Abstract
My project is from the scientific
field of physics. I wanted to measure the light intensity from different
light sources, and see how the distance from the light source affects
the light intensity.
My hypothesis was that as the distance
from the light source increases, the light intensity will decrease as
stated by the Inverse Square Law. I also thought that the energy efficient
bulb would produce the same light intensity as the 60 watt light bulb,
and that the laser light would have the greatest light intensity.
The intensity of the light was measured
at night by a solar cell attached to a digital volt-metre. I compared
a 60 watt light bulb, an energy saving light bulb and a laser pointer,
at distances starting at 20 centimetres from the light source and increased
by increments of 10 centimetres, until a maximum of 300 centimetres from
the light source.
My conclusion is that the Inverse
Square Law was not satisfied because in real life there are reflections,
the room must be pitch black and walls must be black in order to have
no reflections. In my experiment, the light was reflected off the walls
which increased the total amount of light the solar cell was receiving.
Also, for the Inverse Square Law to apply, the light source itself has to
be very small in comparison to the distance at which the measurement is
made. So, for short distances from the light source, the law is not followed
very well. It was also noticed that the laser light, as a light source,
does not follow the Inverse Square Law. This is because the laser light
beam does not spread out and stay focused over large distances. For the inverse
square law to apply, the light emitted by the light source has to spread
out evenly in every spatial direction from the light source. This is clearly
not the case for a laser light
My experiment did not find that the
energy saving bulb (13.5 watt) did not have the same intensity as a
normal 60 watt bulb as advertised. It actually had consistently, less
light intensity over increased distances, although the difference in
light intensity was not noticeable to the eye.
In conclusion, when one switches
to energy saving light bulbs, you may not be getting the same light intensity
as a normal bulb, but you won’t notice it and you will be saving money
and energy.