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Chapter 21: Q67PE (page 778)
After two-time constants, what percentage of the final voltage, emf, is on an initially uncharged capacitor C, charged through a resistance R?
The proportion of the final voltage, emf, is on a capacitor C that was initially uncharged and is now charged via a resistance R is
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Verify the second equation in Example 21.5 by substituting the values found for the currents and
(a) What is the internal resistance of a voltage source if its terminalvoltage drops by 2.00 V when the current supplied increases by 5.00 A?(b) Can the emf of the voltage source be found with the information supplied.
A \(240{\rm{ }}kV\) power transmission line carrying \(5.00 \times {10^2}\;A\)is hung from grounded metal towers by ceramic insulators, each having a \(1.00 \times {10^9}{\rm{ }}\Omega \) resistance. Figure \(21.51\).
(a) What is the resistance to ground of \(100\) of these insulators?
(b) Calculate the power dissipated by \(100\) of them.
(c) What fraction of the power carried by the line is this? Explicitly show how you follow the steps in the Problem-Solving Strategies for Series and Parallel Resistors.
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?
Figure 21.55 shows how a bleeder resistor is used to discharge a capacitor after an electronic device is shut off, allowing a person to work on the electronics with less risk of shock. (a) What is the time constant? (b) How long will it take to reduce the voltage on the capacitor to (5% of 5%) of its full value once discharge begins? (c) If the capacitor is charged to a voltage V0 through a 100-Ω resistance, calculate the time it takes to rise to 0.865V0 (This is about two-time constants.)
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