Phys. Science Exam 3

magnetic force

(1) between magnets, it is the attraction of unlike magnetic poles for each other and the repulsion between like magnetic poles. (2) between a magnetic field and a moving charge, it is a deflecting force due to the motion of the charge: the deflecting force is perpendicular to the velocity of the charge and perpendicular to the magnetic field lines. this force is greatest when the charge moves perpendicular to the field lines and is smallest (zero) when it moves parallel to the field lines

How does a coulomb of charge compare with the charge of a single electron?

1 C is the charge associated with 6.25 billion billion electrons. so one electron has charge of 1/6.25 x 10^^18 C, or 1.6 x 10^^-19 C

In a simple circuit consisting of a single lamp and a single battery, when the current in the lamp is 2 A, the current in the battery is

2 A

What is the power rating of a lamp connected to a 12-V source when it carries 2.5 A?

30 W

How much resistance must a 9-V device have to keep the current about 1 A?

9 omhs

Who is credited with discovering electromagnetic induction?

Faraday and Henry

A transformer works by way of

Faraday's law

The essential physics concept in an electric generator is

Faraday's law

A toaster has a heating element of 15 Ω and is connected to a 120 V outlet. Show that the current drawn by the toaster is 8 V.

I=V/R so (120 V)/ 15 Ω= 8 A

An electric toy draws 0.5 A from a 120 V outlet. Show that the toy consumes 60 W of power.

P= I x V = (0.5 A)(120 V)= 60 W

Which of these cities has the smallest incidence of cosmic rays

Singapore

transformer

a device for transferring electric power from one coil of wire to another by mean of electromagnetic indiction

An electric motor best makes use of the fact that on a current-carrying wire in a magnetic field there exists

a force

electromagnet

a magnet whose field is produced by an electric current. It is usually in the form of a wire coil with a piece of iron inside the coil

Maxwell's counterpart to Faraday's law

a magnetic field is induced in any region of space in which an electric field in changing with time. correspondingly, an electric field is induced in any region of space in which a magnetic field is changing with time

The actual speed of electrons drifting along in a common electric circuit is about the speed of

a slow-moving snail

A galvanometer best makes use of the fact that a magnetic field exits

about a current-carrying wire

The underlying physics of an electric motor is that

ac voltage is induced by a changing magnetic field

How does the charge of one electron compare with the charge of another electron?

all electrons are identical; that is, each has the same mass and the same quantity of negative charge as every other electron

When you thrust a bar magnetic to and fro into a coil of wire, you induce

alternating current

series circuit

an electric circuit with devices connected in such a way that the current is the same in each device

parallel circuit

an electric circuit with two or more devices connected in such a way that the same voltage acts across each one, and any single one completes the circuit independently of all the others

direct current (dc)

an electric current flowing in one direction only

alternating current

an electric current that repeatedly reverses its direction; the electric charges vibrate about relatively fixed point. In the United States, the vibrational rate is 60 HZ

how does an electrically polarized object differ from an electrically charged object?

an electric polarized object differs from an electrically charge object because electrically polarized object usually has its charges divide and thus they are negative and positive while electrically objects depend on acquired or gone charge. Polarized objects do not have surplus charges but electrically charged objects have surplus charges and this makes them to be unstable

generator

an electromagnetic induction device that produces electric current by rotating a coil within a stationary magnetic field

conductor

any material having free charge particles that easily flow through it when an electrical force acts on them

superconductor

any material with zero electrical resistance, in which electrons flow without losing energy and without generating heat

When evaporation occurs in a dish of water, the molecules left behind in the water

are less energetic, have decreased average speeds and result in lowered temperature

How is Coulomb's law similar to Newton's law of gravitation? How is it different?

both laws are inverse-square laws. how they differ is mainly that gravitation is only attractive, whereas electrical forces can repel

How does the magnitude of electrical force between a pair of charged particles charge when the particles are moved twice as far apart? Three times as far apart?

by the inverse-square law, particles twice as far apart have 1/4 the force; particles three times as far apart have 1/9 the force

Which statement is correct

charge flows in a circuit

magnetic domains

clustered regions of aligned magnetic atoms. when these regions themselves are aligned with one another, the substance containing them is a magnet

The lowest resistance in a common electric circuit containing a common lamp is in the

connecting wires

When you double the voltage in a simple electric circuit, you double teh

current

Which of these is the same in identical branches of a parallel circuit?

current, voltage and resistance

A magnetic field can be found surrounding any

current-carrying wire and moving electric charge

Boiling and freezing can occur at the same time when water is subjected to

decreased atmospheric pressure

electric field

defined as force per unit charge, it can be considered an energetic aura surrounding charged objects. about a charged point, the field decreases with distance according to the inverse-square law, like a gravitational field, between oppositely charged parallel plates, the electric field is uniform

As more branches are added to a parallel circuit, the overall resistance of the curcuit

definitely decreases

The amount of energy dissipated by a 100-W bulb in a common parallel curcuit

depends on how long the bulb is lit, is normally 100 joules per second, and depends on the voltage supplied to the lamp

Which has greater electrical resistance: wet skin or dry skin?

dry skin has considerably more electrical resistance than wet skin

An electric field surrounds all

electric charge, electrons and protons

Surrounding moving electric charges are

electric fields and magnetic fields

Distinguish between electric potential energy and electric potential in terms of units of measurement.

