18.4. Controlling Current in Electric Circuits http://www.ck12.org
MEDIA
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URL: http://www.ck12.org/flx/render/embeddedobject/65201Follow up questions:
- What happens to the fuse wire when the recommended current in a circuit is exceeded?
- What is a common mistake made by homeowners when replacing burned fuses?
Review
Questions
- As a wire conductor increases in diameter, the resistance ____.
(a) increases
(b) decreases
(c) stays the same
(d) changes color - The purpose of a fuse in an electrical circuit is to
(a) add another resistor
(b) increase the circuit voltage
(c) limit the maximum current in the circuit
(d) none of these - What is the purpose of a circuit breaker in an electrical circuit?
- In some wire-in-glass fuses, the wire is not the same diameter all the way across the fuse. Many such fuses
have one part of the wire that is considerably more narrow than the remainder of the wire. What is the purpose
of this narrowing of the fuse wire?
- short circuit:A device in a circuit is said to be short-circuited if it is by-passed by a conductor of nearly
zero resistance so that the voltage across the device drops to almost zero and the current in the by-pass circuit
becomes huge. - electrical fuse: A safety device that protects an electric circuit from excessive current, consisting of or
containing a metal element that melts when current exceeds a specific amperage, thereby opening the circuit. - circuit breaker:A reusable device used to interrupt an electrical circuit if the current flow exceeds a chosen
level and becomes dangerous. - surge protector:A device used to eliminate sudden surges or spikes of electrical power in a circuit.
- metal oxide varistor or MOV:A metal oxide varistor is a resistor whose resistance varies nonlinearly with
voltage. Those MOVs used in surge protectors have high resistance with normal voltage, thus disallowing
current flow, but their resistance decreases greatly when voltage sharply increases.
Electrical power is the product of voltage, which is measured in watts, and current, which is measured in amperes.
Resistance to the flow of electricity is measured in ohms. Anything in an electrical circuit that makes use of the flow
of electricity provides some resistance. Electrical resistance within a wire is dependent not only on the material of
the wire, but also on the length of the wire and the amount of current flowing through it. By converting electrical
power to high voltage and low current, power companies can efficiently transfer energy over great distances with
little loss. The power must be converted back at its destination for use in homes and businesses. Circuit breakers and