Resistance Lab
Copy this into your notebook:
How well does current travel through different materials and objects?
How well does current travel through different materials and objects?
In this Investigation, you will:
- Determine how objects differ in their ability to resist current.
- Classify materials as conductors, insulators, or semiconductors.
- Compare the resistance of identical pieces of copper and aluminum wires.
- Determine how electrical resistance varies with length.
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 certain materials. Resistance is the quantity that describes how much an object will prevent (resist) the flow of current. Resistance is measured in units called ohms.
Answer these questions in your notebook:
- What is resistance?
- What unit do scientists use to measure resistance?
Part 1: Measuring Resistance of Everyday Objects
Gather the following materials: electrical meter and its two test leads, and resistance test objects. (Most are found in your bag!)
Your test objects are lead, iron, wood, graphite, rubber, glass, air, and nickel II oxide.
Your test objects are lead, iron, wood, graphite, rubber, glass, air, and nickel II oxide.
- Examine the objects and try to determine what material each is made out of. Include air as one of your test objects. You can ask your teacher for assistance. Record your answers in Table 1.
- Connect the two meter leads to the meter as shown at right.
- Set the meter to measure resistance by pointing the dial at the OHM (see diagram for symbol). The black lead goes into the COM port and the red lead goes into the V/OHM port.
- Measure the resistance of each object. To do this, attach the black negative meter lead to one end of the test object and then attach the red positive meter lead to the other end of the test object. (Use your ruler to measure the resistance of 1 centimeter of air.) To measure the wood of a pencil, be sure to only touch the leads of the meter to wood part. To measure the graphite of the pencil, be sure to only touch the graphite (the gray in the middle of a pencil).
- Some materials may have a high resistance and the meter will read OL. Record these readings as “very high.” Record all resistances in Table 1.
Part 2: Identifying conductors and insulators
To roughly describe the ability of different kinds of materials to conduct current, we say that a material is a conductor (conducts easily), an insulator (conducts poorly), or a semiconductor (in-between). All of these materials are useful when we construct circuits. Copy the table below into your notebook.
- Rearrange the list of objects you tested (in Table 1) so that the readings of resistance go from lowest to highest. Copy your rearranged list of objects and their resistance into Table 2.
- Look at your results and try to classify the objects you tested under one of these three categories: conductors, insulators, and semiconductors. As a guideline, remember that bulbs and wires are conductors and air is an insulator. Write down your classifications in column 3.
Part 3: Measuring the Resistance of Copper and Aluminum
- Get the identical pieces of aluminum and copper from your teacher.
- Measure the resistance of both pieces of metal. You can bend the wire so that the meter leads can reach the ends. Record your results.
- Fold each piece of wire neatly in half and mark the halfway point. Unfold the wire and measure resistance from the halfway point to one end of the wire. Record your results for copper and aluminum.
When done, click the link below to complete the analysis. Remember, this must be completed in one sitting, so if you don't submit, you'll have to start again.