PHY 102 Exam 3 Study Guide Lectures 16 20 How is gravity represented in equations Weight m force due to gravity Force Universal Gravitational Constant Mass of the earth mass of the object distance between the two objects F GMm r2 What is orbital velocity what is escape velocity and how are they related Fg GMm r2 is used to derive vorbital GM r Escape velocity kinetic energy potential energy so it equals 2GM r Remember that orbital velocity square root of GM r and escape velocity is 2GM r because kinetic energy is required to escape into orbit Examples for these concepts What is the gravitational force between a proton and an electron in a Hydrogen atom given the following information mproton 1 673 x 10 27kg me 9 109x10 31kg ro 5 29x10 11m G 6 67x10 11Nm2 kg2 F Gmemp ro2 F 6 67x10 11Nm2 kg2 9 109x10 31kg 1 673x10 27 5 29x10 11 2 What is the orbital velocity of the International Space Station whose altitude is 330 km Take the radius of the Earth to be 6378 1 km The mass of the Earth is 5 97x10 24kg What are key terms regarding Simple Harmonic Oscillation Simple Harmonic Oscillator SHO is anything with a repetitive movement with a restoring force proportional to displacement The period of an SHO is how long it takes to go from one side to the other if it is a pendulum Remember the force has to be equal to the displacement What are key terms regarding waveforms wavelength speed of light time between passage of successive crests number of crest passages per unit time distance from level of crest to level of trough Types of waveforms Longitudinal compressional motion Transverse side to side motion Frequency 1 time of the period F oscillations second Wavelength x frequency speed of the propagation of the wave Examples for these concepts The period of oscillation is 2 7 seconds F 1 t F 1 2 7seconds F 1 2 7 Hertz or Hz What is the appropriate frequency of a 6 563 nm wavelength of light 1 nanometer 1x10 9 m and c 3x108 m s x F speed of light 3 0x108m s What are other properties of waves Polarization when light passes through one lens that only allows one direction of waves i e vertical waves the next lens will be one that only allows the opposite direction i e horizontal waves Oscillation can be up and down side to side or spiral Electrical field vectors can also align and become polarized Diffraction when the slit that a ray passes through approaches the size of the ray of light the light diffracts and disperses One example of this diffraction would be seen in a wave passing through a small opening into a harbor and the dispersal and growth of the wave as it approaches the shore Interference when waves intersect either at the crest or in the middle of the wave The highest amplitude of the wave differs depending on at which point the waves intersect The intensity v distance graph would look very random because waves can interfere at various points Doppler Shift the sound shifts because of the position of the observer This is also observed in space as galaxies appear red because the universe is expanding and the galaxies are all moving farther away How does light interact with its surroundings Large scale light acts as a particle on a large scale It travels in a straight line and creates distinct shadows Small scale light acts as a wave on a small scale It exhibits properties of diffraction and interference causing scientists to propose the idea of photons part particle part wave How does electricity electrostatic work Electrical charges come in and amber being associated with charges and glass being associated with charges These charges are passed by induction not touching and conduction touching The electrons gather in certain areas based on these actions at a distance which also includes applying a repelling or attracting force without touching another object Negative charges These charges occur when electrons are added to an object An electron s charge is 1 6 x 10 19 Positive charges These charges occur when electrons are taken away from an object A proton s charge is 1 6x10 19 Charges are measured in Coulombs What is Coulomb s law and how does it relate to gravitation Coulomb s law is Fe kq1q2 r2 or kQq r2 which parallels the law of gravitational field strength The units of electrical field strength are N c and the strength is shown in electric field lines which show the path that a positive unit test charge would take These field liens appear to exist but have no physical form Examples for these concepts What is the electrical field strength 1 meter away from a 1C positive charge Hint Use both formulas on last slide eliminating one q Fe Eq Fe kQq r2 Eq kQq r2 E kQ r2 9x109 nm2 c2 1C 1m 2 Why does gravity dominate the universe instead of electromagnetism if the forces are so much greater There is no electrical force dominating the earth because the earth is essentially neutral Forces are opposite and equal and cancel out the electrical effect Individual objects are commonly neutral because they contain roughly equal numbers of and charges How do compasses work Marco Polo supposedly used the magnetic compass to point north to tell directions in battle A compass has north and south ends the north end of a compass is the end that points toward the northern magnetic pole Like poles repel and opposite poles attract Magnetic monopoles do NOT exist but should not be confused with electrical monopoles as those do exist What is a field in physics Fields are used to describe action at a distance but do not have a physical presence Types of fields Gravitational The test particle shown is a gram of matter being pulled in the gravitational field These fields are always attractive on a normal scale but may have some repulsive properties on a VERY large scale Electrical Fields The arrows indicate the direction of one single proton Opposites attract in this type of field and likes repel Magnetic Fields The arrows indicate the direction of a motion of a north monopole which DOES NOT EXIST outside of theory When representing a field The concentration of field lines indicate the strength of that field The closer the lines are the more intense the field at that point When the lines point in the same direction this indicates attraction and when the lines point away from each other this indicates repulsion Does the earth have a magnetic field Earth acts as though there is a large bar magnet at its core with its south magnetic pole around 4 degrees from Earth s northern geographic pole The magnetic field