PHYSICS: 2012 Spring Final Review
Formulas to know:
Vocabulary:
Conduction – in heat, the transfer of energy from particle to particle when the materials are in direct contact; in electricity, the flow of charge through a conductor
Convection – a means of heat transfer by movement of the heated substance itself, such as by currents in a liquid
Radiation – energy transmitted by electromagnetic waves; the charged particles and energy given off by radioactive atoms such as uranium
compressional wave – a pulse of compressions followed by a rarefaction
longitudinal wave – when particles of a wave move parallel to the direction of a wave instead of at a right angle to the wave; sound waves are this type of wave; requires a medium to travel
transverse wave –when the particles of a wave move at a right angle to the wave, waves in the stretched strings of musical instruments, the electromagnetic waves that make up radio waves, and light are transverse waves, do not require a medium to travel
frequency – the number of waves per unit of time; measured in hertz (Hz)
amplitude – the distance from the midpoint of a wave to the top of the crest; the distance from the midpoint of a wave to the bottom of a trough
wavelength - the distance from the midpoint of a crest to the midpoint of the next crest; the distance from the midpoint of a trough to the midpoint of the next trough; or the distance from one compression to the end of a rarefaction
standing wave – a wave in which parts of the wave remain stationary and the wave appears not to be traveling; the result of interference between an incident wave and a reflected wave
interference – a pattern formed by the overlapping of two waves that arrive in the same place arising from differing origins; constructive is when the waves are in phase and the troughs and crests overlap each other amplifying the resulting wave; destructive is when the waves are out of phase and a trough overlaps a crest canceling or subtracting the waves amplitudes resulting in either no wave or a reduced wave
resonance – a phenomenon that occurs when the frequency of forced vibrations on an object matches the object’s natural frequency resulting in a dramatic increase of amplitude and sometimes destruction of the substance
Doppler Effect – the apparent change in frequency of a wave due to the motion of the source or of the receiver; when the object moves toward the receiver the pitch is higher and tone louder; when the object moves away from the receiver the pitch is lower and tone softer; the change in pitch and tone is due to the changing frequency of the wave due to compression and decompression of the air
law of reflection – the angle of incidence equals the angle of reflection
refraction – the change in direction of a wave as it crosses the boundary between two media in which the wave travels at different speeds
total internal reflection – the 100% reflection of light that strikes a boundary between two media at an angle greater that the critical angle
insulator – a material that is a poor conductor of heat and that delays the transfer of heat; a material that is a poor conductor of electricity
conductor – a material that is a good conductor of heat and that speeds the transfer of heat; a material that is a good conductor of electricity
resistance – the resistance of the flow of electrons in a circuit
Ohm’s Law – voltage is equal to current times resistance or V=IR; I=V/R current and resistance have an inverse relationship whereas voltage and current are directly related
Circuits
The resistance in a wire is affected by what factors?
Thickness, length, and conductivity or material it is made from. The thicker a wire, the more resistance it provides. The longer a wire the more resistance it provides. When using a material that is less conductive, it will resist the flow of electricity more.
Describe the relationship between current, resistance and voltage.
V=IR or I=V/R
Voltage and current are directly related, Voltage and resistance are inversely related.
What happens to the overall resistance in a circuit as more lamps are added in parallel? Why?
Resistance is equal to the sum of the inverse of each resistor, or it will be smaller than the smallest resistor. 1/R=1/R+1/R…
What happens to the overall resistance in a circuit as more lamps are added in series? Why?
Resistance is equal to the sum of each resistor, or it would be larger than any resistor.
R=R+R+R….
Compare a series circuit and a parallel circuit that each contain a 9v battery and 2 light bulbs. What happens to the remaining bulb when one of the bulbs is unscrewed? How does the brightness or dimness of the light from the 2 different types of circuits compare?
Series circuit the current is the same for all bulbs so the bulb would not change. I=I=I
Parallel circuit the current is split between bulbs and the bulb would shine brighter when one is removed because it would get more current. I=V/R
A circuit is made by connecting a 6V battery to three resistors in series, each with a resistance of 4Ω. What is the total current in the circuit?
