PHYSICS TEST PRACTICE School's out forever, School's out for summer, School's out with fever, School's out completely. --- A. Cooper Some Potentially useful constants: Wavelength of peak sensitivity in human vision = 555nm Coulomb’s Law constant k = 8.9875517873681764*109 N·m2 / C2 Permittivity of free space 0 = 8.85418782*10-12 C2 / N·m2 Permeability of free space 0 = 4*10-7 T·m / A electron charge: e = 1.60217662*10-19 C mass of an electron: me = 9.109383*10-31 kg mass of a proton: mp ≈ 1.6726219*10-27 kg mass of a neutron: mn ≈ 1.6749274*10-27 kg Acceleration due to gravity g = 9.80665 m / s2 Newtons Gravitational constant G = 6.67408 ×10−11 N⋅m2/kg2 Planck’s constant h = 6.626070040*10-34 Js Speed of light in vacuum c = 2.99792458*108 m/s Note that for small angles sin(radians )  tan(radians )  radians The threshold of hearing Io =10-12 W/m2 A sphere=4r2 & A circle=r2 One Year 365.24 days Mechanics Formulas: v f = vi + at  f = i +  t x f = xi + vi t + 12 at 2  f = i + i t + 12  t 2  F = ma  = I PHYSICS TEST PRACTICE 1 1 1 h ' −i = + m= = f i o h o 1) Electromagnetic waves (multiple Choice) Which of these are electromagnetic waves? a. visible light b. TV signals c. cosmic rays d. Radio signals e. Microwaves f. Infrared g. Ultraviolet h. X-Rays i. gamma rays 2) A/C Transformer The input voltage to a transformer is 120V RMS AC to the primary coil of 1000 turns. What are the number of turns in the secondary needed to produce an output voltage of 10V RMS AC? 3) “Charging” the magnetic field of an inductor 60.000m of wire is wound on a cylinder, tight packed and without any overlap, to a diameter of 2.00 cm (rsolenoid=0.0100m). The wire has a radius of rwire = 0.00100m and a total resistance of 0.325 . This inductor initially has no current flowing in it. It is suddenly connected to a DC voltage source at time t=0.000 sec. Vs=2.00Volts. After 2 time constants, the current across the inductor will be…. Hint: first find the inductor currents It=o, It=∞, … 4) D/C Transformer The input voltage to a transformer is 120V DC to the primary coil of 1000 turns. What are the number of turns in the secondary needed to produce an output voltage of 10V DC? Page 3 5) Sound level of fireworks At a fireworks show, a mortar shell explodes 25 m above the ground, momentarily radiating 75 kW of power as sound. The sound radiates from the explosion equally efficiently in all directions. You are on the ground, directly below the explosion. Calculate the sound level produced by the explosion, at your location. 6) Dr Examines Image of a patients tiny mole w/ magnifying lens A doctor (Veterinarian) examines a mole that is 15.3cm away from a magnifying lens, as shown below. The lens has a focal length of 19.7cm. What is its magnification? Hint: Where is the image of the mole? 0.55 T 8 0.1 m V 7) Calculating with Faradays law and magnetic flux A flat circular coil of wire has a radius of 0.18 m and is made of 75 turns of wire. The coil is lying flat on a level surface and is entirely within a uniform magnetic field with a magnitude of 0.55 T, pointing straight into the paper. The magnetic field is then completely removed over a time duration of 0.050 s. Calculate the average magnitude of the induced EMF during this time duration. Page 4 8) Electron accelerated in an E field An electron passes between two charged metal plates that create a 100N/C field in the vertical direction. The initial velocity is purely horizontal at 3.00x106 m/s and the horizontal distance it travels within the uniform field is 0.040m . What is the vertical component of its final velocity? 9) Diffraction A 532nm laser hits a slit at normal incidence and then travels 1.5m to a wall. The slit is 0.001mm wide. What is the angle to the 1st order (m=1) minimum. 