electric potential energy is measured in joules; electric potential in volts

To say an object has a negative charge is to say it has an excess of what kind of charge?

electrons

Thermal convection is linked mostly to

fluids

When a pair of charged particles are brought twice as close to each other, the force between them becomes

four times as strong

A 12-V battery moves 4 C of charge from one terminal to the other. Show that the battery does 48 J of work.

from voltage= energy/charge, we get energy = voltage x charge = (12 V)(4 C)= 48 J

An electron beam passing perpendicularly through a magnetic field is defected. If the beam were instead composed of protons, the beam would be defected

in the opposite direction

When air is rapidly compressed, its temperature normally

increases

Charge polarization is normally produced by

induction

Which of these electromagnetic waves has the lowest frequency?

infrared

To say a substance is electrically polarized is to say that its net charge is

is normally zero with opposite charges on opposite ends

What is the unit of electrical resistance?

is the ohm Ω

To say that charge is conserved is to say that charge

is transferred, but never created or destoyed

What kind of charge does an object acquire when electrons are stripped from it?

it has a positive charge

Which of these are correct for an electric field

it's a vector quantity, and can be cancelled, it's the altered space surrounding electric charge and stores electric energy

Electric potential energy is measured in units of

joules per coulomb, or volts

Electricity and magnetism connect to form

light

In a circuit with two lamps in parallel, if the current in one lamp is 2 A, the current in the battery is

more than 2 A

What is the key ingredient of electromagnetic induction?

motion

The key ingredient in anything magnetic is

moving electric charge

When we say charge is conserved, we mean that charge can

not be created or destroyed

Electric potential and electric potential energy are

one and the same in most cases and two terms for the same concept

A magnetic force acting on a beam of electrons can chage

only the direction of the beam

Glass is transparent to short-wavelength light and is

opaque to light of longer wavelengths

A fire walker walking barefoot across hot wooden coals depends on wood's

poor conduction

The number of electrons that move about the nucleus of an electrically neutral atom is the same as the number of

protons in the nucleus

If you double both the current and the voltage in a circuit, the power

quadruples

An object that absorbs energy well also

radiates well

When steam changes phase to water, it

releases energy

Compared with terrestrial radiation, the radiation from the Sun has a

shorter wavelengths

electrically polarized

term applied to an atom or molecule in which the charges are aligned so that one side has a slight excess of positive charge and the other side a slight excess of negative charge

What is meant by saying that charge is conserved?

that when somethings is charged electrons are neither created nor destroyed but are simply transferred from one material to another

coulomb

the SI unit of electric charge. one coulomb (C) is equal in magnitude to the total charge of 6.25 x 10^^18 electrons

Ohm's law

the current in a circuit varies in direct proportion to potential difference or voltage and inversely with the resistance: current = voltage/ resistance. a current of 1 A is produced by a potential difference of 1 V across a resistance of 1 Ω

potential difference

the difference in potential between two points, measured in volts and often called voltage difference

electric potential

the electric potential energy per amount of charge, measured in volts and often called voltage

electric potential energy

the energy a charge possesses by virtue of its location in an electric field

electric current

the flow of electric charge that transports energy from one place to another

electromagnetic induction

the induction of voltage when a magnetic field changes with time

Faraday's law

the law of electromagnetic induction, in which the induced voltage in a coil is proportional to the number of loops multiplied by the rate at which the magnetic field changes within those loops. (the induction of voltage is actually the result of a more fundamental phenomenon: the induction of an electric field) Voltage induced ~ number of loops x change in magnetic field/time

How does the masses of electrons compare with the masses of protons?

the masses of electrons are much less than the masses of protons (1:2000)

The source of all magnetism is

the motion of electrons

Which part of an atom is positively charged, and which part is negatively charged?

the nucleus and protons are positive and the electron are negative

electrical resistance

the property of a material that resists the flow of an electric current through it, measured in ohms Ω

electric power

the rate of energy transfer, or the rate of doing work; the amount of energy per unit time, which can be measured by the product of current and voltage: power=current x voltage. it is measured in watts (or kilowatts), where 1 A x 1 V = 1 W

magnetic field

the region of magnetic influence around a magnetic pole or a moving charge particle

Coulomb's Law

the relationship among electrical force, charge, and distance: if the charges are unlike, the force is attractive

What is the source of electrons that produces a shock when you touch a charged conductor?

the source of electrons producing a shock is own body

Which has greater resistance; a thick wire or a thin wire of the same length?

the thin wire resist electric current more than thicker wires and length contributes to resistance also

What is the function of the third prong on the plug of an electrical appliance?

the third prong connects the body of the appliance directly to ground. any charge that builds up on an appliance is therefore conducted to the ground

ampere

the unit of electric current; the rate of flow of 1 coulomb of charge per second

If 6 V were impressed across the circuit of two lamps connected in series, and the voltage across the first lamp were 2 V, what would be the voltage across the second lamp?

the voltage across the second lamp would be 4 V, so the sum of the two is 6 V

How does the number of protons in the atomic nucleus normally compare with the number of electrons that orbit the nucleus?

they are normally equal so the atom has zero net charge

Touch a 5000-V charged balloon and you're not harmed because, although the energy-charge ratio is high, there is

very little energy on the balloon

A step-up transformer in an electric circuit can step up

voltage

Electric current is a flow of electric charge that moves due to an electric pressure called

voltage

The current in a circuit is directly proportional to the impressed

voltage