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Chapter 25: Q. 73 (page 713)
The wire in FIGURE P25.73 has linear charge density . What is the electric potential at the center of the semicircle?
The electric potential at the center of the semicircle is.
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Your lab assignment for the week is to measure the amount of charge on the 6.0-cm-diameter metal sphere of a Van de Graaff generator. To do so, you鈥檙e going to use a spring with a spring constant of 0.65 N/m to launch a small, 1.5 g bead horizontally toward the sphere. You can reliably charge the bead to 2.5 nC, and your plan is to use a video camera to measure the bead鈥檚 closest approach to the edge of the sphere as you change the compression of the spring. Your data is as follows:
Use an appropriate graph of the data to determine the sphere鈥檚 charge in nC. You can assume that the bead鈥檚 motion is entirely horizontal, that the spring is so far away that the bead has no interaction with the sphere as it鈥檚 launched, and that the approaching bead does not alter the charge distribution on the sphere.
A capacitor with plates separated by distance is charged to a potential difference . All wires and batteries are disconnected, then the two plates are pulled apart (with insulated handles) to a new separation of distance.
a. Does the capacitor charge change as the separation increases?
If so, by what factor? If not, why not?
b. Does the electric field strengthchange as the separation increases? If so, by what factor? If not, why not?
c. Does the potential difference change as the separation increases? If so, by what factor? If not, why not?
Two 2.0-cm-diameter disks spaced 2.0 mm apart form a
parallel-plate capacitor. The electric field between the disks is
.
a. What is the voltage across the capacitor?
b. An electron is launched from the negative plate. It strikes the
positive plate at a speed of .
What was the electron鈥檚 speed as it left the negative plate?
Living cells 鈥減ump鈥� singly ionized sodium ions, Na+, from the inside of the cell to the outside to maintain a membrane potential 鈭哣membrane = Vin - Vout = - 70 mV. It is called pumping because work must be done to move a positive ion from the negative inside of the cell to the positive outside, and it must go on continuously because sodium ions 鈥渓eak鈥� back through the cell wall by diffusion. a. How much work must be done to move one sodium ion from the inside of the cell to the outside? b. At rest, the human body uses energy at the rate of approximately 100 W to maintain basic metabolic functions. It has been estimated that 20% of this energy is used to operate the sodium pumps of the body. Estimate鈥攖o one significant figure鈥攖he number of sodium ions pumped per second.
shows three points near two point charges. The charges have equal magnitudes. For each part, rank in order, from most positive to most negative, the potentials to .
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