Physics Exam 3

Hw 7, electricity practice, hw 8, hw 8 practice

Modern automobile headlights are connected in

parallel

As more lamps are connected in a series circuit, the overall current in the power source

decreases

The equivalent (combined) resistance of 1-ohm, 2-ohm, and 3-ohm in series is about

6 ohms

Compared to a single lamp connected to a battery, two lamps connected in parallel to the same battery will carry

more current

The safety fuse in an electric circuit is connected to the circuit in

series

Connect a pair of lamps in series and current is drawn from the battery. Connect the same lamps in parallel and the current drawn is

more

Electrons flow in an electrical circuit by

interacting with an established electric field

The resistance of a filament that carries 2 A when a 10-V potential difference across it is

5 ohms

The voltage across a 10-ohm resistor carrying 5 A is

50V

Current in a conductor can be increased by

increasing the voltage across it AND reducing its resistance

Electric resistance in our skin is lowered when our skin is

moist

Ohm's law tells us that the amount of current produced in a circuit is

directly proportional to voltage AND inversely proportional to resistance

Alternating current is normally produced by a

generator

If you stretch a copper wire so that it is thinner, the resistance between its ends

increases

The unit of electrical resistance is the

ohm

An ampere is a unit of electric

current

Electrons flow in a wire when there is

a difference in potential energy across its ends

Just as a sustained flow of water in a hydraulic circuit needs a pump, in electric circuits the flow of charge needs

voltage

Just as water flows from a region of high pressure to a region of low pressure, electric charge flows from a region of

high electric pressure to a region of low electric pressure

If 10 J of work is used in pushing 1 C of charge into an electric field, its electric potential relative to its starting position is

10V

The operation of a microwave oven makes use of

an oscillating electric field

Two charged particles repel each other with a force F. If the charge of one of the particles is doubled and the distance between them is halved, then the force will be

8F

Two charges that are separated by one meter exert 1-N forces on each other. If the charges are pushed together so the separation is 25 centimeters, the force on each charge will be

16N

It is said that electric charge is conserved, which means that electric charge

can neither be created nor destroyed

If electrons are stripped from an atom it becomes a

positive ion

To become a negative ion, an atom must

gain an electron

Which of these does NOT have an electrical charge?

neutron

An electron and a proton

attract each other

In an electrically neutral atom the number of protons in the nucleus is equal to the number of

electrons that surround the nucleus

A fundamental rule of electricity is that

like charges repel, unlike charges attract

The force that binds atoms together to form molecules is

electrical

The fundamental force underlying all chemical reactions is

electrical

To say that electric charge is conserved means that no case has ever been found where

net charge has been created or destroyed

An electrically charged atom is an

ion

To become a positive ion, an atom must

lose an electron

A positive ion has more

protons than electrons

When the distance between two charges is halved, the electrical force between them

quadruples

Two charges that are separated by one meter exert 1-N forces on each other. If the magnitude of each charge is doubled, the force on each charge is

4N

Two charged particles repel each other with a force F. If the charge of one of the particles is doubled and the distance between them is also doubled, then the force will be

F/2

Two charged particles repel each other with a force F. If the charge of both particles is tripled and the distance between them is also tripled, then the force will be

F

Two charged particles attract each other with a force F. If the charges of both particles are doubled, and the distance between them also doubled, then the force of attraction will be

F

The electrical force on a 2-C charge is 60 N. The electric field where the charge is located is

30N/C

Electric potential, measured in volts, is the ratio of electric energy to the amount of electric

charge

Assume that 10 J of work pushes a charge initially at rest into an electric field. If the charge is then released, it flies back to its starting position with a kinetic energy of

10J

The current produced by voltage in a circuit is impeded by

electric resistance

If two copper wires of the same length have different thickness, then the thicker wire has

less resistance

Heat a copper wire and its electric resistance

increases

Direct current is normally produced by a

battery

Current that is typically 60 hertz is

alternating current

If an electric toaster rated at 110 V is accidently plugged into a 220-V outlet, the current drawn by the toaster will be

twice its normal value

The current in a light bulb is 0.25 A. The voltage across both bulbs is 110 V. The resistance of the light bulb is

440 ohms

When two lamps are connected in series to a battery, the electrical resistance that the battery senses is

more resistance of either lamp

When a pair of identical lamps are connected in parallel

voltage, current, and power dissipated across each is the same

On some early automobiles both headlights failed when one bulb burned out. The headlights were likely connected in

series

Compared to a single lamp connected to a battery, two identical lamps connected in series to the same battery will carry

less current

A circuit breaker often serves the same purpose as a

fuse

Sometimes the current in lamps is too feeble to produce glowing of the lamp filaments, which occurs when

too many lamps are connected in series

As more lamps are connected in a parallel circuit, the overall current in the power source

increases

like kinds of magnetic poles repel while unlike kinds of magnetic poles?

attract

whereas electric charges can be isolated, magnetic poles

cannot

surrounding every magnet is

a magnetic field

magnetism is due to the motion of electrons as they

move around the nucleus and spin on their axes

the shape of a magnetic field surrounding a current-carrying conductor is

circular

magnetic field lines about a current-carrying wire

circle the wire in closed loops

when current reverses direction in a wire, the surrounding magnetic field

also reverses direction

as the number of loops in a current-carrying wire is increased, the

stronger the enclosed magnetic field

a current-carrying coil wire is

an electromagnet

Place an iron rod inside a current-carrying coil of wire and you

increase the strength of the electromagnet

a galvanometer can be calibrated to measure

electric current and electric voltage

The intensity of cosmic rays bombarding the Earth's surface is most at the

poles

Pigeons navigate primarily by

magnetic sensors in their heads

The discovery of electromagnetic induction is credited to

Joseph Henry in America and Michael Faraday in England

When a change occurs in the magnetic field in a closed loop of wire

a voltage is induced in the wire, a current is created in the loop of wire, and electromagnetic induction occurs

When voltage is induced in a coil of wire, current is

also induced

Electromagnetic induction occurs in a coil when there is a change in

magnetic field intensity in the coil

Voltage can be induced in a wire by

moving the wire near a magnet, moving a magnet near the wire, changing the current in a nearby wire

When a magnet is moved to and fro in a wire coil, voltage is induced. If the coil has twice as many loops, the voltage induced is

twice

The amount of current produced by electromagnetic induction depends on the

amount of induced voltage and stance of the circuit to which it is connected

The metal detectors that people walk through at airports operate via

Faraday Law

A device that transforms mechanical energy into electrical energy is a

generator

The current produced by a common generator is

ac

If the voltage produced by a generator alternates, it does so because

the changing magnetic field that produces it alternates.

A transformer actually transforms

voltage

The output power of an ideal transformer is

equal to the input power

Transformers use ac to satisfy the required

change in magnetic field for operation

Compared to the primary voltage, the secondary voltage can be

higher, lower, or the same

The principle difference between a step-up and step-down transformer is

different ratios of turns of wire for each

A transformer DOES NOT produce

energy, power, or transforms mechanical energy to electric energy

A step-up transformer steps up voltage by ten times. If voltage input is 120 volts, voltage output is

1200 V