Chapter 23
How does wetness affect the resistance of your body?
Wet bodies have lower resistance
A flow of electric charge in a wire normally requires a
potential difference across the ends of the wire
In a circuit of two lamps in series, where the current through one lamp is 1 A, what is the current through the other lamp?
1 amp. The same current flows through lamps in series
If a voltage of 6 V is impressed across the circuit in the preceding question and the voltage across the first lamp is 2 V, what is the voltage across the second lamp? Defend your answer.
4 volts. The sum of the voltages across each lamp must add up to the total voltage across both lamps.
In a circuit of two lamps in parallel, where there is a voltage of 6 V across one lamp, what is the voltage across the other lamp?
6 volts
Does electric charge flow across a circuit or through a circuit? Does voltage flow across a circuit or is it impressed across a circuit?
Charge flows through and voltage is impressed across a circuit.
Why are electrons, rather than protons, the principal charge carriers in metal wires?
Electrons are free to move through the metal, whereas protons are fixed in place.
Part complete Calculate the current in the 280-Ω filament of a bulb connected to a 170-V line. Express your answer to two significant figures and include the appropriate units.
I = 0.61 A
What is the function of the round third prong in a modern household electric plug?
It grounds the case to zero potential.
Does heating a metal wire increase or decrease its electrical resistance? Why?
It increases resistance because atoms at higher temperatures jostle into the way of moving electrons.
What property of a diode enables it to convert ac to pulsed dc?
It is a one-way valve that allows electrons to in one direction only
If the resistance of a circuit remains constant while the voltage across the circuit decreases to half its former value, what change occurs in the current?
It is cut in half.
If the voltage impressed across a circuit is held constant while the resistance doubles, what change occurs in the current?
It is cut in half.
What is the unit of electrical resistance?
Ohm
Calculate the power of a hair dryer that operates on 130 V and draws a current of 5.0 A . Express your answer to two significant figures and include the appropriate units.
P= 650 W
What is the relationship among electric power, current, and voltage?
Power is current times voltage.
Does a battery produce dc or ac? Does the generator at a commercial power station produce dc or ac?
The battery is dc; the generator is ac.
Double the resistance of the resistor by changing it from 10 Ω to 20 Ω. What happens to the current flowing through the circuit?
The current decreases by a factor of two.
In what direction is the (conventional) current flowing through the circuit? Recall that current is the flow of positive charge.
The current flows from the positive terminal, through the wires and resistor, and into the negative terminal.
For the circuit containing one resistor and one battery, what happens to the current if the voltage is doubled?
The current increases by a factor of two.
Part complete For the circuit containing one resistor and one battery, what happens to the current if the voltage is tripled and the resistance is doubled?
The current increases.
How does the brightness of the light bulb depend on its resistance?
The light bulb gets dimmer as the resistance is increased
What is the function of fuse or circuit breaker in a circuit?
To prevent over loading the circuit with current
Why does a wire that carries electric current become hot?
Why does a wire that carries electric current become hot?
Will water flow more easily through a wide pipe or a narrow pipe? Will current flow more easily through a thick wire or a thin wire?
Wide pipe and thick wire
What is the error in saying the source of electrons in a circuit is the battery or generator?
Wires are full of mobile electrons.
When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally
continue glowing as brightly
When your body undergoes electric shock, the source of moving electrons is
electrons already in your body
Electric power in a circuit is the rate at which
energy dissipates
Part complete For the circuit in the previous part, the current flowing in the wire between the positive terminal of the battery and the resistor is ___________ the current flowing between the resistor and the negative terminal of the battery.
equal to
When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally
go out
To connect a pair of resistors so that their combined (equivalent) resistance will be less than the resistance of either one, should you connect them in series or in parallel?
in parallel
To connect a pair of resistors so that their combined (equivalent) resistance will be greater than the resistance of either one, should you connect them in series or in parallel?
in series
Which end of the battery is the positive terminal?
the orange end
