Discussion Questions: Inverse Square Law

We've seen from the video that the Inverse Square Law applies to light. To what other types of energy can the Inverse Square Law be applied?

Answer

Gravity, sound, electric force, and radiation because they can radiate in all directions.

Describe in your own words what is meant by, “The intensity falls in proportion to the inverse of the distance squared.”

Answer

The intensity of a source of energy is dependent on the distance from the source squared, and since it is diminishing with distance it must be dependent on the inverse of this number so that when the distance increases, the intensity decreases.

Does a laser beam diminish in intensity according to the Inverse Square Law? Why or why not?

Answer

No. A laser beam of light does not spread vertically or horizontally, so there is no diminishing of its intensity with distance.

Would you see a larger difference in light intensity if you
a. moved from 1 meter away to 2 meters away or
b. moved from 10 meters away to 11 meters away?

Answer

The answer is "a." The intensity would go from I/1² = I to I/2² = I/4, or a change of 400%. In "b" the intensity falls from I/10² = I/100 to I/11² = I/121, or a change of 21%.

If you can hear a single speaker comfortably from 1 meter away, how many speakers would you need to listen comfortably to the same music from 100 meters away?

Answer

Approximately 10,000 speakers. If the initial intensity was I/1² = I, and the new intensity is I/100² = I/10,000, you’d need (10,000 speakers)*(I/10,000) = I to have the same intensity as you originally had with 1 speaker at 1 meter.

According to the Inverse Square Law, the effects of gravity (and thus an object’s weight) are affected by the distance from the center of the Earth. Using this information, would a company make more money if they sold apples by the pound in a city of higher or lower elevation?

Answer

Lower elevation. At a lower elevation the distance from the center of the earth is smaller so the intensity of gravity would be greater, and thus fewer apples would be needed for a pound.