I=V/R and R in a series=R+R+R
I=6/(4+4+4)I=6/12I=0.5 Amps
What is the total resistance of a 24Ω, a 45Ω and a 12Ω resistor wired in series? If the resistors are connected to a 120V power source, what would be the total current?
R in a series = R+R+RR=24+45+12R=81 Ohms
I = V/RI=120/81I = 1.48 Amps
What is the power rating of a motor if it is plugged into a 120V generator and draws 1.5A of current?
P=VIP=120(1.5)P=180 Watts
Waves: Sound, Light , Mirrors and Lenses
What is the primary different between the different waves of the electromagnetic spectrum, i.e., radio waves, microwaves, infrared waves, light, gamma waves? How is the energy of the wave related to this property?
Frequency. The higher the frequency, the more energy the wave carries. Red is lowest frequency and energy, Blue/Violet is the highest frequency and highest energy. Wavelength is opposite. A large wavelength means a low frequency, and a small wavelength means a high frequency.
What type of image is produced and what is its relative size when light reflects off a plane mirror, concave mirror and converse mirror?
Plane mirror – exactly the same size, height, and relative position.
Concave mirror – smaller and farther away
Convex mirror – larger and closer
What is refraction? How does refraction make a pencil look bent that is submerged into a glass of water?
When a wave that is traveling at an angle changes its speed upon crossing a boundary between two media, it bends. An example of this is light traveling through air reaches the water and the light bends causing an object to look “broken/bent”.
Describe how fiber optics works.
Fiber optics are light tubes that carry information from one place to another. They work using the principal of total internal reflection. This occurs when the angle of incidence is larger than the critical angle. Light shines down the fiber and is reflected the length of the fiber.
Draw a transverse wave and label all of the parts, including the crest, trough, amplitude, wavelength and origin.
Crest
Amplitude – distance from node (resting position) to crest
Trough
Wavelength – distance from crest to crest or trough to trough
How are longitudinal waves different than transverse waves? How are they the same?
Longitudinal waves particle motion is parallel to the wave motion (slinky). It is composed of rarefactions and compressions. All longitudinal waves are mechanical waves.
Transverse waves particle motion is perpendicular to the wave motion(snakey). It is composed of crests and troughs. Transverse waves can be mechanical waves(water) or electromagnetic waves(light and all waves in the em spectrum).
What are the parts of a longitudinal wave?
Compressions (particles squeezed together/high density or high pressure) and Rarefactions (particles spread apart/low density or low pressure). A compression and a rarefaction make up one wavelength.
What is frequency? How could you find the frequency of a wave?
Frequency is number of cycles (waves) per second. Measured in hertz. Can be determined two ways depending on the given information:
Divide number of waves by time in seconds.
Divide wave velocity by wavelength.
How are diffraction and refraction different? How are they the same?
Diffraction is spreading of a wave around an edge or an opening. Does not involve change of medium nor speed.
Refraction is bending of a wave as it changes medium, thus the speed changes.
Both of them alter the wave pattern or direction.
What is the relationship between wavelength and frequency of a wave?
Using the wave formula: v = fλ; if velocity is constant wavelength and frequency are inversely related.
Describe the motion of a particle in the path of a wave as it travels through, including the beginning and ending position of the particle.
A particle will move up and down (perpendicular) to the path of a transverse wave. A particle will side to side (parallel) to the path of a longitudinal wave.
When two waves are heading towards each other, how do you know when constructive interference will occur?
If they are in phase, that is crests overlaps crests and troughs overlaps troughs, constructive interference results
When a wave goes from one medium to another, what quantities change and what stays the same?
Velocity changes due to change in medium, frequency is constant. Wavelength changes
Practice Problems: Be able to answer calculation questions similar to the following:
What is the frequency of an electromagnetic wave that has a wavelength of 0.0075m?
