The student engineer of a campus radio station wishes to verify the effectiveness of the lightning rod on the antenna mast (Fig. P21.71). The unknown resistance Rx is between points C and E. Point E is a true ground, but it is inaccessible for direct measurement because this stratum is several meters below the Earth’s surface. Two identical rods are driven into the ground at A and B, introducing an unknown resistance Ry. The procedure is as follows. Measure resistance R1 between points A and B, then connect A and B with a heavy
Figure P21.71
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Chapter 21 Solutions
Principles of Physics: A Calculus-Based Text
- An oceanographer is studying how the ion concentration in seawater depends on depth. She makes a measurement by lowering into the water a pair of concentric metallic cylinders (Fig. P21.66) at the end of a cable and taking data to determine the resistance between these electrodes as a function of depth. The water between the two cylinders forms a cylindrical shell of inner radius ra, outer radius rb, and length L much larger than rb. The scientist applies a potential difference V between the inner and outer surfaces, producing an outward radial current I. Let represent the resistivity of the water. (a) Find the resistance of the water between the cylinders in terms of L, , ra, an rb. (b) Express the resistivity of the water in terms of the measured quantities L, ra, rb, V, and I. Figure P21.66arrow_forwardCalculate the equivalent resistance between points P and Q of the electrical network shown in Figure P29.80.arrow_forwardA 12.0-V emf automobile battery has a terminal voltage of 16.0 V when being charged by a current of 10.0 A. (a) What is the battery’s internal resistance? (b) What power is dissipated inside the battery? (c) At what rate (in °C/min ) will its temperature increase if its mass is 20.0 kg and it has a specific heat of 0.300 kcal/kg • °C, assuming no heat escapes?arrow_forward
- A battery is used to charge a capacitor through a resistor as shown in Figure P27.44. Show that half the energy supplied by the battery appears as internal energy in the resistor and half is stored in the capacitor. Figure P27.44arrow_forward(a) During surgery, a current as small as 20.0A applied directly to the heart may cause ventricular fibrillation. If the resistance of the exposed heart is 300 what is the smallest voltage that poses thisdanger? (b) Does your answer imply that special electrical safetyprecautions are needed?arrow_forwardIn Figure P29.81, N real batteries, each with an emf and internal resistance r, are connected in a closed ring. A resistor R can be connected across any two points of this ring, causing there to be n real batteries in one branch and N n resistors in the other branch. Find an expression for the current through the resistor R in this case.arrow_forward
- If the terminals of a battery with zero internal resistance are connected across two identical resistors in series, the total power delivered by the battery is 8.00 W. If the same battery is connected across the same resistors in parallel, what is the total power delivered by the battery? (a) 16.0 W (b) 32.0 W (c) 2.00 W (d) 4.00 W (e) none of those answersarrow_forwardThe duration of a photographic flash is related to an RC time constant, which is 0.100F for a certain camera, (a) If the resistance of the flash lamp is 0.0400 duringdischarge, what is the size of the capacitor supplying its energy? (b) What is the time constant for charging the capacitor, if the charging resistance is 800 k ?arrow_forwardA 10.00-meter long wire cable that is made of copper has a resistance of 0.051 ohms, (a) What is the weight if the wire was made of copper? (b) What is the weight of a 10.00-meter-long wire of the same gauge made of aluminum? (c)What is the resistance of the aluminum wire? The density of copper is 8960 kg/m3 and the density of aluminum is 2760 kg/m3.arrow_forward
- Two 1.50-V batterieswith their positive terminals in the same directionare inserted in series into a flashlight. One battery has an internal resistance of 0.255 , and the other has an internal resistance of 0.153 . When the switch is closed, the bulb carries a current of 600 mA. (a) What is the bulbs resistance? (b) What fraction of the chemical energy transformed appears as internal energy in the batteries?arrow_forwardIn the figure below, the current in resistance 6 is i6 = 1.20 A and the resistances are R1 = R2 = R3 = 2.00 Ω, R4 = 15.0 Ω, R5 = 8.00 Ω, and R6 = 4.00 Ω. What is the emf of the ideal battery? _________________V (please show the units when working through the problem so that I can follow it easier)arrow_forwarda. An action potential propagates at 64 m/s down an axon that is 30cm long. How much energy is transmitted down the axon if the action potential has a maximum value of 75mV and the resistance is 20,000Ω. b. A 12V battery supplies 0.7mA of current for 4.8hours. How much charge has been transferred? c. The filament in the 100W light bulb has a resistance of 144Ω and is tungsten. It has a diameter of 0.03mm and has a resistivity of 5x10-7Ωm. How long should the filament be?arrow_forward
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