CH 23

What factors does the resistance offered by a piece of conductor depend upon?

both the geometry and the material of the conductor

When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally _________.

go out

A flow of electric charge in a wire normally requires a _________.

potential difference across the ends of the wire

A voltage source in a circuit provides electrical _________.

pressure

What is the flow of current proportional to?

voltage difference between the two ends of the wire

How much energy is supplied to each coulomb of charge that flows through a 12-V battery?

12 joules

What is the current in a bulb if the resistance of its filament is 2 ohms and it is connected across a 6-volt battery?

3 amps

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

Consider the power dissipated by the two circuits in the video. The ratio of power dissipation in the parallel circuit to that in the series circuit is

9

What condition is necessary for the sustained flow of water in a pipe? What analogous condition is necessary for the sustained flow of charge in a wire?

A continuous pressure difference, often provided by a pump, is needed for water to flow. A continuous potential difference, often provided by a battery, is needed for charge to flow.

The brightness of identical bulbs varies depending on whether or not they are connected in series or parallel.

Brightest: Bulb A Dimmest: Bulb B and Bulb C

-The same current flows through each bulb in the current -Adding a bulb makes the other bulbs dimmer -Removing a bulb stops the current flow through the circuit

Always true about a simple series circuit

-Removing a bulb does not stop the current flow throughout the circuit -There is the same voltage across each bulb in the circuit.

Always true about simple parallel circuits

Why is there no proton current in a conductor with a potential difference applied across the circuit?

Because protons are bound inside the nuclei of atoms that are more or less in fixed positions

What is the relationship between current, resistance, and voltage difference?

Current = Voltage Difference / Resistance

What happens to the current in a circuit where the resistance is kept constant and the voltage is double?

Current also doubles.

Which of the following would double the amount of current flowing through a piece of metal wire?

Double the voltage across it.

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.

If the resistivity of copper is less than that of gold at room temperature, which of the following statements must be true?

Electrons in gold are more likely to be scattered than electrons in copper at room temperature when they are accelerated by the same electric field.

At what speed do electrons in a battery driven automotive circuit travel along a wire? At what speed does the electric field propagate along a wire?

Electrons move at 0.01 cm/s. The electric field propagates at nearly the speed of light.

Superconductors have near zero electrical resistance; how is this condition reached?

Expose the conductor to very low temperatures.

Where do the electrons come from that produce an electric shock when you touch a charged conductor?

Inside you

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.

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 does the power company provide to our homes?

It provides energy to move the electrons.

Rank the wires in order of which carries the most current (has the lowest resistance) when connected to batteries with the same voltage difference.

Most: 1. Wire of length L and area 2A Middle: 2. Wire of length L and area A Least: 3. Wire of length 2L and area A

Adding a bulb makes the other bulbs brighter.

Neither

The work done to separate opposite charges results in different values of energy per charge. What is this difference called?

Potential difference or 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.

How does the current change if you increase the resistance, keeping the voltage difference the same?

The current decreases.

What happens to the current supplied by the battery when you add an identical bulb in parallel to the original bulb?

The current doubles.

What is the error in saying the source of electrons in a circuit is the battery or generator?

Wires are full of mobile electrons.

What exactly is an ampere?

The flow of one coulomb per second

What happens to a lamp when you take both ends of the wire connected to it and hold them to the same side of the 12-volt terminal of battery, and why?

The lamp does not light up because there is no voltage difference applied across it.

What happens when you have a voltage difference between the two ends of the lamp, and why?

The lamp lights up because there is a voltage difference applied to it.

A lab technician has six identical lamps and two identical power sources and uses them to build two circuits, one in series and one in parallel. What can be stated about the electrical resistance for each circuit?

The parallel circuit will have a lower resistance.

In a series circuit with two identical bulbs, what happens to the remaining bulb when one is replaced with a wire?

The remaining bulb gets brighter.

How does the resistance of a thick piece of copper wire compare to the resistance of a thin piece of copper wire?

The resistance of the thin piece is greater than that of the thick piece.

How do the currents through the branches of a simple parallel circuit compare with the current in the voltage source?

The sum of the currents in the branches equals the current through the source.

How do the resistances of two conducting wires compare if they have the same length, but one is twice the radius of the other?

The thicker wire has one-fourth the resistance of the thinner wire.

What is the function of fuse or circuit breaker in a circuit?

To prevent over loading the circuit with current

A pipe is filled with water, and there is a piston at each end. If you apply unequal pressures at the two pistons, which way will the water flow in the pipe?

Water will flow from the piston with the higher pressure to the piston with the lower pressure.

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 kind of current runs through the electric wiring in a home?

alternating current

When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally _________.

continue glowing, but slightly brighter

What type of field causes the electrons to do what they do in the wire?

electric field

Of what physical quantity is Hertz a unit of?

number of times per second that the electrons move back and forth in the wire

The electric resistance in a length of wire is doubled when the wire is _________.

twice as long

Electrons in the filament of a lamp that carries ac have a net velocity that is ___________.

zero