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767_Physics ProblemsTechnical Physics

767_Physics ProblemsTechnical Physics - Chapter 27 107...

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Chapter 27 107 Q27.18 Current moving through a wire is analogous to a longitudinal wave moving through the electrons of the atoms. The wave speed depends on the speed at which the disturbance in the electric field can be communicated between neighboring atoms, not on the drift velocities of the electrons themselves. If you leave a direct-current light bulb on for a reasonably short time, it is likely that no single electron will enter one end of the filament and leave at the other end. Q27.19 More power is delivered to the resistor with the smaller resistance, since P = V R 2 . Q27.20 The 25 W bulb has a higher resistance. The 100 W bulb carries more current. Q27.21 One ampere–hour is 3 600 coulombs. The ampere–hour rating is the quantity of charge that the battery can lift though its nominal potential difference. Q27.22 Choose the voltage of the power supply you will use to drive the heater. Next calculate the required resistance R as V 2 . Knowing the resistivity ρ of the material, choose a combination of wire length and cross–sectional area to make A A R F H G I K J = F H G I K J . You will have to pay for less material if you make both
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