Lesson: Resistance and Resistivity of Conductors Physics • 9th Grade

In this lesson, we will learn how to relate the dimensions of and the motion of free electrons through an object to its resistance.

Lesson Plan

Students will be able to

use the formula to relate the resistivity, resistance, and dimensions of a resistor,
diagrammatically represent, in terms of the motion of free electrons, the effects of varying the length, cross-sectional area, and resistivity of a resistor on its resistance,
diagrammatically represent, in terms of the motion of free electrons, the effects of varying the temperature of resistors,
use the formula to relate the current in a resistor to the drift speed of free electrons in the resistor.

Lesson Video

Sample Question Videos

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Lesson Worksheet

Q1:

A wire made of an unknown substance has a resistance of 125 mΩ. The wire has a length of 1.8 m and a cross-sectional area of m². What is the resistivity of the substance from which the wire is made? Give your answer in scientific notation to one decimal place.

Q2:

A copper wire with a resistance of 12.8 mΩ has a cross-sectional area of m². Find the length of the wire. Use Ω⋅m for the resistivity of copper. Give your answer to one decimal place.

Q3:

The diagram shows two identical circuits. Each circuit’s conducting wire has had a section of it greatly magnified to show the ions that the conducting wire is comprised of and the free electrons that move between these ions. The conducting wires are both made of the same substance.

Which of the following statements correctly states how the resistivities of the sections of conducting wire in diagram (a) and diagram (b) compare to each other?

Which of the following statements correctly states how the cross-sectional areas of the conducting wires compare to each other?

Which of the following statements correctly states how the average time taken for a free electron to cross from one side of the section to the other side in diagram (a) compares to the average time taken for a free electron to cross from one side of the section to the other side in diagram (b)?

Which of the following statements correctly states how the resistance of the section of conducting wire in diagram (a) compares to the resistance of the section of conducting wire in diagram (b)?