10) Aquarium of Fishy Death (TIR) An aquarium contains no living fish, because it is filled with deadly carbon disulfide (CS2), having a refractive index of 1.63. The aquarium is made of some unknown type of glass. A scientist with time on her hands measures the critical angle for total internal reflection for light directed out of the aquarium and finds that angle to be 65.2°. Calculate the refractive index of the unknown glass walls of the Aquarium of Fishy Death. unknown glass 65.2° Top View of Fish Tank carbon disulfide (n = 1.63) Page 5 11) One-way mirror coating for “Slimy Joe’s” used car dealership A window is made of glass that has an index of refraction of 1.75. It is to be coated with a thin film of a material whose index is 1.30. The purpose of the film is to reflect light having a wavelength of 532.0 nm back out into the lobby so he can see you (in the bright light) but you can’t see him (in his dark lair of an office). Calculate the smallest positive thickness for this film. Hint: Be sure to consider the phase difference needed, and any phase difference(s) on reflection. 12) Crabby Aliens attack. An invasion fleet from the Andromeda Galaxy is closing in on Earth, ready to invade us and steal away our entire stock of fiddler crabs for their own unspeakable purposes. Their spaceship is powered by a hydrogen ram scoop which uses hydrogen fusion for power. You, the only physics student left on Earth after the Cannibalistic Humanoid Underground Dwellers (C.H.U.D.) ate everyone else, remember that the emission spectrum of hydrogen has a prominent red line in laboratory of 656.3 nm. You note that this line has shifted in the approaching vessels power source to 555.5 nm (a bilious green). What fraction of the speed of light is their ship approaching at (i.e., calculate v/c ). Assume the motion is slow enough that you do not need to include relativistic effects (which is a good thing since we did not study relativistic effects in this class), and that the hydrogen is traveling at the same velocity as the ship. 13) Rayleigh’s criteria for resolution You are a human soldier in the war against the giant, bright yellow, alien Spodders who have invaded earth and plan to sell our body parts fried up as Col. McTerran nuggetsTM to alien restaurants across the galaxy. You are told not to shoot your laser rifle until you can resolve the black dots of their primary pair of eyes. Spodder primary eyes are spaced 6.5cm apart. The diameter of your pupil in the twilight of the battle is 5.0mm. Assume the light you use to see them with is at the peak wavelength of human visual sensitivity (555nm) as is appropriate for humans. At what distance can you resolve two Spodder eyes (and thereby fire on the menacing foe)? (If you are a giant alien Spodder then I apologize for the discriminatory language. Please don’t serve me for dinner.) Page 6 14) Lab: Ohms law and power in a complex circuit In the figure shown, what is the power dissipated in the 2 ohm resistance in the circuit? 15) Putting charge on a capacitor The capacitor shown in the circuit in the figure is initially uncharged when the switch S is suddenly closed. After 2 time constants, the voltage across the capacitor will be…. Hint: first find the cap voltages Vt=o,V t=∞, … 16) Rayleigh’s criteria for resolution You are reading one of those incredibly factual articles in the “International Inquirer”, and it informs you that super-secret CIA spy cameras aboard super-secret satellites are able to read a letter between Presidents Putin and Trump that is sitting on the President’s desk, next to his pool, on his roof top vacation office just outside Moscow. After giving it some thought, you realize that, in order to do this, the super-secret spy camera would have to be able to resolve ink dots that are only 0.50 mm (or 5.00 × 10-4 m) apart. The article tells you that the secret spy camera is in a low Earth orbit, 135 miles (or 2.17 × 10 5 m) above the Earth’s surface. You are skeptical and decide to do a quick calculation. Assuming the super-secret spy camera is using yellowish-green visible light having a wavelength of 5.55 × 10-7 m, what would the minimum aperture diameter of the super-secret spy camera have to be? Super Secret!!! min 2.17 × 105 m 5.00 × 10-4 m Page 7 
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