Electrical and Natural Gas Safety World Teacher's Guide
Middle Left: OPEN. Electricity cannot flow because the wire only goes from the battery to the bulb (or vice versa). There is no return path.
Middle Right: BOTH ANSWERS CAN BE CORRECT. This picture can be read in two ways. If students think it is showing the metal base of the bulb directly touching the bump on the battery, then the circuit is CLOSED. If they think the metal base of the bulb is not directly touching the bump on the battery, then the circuit is OPEN.
Bottom Left: OPEN. Although the loop is closed, electricity cannot travel through the glass top of the lightbulb. So in truth there is not a continuous path for electricity to travel.
Bottom Right: CLOSED. There are actually two closed loops in this example.
Did You Guess Right? Setup: If you are doing this in class with batteries and bulbs, strip the wires ahead of time and make sure the batteries are fresh. Although the illustrations do not show it, it’s helpful to twist the wire around the base of the bulb and to tape the wires to the battery.
Follow-up: When there is a break in a circuit, electricity cannot flow. In that case, we say the circuit is open. When you turn on a light, is that a closed or open circuit? (Closed.) When you turn a light off, is that a closed or open circuit? (Open.)
Page 7: Conductors & Insulators
Objective: To teach students to recognize materials that conduct electricity. To explain that water, metal, and the human body can conduct electricity, making people vulnerable to electrical shock.
Discussion: Why is it important to know the difference between conductors and insulators? (If you know about some common objects that are conductors, you might be more likely to keep these objects out of electricity’s path; i.e., you would know not to stick a metal fork into an outlet or toaster or touch a power line with a metal ladder.) Do you ever use ladders or long tools when working outside around your home? What precautions should you take to stay safe? (Answers may include use nonconductive fiberglass ladders and tools; keep all tools and equipment at least 10 feet away from any power line.) What precautions do you think utility line workers take to avoid electrical shock? (They use specially tested insulating gloves, tools, and equipment, and are specially trained.) Stress to students that only trained people should climb power poles and work on power lines.
Activity: People who work around power lines would be more likely to use the fiberglass ladder, the work gloves, and the safety goggles. Here’s why:
• The metal ladder is a conductor, while fiberglass is an insulator.
• The work gloves are specially tested rubber, while the kitchen gloves are very thin rubber and not designed to insulate from electricity.
• The goggles do not have any metal on them while the glasses do, and metal conducts electricity.
Safety Note: If insulators are wet, damaged, or dirty, or if the voltage is high enough, materials that are insulators can conduct electricity. Teach students never to assume that an insulator will block electricity.
What Do You Think? The characteristic properties of a substance are independent of the amount of the substance. So metal scissors will conduct electricity just as easily as a metal ladder.
Follow-up: Draw a utility worker wearing safety equipment.