Science Praxis: Waves
Which of the following is NOT a necessary part of a conducting circuit if current is to flow safely in the circuit? A a switch B a closed conducting path C a voltage source D resistance
A. A switch allows someone to turn the circuit on and off, but current will flow and the circuit will operate properly without a switch.
Sound waves and seismic waves are alike because they: A both have to travel through a medium. B can only travel through air. C both travel with the same wavelength. D both travel the same speed.
A. Both sound and seismic waves are mechanical waves and travel only through a medium.
As the Pacific Plate and the North American Plate bump past one another, energy is built and stored as potential energy. When that energy is released, what event is most likely to occur? A an earthquake B mountain formation C trench formation D volcanic eruption
A. Energy stored as the result of a plate bumping into another is released as an earthquake.
Gina said "sound waves only travel through a medium." Fernando disagrees, saying "no, sound can travel through a vacuum like the vacuum of space." With whom do you agree, and why? A Gina, because sound is a series of high and low pressure regions and pressure only exists in a medium. B Fernando, because sounds can be heard during space battles in science fiction movies. C Gina, because sound is made from millions of molecules bumping into each other. D Fernando, because all waves can travel through space as well as through a medium.
A. Gina is correct. Sound is a series of high and low pressure regions. Pressure has no meaning when no particles are present. When alternating high and low pressure regions reach our ears, our eardrums vibrate and send signals through our nerves to our brains.
How do the loudness and the intensity of a sound change when the amplitude of the sound wave increases? A The loudness and the intensity both increase. B The loudness and the intensity both decrease. C The loudness increases but the intensity decreases. D The loudness decreases but the intensity increases.
A. The amplitude, loudness, and intensity of a sound wave all increase together. The amplitude is related to the amount of energy that produces the sound wave. The intensity is related to the amount of energy delivered by a sound wave. The loudness is the human perception of the intensity.
Which of the following characteristics of a sound wave is most related to the frequency of the wave? A pitch B intensity C loudness D amplitude
A. The frequency of a sound wave is directly related to pitch. The higher the frequency, or number of waves that pass a given point in one second, the higher the pitch.
An ambulance sounds its siren as it moves rapidly at constant speed away from an observer. Which of the following describes effect of the Doppler shift on the sound heard by the observer? A The sound is lower in pitch than its normal pitch. B The sound is louder than its normal volume. C The sound is higher in pitch than its normal pitch. D The sound is quieter than its normal volum
A. The wavelength of the sound increases relative to an observer when an object moves away from the observer, therefore the frequency of the sound decreases and the observer hears a sound of lower pitch than normal.
Which of the following devices operates mainly because of an electromagnet? A a night light B an audio speaker C a baseball pitching machine D an airplane
B. Audio speakers are made from a coil of wire that is free to move inside the poles of a permanent magnet. An audio signal causes the current to switch back and forth, and the movement of the coil pushes air molecules back and forth, making sound.
All objects in the universe are governed by four universal forces. Which force causes positively and negatively charged particles to interact with one another? A the generated electrical force B the electromagnetic force C the strong electrical force D the electrogravitational forc
B. Electrically charged particles (either positive or negative) will naturally interact with one another due to the electromagnetic force.
Which of the following is the best example of refraction of a light wave? A markings on flowers only being visible while subjected to ultraviolet light B light coming to a focus through a lens C clear ocean water D ink that can only be seen using black lights
B. Light refracts, or bends, when it strikes the boundary between air and a lens. The lens is shaped to bring the light to a focus.
Which of the following categories of electromagnetic waves have the lowest frequencies? A visible light B microwaves C ultraviolet D X-rays
B. Microwaves have the lowest energy and therefore the lowest frequency.
Marah watches a hot air balloon floating in the sky. Suddenly the balloon starts moving toward the east. Which of the following would be the best explanation for why the balloon started moving? A The balloon started moving because its mass equalized the amount of force being applied to it. B The balloon started moving because of a sudden change in gravity. C The balloon started moving due to an unbalanced force acting on it. D The balloon started moving because it had equal and opposite forces acting on it.
