Finding power consumed by an electric razor

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A tourist's 21 W, 120 V AC electric razor is used with a 220 V AC adapter in Europe, leading to questions about its power consumption. The discussion centers on using the formula P=IV and understanding that the razor's resistance remains constant despite the voltage change. Participants clarify that two equations should be set up for the different voltages to find the power consumed. The conversation emphasizes the importance of recognizing that the resistance does not change when calculating power in different voltage scenarios. Ultimately, the problem highlights the risks of using devices with incompatible voltage ratings.
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A tourist takes his 21 W, 120 V AC razor to Europe, finds a special adapter, and plugs it into 220 V AC. What power does the razor consume as it goes up in smoke?


P=IV=deltaVsquared/R


attempt at solution:
I used P=IV for 120 V to find the current, and using that number, plugged the numbers into the equation for 220V. The hint for the problem says that the resistance doesn't change for the razor in Europe... but I don't know how that helps. I feel like I'm missing something very easy but I'm stuck.
 
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Welcome to the PF. The key here is that the resistance doesn't change. I don't think you want to write:

P = \frac{\Delta {V^2}}{R}

Instead, write two equations, one for the US and one for smokey Europe...
 
Last edited:
Oh man that was easy.. I'm a little embarrassed. Thanks for the help!
 
Hey seems like you guys figured it out. Can you help me. I'm stuck on the same question and I don't know what to do.
 
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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