Chapter 5 Question Set.
4. Why does the production of electricity by friction always yield equal amounts of ositive and
negative charge?
Answer:
Rubbing does not create the electric charges that appear as a result. All “uncharged” objects
actually contain equal amounts of positive and negative charge. For some pairs of materials,
rubbing is enough to separate some of the charges from each other. Overall, for the system
of rod and fur, the net neutral charge is conserved.
9. When two objects attract each other electrically, must both of them be charged?
When
two objects repel each other electrically, must both of them be charged?
Answer:
Yes. Yes. like charges repel, opposite charges attract, neutral charges do neither.
Look at Coulomb’s Law. F = K*(Q1Q2)/R2. If the value of Q1 and/or Q2 is zero (neutral
charge) then the value of F is zero.
10. A person can be electrocuted while taking a bath if he or she touches a poorly insulated
light switch. Why is the electric shock received under these conditions so much more
dangerous than usual?
Answer:
Because the water covering our bodies is a much better conductor of electricity than just our
dry bodies themselves allowing much more current to flow from the switch to the ground
through us.
14. Why do you think bending a wire does not affect its electrical resistance even though a
bent pipe offers more resistance to the flow of water than a straight one?
Answer:
Because the charge and current flowing through a wire flows through the metal atoms
themselves. The charge flows through the electron cloud which is diffused around the nuclei
of the metal atoms. Bending that cloud does not create any sort of physical barrier to the
flowing electrons like bending a pipe does to the water.
16. What aspect of superconductivity has prevented its large-scale application thus far?
Answer:
The requirement of super low temperatures need. The warmest superconductor works at
150K. That is -123C.
18. Heavy users of electric power, such as large electric stoves and clothes dryers, are
sometimes designed to operate on 240 V rather than 120 V. What advantage do you think
the higher voltage has in these applications?
Answer:
These items depend on current through an element with specified resistance to generate the
heat they need. Since current = voltage/resistance, increasing the voltage allows for an
increased resistance for the same amount of current, therefore, more heat generated. also
since power equals current X voltage, increased voltage means you can use less current and
still generate the same amount of power. We pay for electricity based on the amount of
current we use.
19. Why is a piece of iron attracted to either pole of a magnet?
Answer:
Because the molecules in iron are randomly distributed as far a polarity so they can be
influenced by either a north or south magnetic pole. The magnetic polarity will rearrange
based on the polarity of the magnet leading to a net attractive force.
24. A current flows west through a power line.
Find the direction of the magnetic field above
and below the power line; ignore the earth’s magnetic field.
Answer:
The direction of the magnetic field above and below the power line will be north and south
and up and down.