Two solids are shown below. One is a semiconductor and one is an insulator. Which one is which? Explain your reasoning.

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Step 1: Understand the properties of semiconductors and insulators. Semiconductors have electrical conductivity between that of a conductor and an insulator, and their conductivity can be altered by adding impurities. Insulators have very low electrical conductivity.

Step 2: Observe the colors of the powders. The yellow powder on the left and the white powder on the right.

Step 3: Note that many semiconductors, such as cadmium sulfide (CdS), are often colored due to their band gap properties. Insulators, like many oxides and salts, are typically white or colorless.

Step 4: Based on the color observation, hypothesize that the yellow powder is likely the semiconductor and the white powder is likely the insulator.

Step 5: Confirm the hypothesis by considering common examples: Cadmium sulfide (CdS) is a yellow semiconductor, while substances like silicon dioxide (SiO2) are white insulators.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Semiconductors

Semiconductors are materials that have electrical conductivity between that of conductors and insulators. They can conduct electricity under certain conditions, such as when doped with impurities or when exposed to heat or light. Common examples include silicon and germanium, which are widely used in electronic devices. Their ability to control electrical flow makes them essential in modern technology.

Insulators

Insulators are materials that resist the flow of electric current, making them poor conductors of electricity. They have high resistivity and are used to protect against unwanted electrical flow, ensuring safety in electrical systems. Common insulators include rubber, glass, and certain ceramics. Their primary function is to prevent electrical leakage and protect users from electric shock.

Band Theory

Band theory explains the electronic properties of solids in terms of energy bands. In semiconductors, the energy gap between the valence band and the conduction band is small, allowing electrons to jump to the conduction band under certain conditions. In insulators, this gap is large, preventing electron movement and thus electrical conduction. Understanding band theory is crucial for distinguishing between conductors, semiconductors, and insulators.