Video for electrical circuits activity
The Science
In this activity, you will explore simple electrical circuits and fundamental concepts of voltage and current.
Electrical circuits are organised in various possible combinations. The two basic arrangements are series (Figure 2) or parallel (Figure 3) connected circuits. The flow of current is described by Ohm’s law, which states the current passing through any conductor between two points is directly proportional to the voltage between the two points. The formula is as follows.
V = IR
Where V is voltage (volts), I is current (amps) and R is resistance (ohms)
The voltage, which comes from a power source (e.g. a battery or potato), serves as the driving force that pushes the electrons through a conductor. The larger the voltage, the more force is available to push the electrons. A suitable analogy to underscore the concept of voltage and current is that of water flowing through a pipe. In Figure 1, we assume there is water in the pipe flowing from A to B. In (1), the water is not moving as both A and B are on the same level. In (2) and (3), A is at a higher potential than B and therefore, the water flows. The pipe is the conductor, the water is the current, and the relative positions of A and B are analogous to voltages. Voltage is the force that pushes electrons through a conductor.
Figure 1 - Voltage and current as water flowing through a pipe
Another set of laws, Kirchhoff’s Laws, quantify how current flows through a circuit and how voltage varies around a loop in a circuit. Based on these for a series connected circuits (e.g. Figure 2), the Ohm’s equation becomes
Vtotal = VLED1 + VLED2 + VLED3
This means that the voltage is shared between all series connected devices.
In parallel connected circuits (e.g. Figure 3), following Kirchhoff’s law, the Ohm’s equation becomes:
Vtotal = VLED1 = VLED2 = VLED3
This means the voltage across all parallel connected devices see the same voltage.
In this activity we will look at how to connect series and parallel circuits and measure the voltage across different circuit elements.
Materials
- Energy sources
- A battery pack (5 or 9 volts)
- Potatoes
- Galvanized screws or nails
- Shiny copper pennies (or copper washers)
- Jumper cables
- Alligator clips
- Breadboard
- 6 Light Emitting Diodes (LED)
- Multimeter (optional - check with your school)
Instructions
- Connect the power to the breadboard
- Build a series circuit
- Connect power to the series circuit
- Additional investigation you can try with your series circuit
- Build a parallel circuit
- Connect power to the parallel circuit
- Change the Power Source (see instruction video for more detail)
- Use the alligator clips to clamp on the battery terminals. The standard practice is to use red for the positive terminal and black for the negative (ground) terminal.
- Optional: use the multimeter to read the voltage of the battery - Set the multimeter to DCV (20) and connect the positive probe to the red wire and the negative probe to the black wire.
- Clamp the other ends of the alligator clip to the jumper cables.
- Connect the positive and the negative terminals of the jumper cables to the red and blue power rails of the breadboard. (Now we can draw power from any of the holes in the power rails)
Further investigation
- You could try boiling the potatoes to get more potential out of them (meaning it should take less potatoes)
- Substitute the potatoes with other food items like lemons, grapefruit or kiwis.
- Once you get the LED to light up brightly with potatoes what happens if you add a second LED in series? In parallel?
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