current. Resistance is measured in units called ohms.
This is the symbol for ohms.
You will learn how to measure resistance across a resistor
You will build circuits using variable and fixed resistors.
You will measure current when resistance is changed.
Materials differ in their ability to allow current to flow through them. This is a good thing! It means that we can build circuits out of metals that easily carry current. We can block the flow of current using air, glass, or plastic. Resistance is the quantity that describes how much an object will prevent (resist) the flow of current. Resistance is measured in units called ohms.
This is the symbol for ohms.
Materials: Multimeter, bulbs, bulb holder, wires, battery, fixed resistors, potentiometer
Procedure: Part 1:
Procedure: Part 1:
- Find the bag with the resistors.
- Create a table to measure the resistance of the different resistors. To identify them, mark down the number on each resistor.
- To measure resistance, place the red wire in the OHM port and the black wire in the COM port, and point the dial at the OHM. Put the black lead on one side of the resistor and the red lead on the other. Record the value in your data table. This is what is meant by "across" the resistor.
- Record the resistance for each resistor in your bag. (There are three).
Procedure: Part 2:
- Build a circuit using the battery, bulb & bulb holder, and one of your fixed resistors.
- Measure the current (refer to previous lab if you can't remember how to set up the multimeter) in the circuit and record the value with your fixed resistor.
- Repeat by switching out the resistor with another and measuring the current again. Do this for all your fixed resistors.
Procedure: Part 3:
Analysis:
- Build a circuit with the battery, bulb and bulb holder, a switch, and your variable resistor. (See the diagram.) A variable resistor is called a potentiometer, and it's similar to a dimmer switch. (Should have a knob on it!)
- Turn the potentiometer all the way to one side (as though it was all the way off). Your bulb should have a tiny bit of light! This is Setting #1.
- Measure the current (refer to previous lab if you can't remember how to set up the multimeter) at point indicated in the diagram and record the value.
- Turn the circuit off (open the switch) and measure resistance from one side of the dimmer switch to the other. BE CAREFUL NOT TO TOUCH THE KNOB. Record the value in your data table.
- Adjust the dimmer switch (potentiometer) so the light bulb is a tiny bit brighter and repeat steps 3 & 4. Continue until you have FIVE settings for the potentiometer.
Analysis:
- Look at your values for current and resistance from parts 1 & 2. What observations can you make about the relationship between current and resistance? Use your data to support your observations.
- Look at your values for current and resistance from part 3. Does your part 3 data agree with the relationship you see between current and resistance from parts 1 & 2? Use your data to support your explanation.