20.1 Current  (Page 6/10)

Which of the following can be explained on the basis of conservation of charge in a closed circuit consisting of a battery, resistor, and metal wires?

1. The number of electrons leaving the battery will be equal to the number of electrons entering the battery.
2. The number of electrons leaving the battery will be less than the number of electrons entering the battery.
3. The number of protons leaving the battery will be equal to the number of protons entering the battery.
4. The number of protons leaving the battery will be less than the number of protons entering the battery.

When a battery is connected to a bulb, there is 2.5 A of current in the circuit. What amount of charge will flow though the circuit in a time of 0.5 s?

1. 0.5 C
2. 1 C
3. 1.25 C
4. 1.5 C

If 0.625 × 10 ²⁰ electrons flow through a circuit each second, what is the current in the circuit?

Two students calculate the charge flowing through a circuit. The first student concludes that 300 C of charge flows in 1 minute. The second student concludes that 3.125 × 10 ¹⁹ electrons flow per second. If the current measured in the circuit is 5 A, which of the two students (if any) have performed the calculations correctly?

Can a wire carry a current and still be neutral—that is, have a total charge of zero? Explain.

Car batteries are rated in ampere-hours ( $\text{A}\cdot \text{h}$ ). To what physical quantity do ampere-hours correspond (voltage, charge, . . .), and what relationship do ampere-hours have to energy content?

If two different wires having identical cross-sectional areas carry the same current, will the drift velocity be higher or lower in the better conductor? Explain in terms of the equation $v_{\text{d}}=\frac{I}{\text{nqA}}$ , by considering how the density of charge carriers $n$ relates to whether or not a material is a good conductor.

Why are two conducting paths from a voltage source to an electrical device needed to operate the device?

In cars, one battery terminal is connected to the metal body. How does this allow a single wire to supply current to electrical devices rather than two wires?

Why isn't a bird sitting on a high-voltage power line electrocuted? Contrast this with the situation in which a large bird hits two wires simultaneously with its wings.