What is the Intensity of Light 12m from a Bulb Shining in All Directions?

In summary, the conversation discusses the intensity of light from a bulb shining equally in all directions. The problem asks for the intensity at a distance of 12m from the lamp, with the given output of 20W. The equation used to solve the problem is 20 / (4 * pi * 122), which gives the correct answer of 0.011 W/m2. The conversation also includes a hint to consider the shape of the illuminated surface, which is not a circle.
  • #1
Rumplestiltskin
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Homework Statement


The light from a bulb shines equally in all directions. If 20W of light is given off, what will the intensity be 12m from the lamp to 2 significant figures? (Consider the shape of the region illuminated if the light hits this surface after traveling 12m in all directions.)

Homework Equations


The Attempt at a Solution


20 / pi * 122 = 0.044 W/m2. Incorrect. I suppose this value would give me the average intensity over the entire area. Halving it should then give me the furthest intensity. 0.022 W/m2, still incorrect.
 
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  • #2
What's the total area of the surface at a radius of 12 m? (hint: the surface is not a circle).
 
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  • #3
gneill said:
What's the total area of the surface at a radius of 12 m? (hint: the surface is not a circle).

Argh, I was considering it shining over a one-dimensional circle.
20 / (4 * pi * 122) = 0.011, correct answer. Thanks!
 

Related to What is the Intensity of Light 12m from a Bulb Shining in All Directions?

1. What is the difference between amplitude and intensity?

Amplitude refers to the maximum displacement or distance from the equilibrium position of a wave, while intensity is the amount of energy that a wave carries per unit area. In simpler terms, amplitude describes the size of a wave, while intensity describes its strength or brightness.

2. How are amplitude and intensity related?

Amplitude and intensity are directly proportional to each other. This means that as the amplitude of a wave increases, its intensity also increases. Similarly, as the amplitude decreases, the intensity also decreases.

3. What is the unit of measurement for amplitude and intensity?

The unit of measurement for amplitude is meters (m) or any other unit of length, depending on the type of wave. Intensity is measured in watts per square meter (W/m²) or any other unit of power per unit area.

4. How does amplitude and intensity affect the perception of sound and light?

In sound, the amplitude and intensity of a wave determine the loudness or volume of the sound. A higher amplitude or intensity results in a louder sound, while a lower amplitude or intensity creates a softer sound. In light, the amplitude and intensity determine the brightness of the light. A higher amplitude or intensity creates a brighter light, while a lower amplitude or intensity creates a dimmer light.

5. Can amplitude and intensity be changed?

Yes, both amplitude and intensity can be changed. The amplitude of a wave can be increased or decreased by changing the energy or force that is causing the wave. Similarly, the intensity of a wave can be changed by altering the amount of energy that the wave carries. For example, the intensity of a light wave can be changed by adjusting the power source that is producing the light.

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