Waves: Intensity

Intensity of a wave

The radiant power passing through a surface per unit area.

Unit of Intensity (I)

Watts per square meter (Wm^-2).

Equation for Intensity

I = P/A, where I is intensity, P is power, and A is the area.

Inverse Square Law

Intensity (I) is directly proportional to 1/r² for waves spreading out from a source.

Effect of doubling distance on intensity

Doubling the distance from the wave source reduces intensity by a factor of 4.

Average distance from Earth to Sun

150 million kilometers.

Intensity of radiation at upper atmosphere

1400 Wm^(-2).

Total power output of Sun equation

Total Power = Intensity × Area.

Area for total power calculation

4π(150 million km)².

Total power output of the Sun

Approximately 3.846 × 10²⁶ Watts.

How to measure intensity with an LDR

Measure resistance of an LDR at different distances, then use a calibration curve to convert to intensity values.

Effect of wave spreading on intensity

As waves spread, intensity drops because energy is more spread out.

Amplitude effect on particle oscillations

Average speed of particle oscillations is proportional to amplitude; halving amplitude reduces speed to 0.5 and kinetic energy to 0.25.

Intensity proportionality to amplitude

For any wave, intensity is proportional to the square of the amplitude.