A person is reading a newspaper while standing 5 feet away from a table that has an unshaded 100 watt bulb.?

Question

Imagine that the table were moved to a distance of 10 feet. How many light bulbs in total would have to be placed on the table to light up the newspaper to the same amount of brightness as before?
a) 1
b) 2
c) 3
d) 4
e) more than 4

Answer 1

Since the amount of light hitting 1 square foot decreases at the rate of 1/d^2, then I would have to say "d" since it is the closest answer.

Assume 750 lumens for a 100 watt light bulb. At 1 foot away, this is is the amount of light striking 1 square foot of area. At 5 feet away, the light striking 1 square foot would be 30 lumens. At 10 feet away, it would be 8 lumens; which is roughly 27% of what you had at 5 feet way. Consequently, you would need 4-100watt lamps.

Answer 2

Consider a point source of light, which would reasonably closely describe a 100 watt incandescent bulb at a 5-foot distance in large room or one with dark walls. Let us also pretend that the bulb is surrounded by a spherical shell of 5-foot radius.

Now let us remove the sphere with a 5-foot radius and replace it with one with a ten-foot radius. Because the surface area of a sphere - or any three-dimensional shape - varies as the square of the linear dimensions, the larger sphere has four times the area that the smaller one did. The same amount of total light falls on this bigger sphere but, because it is bigger, the light is spread out more. The light falling on a specific area of the sphere would therefore be only one quarter of what it would be for the same area of the smaller sphere. To compensate, the source would have to be four times as strong. Hence, the answer is d) 4.

Answer 3

the answer is d.

For every unit (in this case, 5 feet) you move farther from the light source, the amount of light is the inverse square (in this case, 1/2**2, or 1/4 the amount of light is reaching the newspaper. So, you'd need 4 times the light to make up for doubling the distance.

Answer 4

d) 4 because light obeys the inverse square law, where it gets 2*2 = 4 times weaker if the distance is 2 times farther.

Answer 5

Inverse Square Law...

Double the Distance - Quadruple the light to maintain the same lumination...

ANSWER D.

Answer 6

1 because the table has moved but not the light bulb

Answer 7

The question can't be answered because the wattage is irelevant . What matters is the number of lumens produced,