# Amplitude of light and intensity

• hangover
In summary, when light travels from a point source at distance R to a point at distance 2R, the amplitude of the light decreases due to the decrease in intensity caused by the spreading out of the wavefronts over a larger area. This results in a decrease in the detected power at the further point.
hangover

## Homework Statement

Light is emitted from a point source. How does amplitude of light change when light has traveled from R to 2R?

## Homework Equations

Energy=(1/2)kA^2 where k is constant and A is amplitude
Intensity=(Energy/time)/area

## The Attempt at a Solution

My teacher said that:
As area=4piR^2, intensity of light decreases when light travels to 2R. Therefore the amplitude of light decreases. Isn't the energy be constant while intensity changes? I am confused as he said that amplitude of light decreases as light moves further from the source?

What is the cause of the phenonmenon that light becomes dimmer in further distance? Decrease of intensity or decrease of amplitude or both?

It is the decrease in amplitude that results in the decrease in intensity. (since frequency is constant)
The energy of the light does not decrease when it spreads out usually, but becomes spread over a larger area. (for a point or isotropic source, think of the wavefronts as spherical shells) This is the reason why the intensity (and amplitude) detected further away from the source decreases, because the power received at that point is reduced as the wave spreads out and distributes its energy over a larger region.

As light travels from R to 2R, the amplitude of light does not change. The amplitude of light is a measure of the maximum displacement of the electric or magnetic field in a light wave. This maximum displacement remains constant as the light travels. What does change is the intensity of the light. Intensity is a measure of the energy of the light per unit time and per unit area. As the light travels to a larger distance, the same amount of energy is spread out over a larger area, resulting in a decrease in intensity. This is why the light appears dimmer at a further distance.

The decrease in intensity is due to the spreading out of the light waves as they travel. This is known as the inverse square law, which states that the intensity of light is inversely proportional to the square of the distance from the source. So as the distance increases, the intensity decreases drastically. This phenomenon is the cause of the light becoming dimmer at a further distance.

In summary, the amplitude of light does not change as it travels from R to 2R, but the intensity decreases due to the spreading out of the light waves. This decrease in intensity is responsible for the decrease in brightness of the light at a further distance.

## 1. What is the difference between amplitude of light and intensity?

The amplitude of light refers to the maximum displacement of a light wave from its rest position, while intensity refers to the amount of energy carried by the light wave. In simpler terms, amplitude determines the brightness of the light, while intensity determines the strength or power of the light.

## 2. How does the amplitude of light affect the perception of color?

The amplitude of light does not directly affect the perception of color. The wavelength of light is what determines the color we see, but the amplitude can affect the brightness of the color. For example, a higher amplitude of red light will appear brighter than a lower amplitude of red light, but they will both still be perceived as the color red.

## 3. Can the amplitude of light be measured?

Yes, the amplitude of light can be measured using a device called a spectrophotometer. This instrument measures the intensity of light at different wavelengths, which can then be used to calculate the amplitude of the light waves.

## 4. How does the amplitude of light affect the energy of the light wave?

The amplitude of light is directly proportional to the energy of the light wave. This means that as the amplitude increases, the energy of the light wave also increases. This relationship is important in understanding the behavior of light, such as its ability to cause chemical reactions or damage to our eyes.

## 5. Can the amplitude of light be changed or controlled?

Yes, the amplitude of light can be changed or controlled through various methods such as adjusting the intensity of the light source, using filters to block certain wavelengths, or using lenses to focus or spread out the light waves. These methods can be used in practical applications such as photography, laser technology, and medical treatments that utilize light energy.

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