• Support PF! Buy your school textbooks, materials and every day products Here!

Energy transfer in a bulb

  • Thread starter Kushal
  • Start date
437
1
1. Homework Statement

An electric bulb is marked 120 V, 40 W.
(a) Calculate the current in this bulb when operating on a 120 V supply.
(b) Describe 3 different ways in which energy can be transferred from the filament when it is operating normally.
(c) If the light bulb is now connected to a 240 V supply it will work for perhaps an hour as a 160 W bulb before its filament breaks.
(i) How will the relative importance of the answers you have given to (b) change when the bulb is run on this increased voltage?
(ii) Suggest a reason why this bulb can operate for so long a time before its filament breaks.

2. Homework Equations




3. The Attempt at a Solution

(a) i calculated the current using P = IV

(b) the different ways are : conduction, convection and radiation.

(c)(i) I can't understand what the question asks

(ii) I am thinking that maybe it's because the increase in current is small. the current flowing increases from 0.33A to 0.66A
 

Answers and Replies

Gib Z
Homework Helper
3,344
4
c) is asking how the importance of each conduction, convection and radiation, change when the bulbs voltage increases. For example, perhaps it will begin to emit more energy as heat rather than light?
 
437
1
ah well, i suppose the heat transferred by all of these ways will increase because the current increases?! is it right?
 
454
0
ah well, i suppose the heat transferred by all of these ways will increase because the current increases?! is it right?
Have you learned anything about the black body emission, and how it depends on temperature?
 
437
1
errmm no. i'm going to google that. thanks
 

Related Threads for: Energy transfer in a bulb

Replies
2
Views
785
  • Last Post
Replies
13
Views
6K
  • Last Post
Replies
6
Views
647
Replies
5
Views
10K
Replies
6
Views
2K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
2
Views
2K
Top