Lesson: Alternating Current Circuits Physics • 9th Grade

In this lesson, we will learn how to determine the values of electrical quantities in circuits powered by alternating voltages.

Lesson Plan

Students will be able to

use the formula to calculate the induced emf due to the rotation of a conducting coil in a uniform magnetic field,
calculate root-mean-square values of alternating voltage, current, and power,
identify the phase relationship between voltage and current in alternating current circuits that are either resistive, capacitive, or inductive.

Lesson Presentation

Lesson Video

Lesson Explainer

Lesson Playlist

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Lesson Flashcards

Lesson Worksheet

Q1:

An alternating current has a peak value of 1.35 A. What is the root-mean-square value of the current? Give your answer to three decimal places.

Q2:

An ac generator has a frequency of 50 Hz. The coil of the generator is initially parallel to the generator’s magnetic field and its loops are coplanar. At what time after the coil starts rotating is the instantaneous potential difference across the coil equal to the root-mean-square potential difference produced by the generator?

Q3:

An alternating current generator contains 10 rectangular loops of conducting wire with side lengths of 25 cm and 23 cm, the ends of which form terminals. The sides of the loops with the same lengths as each other are parallel to each other. The loops rotate within a 560 mT uniform magnetic field. The peak potential difference across the terminals is 85 V. How many revolutions per second do the loops turn through? Give your answer to the nearest revolutions per second.