# Why Are Electrical Wires Covered in Plastic？| DFRobot Science Lab Season 2 EP01

### Standards

NGSS

5-PS1-3 Matter and Its Interactions：Make observations and measurements to identify materials based on their properties.

### Overview

Observe a phenomenon in daily life, explore the question---"Why are electrical wire covered in plastic?” to lead out the concept of conductivity, and help students get to know conductor and insulator by experimenting so as to understand the principle of electrical wire and learn the electrical safety basics.

### Materials

Play and Learn with Boson Science Design Kit: https://www.dfrobot.com/product-2176.html

Engage

If we observe the electrical equipment in our home, we can find that the electrical wires for household appliances are all wrapped in plastic, but their power plugs are bare metal. Why is that? What is inside an electrical cord? Why does it have plastic coverings? Take a guess!

Explore

After making a supposition about an unknown question, we have to prove it by performing experiments.

This experiment consists of two parts: 1. Find the component of an electrical wire; 2. Explore the properties of all component parts and then explain why electrical wires are covered in plastic.

Part 1 What are the components of an electrical wire?

### Preparation

To explore the composition of electrical wire, we have to prepare electrical cables, and wire stripper (or scissors).

### Step

Cut the end of the Dupont wire and peel off its electric skin.

### Conclusion

From the above, we can see that the electrical wire mainly has two parts: wire core, and plastic coverings.

### Make a Conjecture

Take a guess, what are the functions of each part of the electrical wire?

Part 2 What is the function of electrical wire plastic coverings?

We know that an electrical cable is used to transfer power. But which part of the electrical wire does the work, wire core or plastic coverings? Can the human body transfer power too? Let’s look for the answers one by one through experiments, and record the results in the form below.

### Preparation

Take out the following module blocks from BOSON Science Design Kit.

### Step

1. Build an experimental circuit to detect if the wire core, wire plastic coverings and human body can transfer power?

2. When the circuit building is finished, make the two alligator clips contact each other, then there is a lightning bolt symbol appearing on the screen, which indicates that the electrical power can be transferred; Separate the two alligator clips, the lightning bolt sign disappears, which means the power transmission fails. Therefore, we can clip the two alligator clips onto electrical wire core, plastic coverings, and human body to test whether they can transfer power.

### Conclusion

The experiment results are shown below:

It can be seen from the experiment that only the electrical wire core and human body can transfer electrical power. Did you guess correctly about the previous two questions? Let’s check the right answers.

Question 1: What is the function of electrical wire core?

Answer: The electrical wire core is used to transfer electrical power.

Question 2: What is the function of electrical wire plastic coverings?

Answer: The electrical wire plastic coverings cannot transfer power, but electrical power can pass through our bodies. So, the plastic coverings can insulate the metal wire core from human body so as to protect our safety. (When the electricity reaches a certain range, it will cause damage to human body. We only use a very small amount of electricity in the experiments, so no worries.)

Now you must have known why the electrical wires are always covered in plastic.

Science Background

By the experiment we get known that electrical power can pass through some objects like metal wire core, human body. Actually, objects with such properties are called conductors. Conversely, objects that cannot conduct electricity, like plastic, are insulators. Let’s get to know more details about the conductor and insulator!

### Conductors & Insulators

Conductors——Some materials let electricity pass through them easily. These materials are known as electrical conductors.

Insulators——Some materials do not allow electricity to pass through them. These materials are known as electrical insulators.

What makes a material a conductor or an insulator? Simply put, electrical conductors are materials that conduct electricity and insulators are materials that do not. Whether a substance conducts electricity is determined by how easily electrons move through it.

Electrical conductivity is dependent on electron movement because protons and neutrons don't move—they are bound to other protons and neutrons in atomic nuclei.

*https://www.thoughtco.com/examples-of-electrical-conductors-and-insulators-608315

### How the Body Conducts Electricity

So why is electricity so dangerous? Electricity flows from one point to another along anything that will conduct it. One of the better conductive substances for electricity is water, which happens to represent about 70 percent of the human body. But even with all of that water inside of us, electricity doesn't flow through the human body unobstructed. It encounters resistance along the way, which causes some of the energy from the electric current to turn into heat. That heat from resistance causes one of the dangers of electricity: burns.

According to the industry regulations, the safe voltage should not be higher than 36V, and the safe current is 10mA.

Conclusion

In this project, we explored the question about a common phenomenon—-“Why are electrical wire covered in plastic?”, and learned what the conductors and insulators are. In fact, there are tons of scientific principles behind our various daily life phenomenon. Go and observe things in your everyday life carefully, you will learn more!

That’s all for this lesson. Put all Boson modules in the original box.

Extend

The electrical wires we used at home are always wrapped in plastic coverings, but why are the high-voltage transmission lines not wrapped and insulated?