Velocity = Wavelength (frequency)
Electromagnetic waves are light and 3.0x108 is the speed of light.
3.0x108 = .0075 (Frequency)3.0x108/.0075 = FrequencyFrequency = 4.0 x 1010 Hz
What is the speed of an ocean wave that travels 220m in 12s?
V = Distance / TimeV = 220/12V = 18.3 m/s
Based on that speed, what is the frequency of the waves if the wavelength is 18m?
Velocity = Wavelength ( frequency)18.3 = 18(frequency)
Frequency = 18.3/18Frequency = 1.02 Hz
What is the wavelength of a sound wave that has a frequency of 400Hz (the speed of sound in air is approximately 343m/s)?
Velocity = Wavelength (frequency)343 = Wavelength (400)
Wavelength = 343/400Wavelength = .86 m
If light travels at 3.0x108m/s, what is the frequency of a wave of light that has a wavelength of 4.3x10-7m
Velocity = Wavelength (Frequency)3.0x108m/s = 4.3x10-7m (frequency)
Frequency = 3.0x108m/sFrequency = 6.98 X 10 14
4.3x10-7m
Universal Gravitation, Coulomb’s Law, and Electrostatics:
What happens to the electric force between 2 charged particles when the distance between them doubles and the charge of one of the particle doubles as well?
F = k q1(q2)F = 2q(1q)F = 2F = ½ the original force
d22d2 4
One particle has a charge of charge of 2.5 x 10-5 C while another particle has a charge of 4.0 x 10-2 C. How large is the electric force between them if they are separated by a distance of 0.50 m?
F = k [q1(q2)/d2]F = 8.99x109(2.5X10-5(4.0x10-2)/.52
F = 8.99x109[.000001/.25]F = 8.99X109(.000004)
F = 35,960 Coulomb’s
Use Coulomb’s law to calculate the force of two charges 4-C and 6-C 2 meters apart.
F = k [q1(q2)/d2]F = 8.99X109 [4(6)/22]
F = 8.99X109[24/4]F = 8.99X109(6)
F = 5.39 X1010Coulomb’s
How would that force change if you double the distance?
F = m1(m2)F = 1/2 d2 F = ¼
d2
Distance would reduce the force by the inverse squared, or it would be ¼ the original force.
F= ¼(5.39X1010) = 1.35 x 1010 Newtons/Coulomb’s
In the Van de Graaf, or fur and rod, or shoes on the floor demonstrations; how were charges transferred?
Charges were aligned or separated so that all positive charges are on one side of the object and all negative charges are on the opposite side of the object. This alignment of charges creates a potential difference between the object and other objects, and this potential difference is what allows the “shock” to occur.
Like charges __repel______; unlike charges _____attract____.
Electrical force is measured in __Coulombs___.
Heat Transfer
The second story of a house tends to be warmer than the first story. Which heating method causes this?
Convection is the transfer of energy through the movement of a fluid. Air is a gas and acts like a fluid, therefore the air mass circulates when the hot air rises and cold air sinks, causing the second story to be warmer than the first story.
Describe the flow of thermal energy.
Thermal energy always flows from the warmer object to the cooler one because the higher energy particles transfer energy to the lower energy ones as they collide
Describe and give examples of the 3 types of thermal energy transfer.
Radiation—transfer of energy through electromagnetic waves (aka electromagnetic radiation), like the sun heating the earth, a fire heating a room or a space heater warming something because it is red hot
Conduction—transfer of energy through direct contact of particles, like when you heat one end of an object and the other gets hot, or how you burn yourself when you touch a hot pan
Convection—transfer of energy through the movement of fluid, like how water heats during boiling , how the atmosphere heats, creating wind or how a convection oven heats food faster
What is the difference between the temperature and heat?
Temperature is the measure of the average kinetic energy of all the particles in a substance, whereas heat is the amount of energy transferred between two substances because of a difference in their average kinetic energies
What is the difference between the internal thermal energy and specific heat?
