Chapter 23: Electric Current Flashcards
Electrons are made to flow in a wire when there is
a potential difference across its ends.
Which statement is correct: a) Charge flows in a closed circuit; b) Voltage flows through an open or a closed circuit; c) Resistance flows through an open circuit; d) Current is the primary cause of voltage.
a) Charge flows in a closed circuit.
Heat a copper wire and its electric resistance
increases.
In an ac circuit, the electric field: a) increases via the inverse-square law; b) changes magnitude and direction with time; c) is the same everywhere; d) none of these.
b) changes magnitude and direction with time.
A 10-ohm resistor has a 5-A current in it. What is the voltage across the resistor? a) 5V; b) 10V; c) 15V; d) 20V; e) more than 20V.
e) more than 20V.
V = IR = 5A * 10ohm = 50V
Modern automobile headlights are connected in
parallel.
The source of electrons lighting an incandescent ac light bulb is
atoms in the light bulb filament.
Electrons move in an electrical circuit by
interacting with an established electric field.
On some early automobiles both headlights went out when one bulb burned out. The headlights must have been connected in
series.
The current through a 10-ohm resistor connected to a 120-V power supply is
12A
I = V/R = 120V / 10ohm = 12A
A circuit breaker often serves the same purpose as a
fuse.
Stretch a copper wire so that it is thinner and the resistance between its ends
increases.
Alternating current is normally produced by a
generator.
When two lamps are connected in series to a battery, the electrical resistance that the battery senses is: a) more than the resistance of either lamp; b) less than the resistance of either lamp; c) none of these.
a) more than the resistance of either lamp.
A 100-Watt lamp glows brighter than a 25-Watt lamp. The electrical resistance of the 100-Watt lamp must be
less
The electric power of a lamp that carries 2 A at 120 V is
240 Watts.
P = I * V = 2A * 120V = 240W
In a common dc circuit, electrons move at speeds of: a) a fraction of a centimeter per second; b) many centimeters per second; c) the speed of light; d) none of these.
a) a fraction of a centimeter per second.
The difference in electrical potential between two points, measured in volts.
Potential difference;
When two points of different electric potential are connected by a conductor, charge flows so long as a potential difference exists. (Synonymous with voltage difference.)
The flow of electric charge that transports energy from one place to another.
Electric current;
Measured in amperes, where 1 A is the flow of 6.25 x 10^18 electrons per second, or 1 coulomb per second.
The property of a material that resists electric current.
Electrical resistance;
Measured in ohms.
The statement that the current in a circuit varies in direct proportion to the potential difference or voltage across the circuit and inversely with the circuit’s resistance.
Ohm’s law;
Current = voltage / resistance; A potential difference of 1 V across a resistance of 1 ohm produces a current of 1 A.
Electrically charged particles flowing in one direction only.
Direct current (dc)
Electrons always move from the negative terminal toward the positive terminal.