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Chapter 4: Q17DQ (page 873)
The emf of a flashlight battery is roughly constant with time, but its internal resistance increases with age and use. What sort of meter should be used to test the freshness of a battery?
An ohmmeter is used to test the freshness of a battery.
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In Europe the standard voltage in homes is 220 V instead of the 120 used in the United States. Therefore a 鈥�100-W鈥� European bulb would be intended for use with a 220-V potential difference (see Problem 25.36). (a) If you bring a 鈥�100-W鈥� European bulb home to the United States, what should be its U.S. power rating? (b) How much current will the 100-W European bulb draw in normal use in the United States?
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 magnetic force on a moving charged particle is always perpendicular to the magnetic field. Is the trajectory of a moving charged particle always perpendicular to the magnetic field lines? Explain your reasoning.
A particle with chargeis moving in a uniform magnetic fieldrole="math" localid="1655717557369"
The magnetic force on the particle is measured to berole="math" localid="1655717706597" (a) Calculate all the components of the velocity of the particle that you can from this information. (b) Are there
components of the velocity that are not determined by the measurement of the force? Explain. (c) Calculate the scalar product. What is the angle between velocity and force?
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鈥檚 heating element at its operating temperature? (c) At 11 cents per kWh, how much does it cost per hour to operate the dryer?
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