Current Electricity

Current Electricity

grade 2-grade 6-grade 9-grade 11-grade 12-physics-physical science-technology education-electricity-electric current-voltage-current-resistance-electric circuit-electrons

 

Introduction

Electric current is the flow of electrons through a completed circuit of conductors. It is used to power everything from our lights to our trains. In these activities, students will explore different kinds of circuits and investigate what is required to make up a complete circuit.

Objectives

  • Describe the components required to complete an electric circuit.
  • Demonstrate the different ways to complete a circuit (parallel or series).
  • Identify how electricity is used in household appliances.
  • Describe the relationship between an electron and current electricity.

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Background

Electricity is used to operate your cell phone, power trains and ships, run your refrigerator and power motors in machines like food processors. Electric energy must be changed to other forms of energy such as heat, light or mechanical to be useful.

Everything we see is made up of tiny little parts called atoms. The atoms are made of even smaller parts. These are called protons, electrons and neutrons. An atom usually has the same number of protons (which have a positive charge) and electrons (which have a negative charge). Sometimes electrons can be moved away from their atoms.

Electric current is the movement of electrons through a wire. Electric current is measured in amperes (amps) and refers to the number of charges that move through the wire per second. In order for a current to flow, the circuit must be closed; in other words, there must be an uninterrupted path from the power source, through the circuit, and back to the power source.

Voltage is measured in volts and is sometimes called electric potential. The voltage between two points in a circuit is the total energy required to move a small electric charge from one point to the other, divided by the size of the charge.

Resistance is measured in ohms and refers to the forces that oppose the flow of electron current in a wire. We can use resistance to our benefit by transforming the electrical energy lost in a resistor into heat energy (electric stove), light energy (light bulb), sound energy (radio), mechanical energy (electric fan), or magnetic energy (electromagnet). However, if we want current to flow directly from one point to another, we should use a wire that has as little resistance as possible.

A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure that pushes water out, the current is equivalent to the flow rate, and the resistance is like the pipe width. The thinner the pipe, the higher the resistance.

In this series of activities, students will experiment with wires, batteries, and switches to create their own circuits while learning about voltage, current, and resistance at the same time.

Fun Fact

You may notice that the symbols for several of the SI units in this module are capitalized, such as the volt (V) and the ampere (A), as opposed to the ones you're used to using (m, kg). It is tradition to use a capital letter when the unit is named after a person. In these cases, the units were named after Alessandro Volta and André-Marie Ampère. The unit for resistance was also named after a person (Georg Simon Ohm), but uses the symbol Ω which represents the Greek letter omega. These rules are important to follow since the small and capital letters may represent different units, such as the tonne (t) and the tesla (T). The one exception is that it is acceptable to use L for litres since the letter 'l' is often confused for the number '1'.

Entire Lesson

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Comments  

 
#1 Activity Delivery tips — Eugene Luk 2012-03-08 13:31
•Electrons on the Go: masking-tape outline on floor really helps prevent circle from squishing inwards.
•Lemon Battery: voltage will be extremely weak; you'll need at least 3 lemons per battery for any visible movement on voltometer. Probably better as demo rather than class-wide activity.
•Conductivity Tester: can use "UFO/circuit balls" (http://www.xump.com/science/UFOBall.cfm, found in most toy or novelty stores) instead of batteries as tester. Circuit balls are good substitute b/c they demonstrate how humans are good conductors too.
•Steady Hand Game: this M&T requires a fair bit of prep, so set aside plenty of prep time. Prep copper wires by loosely looping the ends around a popsicle stick a few times, and attach the short wire to one end of copper wire. Also, test out all X-mas light bulbs beforehand to ensure they work! Before class arrives, set up M&T stations at one end of classroom and pre-rip 2 short and 2 long strips of tape for each student. Make sure all facilitators understand how to construct M&T; during session, divide class into groups and have each facilitator lead a group through M&T.