A meter is an instrument for measuring electrical quantities, such as voltage, current and continuity. A digitalmultimeter (DMM) can measure any of these quantities, depending on how it is set up, and display the result on a digital readout, like a pocket calculator. Using a DMM, you can troubleshoot a circuit quickly to find a bad connection or component. A meter also helps to answer questions about circuits, such as:
Why does a red LED make a blue LED turn off, when both are connected in parallel with a coin battery?
Why does it matter how two batteries are connected to each other, in order to double the voltage?
Why do batteries come in different sizes?
Why won't a coin battery run a motor?
What happens to a motor when it is working harder?
This Appendix develops troubleshooting techniques, and explorations of circuit questions, using a digital multimeter. The activities can be done as a complete sequence, or performed separately whenever they are needed.
2. Learning about LEDs. In Lesson 1, students learned that some LEDs of different colors will both come on in parallel, but others won't. For example, the same battery will turn on a red and yellow LED, or a blue one and a green one, but either red or yellow will turn a blue or green one off. Click here for an experiment to find out why this happens.
8. More experiments with batteries and motors. You can use a DMM to find out how a D cell is different from an AA battery, or what happens to motor when it is doing more work. Click here for these experiments.