C. An object changes its state of motion when an unbalanced force acts on it. An unbalanced force, or net force, occurs when the forces acting the object do not cancel each other. For example, if a pen moves when you push it across a desk, then the force you apply is greater than the resisting force of friction and an unbalanced force acts on the pen. However, if the pen keeps moving at constant speed (no additional change in motion), then your applied force and the force of friction are equal and opposite, so they cancel each other. At that time, no unbalanced forces act on the pen.
Karol placed a small cardboard box of books on a metal rolling cart. On her way to the bookshelf, her dog Nixie ran out in front of the cart, causing Karol to stop suddenly. Although the cart stopped suddenly, the box stayed in place on the cart. What force kept the box of books on the cart when she stopped? A magnetism B air pressure C friction D buoyancy
C. Friction is a force that depends upon an object's mass and how hard the force of gravity pulls two surfaces together. The friction between the box and the cart kept the box in place.
Which of the following statements about sound is true? A Sound travels the same speed in water and in air. B Nothing can move faster than the speed of sound. C Sound is a longitudinal wave. D Sound is a transverse wave.
C. Sound is a disturbance carried by a vibrating medium, therefore it is a wave. Sound waves cause the medium to vibrate along the same axis as the sound moves, therefore it is longitudinal.
Which of the following describes the speed of a wave? A How fast a wave vibrates. B How fast one point on a wave moves up and down. C How fast a wave crest moves from one place to another. D How much time goes by between wave crests.
C. Wave speed is the rate at which wave energy travels from one place to another, and could be described as how fast a wave crest moves across a distance.
..... (or schematics) are drawings that use symbols to show how components should be connected in a circuit. In the circuit diagram below, conducting wires connect the battery to a switch and two light bulbs. The same circuit is shown in picture form below the circuit diagram, but a picture is harder to draw and usually does not appear with a circuit diagram. Notice that when the switch is open, the circuit loop is not complete, and no current will flow. When the switch is closed, current can flow through the wires and through the light bulbs, from one battery terminal to the other.
Circuit diagrams
........ lenses, also called diverging lenses, are thinner in the center and thicker on the edges. They cause light rays to diverge, or spread apart, and produce virtual images. The viewfinder of a camera is usually a concave lens.
Concave
..... lenses, also called converging lenses, are thicker in the center and thinner on the edges and bring light from one side of the lens to a focus on the other side of the lens.
Convex
One likely medium for a sound wave is: A empty space. B amplitude. C frequency. D air.
D. A medium is the material that vibrates as a wave passes through. All mechanical waves require a medium. Sound is often carried by air. Other media for sound include water and other liquids and solids.
What device is used to measure the magnitude of an Earthquake? A Richter scale B seismogram C focus locator D seismometer
D. A seismometer measures the amplitude of seismic waves and determines the magnitude of an Earthquake.
The burner on a stove glows red. A fire can be orange, yellow, or red after it dies into embers. The sun glows white, a combination of all colors. Some of the hottest stars glow with a blue light. The frequency of light emitted from a glowing object is directly proportional to the temperature of the object. Of those listed, which color of light has the highest frequency? A yellow B orange C red D blue
D. Blue light has the highest frequency. The hottest stars glow with a blue light.
Ms. Sanborn wants to make a magnet with only a north pole and another magnet with only a south pole. She only has normal rectangular magnets with north poles on one of the long ends and south poles on the other long end. What should she do? A Cut a magnet in half through the centerline between the north and south poles. B Cut a magnet in half lengthwise, from the middle of the north pole to the middle of the south pole. C Place two magnets together, matching a north pole with a south pole on each end. D None of these efforts will produce magnets with only a north pole or with only a south pole.
D. No one has ever formed or seen a monopole (a magnet with a single pole). Ms. Sanborn will have to discard her idea.
Of the choices listed, which is the best analogy for resistance in a circuit? A a tunnel through which wind can blow B the height difference between the top and bottom of a hill C parts moving through an assembly line on a conveyor belt D security screening at the airport
D. Resistance can be modeled as security screening at the airport, which reduces the number of people that get through the airport. Resistance in a circuit reduces the current, which is flow of charge.
