Can Bulb Resistance Change with Different Voltage Sources?

  • Thread starter Thread starter Peter G.
  • Start date Start date
  • Tags Tags
    Resistance
Click For Summary

Homework Help Overview

The discussion revolves around the resistance of a bulb rated at 10 V and 12 W when connected to a 4 V battery. Participants are exploring the implications of using the rated values to calculate resistance and the effects of temperature on resistance.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are attempting to calculate the resistance of the bulb using its rated voltage and power, while questioning whether this resistance can be assumed to hold at a lower voltage. There is a discussion on the temperature dependence of the bulb's resistance and how it may affect calculations.

Discussion Status

Some participants have provided insights into the temperature effects on resistance and the implications of using rated values for calculations. There is an ongoing exploration of methods for estimating resistance without additional data.

Contextual Notes

Participants are considering the effects of operating conditions on resistance, particularly the temperature changes when the bulb is powered by a lower voltage than its rated value. The discussion acknowledges the complexity of accurately estimating resistance without empirical data or graphs.

Peter G.
Messages
439
Reaction score
0
"Estimating" Resistance

Hi,

So, suppose I have a bulb labelled 10 V, 12 W. This is connected to a 4 V e.m.f battery. Can I calculate the Resistance from 10 V, 12 W (Using P = VI and R = V/I) and assume that it is the resistance when it connected to a 4V battery?

Thanks!
 
Physics news on Phys.org


Generally speaking, the resistance of a bulb vary with temperature. If ignore this feature, I think your answer is right.
 


Peter G. said:
Hi,

So, suppose I have a bulb labelled 10 V, 12 W. This is connected to a 4 V e.m.f battery. Can I calculate the Resistance from 10 V, 12 W (Using P = VI and R = V/I) and assume that it is the resistance when it connected to a 4V battery?

Thanks!
If the bulb is rated 12W at 10V, that likely means that it produces a reasonable of light at 10 V. The filament of the bulb, under such conditions, will be near its maximum operating temperature.

At 4 V, the same bulb would be operating at a considerably lower temperature. The resistivity of tungsten is very temperature dependent, so the resistance of the bulb would be much less than when it operates at 10 V .
 


Without a graph, however, is there any more precise method of estimation?
 

Similar threads

Replies
2
Views
1K
Replies
4
Views
2K
Replies
9
Views
1K
Replies
6
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
11
Views
2K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 31 ·
2
Replies
31
Views
5K