BIO SPIDERWEB CONDUCTIVITY . Some types of spiders build webs that consist of threads made of dry silk coated with a solution of a variety of compounds. This coating leaves the threads, which are used to capture prey, hygroscopic —that is, they attract water from the atmosphere. It has been hypothesized that this aqueous coating makes the threads good electrical conductors. To test the electrical properties of coated thread, researchers placed a 5-mm length of thread between two electrical contacts* The researchers stretched the thread in 1-mm increments to more than twice its original length, and then allowed it to return to its original length, again in 1-mm increments. Some of the resistance measurements are shown in the table: *Based on F. Vollrath and D. Edmonds. “Consequences of electrical conductivity in an orb spider’s capture web.” Natunvissenschaften (100:12. December 2013, pp. 1163-69). 25.80 If the conductivity of the thread results from the aqueous coaling only, how does the cross-sectional area A of the coating compare when the thread is 13 mm long versus the starting length of 5 mm? Assume that the resistivity of the coaling remains constant and the coating is uniform along the thread. A 13mm is about (a) 1 10 A 5 mm ; (b) 1 4 A 5 mm ; (c) 2 5 A 5 mm ; (d) the same as A 5 mm .
BIO SPIDERWEB CONDUCTIVITY . Some types of spiders build webs that consist of threads made of dry silk coated with a solution of a variety of compounds. This coating leaves the threads, which are used to capture prey, hygroscopic —that is, they attract water from the atmosphere. It has been hypothesized that this aqueous coating makes the threads good electrical conductors. To test the electrical properties of coated thread, researchers placed a 5-mm length of thread between two electrical contacts* The researchers stretched the thread in 1-mm increments to more than twice its original length, and then allowed it to return to its original length, again in 1-mm increments. Some of the resistance measurements are shown in the table: *Based on F. Vollrath and D. Edmonds. “Consequences of electrical conductivity in an orb spider’s capture web.” Natunvissenschaften (100:12. December 2013, pp. 1163-69). 25.80 If the conductivity of the thread results from the aqueous coaling only, how does the cross-sectional area A of the coating compare when the thread is 13 mm long versus the starting length of 5 mm? Assume that the resistivity of the coaling remains constant and the coating is uniform along the thread. A 13mm is about (a) 1 10 A 5 mm ; (b) 1 4 A 5 mm ; (c) 2 5 A 5 mm ; (d) the same as A 5 mm .
BIO SPIDERWEB CONDUCTIVITY. Some types of spiders build webs that consist of threads made of dry silk coated with a solution of a variety of compounds. This coating leaves the threads, which are used to capture prey, hygroscopic—that is, they attract water from the atmosphere. It has been hypothesized that this aqueous coating makes the threads good electrical conductors. To test the electrical properties of coated thread, researchers placed a 5-mm length of thread between two electrical contacts* The researchers stretched the thread in 1-mm increments to more than twice its original length, and then allowed it to return to its original length, again in 1-mm increments. Some of the resistance measurements are shown in the table:
*Based on F. Vollrath and D. Edmonds. “Consequences of electrical conductivity in an orb spider’s capture web.” Natunvissenschaften (100:12. December 2013, pp. 1163-69).
25.80 If the conductivity of the thread results from the aqueous coaling only, how does the cross-sectional area A of the coating compare when the thread is 13 mm long versus the starting length of 5 mm? Assume that the resistivity of the coaling remains constant and the coating is uniform along the thread. A13mm is about (a)
1
10
A5 mm; (b)
1
4
A5 mm; (c)
2
5
A5 mm; (d) the same as A5 mm.
Figure (a) gives the magnitude E(x) of the electric fields that have been set up by a battery along a resistive rod of length L = 9.00 mm (see Figure (b)). The vertical scale is set by Es = 3.20 ×103 V/m. The rod consists of three sections of the same material but with different radii. (The schematic diagram of the figure (b) below does not indicate the different radii.) The radius of section 3 is 2.22 mm. What is the radius of (a) section 1 and (b) section 2?
A wire with a radius of 2.22mm is made of a conducting material that has an atomic mass of 72.0 grams/mole and a mass density of 6.17x103 kg/m3. You can assume that each atom of the material has one free electron associated with it. What is the drift speed vd in a 19.3 cm long section of wire that is carrying 664 Amps?
Assume 3 significant digits and units of mm/s.
What is the number density of free electron carries in the metallic element nickel if the electrons available for electrical conduction is 1 e- per nickel atom? The atomic mass of nickel is 58.6934 g/mole and the density of nickel is 8.902 g/cm3.
a.
3.32 x 1028 e- ' s /m3
b.
1.56 x 1029 e- ' s /m3
c.
5.64 x 1028 e- ' s /m3
d.
9.13 x 1028 e- ' s /m3
e.
7.63 x 1028 e- ' s /m3
Chapter 25 Solutions
Mastering Physics with Pearson eText -- Standalone Access Card -- for University Physics with Modern Physics (14th Edition)
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