You have 100 foot candles at two feet. If the source is moved back to four feet, how many foot candles do you have?

To determine the foot candle measurement when a light source is moved from two feet to four feet away, it's essential to understand the inverse square law of lighting. This principle states that the intensity of illumination (foot candles) is inversely proportional to the square of the distance from the light source.

Initially, when the source is at two feet, the measurement is 100 foot candles. If the distance is then doubled to four feet, you square the distance ratio. The distance changes from two feet to four feet is a change of a factor of 2 (4/2 = 2). Thus, you square this factor for the calculation:

[

\text{New Foot Candles} = \text{Old Foot Candles} / (\text{Distance Factor})^2

]

In this case:

[

\text{New Foot Candles} = 100 \text{ foot candles} / (2^2) = 100 / 4 = 25 \text{ foot candles}

]

Since 25 foot candles is not listed among the options provided, the correct conclusion is that none of the choices reflect the accurate value after the move to four feet. Therefore, "none of the above" is