A single transverse mechanical wave travels from left to right. In what directions do the particles in the medium vibrate? A counterclockwise spirals B clockwise spirals C left and right D up and down
D. The particles in the medium that carries a transverse wave vibrate perpendicular to the direction the wave travels.
Which of the following could be the measure of the period of a wave? A 2 miles per hour B 2 centimeters C 2 inches D 2 seconds
D. The period of a wave is the time to complete one wave cycle, and is measured in units of time.
Of the choices listed, which is the best analogy for voltage in a circuit? A security screening at the airport B parts moving through an assembly line on a conveyor belt C a tunnel through which wind can blow D the height difference between the top and bottom of a hill
D. Voltage is related to the potential energy of the charges in a circuit. For example, charges at one terminal of a disconnected battery have the "potential" to make current flow as soon as the battery is connected.
The ....... is associated with sound waves. It occurs because sound waves have a constant speed in a given medium.
Doppler effect
....... occur at convergent and transform boundaries where the plates are rubbing against one another, or along ....., which are cracks in the Earth's crust.
Earthquakes faults
....... exist because electric charges push and pull on each other and because magnetic poles form when charges move. The electromagnetic force is one of the four universal forces and has an infinite range. Because like charges repel, and opposite charges attract, the electromagnetic force can both push and pull. It is a very strong force. The electromagnetic force is 1036 (a 1 followed by 36 zeros) times stronger than the force of gravity on Earth's surface.
Electromagnetic forces
............ are emitted by everything with a temperature above absolute zero. The frequency of the emitted electromagnetic waves is greater for glowing objects with higher temperatures.
Electromagnetic waves
......... in excited atoms are another source of visible light.
Electron transitions
..... is a form of electromagnetic radiation. Light does not behave like anything in our everyday world.
Light
Similar, or "like", charges repel. .... charges repel positive charge and ...... charges repel negative charges. Opposite charges attract one another, negative to positive. Sodium chloride, or table salt, forms because positive sodium ions attract and stick to negative chlorine ions. Static cling occurs when the electrons from one material rub off one material and onto the other material. The two materials are oppositely charged and "cling" together. Lightning occurs when the negative charges in clouds are attracted to positive charges on the ground.
Positive negative
Wavelengths: .... is long. .... is short. Frequency: .... is short. .... is long.
Red Violet Red Violet
Sunlight is made of the full spectrum of visible colors, but looks white when the colors of the rainbow are combined. .... bends different colors by different amounts, because colors do .... travel at the same speeds in all materials. The colors in white light each bend at a unique angle at each surface of a prism, so a prism separates the colors of white light.
Refraction not
... is added to a circuit to control the current. Electrical components, such as resistors, light bulbs, and electric motors, provide resistance in a circuit. In some ways, resistance in a circuit can be compared to a dam on a river. The dam partially blocks the flow of water, allowing engineers to control the amount of water that flows from the dam. In a similar manner, resistors control the amount of current flowing from the voltage source. Resistance is measured in ohms (Ω).
Resistance
...... occurs when the frequency of a forced vibration matches the object's natural frequency. The amplitude of the vibration increases during resonance, because the forcing matches the object's vibration rate. A type of resonance occurs when pumping a swing at just the right rhythm. When the frequency of the pumping action matches the natural frequency of the swing system, the amplitude of the swinging motion increases. If the swing is pumped with a different rhythm, the amplitude of the swinging motion dies out.
Resonance
The seismometer indicates the strength of an earthquake on a scale of one to ten called the .......... Each whole number on the scale indicates a tenfold increase in the earthquake's magnitude.
Richter scale
....... waves need a medium, or a material that carries the wave. The medium can be a solid, liquid, or gas. Sound will not travel in the vacuum of space where there is very little matter. However, light waves can travel through space
Sound
...... waves are longitudinal ........, meaning the wave energy creates areas of high and low pressure, or high and low density. In contrast, light waves are transverse waves.
Sound compression waves
........ occurs when a light beam in glass strikes the boundary between the glass and air at an angle greater than the critical angle of glass, which is 41°, and is measured from the normal. In total internal reflection, all of the light reflects from the inside surface of the glass and none passes through the surface. This makes a prism the perfect reflector. The same principle is used to transmit light through a fiber optics cable.
