On my honor, I have neither given nor received unauthorized aid on this examination.

Transcription

1 Instructor(s): Kumar/Stewart PHYSIS DEPRTMENT PHY 05 Exam 1 September 7, 011 Name (print, last first): Signature: On my honor, I have neither given nor received unauthorized aid on this examination. YOUR TEST NUMER IS THE 5-DIGIT NUMER T THE TOP OF EH PGE. (1) ode your test number on your answer sheet (use lines on the answer sheet for the 5-digit number). ode your name on your answer sheet. DRKEN IRLES OMPLETELY. ode your UFID number on your answer sheet. () Print your name on this sheet and sign it also. (3) Do all scratch work anywhere on this exam that you like. ircle your answers on the test form. t the end of the test, this exam printout is to be turned in. No credit will be given without both answer sheet and printout. () lacken the circle of your intended answer completely, using a # pencil or blue or black ink. Do not make any stray marks or some answers may be counted as incorrect. (5) The answers are rounded off. hoose the closest to exact. There is no penalty for guessing. If you believe that no listed answer is correct, leave the form blank. (6) Hand in the answer sheet separately. Useful onstants: k e = Nm / ɛ 0 = /(Nm ) V=volt N=newton electron charge = electron mass = kg J=joule m=meter milli =10 3 micro =10 6 n= nano =10 9 pico =10 1 =coulomb g = 9.8 m/s 1. Positive charges are arranged at the vertices of an equilateral triangle as shown (all three angles are 60, all three sides are in length. t vertex is 1 of charge, at vertex, 3, at vertex, 1. alculate the total of the oulomb forces on the charge at from the charges at and. What is the ratio of the magnitude of the total force on the charge at from both charges at and in the y-direction to the magnitude of the total force on charge in the (1) 1.0 () 0.7 (3) 0.96 () 0.87 (5) Positive charges are arranged at the vertices of an equilateral triangle as shown (all three angles are 60, all three sides are in length. t vertex is 1 of charge, at vertex, 3, at vertex,. alculate the total of the oulomb forces on the charge at from the charges at and. What is the ratio of the magnitude of the total force on the charge at from both charges at and in the y-direction to the magnitude of the total force on charge in the (1) 0.7 () 1.0 (3) 0.96 () 0.87 (5) Positive charges are arranged at the vertices of an equilateral triangle as shown (all three angles are 60, all three sides are in length. t vertex is 1 of charge, at vertex,, at vertex, 1. alculate the total of the oulomb forces on the charge at from the charges at and. What is the ratio of the magnitude of the total force on the charge at from both charges at and in the y-direction to the magnitude of the total force on charge in the (1) 0.87 () 0.7 (3) 0.96 () 1.0 (5) 1.00

2 . n electron, q = , is accelerated in a uniform electric field of 100 N/. What is the acceleration of the (1) 1.8 () 0.6 (3) 0.9 () 1. (5) n electron, q = , is accelerated in a uniform electric field of 33 N/. What is the acceleration of the (1) 0.6 () 1.8 (3) 0.9 () 1. (5) n electron, q = , is accelerated in a uniform electric field of 50 N/. What is the acceleration of the (1) 0.9 () 0.6 (3) 1.8 () 1. (5) charge of +5 is located at the origin, and a charge of 0 is located at x = m, i.e., m away from the origin on the x-axis. Ignoring infinity, where along the x-axis in units of meters is the oulomb force equal to zero? (1) () +1 (3) 1 () 3 (5) charge of +5 is located at the origin, and a charge of 5 is located at x = m, i.e., m away from the origin on the x-axis. Ignoring infinity, where along the x-axis in units of meters is the oulomb force equal to zero? (1) 1 () +1 (3) () 3 (5) charge of +5 is located at the origin, and a charge of 80 is located at x = m, i.e., m away from the origin on the x-axis. Ignoring infinity, where along the x-axis in units of meters is the oulomb force equal to zero? (1) 0.67 () +1 (3) () 3 (5) uniform electric field, E=100 N/, is directed along the +x direction. If a area plate is placed along the x-axis perpendicular to the electric field (see figure), what is the total flux (E ) in units of Nm /? Dashed lines are E=100 N/ uniform electric field in the +x direction. The thick, solid black line is a area seen edge-on that is perpendicular to the x- axis and to the E field lines. x-axis (1) 100 () 0 (3) 50 () ( 3/) * 100 (5) spherical volume of radius R contains +1 in charge located at r = 0. What is the electric field vector magnitude at the surface of the sphere? (1) (1 )/(πr ɛ o ) () (1 )/(πrɛ 0 ) (3) (1 )/( πrɛ o ) () (1 )/( πr ɛ 0 ) (5) (1 )/ (R ɛ 0 )

