Download Conceptual Questions Chap. 13

Conceptual Questions Chap. 18
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.
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.
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.
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.
3.
Why is it dangerous to turn on a light when you are in a bathtub?
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.
4.
Would a fuse or circuit breaker work successfully if it were placed in parallel
with the device it was supposed to protect?
No, since there would still be a current path through the device even if the circuit
breaker were to trip.
1.