Total internal reflection
......., the light humans see, is one small portion of the electromagnetic spectrum of radiation. Nuclear reactions in the core of the sun make the sun very hot. It radiates a broad spectrum of electromagnetic waves, including visible light. The filament of a standard lightbulb is much cooler than the sun, but is still hot enough to give off visible light.
Visible light
...... is a difference in potential measured from one point to another.
Voltage
Surfaces appear colored because they ..... certain frequencies (colors) and reflect others. For example, a red wagon looks red because the wagon's paint absorbs blue, green, yellow and most of the other light frequencies, but reflects red. A white kitten reflects nearly all colors, so it looks white (a combination of all the colors of the rainbow). A plant leaf absorbs most of the light that strikes it, reflecting only a portion of green that it can't use for photosynthesis.
absorb
The ...... is the maximum distance particles of the medium move away from their normal (non-vibrating) positions.
amplitude
The ....... of a wave describes how far the medium moves in each direction as it vibrates from its normal, non-vibrating position. In other words, the amplitude of a transverse wave is the distance from the center of the wave (between a crest and a trough) to a crest. A common misconception is to think the amplitude is the total distance of the vibration, from trough to crest, but the amplitude is actually half of that distance. Amplitude is measured in distance units, and is proportional to the amount of energy in the wave: the more energy, the greater the amplitude.
amplitude
Opposite poles (north and south) ...... each other and similar poles (south and south, or north and north) repel. A compass needle is a tiny magnet; the earth is a great big magnet. The north pole of a compass needle points toward the earth's north geographic pole.
attract
Police radar guns and Doppler weather both rely on the Doppler effect. The same effect occurs with light waves, however, when a glowing object moves toward an observer we call it a blueshift, and when the glowing object moves away from an observer we call it a redshift. This is because the observed frequency shifts toward the .... end of the spectrum (shorter wavelengths, higher frequencies) when the object and observer approach each other, and toward the .... end of the spectrum (longer wavelengths, lower frequencies) when they move away from each other.
blue red
Electricity and magnetism are possible because matter is composed of atoms made from particles with both positive and negative ..... The positive protons are inside the nucleus and cannot escape. The negative electrons orbit around the outside of the nucleus of the atom and can escape.
charges
A ....... mirror curves inward (away from you in the center) and produces a real, enlarged image if the object is farther than one focal length from the mirror. A concave mirror produces a virtual image when the object is within one focal length from the mirror. Makeup mirrors are concave mirrors.
concave
A .......... curves outward (toward you in the center) and produces a smaller, virtual image. Side-view mirrors on cars are convex mirrors and in the U.S. carry the message "Objects in mirror are closer than they appear". Since the image is reduced, cars in the side mirror appear to be farther away.
convex mirror
A transverse wave can look like a series of hills and valleys. The peaks of the hills are called ......, and the lowest points of the valleys are called ........ Electromagnetic waves are transverse waves.
crests troughs
The rate at which charge flows through a circuit is called the ...., which is measured in amps (A). When many charges are flowing through a circuit each second, the current is high.
current
Light reflecting from rougher surfaces is ....... The bumps in a surface, such as a textured wall, scatter the light rays in many directions and the image is lost.
diffuse
Notice the reflected rays ...., or spread apart, as they approach the eye and do not come to a focus.
diverge
Earth Quake As the plates try to move past each other, friction causes parts of the plates to stick together and start to bend. As the plates continue to move, it causes ........ to build up in the rock around the points of friction. Eventually, the elastic energy overcomes the friction and the plates break free from one another and release all the stored energy as an earthquake.
elastic energy
Waves can be ........, such as radio waves and light, or ......., such as sound and vibrations on a string. Electromagnetic waves are vibrations of electric and magnetic fields.
electromagnetic mechanical
Visible light, the light we see everyday, is part of the ....... which includes the entire range of frequencies of electromagnetic waves.
electromagnetic spectrum,
The place on the surface directly above the earthquake is called the ......, while the actual center of activity deep in the Earth is called the ......
