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UF PHY 2054 - Exam2_Answers

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77777 77777Instructor(s): Reitze/KumarPHYSICS DEPARTMENTPHY2054 Exam 2 November 8, 2010Name (print, last first): Signature:On my honor, I have neither given nor received unauthorized aid on this examination.YOUR TEST NUMBER IS THE 5-DIGIT NUMBER AT THE TOP OF EACH PAGE.(1) Code your test number on your answer sheet (use lines 76–80 on the answer sheet for the 5-digit number).Code your name on your answer sheet. DARKEN CIRCLES COMPLETELY. Code your UFID number on youranswer sheet.(2) Print your name on this sheet and sign it also.(3) Do all scratch work anywhere on this exam that you like. Circle your answers on the test form. At the end of thetest, this exam printout is to be turned in. No credit will be given without both answer sheet and printout.(4) Blacken the circle of your intended answer completely, using a #2 pencil or blue or black ink. Do notmake any stray marks or some answers may be counted as incorrect.(5) The answers are rounded off. Choose the closest to exact. There is no penalty for guessing. If youbelieve that no listed answer is correct, leave the form blank.(6) Hand in the answer sheet separately.Useful Constants:ke= 8.99 × 109Nm2/C2²0= 8.85 × 10−12C2/(Nm2) V=volt N=newtonµ0= 4π × 10−7Tm/A k0= µ0/(4π) = 10−7Tm/A g = 9.8 m/s2electron charge = −1.6 × 10−19C electron mass = 9.11 × 10−31kg C=coulomb“milli”=10−3“micro”=10−6n=“nano”=10−9“pico”=10−12J=joule m=Meter1. A battery with an internal resistance of 0.5Ω is connected to a 10Ω resistor. If the voltage across the battery (theterminal voltage) is 20 Volts, what is the EMF of the battery (in Volts)?(1) 21 (2) 20 (3) 19 (4) 24 (5) 222. If ∆V = 6 V and if the resistor R in the figure dissipates 12 W of power, whatis R (in Ω)?R∆V(1) 3 (2) 2 (3) 5 (4) 72 (5) 243. For what value of the resistor R will there be no current flowing through the10Ω resistor shown in the figure? (HINT: If there is no current flowing throughthe 10Ω resistor, what is the potential difference between points A and B?(1) 10Ω(2) 5Ω(3) 15Ω(4) 30Ω(5) 4Ω4. A negatively charged particle enters a region of uniform magnetic field which points in the positive x-direction. If itexperiences a magnetic force in the positive y-direction, its velocity must be:(1) in the negative z direction(2) in the positive z direction(3) in the positive x direction(4) in the negative x direction(5) in the positive y direction77777 777775. An electron (charge q = −1.6 × 10−19C) is undergoing uniform circular motion with a radius R = 2 × 10−8m producesa magnetic field at the center of the circle with a magnitude of 0.8 microTesla. What is the speed of the electron (inkm/s)?(1) 20 (2) 10 (3) 40 (4) 5 (5) 5,0006. Two particles are undergoing circular motion in a uniform magnetic field that is perpendicular to their velocities.Particle 1 has a charge of 0.1 C, a mass of 2 grams, and a radius for its circular motion of 0.5 m. Particle 2 has a chargeof 0.2 C, a mass of 4 grams, and a radius for its circular motion of 2 m. If it takes particle 1 one second to make onecomplete revolution, how long (in s) does it take particle 2 to make one complete revolution?(1) 1 (2) 2 (3) 0.5 (4) 4 (5) 87. Two infinitely long parallel wires lie in the xz-plane and are lo cated at x = −d/2and x = d/2 as shown. The left wire (x = −d/2) carries a current I (into thepage), while the right wire (x = d/2) carries a same current I (out of the page).What is the y-component of the magnetic field on the x-axis at x = d? (Notethat k0= µ0/(4π).)PI out x x-axisy-axisI in d(1) 8k0I/(3d) (2) −8k0I/(3d) (3) 8k0I/d (4) −8k0I/d (5) zero8. In the previous problem, what is the y-component of the magnetic field on the x-axis at x = 0?(1) −8k0I/d (2) 8k0I/(3d) (3) −8k0I/(3d) (4) 8k0I/d (5) zero9. Three circular concentric loops of wire, each having 10 turns, are shown in thefigure. The inner loop has a radius of 10 cm, the middle loop has a radius of20 cm, and the outer loop has a radius of 35 cm. The current in the inner loopis I1= 2.0 A and the current in the middle loop is I2= 4 A. Both the innerand middle loop currents are traveling in a counterclockwise direction. Whatis the current I3(magnitude and direction) in the outer loop if the magneticfield at the center is 1.8 × 10−4T directed into the page?III = ?123(1) 24.0 A, clockwise(2) 8.5 A, clockwise(3) 14.0 A, counterclockwise(4) 8.5 A, counterclockwise(5) 32.0 A, clockwise10. Two parallel long wires separated by a distance d carry the same current and repel each other with a force F per unitlength. If both these currents are doubled and the wire separation is increased to 4d, the force per unit length is now:(1) F (2) 4F (3) 2F (4) F/2 (5) F/411. Compute the self inductance in a coil that experiences a 20 V induced EMF when the current is changing at a rate of100 A/s.(1) 200 mH (2) 0.2 mH (3) 50 mH (4) 5.0 H (5) 32 mH77777 7777712. Consider the RL circuit shown in the figure. The switch is closed at time t = 0?A current, Ishort, passes through resistor R1immediately after the switch isclosed (i.e., t ¿ τ) and a current, Ilong, passes through resistor R1a long timeafter the switch is closed (i.e., t À τ). What is the ratio Ilong/Ishort?R1= 1 ΩR2= 3 ΩLε(1) 4 (2) 3 (3) 2 (4) 0.25 (5) 0.513. A conducting bar with mass M = 10 kg can slide with no friction along twoconducting rails separated by distance L = 0.5 m, as shown in the figure. Auniform 5 Tesla magnetic field points into the page, as indicated by crosses.An external force Fapppulls the bar to the right with a constant accelerationa = 2 m/s2. The bar starts from rest at x = 0 at t = 0. What is themagnitude and direction of the induced current in the R = 0.5 Ohm resistorat time t = 2 seconds?(1) 20 Amps counter-clockwise(2) 20 Amps clockwise(3) 10 Amps clockwise(4) 10 Amps counter-clockwise(5) 40 Amps counter-clockwise14. In the previous problem, what is the magnitude of the external force Fapp(in N) at time t = 2 seconds?(1) 70 (2) 50 (3) 20 (4) 30 (5) 4515. The sun has a mass of 1.99 × 1030kg, a radius of 6.96 × 108m, and a radiation power of 3.90 × 1026W. What is theintensity of the electromagnetic radiation (in kW/m2) at the surface of the sun?(1) 6.4 × 104(2) 1,020 (3) 1.6 × 104(4) 6,400 (5) 1.6 × 10516. In general the index of refraction of quartz depends on the wavelength of thelight. Suppose that a ray of light is incident normally of face ab of a quartzprism in the shape of an


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