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Chapter 21: Q12CQ (page 771)
Some light bulbs have three power settings (not including zero), obtained from multiple filaments that are individually switched and wired in parallel. What is the minimum number of filaments needed for three power settings?
Three power settings can be obtained from a minimum of 2 filaments.
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(a) What resistance would you put in parallel with a \(40.00 - \Omega \) galvanometer having a \(25.0 - \mu A\) sensitivity to allow it to be used as an ammeter that has a full-scale deflection for \(10.0{\rm{ }}\mu A\) ?
(b) What is unreasonable about this result?
(c) Which assumptions are responsible?
Electric fish generate current with biological cells called electro-plaques, which are physiological emf devices. The electro-plaques in the South American eel are arranged in \(140\) rows, each row stretching horizontally along the body and each containing \(5000\) electro-plaques. Each electro-plaque has an emf of \(0.15{\rm{ }}V\) and internal resistance of \(0.25{\rm{ }}\Omega \). If the water surrounding the fish has resistance of \(800{\rm{ }}\Omega \), how much current can the eel produce in water from near its head to near its tail?
(a) What is the internal resistance of a \(1.54{\rm{ }}V\) dry cell that supplies \(1.00{\rm{ }}W\) of power to a \(15.0{\rm{ }}\Omega \) bulb?
(b) What is unreasonable about this result?
(c) Which assumptions are unreasonable or inconsistent?
(a) Given a battery and andresistors, find the current and power for each when connected in series. (b) Repeat when the resistances are in parallel.
A heart defibrillator being used on a patient has an RC time constant of due to the resistance of the patient and the capacitance of the defibrillator. (a) If the defibrillator has ancapacitance, what is the resistance of the path through the patient? (You may neglect the capacitance of the patient and the resistance of the defibrillator.) (b) If the initial voltage is, how long does it take to decline to?
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