physical science test 3

define refraction

change in a wave's direction as it enters a different medium

define reflection

change in a wave's direction when it strikes an obstacle

in a simple direct-current electric motor, the ____________________ reverses the current periodically

commutator

a____________________ is a substance through which electric charge can flow.

conductor

the ____________________ is the basic unit of electric charge.

coulomb

a flow of charge from one place to another is an electric ____________________.

current

define benjamin franklin

described charges as either positive or negative

*the bending of waves around the edge of an obstacle in their path is an example of

diffraction

define christian oersted

discovered that every electric current generates a magnetic field

when the rubber rod is stroked against the piece of fur

electrons are transferred from the fur to the rubber rod

*the greater the amplitude of a wave, the greater its

energy

define wave speed

equal to wavelength times frequency

*the current with which a transformer is used

must be ac

*a positive electric charge

repels other positive charges

*in an electromagnetic wave, the electric field is

perpendicular to both the magnetic field and the wave direction

define dispersion

separation of white light into its individual colors or frequencies

define ultrasound

sound frequencies above 20,000 Hz

*two charges of +Q are 1 cm apart. if one of the charges is replaced by a charge of -Q, the magnitude of the force between them is

the same

define alessandro volta

the unit of potential difference is named for him

define georg ohm

the unit of resistance is named for him

define period

time needed for a wave to pass a given point

*direct electric current cannot be used to operate

transformers

true or false the speed of light in a medium such as air or glass is slightly different for different frequencies.

true

if you divide voltage by resistance, the answer will be in units of

amperes

human ears are most sensitive to sounds whose frequencies are between

3000 and 4000 Hz

*relative to the radio signals sent out by a spacecraft headed away from the earth, the signals that are received on the earth have

a lower frequency

oersted's experiment demonstrated that

a magnetic field surrounds every electric current

which one of the following wave quantities is not related to the others?

amplitude

define kamerlingh onnes

discovered the phenomenon called superconductivity

define michael faraday

discovered the principle of the generator

a narrow beam of white light is passed through a prism and is separated into beams of light of various colors. this is an example of

dispersion

*the conventional unit of battery capacity is the ampere-hour, which is actually a unit of

electric charge

the ampere is the unit of

electric current

radio waves and X-rays are examples of

electromagnetic waves

*the particle easiest to remove from an atom is an

electron

____________________ are elementary particles found in atoms and have a negative electrical charge.

electrons

an electrically neutral atom has equal numbers of protons and _____________________.

electrons

if the violin string in question 6 was not touched and allowed to vibrate as a whole, its frequency relative to the frequencies of the two vibrating sections would be

lower

define thales of miletus

made the first recorded studies of electricity

*at different places on the earth's surface, the earth's magnetic field

may be different in both magnitude and direction

ohm's law holds only for

metallic conductors

the elementary particle that has no electric charge is the

neutron

neutrons and protons are found in the ____________________ of an atom.

nucleus

the unit of electrical resistance is the ____________________.

ohm

a violin string is bowed and at the same time is touched lightly in the middle, causing the string to vibrate in two sections. the two vibrating sections produce sound frequencies called

overtones

*a current-carrying loop in a magnetic field always tends to turn until the plane of the loop is

parallel to the field

*in a transverse wave, the individual particles of the medium move

perpendicular to the direction of travel

the ____________________ of an electric current is the rate at which it does work.

power

____________________ is the property of a conductor that opposes the flow of charge passing through it.

resistance

the portion of the eye that contains the light-sensitive receptors is the

retina

when the resistors in an electric circuit are joined end-to-end with the same current flowing through all of them, the resistors are in ____________________; when the resistors are arranged so that the total current is split among them, they are in ____________________.

series, parallel

a _____ circuit results when the connecting wires of an electric circuit accidently touch each other or are joined by a stray conductor

short

define charles coulomb

showed how the force between charges varied with their distance apart and the magnitude of

*an atom consists of a

small positive nucleus surrounded at a distance by electrons

the plastic ball flies away from the rubber rod because

some of the charge flows from the rod to the plastic ball and like charges repel

when the plastic ball is touched by the rubber rod

some of the charge is transferred from the rubber rod to the plastic ball

define infrasound

sound frequencies below 20 Hz

*an example of a purely longitudinal wave is a

sound wave

*of the following kinds of waves that cannot travel through a vacuum are

sound waves

which one of the following waves cannot travel through a vacuum?

sound waves

*a magnetic field does not interact with a

stationary electric charge

*protons and electrons have different masses. When they are the same distance apart, the electric force between two electrons

the same as the force between two protons

define andre amperes

the unit of electric current is named for him

*sound waves whose frequency is 300 Hz have a wavelength relative to sound waves in the same medium whose frequency is 900 Hz that is

three times as great

true or false a stationary electric charge has no magnetic properties

true

true or false electric energy is useful partly because it is easily transformed into other kinds of energy

true

true or false electromagnetic waves differ from mechanical waves in their ability to travel through a vacuum as well as matter.

true

true or false in 1864, James Clerk Maxwell proposed that an accelerated electric charge generates combined electrical and magnetic disturbances called electromagnetic waves.

