Efficiency of a Lightbulb

  • Thread starter Molly1235
  • Start date
  • #1
77
4
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?
 

Answers and Replies

  • #2
86
0
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.
 
  • #3
77
4
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 :)
 

Related Threads on Efficiency of a Lightbulb

  • Last Post
Replies
1
Views
4K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
1
Views
6K
  • Last Post
Replies
4
Views
304
Replies
1
Views
5K
Replies
5
Views
2K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
2
Views
4K
Replies
1
Views
11K
  • Last Post
Replies
1
Views
800
Top