Efficiency of a Light Bulb: Calculating Energy Transfer

AI Thread Summary
A light bulb with 85% efficiency converts 60J of electrical energy into usable light energy. The calculation shows that 51J is emitted as light, while 9J is lost as heat. The discussion clarifies that "efficiency" refers to the energy converted into light, not energy remaining in the circuit. Thus, the useful energy output is confirmed to be 51J of light energy. The conversation concludes with appreciation for the clarification provided.
Molly1235
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Homework Statement

"A light bulb is 85% efficient. If it is supplied with 60J of electrical energy, how much of this energy is transferred to its surroundings as light energy?


The attempt at a solution

So I calculated that 85% of 60 is 51J, however I don't know if being "efficient" refers to energy that remains in the circuit, or energy that is released as light energy, seeing as this is the main purpose of a light bulb? I'm thinking it's the first, which would mean 9J is lost as light energy?
 
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I think it's safe to assume that the useful energy in this case is the light being emitted from the bulb. Which would mean that 51 J of light energy is emitted. The other energy doesn't "remain in the circuit" it is lost to heat.
 
Millacol88 said:
I think it's safe to assume that the useful energy in this case is the light being emitted from the bulb. Which would mean that 51 J of light energy is emitted. The other energy doesn't "remain in the circuit" it is lost to heat.

Ah ok! Thank you very much :)
 

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