true

true or false in a transformer, the electrical power is the same in both coils independent of the number of turns in each coil

true

true or false the force between two charged objects depends upon the distance between the objects and the magnitude of each charge

true

true or false the size and shape of a musical instrument is largely responsible for its natural frequencies of vibration or resonance.

true

true or false the sun appears a brilliant red at sunset because the atmospheric molecules and dust particles scatter the blue light more than the red.

true

define hertz

unit of frequency

define decibel

unit of sound intensity

the ____________________ is the unit of potential difference.

volt

electric power is the product of current and ____________________.

voltage

the ____________________ , or potential difference, between two points is the work needed to take a charge of 1 C from one of the points to the other.

voltage

*an example of a wave that is partly longitudinal and partly transverse is a

water wave

the unit of electric power is the

watt

*relative to the electric force between two protons, the gravitational force between them is

weaker

*the watt, the unit of power, is equal to the

(volt)(ampere)

*ocean waves whose period is 8 s are observed to have a wavelength of 100 m. their speed is

12.5 m/s

*the musical note A has a frequency of 440 Hz and its wavelength in seawater is 3.5 m. the speed of sound in seawater is

1540 m/s

two waves having the same frequency and equal amplitude A meet exactly in step at the same point. The resulting amplitude is

2 A

*two 240-watt light bulbs are connected in parallel across a 120-V power line. The current in each bulb is

2.0 A

*a charge of +Q attracts a charge of -Q 1 cm away with a force of F. another charge of +Q is placed next to the first one. the force on the charge of -Q is now

2F

*the primary coil of a transformer has 200 turns and its secondary coil has 50 turns, and the current in the secondary coil is 40 A. when a 12-V alternating current is applied to the primary coil of the transformer, the secondary voltage will be

3 V

*the primary coil of a transformer has 200 turns and its secondary coil has 40 turns. if the current in the secondary coil is 25 A, the current in the primary coil is

5 A

*the voltage needed to produce a current of 8 A in a resistance of 12 ohms is

96 V

true or false cutting a magnet in half results in one-half having a single north pole and no south pole, and the other half having a single south pole and no north pole

false. each half has both a north pole and a south pole; magnetic poles always come in pairs.

true or false ohm's law applies to metallic and liquid conductors, but not to gaseous conductors

false. ohm's law applies only to metallic conductors and not to gaseous or liquid conductors.

____________________ is the loss of all electrical resistance by certain materials at extremely low temperatures.

superconductivity

*when a rubber rod is stroked with a piece of fur

the rod becomes negatively charged and the fur becomes positively charged

true or false a person suffering from nearsightedness can see distant objects clearly, but cannot focus on nearby objects.

false. a nearsighted person can see nearby objects clearly but has difficulty focusing on distant objects.

true or false hearing the noise of a car horn around the corner of a building is an example of reflection.

false. hearing the noise of a car horn around the corner of a building is an example of diffraction.

true or false sound waves travel faster in air than in liquids or solids.

false. sound waves travel faster in liquids and solids.

true or false the electrons in a metallic conductor carry the current

false. the electrons in a metallic conductor do not carry the current; the moving electrons are the current

true or false the force a magnetic field exerts on an electric current disappears when the current is perpendicular to the magnetic field

false. the force a magnetic field exerts on an electric current is perpendicular to the magnetic field.

true or false rubbing a glass rod with silk creates positive electric charges within the glass rod, giving it an overall positive charge

false. the glass rod, prior to rubbing with silk, was electrically neutral, meaning it had equal amounts of positive and negative charges. rubbing with silk removed some of the rod's negative charges (electrons), giving the rod an overall positive charge

true or false heating or hammering a magnet destroys the magnetic fields of its atoms or molecules

false. the magnetic properties of the magnet's atoms or molecules are not destroyed by heating or hammering the magnet. instead, the atoms and molecules become randomly arranged, which cancels out their collective magnetic effect.

true or false in a transverse wave, the particles of the medium move parallel to the wave direction.

false. the particles move perpendicular to the wave direction in a transverse wave.

true or false the smaller the f-number of a camera lens, the smaller the lens opening

false. the smaller the f-number, the larger the lens opening

define alex muller and george bednorz

first to discover a material superconducting above 23 K

a ____________________ or circuit breaker interrupts a power line whenever an unsafe amount of current passes through it.

fuse

____________________ is the method of removing the charge from an object.

grounding

*a sound wave whose frequency is 50 Hz

has a relatively long wavelength

*superconductors

have no electrical resistance

when electric currents are transmitted, some of the electrical energy is lost as ____________________.

heat

a stationary observer hears the whistle of an approaching train. to the observer, the frequency of the sound produced by the whistle appears to be

higher before the train reaches the observes as after the train passes the observer

in a(n) ____________________, charge can flow only with great difficulty.

insulator

____________________ are atoms or molecules that have lost or gained one or more electrons.

ions

*you are looking at the bottom of a lake 1.2 m deep from a boat. to you the lake seems to be

less than 1.2 m deep