8.02x - Lect 7 - Capacitance, Electric Field Energy

About this video

• Video Title: 8.02x - Lect 7 - Capacitance, Electric Field Energy
• Channel: Lectures by Walter Lewin. They will make you ♥ Physics.
• Speakers: Walter Lewin
• Duration: 00:49:23

Overview

In this lecture, Walter Lewin introduces the concept of capacitance and its relationship to electric field energy. He explains how to calculate the energy stored in electric fields and the capacitance of various objects, including spheres and parallel plate capacitors. The lecture also demonstrates practical applications like photo flashes and the function of fuses.

Key takeaways

• Electric Field Energy: The energy stored in an electric field is equivalent to the work done to assemble charges. This energy can be expressed as the integral of the electric field energy density (1/2 * epsilon_0 * E^2) over all space.
• Capacitance Definition: Capacitance is defined as the charge on a conductor divided by its potential. The unit of capacitance is the Farad.
• Parallel Plate Capacitor: The capacitance of a parallel plate capacitor is directly proportional to the area of the plates and inversely proportional to the distance between them.
• Energy Storage: Capacitors are devices that store electric energy. The energy stored is given by 1/2 * Q * V or 1/2 * C * V^2.
• Photo Flashes: Photo flashes utilize capacitors to store energy, which is then rapidly discharged through a light bulb, creating a bright flash.
• Fuses: Fuses are safety devices that protect electrical circuits from overcurrent by melting and breaking the circuit when the current exceeds a safe level.