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## CONDUCTORS RESISTORS AND INSULATORS

Modern world cannot think to live without electricity, because every aspect of our life is influenced by electricity. For example, without electricity there would be no television, radio, computers, videogames, electric lights, refrigerators, air conditioners and many other things. In this chapter we shall discuss electricity and its heating and chemical effects.

Conductors

Those substances through which electric current can pass easily are called conductors. Conductors have very low electrical resistance. For example, silver, copper and aluminium are conductors of electricity. Out of these metals silver metal is the best conductor of electricity. It should be noted that electricity can pass through conductors due to the presence of free electrons in them.

Resistors

Those substances which have high electrical resistance as compared to conductors are called resistor .e.g. eureka, nichrome and manganin.

Insulators

Those substances through which electric current cannot pass are called insulators. Insulators have very high electrical resistance. For example, wood, rubber, glass, paper, plastic and wax are insulators of electricity. Insulators cannot conduct electricity due to absence of free electrons in them.

Superconductors

In 1911 prof. H. Kammerling Onnes discovered that certain substance loses their resistance at very low temperature. This phenomenon of loosing electrical resistance by a substance on cooling it to very low temperature is known as superconductivity and the substances showing this property are called superconductors.

The very low temperature below which a substance becomes a super conductor is known as critical temperature or transition temperature. Below critical temperature the resistance of super conductors becomes zero and therefore current passes through it easily. The value of critical temperature is different for different metals. For example, mercury becomes superconductor below its critical temperature of 4.2 K and lead becomes superconductor below its critical temperature of 7.25 K.

1. What are conductors? Give 2 examples.

2. What are resistors? Give 2 examples.

3. What are electrical insulators? Give 2 examples.

4. Name the best conductor of electricity.

5. What are superconductors?

6. What is critical temperature?

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