epicenter focus
Electrical energy is absorbed by electrons in the atoms of LED lights, neon lights, and compact fluorescents. The energetic electrons are called ............ The bulbs glow with visible light when the electrons give up their energy and return to their normal state. The light carries away some of the excited electrons' energy.
excited electrons
A ... occurs when something is made to vibrate by an external force. Violins, cellos, and pianos each have a sounding board that is forced to vibrate when a string is plucked or bowed.
forced vibration
The ...... of a wave is the number of full cycles that happen each second. A high frequency wave has a short period since it vibrates very rapidly, and a low frequency wave has a long period since it vibrates more slowly.
frequency
The ......... of sound, or the number of wave cycles that pass in a specific length of time, is related to the ......., or how high or low the notes sound. The unit for frequency is the hertz (Hz), which is cycles per second. For example, a cello's lowest note, the C string, has a frequency of 261.6 Hz, and a violin's highest open string, the E string, has a frequency of 659.3 Hz. Humans can generally hear sounds between 20 and 20,000 Hz.
frequency pitch
The amount of energy carried by light depends on the frequency of the light and the amplitude of the light. The higher the frequency for a given amplitude, the more energy the light carries. Conversely, for a given frequency, the ...... amplitude light carries more energy. Energy carried by light to our eyes triggers electrical changes in our retinas, which sends a signal to our brains, enabling us to see. Light absorbed by plants is the energy source for photosynthesis.
higher
The ...... is related to the amount of energy transported by the wave and is measured in decibels (dB).
intensity
Electrons can be added to or removed from certain atoms, giving the atom a net positive or negative charge. For example, one electron in sodium is loosely bound to the atom. The electron is easily removed, giving the sodium atom a positive charge. Each chlorine atom tends to attract an extra electron, giving the chlorine atom a negative charge. A charged atom is called an ....
ion
There, they obey the ....... as they strike the mirror's surface, traveling away from the mirror at the same angle from the normal as the incoming ray.
law of reflection
In a ......... wave, the direction of vibration is parallel to the direction the energy travels. Sound waves are longitudinal waves. For example, when the energy in a sound wave travels across a long room, the air particles vibrate in place along the length of the room. The amplitude of a longitudinal wave is the maximum distance a single particle of the medium moves, in one direction, from its normal (non-vibrating) position.
longitudinal
In a ...... wave, the vibration is along with the motion. In a ....... wave, it's perpendicular.
longitudinal transverse
The ........ of a sound depends on human perception of the intensity.
loudness
The area of magnetic influence that surrounds a magnet is called its ....... A magnetic field can be "seen" using iron shavings spread around the magnet, as seen here.
magnetic field
The ......... is the material that carries a mechanical wave. The .... for a sound wave can be air or water or another material. The medium for a wave on a string is the string. Electromagnetic waves are the only waves that can travel without a medium.
medium
All rigid objects have a ....., the frequency at which they naturally vibrate when struck. When you strike a bell or a tuning fork, the frequency of the sound you hear is the natural frequency of that object, and depends upon the object's shape and material. Large bells and big tuning forks vibrate at lower frequencies than smaller bells and smaller tuning forks, and the sound made by a dropped metal spoon has a different pitch than the sound made by a dropped metal wrench.
natural frequency
A ...... material has an equal number of positive and negative charges. Neutral materials do not react to other neutral charges. However, neutral materials DO attract all charged objects, whether positive or negative.
neutral
Angles in optics are measured from the ........, which is a line perpendicular to the surface.
normal line
The ..... is the time it takes to complete one full wave cycle and is measured in seconds. For example, the time between the top of one wave passing a pier post and the next wave top passing the pier post would be one period.
period
A light beam is both a series of particles, called ......, and a ....... wave.
photons transverse
When you look at yourself in a flat mirror, also called a ....., you see the reflected light that traveled from your body, to the mirror, and back to your eye.
plane mirror
Magnets have two ....., a north pole and a south pole. Unlike electric charges, magnetic poles always come in north-south pairs and are never found alone. A common misconception is that a magnet can be broken into one north and one south magnet. However, it would just become two smaller magnets, each with one north and one south pole. Another misconception is that the north and south poles of a magnet are positive and negative electrical charges.
