Active Physics

In this activity you identified various light sources. Fire Long ago, people had to limit many of their activities to daylight hours because they could not overcome the dark of night. Today, you have the capability to use a combination of natural and artificial light sources to keep going 24 hours per day. You also measured the illuminance at different distances from a candle and an electric light. You discovered that a mathematical relationship exists between illuminance and distance. The illuminance at a particular distance from a point source of light varies inversely with the square of the distance from the source. Your challenge requires you to analyze the quantity of light in the setting of your choice. The information from this activity will be helpful.

PHYSICS TO GO

1. How could you measure the luminous intensity, in candela (cd) of a light source? Describe the equipment you would need and how you would find an answer. Draw a picture to support your explanation.
2. The illuminance at a particular distance from a point source of light varies inversely with the square of the distance from the source. Complete the following sentences in your log.: a) If the distance from the light source is tripled, the illuminance will become ___ the original amount.; b) If the distance is increased to six times the original amount, the illuminance will become ___ the original amount.; c) If the distance is decreased to one-half the original amount, the illuminance will become ___ the original amount.