## Thursday, November 25, 2010

### How does the resistance of the bulb change as the voltage is increased from 10V to 20V?

How does the resistance of the bulb change as the voltage is increased from 10V to 20V?

Please answerHow does the resistance of the bulb change as the voltage is increased from 10V to 20V?The resistance of the bulb will increase. Light bulbs are a famous example of how temperature affects resistance. It's a classic lab experiment.

Light bulbs exhibit non ohmic relation between current and voltage. Here's a graph and some info:

http://www.bbc.co.uk/schools/gcsebitesiz…

http://www.gcsescience.com/pe9.htmHow does the resistance of the bulb change as the voltage is increased from 10V to 20V?Resistance will remain (roughly) unchanged. The filament will slightly increase in resistance from the increase in temperature, but this is negligible for your purposes, and will possibly be canceled by the effects of thermal expansion.How does the resistance of the bulb change as the voltage is increased from 10V to 20V?If the physical condition of a conductor remain constant then the Resistance of a conductor will remain constant.So the resistance is not going to change when the voltage is increased from 10V to 20V,but the quantity of current is going to increase from i(1) = 10/R to i(2) = 20/R.How does the resistance of the bulb change as the voltage is increased from 10V to 20V?What kind of bulb are you referring to ?

Assuming you mean a light globe with a hot wire filament.

If the resistance does NOT change, then doubling the voltage will cause the energy dissipation of the filament to quadruple ( because the current will also double. ) This energy can only be dissipated as infrared radiation. The temperature of the filament must rise. The size of the temperature rise depends on a large number of factors ( length of wire, cross-sectional area of wire, resistivity of wire......). For metallic wires increase in temperature almost always leads to an increase in resistance. This increase can be large if the increase in temperature is large. For a typical 100W incandescent bulb, the %26quot;cool%26quot; zero current resistance might be 50Ω, while the operating (hot) resistance can be about 600Ω.

It is not possible to determine by how much the resistance of your bulb will have changed, given that we have no idea what the expected operating voltage of the bulb actually is. The most that can be said is that the resistance will have increased. Not by very much if its a high voltage ( 110, or 240 V ) bulb, or a huge amount is its a low voltage ( 12V ) bulb.

Note - the increase in resistance is not linearly related to the voltage, or indeed to the energy dissipated - there are numerous factors involved - its complicated.