poles
Convex lenses often produce a .......; however, if the object is close to the lens, the image is virtual. Magnifying glasses, telescope lenses, and microscope lenses are convex.
real image
Light ..... from, or bounces off, surfaces in different ways, depending on the smoothness and the color of the surface.
reflects
Light changes speed and direction when moving at an angle from one material to another; this is known as ...... Refraction makes a pencil sticking out of a beaker of water look bent at the surface of the water. A lens bends light when the light enters the lens and again as it leaves the lens. Lenses are used to bring light to a focus. Optical systems such as a camera, microscope, and the human eye all have lenses and use the methods of refraction and reflection to record and project a visual images.
refraction
Earthquakes are measured by a ........ The seismometer measures the amplitude of the ........ made by the earthquake.
seismometer seismic waves
Safety precaution: current keeps increasing in a circuit unless something gets in its way or the voltage runs out. Runaway current occurs when a conducting wire is connected directly across the two battery terminals. This is called a ....... A short circuit can be dangerous because the system can get very hot.
short circuit
The circuit diagram shown has a battery, two lamps, a switch and several conducting wires, however when the switch is closed, the lamps will not light and the battery will get hot. There is something wrong with the circuit. What is this kind of circuit called?
short circuit This is a short circuit. A conducting wire connects directly across the battery. A conducting wire has no resistance to the flow of current, so all of the current will flow through the wire and none will flow through the lamps. A short circuit can be dangerous as the battery will try to supply an infinite amount of current and the system could get very hot.
Different frequencies of light appear to humans as different colors. Violet light is on one end of the visible light spectrum. Violet has the ..... wavelength and the highest frequency of visible light. Red is on the other end of the spectrum. Red has the ...... wavelength and the lowest frequency. In between are the rest of the colors of the rainbow.
shortest longest
Light reflecting from a mirror is .......; all the light rays stay in order and the reflection looks like the image that produced it.
specular
Sound waves travel away from the source in all .... dimensions. If the source moves after emitting a sound, the source will approach the already moving wave fronts in one direction and move further from these wave fronts in the other direction.
three
A sound of 0 dB is called the ............and is the softest sound a human can hear.
threshold of hearing
A sound at 120 dB is generally defined as the "....................."
threshold of pain
The period and the wavelength may look the same on a drawing of a wave, but remember, the period is a ..... and the wavelength is a ...... They are not the same.
time distance
Light undergoes ........ only when it originates from a wide angle in the more optically dense medium (glass or water for a boundary with air).
total internal reflection
In a .........., the direction of the vibration is perpendicular to the direction the energy travels, that is, the vibration is up and down or side to side when the wave travels forward. For example, shaking one end of a jump rope up and down may produce a transverse wave. The rope itself vibrates up and down, but the wave energy travels up and down the length of the jump rope.
transverse wave
In order to determine an epicenter of an earthquake, three seismometers spread out over the Earth must be used to ...... the origin.
triangulate
Waves can .... in two different ways: transverse and longitudinal.
vibrate
The image you see appears to come from behind the mirror and is therefore a ..........
virtual image
A ...... is a disturbance that moves through space and time. Waves carry energy from one place to another, but waves do not carry matter from one place to another. For example, when a sound wave travels across a long room, the air particles do not move across the room; they vibrate in place. You can see this principle in action by watching a stick in the ocean. The stick moves up and down with the waves, but unless the something else (wind or currents) pushes it, the stick does not actually go anywhere.
wave
The ........ tells how fast the wave energy moves from one place to another, and is just like any other speed. The speed of all electromagnetic waves in a vacuum is the same as the speed of light. Mechanical waves travel much more slowly, and at many different speeds.
wave speed
........ = wavelength x frequency ........ = 1 / frequency
wave speed wave period
The ....... is the length of one complete wave cycle and is measured in distance units. ...... can be measured as the distance from the top of one wave crest to the top of the next wave crest. For example, the distance between two tops of a tsunami wave would be the wavelength.
wavelength
