Download In-Class Worksheet on Displacement and Velocity

Worksheet #4, May 24, 2005, Name:__________________________
1. In electric circuits, we have an analogy with skiing. The skiers represent the charges and the
path down which they ski is like the wire through which the charges move. If this is so, then
there is a device needed to raise their potential energy. In skiing, this device is the ski lift, which
raises the gravitational potential energy. What do you think is the analogous device in electric
circuits that will raise the voltage of the charges (hint: what do you need to have inside a
flashlight aside from the bulb?)?
2a. Which course would allow for more skiers to be traveling through at any given instant, one
with a large vertical drop where the skiers can build up a lot of speed, or one with a short vertical
drop, where they don’t build up as much speed?
2b. Which course would allow for more skiers to be traveling through at any given instant, one
with a lot of resistance to slow down skiers, or one with very little resistance to it?
2c. We have an analogy between change in height, h, and change in voltage, V. We also have
an analogy between the number of skiers per second and electrical current, I. Using these
analogies, determine how the current depends upon the change in voltage and the resistance of the
path.
3a. Will the power exerted by the ski lift increase with the number of skiers using it each instant
or decrease?
3b. Will the power exerted by the ski lift increase with the vertical height up which it lifts the
skiers or decrease?
3c. Using our analogy as before, determine an expression relating the power used by the circuit
as it depends upon the current, I, and the change in voltage, V.
4a. Imagine watching a charge that is oscillating up and down. Would you sense a constant
electric field or a changing electric field?
4b. A magnetic field is produced by a moving charge. Given the situation in 1a, do you think
there’s a magnetic field that exists when a charge oscillates back and forth?