Internal thermal energy is the total amount of energy, both kinetic and potential, that a particular object or substance possesses. Specific heat is the amount of energy needed to change the average kinetic energy of particles…or in other words, the specific heat tells you how much that energy added to the existing internal thermal energy will change the temperature of an object
Why do many metals feel colder to the touch than do materials such as fabric and wood?
Metals have a lower specific heat, which means they tend to lose and/or gain heat easier, so it cools your hand (accepts heat transferred from your hand to the metal) much faster than wood or fabric.
Draw a diagram of the heating curve for water. Label areas of temperature change and areas of phase change.
What happens to the thermal energy as a substance goes from solid to liquid? What happens to the temperature when a substance changes phase?
As a substance changes phases, like going from solid to liquid, the thermal energy does not go to increasing the average kinetic energy of particles (making the particles go faster) like it does when not changing phases, so the temperature does not increase. Instead, the energy goes into breaking the bonds between the molecules. This can be seen on a phase change curve (aka a heating curve) in the flat spaces between the diagonal lines, which show that energy is put in, but the temperature isn’t changing because the energy breaks bonds instead.
What is the first law of thermodynamics?
For a thermodynamic process, the net heat supplied to the system equals the net work done by the system. In other words, the amount of heat put in is equal to the work put out…basically that means that heat is just another type of energy transfer like work, and that you can’t create or destroy energy (which is a restatement of the law of conservation of energy)
What is the second law of thermodynamics?
The entropy (the measure of disorder or randomness or chaos) of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium. In other words, all systems tend towards a maximum amount of disorder—for example, left to its natural state, your room tends to get messier, or more disordered and does not organize itself, or a drop of food coloring put into water disperses as far as it can, it doesn’t stay together in one area.
A piece of metal has a temperature of 15°C. A second identical piece of metal is two times as hot (has twice the thermal energy). What is its temperature of the second piece of metal?
Remember, temperature and KE are only proportional when the temperature is in an absolute scale, so it must be converted to Kelvin first.. So:
K = 15 + 273 = 288K twice as hot would be 288 x 2 = 576K In Celsius this is 576 – 273 = 303oC
A 10.5 kg block of carbon absorbs 127,000 J. What will be its final temperature if initially the carbon has a temperature of 20.0 oC?
Q = mC∆T 127000 = 10.5 x 710 x T ∆T = 127000/ (10.5 x 710) = 17oC Tf = 20oC + 17oC = 37oC
How much heat is required to completely melt a 0.45 kg lead cube?
Q = mHf Q = (0.45)(2.04x104) = 9180J We used Hf because the cube is going from solid to liquid (melting)
A 40 g cylinder of a particular metal absorbs 560,000 joules of heat from its surroundings when its temperature changes from 20 oC to 30 oC. Calculate the specific heat capacity of the metal from this data.
Q = mC∆T560000 = (.04)(C)(30-20)560000/(.04x10) = C C = 1,400,000 J/kgoC
How much heat is required to completely convert 500 g ice at -25.0 oC to water at 0 oC?
Two things must occur in order for this to occur; it has to be heated to the melting point, then melted.
Heating up:Q = mC∆TQ = (.5)(2060)(25)Q = 25750J
Melting:Q = mHfQ = (.5)(3.34x105)Q = 167000J
So the total would be:Q = 25750 + 167000 = 192750J
Extra notes from modern physics:
Photoelectric Effect
“The emission of electrons by a substance when illuminated by electromagnetic radiation.”
From the gizmo, it depends on the intensity, or brightness of the light and the wavelength of the light.
The higher the voltage, the more electrons emitted.
The shorter the wavelength (violet or blue), the more electrons emitted.
Dual Nature of Light
The debate over whether light was a particle or a wave raged among scientists for many years.
The modern, or quantum theory of light recognizes that light can act as a particle and a wave.
The photoelectric effect proves that light acts as particles.
Reflection, Refraction, Diffraction, Polarization and Interference of light all prove that light acts as a wave.