Conceptual Physics

why not.

i. It matters

ii. It does not matter

C.11You buy a light bulb in the U.S. labeled 75 watts. Since you bought it in the U.S., the power rating assumes that the potential
difference across the light bulb will be 120 volts. Instead, you provide it with a potential difference of 220 volts (the potential
difference provided by wall outlets in most European countries). Will the light bulb dissipate 75 watts of power? Explain.
Yes No

C.12Solar panels are priced based on the number of kilowatts they generate. You pay the utility an amount based on the number

of kilowatt-hours you use. What is the connection between kW and kW·h?

C.13You receive your bill from the electric company, and it states that you have used 3470 kW·h (kilowatt·hours) of electricity this

month, and that due to the energy crisis in your town your bill is an astronomical $832.80. What is it, exactly, that you are

paying for?

i. Electric power

ii. Electric energy

iii. Electric potential

iv. Some hotshot energy trader's vacation in Tahiti

Section Problems

Section 1 - Electric current

1.1 A current of 1.00 mA passes through a copper wire for 60.0 s. (a) How many coulombs of charge pass any point in the wire
during this time period? (b) How many electrons pass any point in the wire during this time period? (c) How many protons
pass any point in the wire during this time period?
(a) C
(b) electrons
(c) protons

1.2 In a Crooke's Tube, a stream of electrons boils
off a negative electrode, or cathode, and flies
through a vacuum toward a positive electrode,
or anode. Often, the anode is given a
distinctive shape, like a cross, so that the
electrons that miss it and fly past will create a
dramatic shadow on the far end of the glass
tube. The stream of electrons is flowing past a
certain point between the cathode and the
anode at a rate of 3.50 A. If 95.0% of the
electrons reach the anode, (a) what amount of
charge reachs the anode during a period of 15.0 s? Be careful of the sign of your answer. (b) How many electrons reach the
anode during a period of 15.0 s?
(a) C
(b) electrons

1.3 A mouse sits next to a cell phone charger cord for 4.10 seconds, debating whether it is something worth chewing on. If the

cord carries a current of 3.00 amperes, what is the magnitude of the charge that goes by the mouse while it thinks?

C

1.4 According to the Bohr model, a hydrogen atom in its lowest energy state has a nucleus consisting of a single proton, which is

orbited by a single electron. The speed of the electron is 2.19×10^6 m/s and the radius of its orbit (the "Bohr radiuis") is

5.29×10í^11 m. What is the magnitude of the "current" flowing around the nucleus in the Bohr model?

A

1.5 A wire spans two telephone poles. A tightrope walker picks up a sphere with a charge of 5.3 microcoulombs at one end and

carries it to the other end in 7.2 seconds. What is the average current from one end of the wire to the other?

A

1.6 A wire etched onto a computer chip carries a current of 4.1eí8 A. In 1.8 milliseconds, how many electrons flow past a point

on the wire?

electrons

Copyright 2007 Kinetic Books Co. Chapter 25 Problems^471