Energy, Intensity and Momentum of Electromagnetic Waves

Name: Energy, Intensity and Momentum of Electromagnetic Waves
Author: StemPy Lab

Sunlight warms your hand and also pushes on it, very gently.

We find the energy stored in the fields, the intensity of a beam and the strengths of E and B that go with it, then the momentum and the pressure of radiation.
The last lesson gathers the calculations that tests ask and says where other books write them differently.
It serves the Indian syllabus (NCERT, JEE Main, NEET) and the matching topic of A-Level, IB and AP.

3 lessons, about 1 h 35 min3 simulations10 problems6 practice questionsPython in every lesson

Created by StemPy Lab

Course outline (3 lessons)

Lesson 1about 30 min
Energy density and intensity
A wave carries energy in its electric field and in its magnetic field, and the two parts are equal. The average energy density is $\tfrac{1}{2}\varepsilon_0 E_0^2$ , and the intensity is $I = \tfrac{1}{2}\varepsilon_0 c E_0^2$ . The Poynting vector gives the direction and the rate of the flow of energy. From a given power we can find $E_0$ and $B_0$ at any distance.
1 simulation2 practice questions1 Python program3 problems1 Python lab
Read the lesson
Lesson 2about 35 min
Momentum and radiation pressure
An electromagnetic wave carries momentum as well as energy. Energy $U$ that is absorbed brings momentum $U/c$ . A surface that absorbs light feels the pressure $I/c$ , and a perfect mirror feels $2I/c$ . For sunlight these are a few micropascal. They are small, but over long times they move a solar sail, bend the tail of a comet and push on dust grains.
1 simulation2 practice questions1 Python program4 problems1 Python lab
Read the lesson
Lesson 3about 30 min
Standard calculations and where books differ
Tests on this chapter ask a small set of calculations again and again: the fields of a beam or a pulse, the force on a target, the displacement current from $dE/dt$ and the energy in a length of beam. This lesson works through them with one method. It also lists where A-Level, IB and university books write the same things in a different way.
1 simulation2 practice questions1 Python program3 problems1 question set1 note
Read the lesson

Test Your Learning

Electromagnetic Waves: Chapter Test

NEET format20 questions · 20 min

Not started

Your teacher

StemPy Lab

← All Courses

← The Electromagnetic SpectrumNext →

More onWaves & Sound › Electromagnetic Waves

Discussion (0)

Loading…

Energy, Intensity and Momentum of Electromagnetic Waves

Course outline (3 lessons)

Energy density and intensity

Momentum and radiation pressure

Standard calculations and where books differ

Test Your Learning

Your teacher

Discussion (0)