Chapter 4: Q4DQ (page 744)
A certain region of space bounded by an imaginary closed surface contains no charge. Is the electric field always zero everywhere on the surface? If not, under what circumstances is it zero on the surface?
The electric field doesn’t need to be zero on the surface.
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(a) At room temperature, what is the strength of the electric field in a
12-gauge copper wire (diameter ) that is needed to cause a
current to flow? (b) What field would be needed if the wire were made of silver
instead?
High-voltage power supplies are sometimes designed intentionally to have rather large internal resistance as a safety precaution. Why is such a power supply with a large internal resistance safer than a supply with the same voltage but lower internal resistance?
Ordinary household electric lines in North America usually operate at 120 V . Why is this a desirable voltage, rather than a value considerably larger or smaller? On the other hand, automobiles usually have 12 V electrical systems. Why is this a desirable voltage?
We have seen that a coulomb is an enormous amount of charge; it is virtually impossible to place a charge of 1 C on an object. Yet, a current of is quite reasonable. Explain this apparent discrepancy.
Current passes through a solution of sodium chloride. In
ions arrive at the negative electrode and
ions arrive at the positive electrode. (a) What is the current passing between
the electrodes? (b) What is the direction of the current?
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