Phys 4: College Physics Key Name MULTPLE CHOCE 1) 4 How much kinetic energy will an electron need to get from point (at a potential of +0 ) to point B (at a potential of +50 ) in the figure below? 0 a) none 19 18 b) 50 J KE q ( 1.6 = Δ = )( 50 0) = 8 c) 8.0 x -18 J 18 KE = 8 J d) 2.4 x -17 B 50 J e) 1.14 x -27 J 2) 4 a) When resistors (R 1 R 2 ) are in series, the i) current flowing through each is the same. ii) the voltage across each is the same. b) When resistors (R 3 R 4 ) are in parallel, the i) current flowing through each is the same. ii) the voltage across each is the same. c) Capacitors 1 & 2 i) are at the same voltage. ii) have the same charge. d) Capacitors 3 & 4 i) are at the same voltage. ii) have the same charge. E R 1 + R 3 R 2 C 1 C 2 E + R 4 C 3 C 4
Phys 4: College Physics Exam 1 Spring 20 SHORT NSWER 1) 4 There are four graphs shown below. On each graph circle whether the device is ohmic or nonohmic (circle your choice below each graph) ND whether the resistance is increasing, decreasing or staying constant as voltage increases. B C D Non- Non- Non- Non- R is Decreasing R is Constant R is ncreasing R is Decreasing 2) 4 capacitor is connected to a battery. What happens to the following when the distance between the plates is doubled? (circle one choice in each part). 0 a) C, the capacitance (increases, decreases, stays the same). C = E d b) Q, the charge on the capacitor (increases, decreases, stays the same). Q = C c), the voltage on the capacitor (increases, decreases, stays the same). d) E, the electric field in the capacitor (increases, decreases, stays the same). = Ed +4µC C 3.0 cm 6.0 cm B -8µC 3) 4 For charges = +4.0 µc, B = -8.0 µc and C = +3.0 µc shown, a) What are the magnitude and direction of the electric force on C due to? b) What are the magnitude and direction of the electric force on C due to B? c) What are the magnitude and direction of the electric force on C due to and B? a) b) F 9 6 6 ( 8.99 )( 4 )( 3 ) kq q = = = 120 N to the right r 0.03 C E 2 2 C F ( ) 9 6 6 ( 8.99 )( 8 )( 3 ) kq q = = = 60 N to the right r 0.06 C EB 2 2 C ( ) c) F = F + F = 120 + 60 = 180 N to the right Eboth E EB
Phys 4: College Physics Exam 1 Spring 20 PROBLEMS: CHOOSE 3 OF 4. 1) For the charges -8.00 µc at (0.80,0.30) and +5.00 µc at (0, 0) and points at (0, 0.30) and B at (0.40, 0.80). Find a) the potential energy. b) the electric potential at point. c) the electric potential at point B. d) the change in potential energy for a 2 μc charge moved from point to point B. e) the work done by the electric force to move a 2 μc charge from point to point B. 0.8 m Y(m) 0.3 m 5 μc B 0.89 m 0.64 m -8 μc 0.85 m 0.4 m 0.8 m X (m) a) The potential energy is that of the two charges with U 0 as r 9 6 6 kq q ( 8. 99 )( 50. )( 8. 0 ) 5 8 U = = = -0.423 J r 085. 58 ( ) b) The potential at is due to both charges 6 6 kq kq ( 50. ) ( 80. ) 5 8 9 3 = + = ( 899. ) + = 59.9 = 59.9 k r r 5 8 ( 03. ) ( 08. ) c) The potential at B is due to both charges 6 6 kq kq ( 50. ) ( 80. ) 5B 8B 9 3 = + = ( 899. B ) + = -61.9 = -61.9 k r r 5B 8B ( 089. ) ( 064. ) d) The change in potential energy in moving q from to B B B 6 3 3 ( 20 )( ) Δ U = q - q =. -61.9 59.9 = -0.244 J t s negative because is at higher potential so q loses potential energy in the move e) The work done by the field in moving q from to B is positive since the particle loses potential energy (it moves the way the field would move it) W = ΔU = + 0.244 J Efield B
Phys 4: College Physics Exam 1 Spring 20 2) particle of m = 2.0 x -17 kg and Q = +12 µc is moving in the +x direction at v = 5.0 x 7 m/s when it enters a uniform field, E = 6.00 x 4 N/C between two charged plates that are 5.0 cm long. a) Draw an arrow indicating the direction of the E-field between the plates. b) ndicate (with + and -) the charges on the plates c) What is the magnitude of the acceleration of the particle due to the E-field? d) How long does the particle stay between the plates. e) Find the vertical deflection, d, of the particle as it leaves the plates. a) Electric field is down in the picture 5.0 cm b) Top plate is positive. d c) Use Newton s Second Law F = ma 6 4 ( 12 )( 6. 0 ) 17 ( 20. ) F qe 16 m a = = = = 3.6 2 m m s d) Use kinematics x = v t ox x 005. 9 t = = = 1 = 1 ns 7 v 0x 50. e) Use kinematics ( )( ) 2 1 1 36 1 2 2 2 16 9 2 y = a t =. = 1.8 = 1.8 cm oy
Phys 4: College Physics Exam 1 Spring 20 3) For the circuit shown, where E = 20.0, R 1 = R 2 = 12.0 Ω, R 3 = 20.0 Ω and R 4 = 40.0 Ω a) Find the equivalent resistance for the network of resistors. b) Find the voltage across resistor R 3 c) Find the current through resistor R 3 d) Find the power dissipated across resistor R 3. E a) Resolve each parallel pair of resistors: 12 212 ( ) ( 12)( 12) 1 1 1 R + R 1 R R R RR 6 1 2 = + = = = 1 2 1 2 R = 12 6 Ω R 1 R 2 R 3 R 4 1 1 1 R + R 3 4 20+ 40 6 = + = = = R R R RR 80 34 3 4 3 4 ( 20)( 40) R = 13. 3 Ω 34 R 12 Resolve the right side series: R = R + R = 6+ 13. 3 = 19. 3 Ω 1234 12 34 b) oltage across R 3 is that across the R 34 pair. E 20 = R = R = 12 12 ( 13. 3) = 13. 7 12 R 19. 3 1234 c) Current through R 3 13. 7 34 = 3 = = 0.69 R 20 3 E E R 34 R 1234 d) Power dissipated across R 3 P = R = 0.69 2 3 3 3 2 ( ) ( ) 29 0 = 9.50 W
Phys 4: College Physics Exam 1 Spring 20 4) heart defibrillator passes.0 through a patient s torso for 5.00 ms in an attempt to restore normal beating. a) How much charge passed through the patient? b) What power was applied if 500 J of energy was dissipated? b) What voltage was applied? c) What was the path s resistance? a) Use the definition of current q Δt ( )( ) 3 2 = q = Δ t = 5. 0 = 5. 0 = 50.0 mc b) Use the definition of power 5 P = = = 1 = 0 kw 3 c) The voltage is found from the power dissipated P = P 1 5 4 = = = 1 = k d) Use Ohm s law = R U 500 Δ t 5 4 1 R = = = 00 Ω