Sort materials: conductor, semiconductor, insulator

Which quantity does an electric current measure?

A power cord is two materials in one object: metal on the inside, plastic wrapped around it. Why build it from two materials?

Materials differ enormously in how freely they let charge flow. The cord uses one material for each job. This lesson sorts materials into three classes by that one behavior.

Start with the cord's metal core: copper. Connect a strip of copper into a circuit, and charge flows through it freely.

A material that lets charge flow freely is called a conductor. Copper is a conductor.

And aluminum lets charge flow freely too. Aluminum is a conductor.

But the cord's plastic cover lets almost no charge flow.

A material that lets almost no charge flow is called an insulator. Plastic is an insulator.

And rubber lets almost no charge flow. Rubber is an insulator too. And glass lets almost no charge flow. Glass is an insulator too.

But silicon sits between the two classes. Silicon lets charge flow, but only a little: far more than glass, far less than copper.

A material that lets charge flow only a little, between a conductor and an insulator, is called a semiconductor. Silicon is a semiconductor.

And germanium lets charge flow only a little too. Germanium is a semiconductor.

The sort runs on one question: how freely does the material let charge flow? If charge flows freely, the material is a conductor. If only a little flows, it is a semiconductor. If almost none flows, it is an insulator.

Copper's row first: how freely it lets charge flow, and the class that behavior earns.

Rubber's row joins at the other end of the behavior range.

One question sorts every material: how freely does it let charge flow?

Which pairing of behavior and class is correct?

A test strip of nichrome metal is connected into a circuit, and charge flows through it freely. Which class is nichrome?

Name the behavior:

Nichrome lets charge flow freely.

Apply the sort:

A material that lets charge flow freely is a conductor.

Nichrome is a conductor.

Silver lets charge flow freely. Ceramic lets almost no charge flow. Which classification is correct?

A strip of dry wood is connected into the same circuit, and almost no charge flows. Which class is dry wood?

Name the behavior:

Dry wood lets almost no charge flow.

Apply the sort:

A material that lets almost no charge flow is an insulator.

Dry wood is an insulator.

The table lists four tested materials. Which one is a semiconductor?

That is the cord's design: a conductor to carry the charge, an insulator to keep it off your hand.

Your turn

Tungsten lets charge flow freely. Porcelain lets almost no charge flow. Which classification is correct?

Which pairing of class and behavior is correct?

In a parts drawer, steel wire lets charge flow freely and a silicon-carbide wafer lets charge flow only a little. Which classification is correct?