Can Bulb Resistance Change with Different Voltage Sources?

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The resistance of a bulb is influenced by temperature, which varies with voltage. A bulb rated at 10 V and 12 W will have a different resistance when connected to a 4 V battery due to lower operating temperatures. At 4 V, the filament will not reach the same temperature as at 10 V, resulting in decreased resistance. While calculations using P = VI and R = V/I can provide an estimate, they may not accurately reflect the bulb's behavior at different voltages. Therefore, without additional data, precise estimation of resistance at varying voltages remains challenging.
Peter G.
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"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!
 
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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?
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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