3 1. cube of side L sits at the origin as shown. 1 of charge is inside the cube at its center. What is the total electric flux through the surface of the cube? Y (1) 1 /ɛ 0 () (6 L ) * (1 )/ ɛ 0 (3) (6 L ) * cos5 * (1 )/ ɛ 0 () (6 L ) * sin5 * (1 )/ ɛ 0 (5) 0 Z L X 13. n electric car has a battery voltage of 00 V. fter 130 km of driving, the battery needs 10 8 J of electrical energy restored to fully recharge the battery. How many oulombs have to be put into the positive terminal of the car battery (which remains at 00 V during the recharging process) by the battery charger? (units of oulombs) (1) 10 6 () 10 3 (3) 10 () 10 5 (5) The electric potential at the center of the square due to the +1 n (nanooulomb, or 10 9 ), + n, +3 n, and 1 n charges at the corners of the square is 31.8 V. What is the length of the edge of the square, in m? (1) () 3 (3).5 () 1.5 (5) 1? +1 n + n 1 n +3 n 15. See sketch. Points and each have 3q charges, while point D has an unknown charge. Points and are each a distance d from point, while point D is a distance of d away. If the electric field at point is zero, find the charge at point D in terms of q. D (1) 8q () 36q (3) q () 1q (5) 0q 16. Two point charges, each with charge Q, are held a distance r apart. Under these conditions, the force between the two point charges is F. Now 1/ of the charge Q from one of the point charges is taken away and placed on the other point charge, without the distance r being changed. In terms of the original force F, what is the new force between the two point charges? (1) (3/)F () still F (3) (1/)F () (/3)F (5) (3/)F 17. The capacitances of the four capacitors shown are given in terms of a certain quantity. In ratio to, what is the equivalent capacitance between points and D? (First imagine that a battery is connected between those two points; then reduce the circuit to an equivalent capacitance.) (1) 0.85 () 0.1 (3) 13 () 0.63 (5) None of these 6 D 18. In the above problem, now consider a battery connected between points and. What fraction of the charge is stored on the capacitor? Express your answer as a ratio to the charge stored on the capacitor. (1) None of these () 6 (3) 0.5 ().0 (5) 0.73

4 19. In the circuit shown all capacitors are 6.0µF and the power supply is 5 V. The charge (in µ) on the capacitor labeled q is: (1) 1 () 18 (3) 38.5 () 9 (5) None of these + V q 0. Find the energy stored (in Joules) in the system. The values are V = 10V, 1 = F, = F, 3 = 9F, = 1F, and 5 = 3F. V (1) 18 () 171 (3) 13 () 196 (5) 5 1. In the electric circuit shown, capacitors 1- have the same capacitance of.0µf each, and the amount of charge stored in capacitor is 3.0µ. What is the (1) 7 () 8 (3) 3 ().5 (5) None of these. In the electric circuit shown, capacitors 1- have the same capacitance of.0µf each, and the amount of charge stored in capacitor is.0µ. What is the (1) 8 () 7 (3) 3 ().5 (5) None of these 3. In the electric circuit shown, capacitors 1- have the same capacitance of 3.0µF each, and the amount of charge stored in capacitor is.0µ. What is the (1) 3 () 8 (3) 7 ().5 (5) None of these. copper cable with resistivity ρ = Ω-m is designed to carry a current of 00 mps with a power loss of.0 W/m. What is the required radius of this cable (in cm)? (1).08 () 1.0 (3) 0.5 () 1.56 (5) copper cable with resistivity ρ = Ω-m is designed to carry a current of 00 mps with a power loss of.0 W/m. What is the required radius of this cable (in cm)? (1) 1.0 ().08 (3) 0.5 () 1.56 (5) copper cable with resistivity ρ = Ω-m is designed to carry a current of 100 mps with a power loss of.0 W/m. What is the required radius of this cable (in cm)? (1) 0.5 () 1.0 (3).08 () 1.56 (5) 0.66

5 7. 10 pf capacitor is charged to a potential difference of 60 V, and the charging battery is disconnected. The capacitor capacitor drops to 8 V, what is the capacitance of this second capacitor? (1) 35 pf () 0 pf (3) 10 pf () 15 pf (5) none of these pf capacitor is charged to a potential difference of 60 V, and the charging battery is disconnected. The capacitor capacitor drops to 5.5 V, what is the capacitance of this second capacitor? (1) 0 pf () 35 pf (3) 10 pf () 15 pf (5) none of these pf capacitor is charged to a potential difference of 60 V, and the charging battery is disconnected. The capacitor capacitor drops to 56 V, what is the capacitance of this second capacitor? (1) 10 pf () 0 pf (3) 35 pf () 15 pf (5) none of these 30. Suppose the electric company charges 10 cents per kwh. How much does it cost to use a 15 W lamp 8 hours a day for (1) $3.00 () $1.50 (3) $.5 () $1.88 (5) $ Suppose the electric company charges 10 cents per kwh. How much does it cost to use a 15 W lamp 6 hours a day for (1) $.5 () $1.50 (3) $3.00 () $1.88 (5) $ Suppose the electric company charges 10 cents per kwh. How much does it cost to use a 15 W lamp hours a day for (1) $1.50 () $3.00 (3) $.5 () $1.88 (5) $ Two unknown point charges Q 1 and Q are joined by a line. t a point on the line one-fourth of the way from Q 1 to Q the electric field is zero. What is the ratio Q 1 /Q? Q 1 1 E = 0 Q (1) 1 9 () 9 16 (3) 3 () 1 16 (5) 1 3. Two separate capacitors with capacitances 1 = 5F and and = F are charged. oth have the same charge Q. The charged capacitors are then brought in contact with each other, positive plate to positive plate (the total charge stays the same). What is the percent change in the total energy ((U f U i )/U i ) 100? negative sign here indicates that the final total energy is less than the initial total energy. (1) 1.3 () +1.3 (3) () + (5) None of these