A searchlight uses a parabolic reflector and a 2000 watt electric arc lamp that emits light equally in all directions to produce a parallel beam of light. Assuming that the focal point of the reflector lies in the plane defined by the rim of the reflector, how many watts of power are contained in the main beam of the searchlight? Using the same parabolic reflector and lamp, how could you modify the searchlight so that you could get more of the light into the main beam?

 

I am not sure how to approach this. Would the beam still have 2000 watts (conservation of energy), or perhaps more than 2000 watts since it is enhancing and reflecting some of the energy/light from the lamp? To get more light into the main beam, would it make sense to add a second reflector near the rim of the original reflector in order to catch some of the light that might be leaving the beam?

 

Thanks in advance!

 

A searchlight uses a parabolic reflector and a 2000 watt electric arc lamp that emits light equally in all directions to produce a parallel beam of light. Assuming that the focal point of the reflector lies in the plane defined by the rim of the reflector, how many watts of power are contained in the main beam of the searchlight? Using the same parabolic reflector and lamp, how could you modify the searchlight so that you could get more of the light into the main beam?

 

I am not sure how to approach this. Would the beam still have 2000 watts (conservation of energy), or perhaps more than 2000 watts since it is enhancing and reflecting some of the energy/light from the lamp? To get more light into the main beam, would it make sense to add a second reflector near the rim of the original reflector in order to catch some of the light that might be leaving the beam?

 

I sugest you reconsider your answer to part (i), which I have underlined.

 

Setting aside the inefficiency of light conversion (typically less than 10%), and given the configuration mentioned what % of the light from the source reaches the reflector?

 

This should then help with ideas for part (ii)

Edited February 14, 201411 yr by studiot

A searchlight uses a parabolic reflector and a 2000 watt electric arc lamp that emits light equally in all directions to produce a parallel beam of light. Assuming that the focal point of the reflector lies in the plane defined by the rim of the reflector, how many watts of power are contained in the main beam of the searchlight? Using the same parabolic reflector and lamp, how could you modify the searchlight so that you could get more of the light into the main beam?

 

I am not sure how to approach this. Would the beam still have 2000 watts (conservation of energy), or perhaps more than 2000 watts since it is enhancing and reflecting some of the energy/light from the lamp? To get more light into the main beam, would it make sense to add a second reflector near the rim of the original reflector in order to catch some of the light that might be leaving the beam?

 

Thanks in advance!

 

 

Probably, this is not what you want to hear, but I'll give it a try:

 

Position the parabolic reflector so, that the beam will strike the reflector perpendicular to the tangent of the top of the parabola, which will result in a concentration of all beams in the focus of the parabola