What is the Light Intensity 3 Meters from the Bulb?

[dewdrop714]

stuck on light intensity problem...

1. Homework Statement

http://s685.photobucket.com/albums/vv212/dewdr0p714/?action=view&current=physicsexam2q5withoutphotocell.jpg

A conducting rod slides down 2 frictionless copper tracks at a constant velocity.
There is a .50 T magnetic field perpendicular to the rod. The rod maintains electrical contact at all times. The rod has a length of 1.0 m and a mass of .25kg. A 1.5 Ohm light bulb is attached between the tops of the tracks.

What is the intensity of the light from the light bulb at a distance 3.0 away from the bulb?



2. Homework Equations

S = c / (magnetic permeability of free space) * B^2


3. The Attempt at a Solution

S = ?
B = .50
c = 3.00 *10^8 m/s
(magnetic permeability of free space) is a constant... = 4pi *10^-7 T*m/a

if all these variables are plugged into the equation i can solve for S and get the intensity. But "3 meters" is mentioned in the problem. I know I am using the wrong formula...which one am i supposed to use?

 

[Delphi51]

The rod moving through the magnetic field acts as a generator. The generator formula is
V = LvB (potential = length x velocity x magnetic field).
Knowing the potential, you can use electricity formulas to find the current and power delivered to the light bulb.

Unfortunately no efficiency is given for the light bulb - perhaps you are supposed to look up the efficiency of a typical incandescent bulb in order to estimate the light power produced. The light will spread out in every direction, illuminating an imaginary sphere 3 m in radius, and you want the number of watts of power per square meter on it.

 

[nlightner]

As a scientist, it is important to carefully read and understand the problem before attempting to solve it. In this case, the problem is asking for the intensity of light at a distance of 3.0 meters away from the bulb. This means that the intensity of light will decrease as it travels away from the bulb.

To solve this problem, you will need to use the inverse square law for light intensity, which states that the intensity of light is inversely proportional to the square of the distance from the source. This means that as the distance from the light source increases, the intensity of light decreases.

The equation for the inverse square law is:

I1/I2 = (r2/r1)^2

Where I1 is the initial intensity, I2 is the final intensity, r1 is the initial distance, and r2 is the final distance.

In this problem, we can assume that the initial intensity is the intensity of the light at the bulb itself, which we can calculate using the given equation: S = c / (magnetic permeability of free space) * B^2

Once we have the initial intensity, we can use the inverse square law to calculate the final intensity at a distance of 3.0 meters away from the bulb. This will give us the answer to the problem.

Remember to always carefully read and understand the problem before attempting to solve it. And don't be afraid to ask for help if you are stuck on a problem. As a scientist, collaboration and seeking out new knowledge are essential skills.