14 December Physics Final Exam. Class PIN. Please give all your answers in 3 significant figures And remember units!

Transcription

1 14 December 2011 Physics 2220 Final Exam Class PIN Please give all your answers in 3 significant figures And remember units! Closed Book Equation Sheets Permitted (Unmarked) Non-programmed Calculators Permitted c = m s µ 0 = 4π 10 7 T m A e = C t 1 J 2 m e =.511 MeV c 2 = kg hc = 1238eV nm

2 True/False The following questions are all true/false questions. Please Mark [a] on your Scantron sheet for true and [b] for false. 1) True or False? A lens produces a sharply focused, inverted image on a screen. When the lens is removed, the image will be inverted and blurry. 2) True or False? The electric field strength in a region is N/C. The electric flux through a 10 cm 10 cm plane, which makes a 60 degree angle with the electric field, is 25Nm 2 /C. 3) True or False? An electromagnetic wave is traveling in the positive x-direction. The electric field at one instant of time is in the positive z-direction. The magnetic field at this position points in the negative y-direction. 4) True or False? A wave on a string with an angular frequency of 5.0 rad/s and traveling to the left at 3.0 m/s has a wavelength of 0.6 m. 5) True or False? A current carrying wire is pulled away from a conducting loop in the direction shown. As the wire is moving, there is a counter clockwise current around the loop. Multiple Choice The following questions are multiple choice. Please mark the best choice on your Scantron sheet. 6) A guitar string with linear density of 2.0grams/m is stretched between supports 65cm apart. The string is observed to form a standing wave with four antinodes when driven at a frequency of 420Hz. What is the frequency of the 3rd harmonic? (a) 210 Hz (b) 315 Hz (c) 427 Hz (d) 675 Hz 7) Two small spheres each have a mass of 2.5 g and a charge of 40.0 nc. They are placed 3.0 cm apart (center to center). What is the magnitude of the electric force on each sphere? (a) N (b) N (c) N (d) N 8) You plan to construct a 120 pf capacitor. You plan to cut two metal squares and insert spacers between them. The thinnest spacers you have are 0.25 mm thick. What is the area of the square needed? (a) 2.13 cm 2 (c) 21.3 cm 2 (b) 3.39 cm 2 (d) 33.9 cm 2 9) A helium-neon laser (λ = 633 nm) illuminates a diffraction grating. The distance between the m = 1 and m = +1 bright fringes is 32 cm on a screen 2.0 m behind the grating. What is the spacing between the slits of the grating? (a) m (b) m (c) m (d) m 10) You wish to generate a 0.10 T magnetic field near the center of a 10 cm-long solenoid. How many turns are needed if the wire can carry a maximum current of 10 A? (a) 100 turns (b) 200 turns (c) 400 turns (d) 800 turns

3 True/False The following questions are all true/false questions. Please Mark [a] on your Scantron sheet for true and [b] for false. 11) True or False? The quantized energy of both a particle in a 1-dim box and an e orbiting a hydrogen atom is directly proportional to the principle quantum number, n. 12) True or False? The angular momentum of an electron around a hydrogen atom is measured to be L = 6 h. The angular momentum quantum number is l = 2. 13) True or False? The range of the strong nuclear force extends across the diameter of a helium atom. 14) True or False? When a nucleus emits γ radiation its atomic number, A, changes by one. 15) True or False? The wave function of a particle in a box is shown at right. The probability of finding the particle at a and b is different. a b Multiple Choice The following questions are multiple choice. Please mark the best choice on your Scantron sheet. 16) How long will 200 g of 235 U take to decay to only 5 g? (t 1 2 = yrs) (a) yrs (b) yrs (c) yrs (d) yrs 17) How many photons are emitted per second from a 7.6 mw ruby laser, λ = 694 nm. (a) photons (b) photons (c) photons (d) photons 18) Which electron configuration below is that of a K, (Z = 19) atom in its ground state? (a) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 (c) 1s 2 2s 2 2p 6 3s 1 3p 6 4s 2 (b) 1s 2 2s 2 2p 6 3s 2 3p 6 3d 1 (d) 1s 2 2s 2 2p 6 3s 2 3p 5 3d 1 19) What is the smallest wavelength in the emission spectrum of the atom with the adjacent energy level diagram? (a) 97.6 nm (b) 206 nm (c) 496 nm (d) 871 nm n=3 n=2 2.5eV n=1 6eV 20) What is the penetration distance of an electron in a finite potential well if the electrons energy is 0.05 ev less than the height of the barrier? (a) 0.87 nm (b) 3.86 nm (c) 39.0 nm (d) 173 nm

4 21) A ball is attached to a wire that goes over a frictionless pulley as shown. The linear mass density of the wire is 2.10 grams/m. The distance from the wall to the pulley is 4.32 m. A transverse wave traveling on the wire is described by y = (3.1nm) sin[(3.5 rad rad m )x (650 s )t]. (a) What are the angular frequency, amplitude, and wavenumber of the wave? (b) What are the frequency, wavelength, and velocity of the wave? (c) Assuming the ball does not move, what is the mass of the ball? 22) What are the strength and direction of the electric field at the position indicated by the dot in the figure? Specify the direction as an angle above or below the horizontal. 23) A rectangular 10 loop copper wire coil lies in the x-y plane. The length and width of the coil are 23.5 cm and 15.6 cm respectively. A magnetic field described by B = (.336T ) + (.02T/s) t is tilted 15 from the z-axis. (a) What is the magnetic flux through the coil at 2 sec? (b) Calculate the induced emf in the coil. (c) If the coil has a resistance of ohms per loop, calculate the current flowing in the coil.

5 24) Use the graph below of the wave function squared of a quantum system to answer the following questions. (a) What is the probability, in terms of A, of finding a Ψ 2 particle between x = 1 nm and x = 0 nm? 2A A (b) What is the probability, in terms of A, of finding a particle between x = 2 nm and x = 6 nm? -4-2 A/ x(nm) (c) What is the value of A? (Don t forget units) 25) Assume that an electron orbiting a hydrogen atom has an angular momentum quantum number of l = 3. (a) What would be the magnitude of the angular momentum of this electron? (b) What is the lowest value of L z that this electron can have? (c) What is the angle between the angular momentum vector and the Z axis for l = 3 and m = 1? 26) What is the binding energy in MeV, per nucleon, of 43 Ca? (Z=20 for Ca) Constituent Mass (u) n H Ca