Chapter 4: Q4DQ (page 744)
A certain region of space bounded by an imaginary closed surface contains no charge. Is the electric field always zero everywhere on the surface? If not, under what circumstances is it zero on the surface?
The electric field doesn’t need to be zero on the surface.
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A typical small flashlight contains two batteries, each having an emf of, connected in series with a bulb having resistance. (a) If the internal resistance of the batteries is negligible, what power is delivered to the bulb? (b) If the batteries last forwhat is the total energy delivered to the bulb? (c) The resistance of real batteries increases as they run down. If the initial internal resistance is negligible, what is the combined internal resistance of both batteries when the power to the bulb has decreased to half its initial value? (Assume that the resistance of the bulb is constant. Actually, it will change somewhat when the current through the filament changes, because this changes the temperature of the filament and hence the resistivity of the filament wire.)
The heating element of an electric dryer is rated at 4.1 kW when connected to a 240-V line. (a) What is the current in the heating element? Is 12-gauge wire large enough to supply this current? (b) What is the resistance of the dryer’s heating element at its operating temperature? (c) At 11 cents per kWh, how much does it cost per hour to operate the dryer?
Two copper wires with different diameter are joined end to end. If a current flow in the wire combination, what happens to electrons when they move from the large diameter wire into the smaller diameter wire? Does their drift speed increase, decrease, or stay the same? If the drift speed change, what is the role the force that causes the change? Explain your reasoning.
In the circuit shown in Fig. E26.20, the rate at which R1 is dissipating electrical energy is 15.0 W. (a) Find R1 and R2. (b) What is the emf of the battery? (c) Find the current through both R2 and the 10.0 Ω resistor. (d) Calculate the total electrical power consumption in all the resistors and the electrical power delivered by the battery. Show that your results are consistent with conservation of energy.
A particle with massand a charge of has, at a given instant, a velocity.What are the magnitude and direction of the particle’s acceleration produced by a uniform magnetic field?
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