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
