Intensity: 4∏D2 vs. ∏r2 Explained

Thread starter davev
Start date Dec 1, 2013
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Intensity

In summary, the intensity formula 4∏D2 is used to calculate the intensity of a light source at a specific distance from the source, while ∏r2 is used to calculate the intensity at a specific point on a surface. The formula 4∏D2 is more accurate for calculating the intensity of a light source at a distance. Both formulas can be used to calculate the intensity of a laser beam, but 4∏D2 is more accurate for distance measurements. The D in the formula 4∏D2 represents the distance between the light source and the point at which intensity is being measured, and the unit for intensity in both formulas is watts per square meter (W/m2).

Dec 1, 2013

davev

Can someone please explain why the are used is 4∏D²? Shouldn't it just be ∏r²?

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Dec 1, 2013

sandy.bridge

The intensity spreads out over the surface of a sphere. Your formula is for the area of a circle.

Dec 1, 2013

davev

sandy.bridge said:

The intensity spreads out over the surface of a sphere. Your formula is for the area of a circle.

That makes much more sense! Can't believe I totally missed that. Thank you!

1. What is the difference between the intensity formula 4∏D2 and ∏r2?

The intensity formula 4∏D2 calculates the intensity of a light source at a specific distance from the source, where D represents the distance. This formula takes into account the surface area of a sphere with the light source at its center. On the other hand, ∏r2 is used to calculate the intensity at a specific point on a surface, where r represents the distance between the point and the light source. This formula takes into account the surface area of a circle with the light source at its center.

2. Which formula should I use to calculate intensity at a specific distance from the light source?

The formula 4∏D2 should be used to calculate intensity at a specific distance from the light source. This is because it takes into account the surface area of a sphere, which is more accurate for calculating the intensity of a light source at a distance.

3. Can I use either formula to calculate the intensity of a laser beam?

Yes, both formulas can be used to calculate the intensity of a laser beam. However, it is important to note that the 4∏D2 formula is more accurate for calculating the intensity at a specific distance from the laser source.

4. What does the D in the formula 4∏D2 represent?

The D in the formula 4∏D2 represents the distance between the light source and the point at which the intensity is being measured. This distance is measured in meters and is a crucial factor in determining the intensity of the light source.

5. Is there a specific unit for intensity in these formulas?

Yes, the unit for intensity in both formulas is watts per square meter (W/m2). This unit is commonly used in physics to measure the amount of energy per unit area of a surface.