Chapter 27107Q27.18Current moving through a wire is analogous to a longitudinal wave moving through the electrons ofthe atoms. The wave speed depends on the speed at which the disturbance in the electric field canbe communicated between neighboring atoms, not on the drift velocities of the electronsthemselves. If you leave a direct-current light bulb on for a reasonably short time, it is likely that nosingle electron will enter one end of the filament and leave at the other end.Q27.19More power is delivered to the resistor with the smaller resistance, since P=∆VR2.Q27.20The 25 W bulb has a higher resistance. The 100 W bulb carries more current.Q27.21One ampere–hour is 3 600 coulombs. The ampere–hour rating is the quantity of charge that thebattery can lift though its nominal potential difference.Q27.22Choose the voltage of the power supply you will use to drive the heater. Next calculate the requiredresistance Ras ∆V2. Knowing the resistivity ρof the material, choose a combination of wire lengthand cross–sectional area to make AARFHGIKJ=FHGIKJ. You will have to pay for less material if you make both
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