Conceptual Questions Chap. 18

1
Conceptual Questions Chap. 18

1. A short circuit is a circuit containing a path
   of very low resistance in parallel with some
   other part of the circuit. Discuss the effect of
   a short circuit on the portion of the circuit it
   parallels. Use a lamp with a frayed cord as an
   example.
2. If electrical power is transmitted over long
   distances, the resistance of the wires becomes
   significant. Why? Which mode of transmission
   would result in less energy loss high current
   and low voltage or low current and high voltage?
   Explain your reasoning.
3. Why is it dangerous to turn on a light when you
   are in a bathtub?
4. Would a fuse or circuit breaker work successfully
   if it were placed in parallel with the device it
   was supposed to protect?

A short circuit in a lamp cord means the 2
conducting wires touch each other, opening a
low-resistance branch in parallel with the lamp.
Then the lamp goes out immediately. However, a
very large current will be produced in the power
source, the house wiring, and the wire in the
lamp cord up to and through the short. The
circuit breaker will interrupt the current
quickly, but not before considerable heating has
occurred.
Resistance is proportional to the length of wire.
Thus as the length increases, so does the
resistance. It is most efficient to use low
current at high voltage. A high current would
make P I2R very large. A lower power loss is
obtained for high voltages, since P (DV)2 / R
would not be as large since R is already large.

Since water is a good conductor, if you should
become part of a short circuit while energizing
any electrical circuit while in a bathtub, the
current would follow a pathway to ground through
you, resulting in electrocution.
No, since there would still be a current path
through the device even if the circuit breaker
were to trip.