# Relationship between light intensity and amplitude

### Relationship between light amplitude and intensity | Physics Forums

In astronomy, amplitude of a light's wave is important because it tells you about the intensity or brightness of the light relative to other light waves of the same. what is the relationship between amplitude and intensity is intensity just the amplitude squared?. The amplitude of a wave varies in a sinusoidal manner with time whereas the intensity of the wave varies as sine squared. These two variations are shown in.

Pressure fluctuations caused by sound waves are much easier to measure. Animals including humans have been doing it for several hundred million years with devices called ears.

Humans have also been doing it electromechanically for about a hundred years with devices called microphones. All types of amplitudes are equally valid for describing sound waves mathematically, but pressure amplitudes are the one we humans have the closest connection to.

In any case, the results of such measurements are rarely ever reported. Instead, amplitude measurements are almost always used as the raw data in some computation.

### schoolphysics ::Welcome::

When done by an electronic circuit like the circuits in a telephone that connect to a microphone the resulting value is called intensity. When done by a neuronal circuit like the circuits in your brain that connect to your ears the resulting sensation is called loudness.

The intensity of a sound wave is a combination of its rate and density of energy transfer. It is an objective quantity associated with a wave. Loudness is a perceptual response to the physical property of intensity. It is a subjective quality associated with a wave and is a bit more complex.

Wave Amplitude

As a general rule the larger the amplitude, the greater the intensity, the louder the sound. Sound waves with large amplitudes are said to be "loud". Sound waves with small amplitudes are said to be "quiet" or "soft". The larger the balloon gets the paler the colour - eventually it turns pink or pops, but that's not the point of our example You can think of the surface of the balloon as being like the wave front radiating out from a wave source - say a loudspeaker.

The depth of colour of the balloon is like the intensity of the wave.

## Relationship between light amplitude and intensity

We've also heard this explained by thinking about the thickness of jam you could spread on a table -tennis ball, a cricket ball and a football, if you only have the same amount of jam wave power available in each case - but this sounds messier than the balloon idea! The key thing to remember is that the energy from the source is always the same - it is simply distributed over a larger area, the further away from the source you try to measure.

So - what has all this to do with the 'inverse-square' law? It comes down to the geometry of the area over which the power spreads out.

• Intensity and amplitude

Let's make it easy for ourselves, and assume the power spreads out equally in all directions, in which case the area is the surface of a sphere and our balloon should be spherical!

Remember - the inverse-square law applies, where energy spreads out spherically.

### Intensity – The Physics Hypertextbook

Amplitude and intensity The energy of a wave is proportional to the square of its amplitude. Therefore the intensity of a wave is also proportional to the square of its amplitude.

If we move twice as far from a loudspeaker, the sound intensity will decrease to one-quarter its original value, and the sound pressure ampitude will go down to one-half.

Here are some slow-motion videos which may be useful in showing waves propagating from a source. Look at these ripples spreading out in water. How are they different, and does the inverse-square law apply?