Conversions 1km hr 277777m s Symbol Prefix tera giga mega kilo hecto deca base deci centi milli micro nano pico T G M k h da d c m n p 10 x 12 9 6 3 2 1 0 1 2 3 6 9 12 EXAM 1 Constants K dielectric current 8 99E9 1 if in the air time constant RC Electrostatics Electric Fields Positive In Negative Out Magnitude Ef KQ R2 N C or V m Electrostatic Force FE kQ1Q2 R2 Gravitational Force FG GM1M2 Definition of a Coulomb C A s Potential at point r away from Q V kQ r Electric Potential Energy EPE q0V Direct Currents DC Definition of Current I Q t Definition of Ampere A C s Reaction between current and drift velocity I enAvd n of electrons Ohm s Law V IReq Resistivity R L A or R A L Temperature Dependence of resistivity t 1 T or Rt R 1 T Power Dissipated in a resistor P I2R V2 R Resistors in series Req R1 R2 R3 Resistors in parallel 1 Req 1 R1 1 R2 1 R3 Voltage on a load due to a battery with internal resistance rb IR V Irb W q V potential difference change in volts Capacitors Definition of a capacitance C Q V Unit of capacitance Farad 1Coluomb per volt Capacitance of parallel plates C A 4 kd or C 0AdK d Capacitor with dielectric Ck KC0 Electric Potential Energy stored in a capacitor U Q2 2C CV2 2 QV 2 Capacitor discharging through a resistor Q t Q0e t RC Q I t Q C v I t C V Capacitance in series 1 Ceq 1 C1 1 C2 1 C3 Capacitance in parallel Ceq C1 C2 C3 Lon Capa While wearing rubber soled shoes you rub a helium balloon on your sweater The balloon becomes negative charged now released the balloon When the balloon is at the ceiling you are Some electric fluid flowed from the fur to the amber F fur F amber T fur F Electrons were transferred from the amber to the Electrons were transferred from the fur to the Some electric fluid flowed from the amber to the Amber is rubbed with cat s fur The amber is then negatively charged In other words Some electric fluid flowed from the fur to the amber F Electrons were transferred from the amber to the fur F Electrons were transferred from the fur to the amber F Some electric fluid flowed from the amber to the fur F True or False Coulomb s law states that the force between static charges Q1 and Q2 Click on the arrow which best represents the force on the lower pink charged sphere Is KQ1Q2 r2 where K is a universal constant T Is a force of attraction F Is KQ1Q2 r where K is a universal constant F Is proportional to 1 r F Is proportional to the total charge Q1 Q2 F Bottom arrow A balloon is rubbed with a wool glove The two items attract on another with a force of strength 1 5 N when they are 1cm apart If they have equal but opposite charges what is the magnitude of the charge F k q2 r2 1 5 8 99E9 q2 012 1 29E 7 convert 1cm 01m How many electrons were transferred Total Charge pt 1 charge of electron 1 29E 7 1 6E 19 8 06E11 It is known that the electric force of repulsion between two electrons is much stronger than the gravitational attraction For two electrons at a distance d apart calculate the ratio of the size of the electrostatic repulsion to that of the gravitational attraction Data given k 8 99x109 e 1 6x10 19 G 6 67x10 11 me 9 11x10 31 kq1q2 r2 Gme1me2 r2 8 99E9 1 6E 19 2 6 67E 11 9 11E 31 2 4 16E42 Calculate the magnitude of the force between a gold nucleus and an electron on an orbit with radius 1 19x10 12m around the nucleus The gold nucleus has a charge of 79e F kq1q2 r2 F 8 99E9 1 6E 19 79 1 6E 19 1 9E 12 2 01285N A positive point charge q is placed at point p to the right of two charges A and B The net force on the q charge is found to be zero True or False Reversing the sign of q to q would make the force on it B must have the opposite sign from A and be less in nonzero F magnitude T Either A or B must be positive T A must be negative F B must have the same sign as A and be less in magnitude F Three electric charges are arranged on a straight line as shown in the figure True or False If Q1 is positive Q2 is negative and Q3 is negative then Q2 MUST feel a net force to the right F If Q1 is positive Q2 is negative and Q3 is positive then Q2 MIGHT feel a net force to the right T If Q1 is positive Q2 is negative and Q3 is positive then Q2 MUST feel a net force to the right F If Q1 is negative Q2 is negative and Q3 is positive then Q2 MUST feel a net force to the right T In the above figure R 1 56m Q1 1 99x10 6 C Q2 Q1 and Q3 Q1 Calculate the total force on Q2 Give your answer with a positive number for a force directed to the right F kq1q2 r2 F2 F1 F3 F 8 99E9 1 99E6 2 1 562 F F 2 2 93E 2N An electric point charge of Q1 6 03nC is placed at the origin of the real axis Another point charge of Q2 3 87nC is placed at a position of p 2 89m on the real axis At which position can the third point charge of q 5 27nC be placed so that the net electrostatic force on it is zero F1q F2q F kqQ2 r2 8 99E9 q 6 03E 9 r2 8 99E9 q 3 87E 9 2 89 r 2 cancel k q then cross multiply 6 03E 9 2 89 r 2 3 87E 9 r2 foil and solve for r using quadratic 1 605m Let the sign of Q2 be changed from position to negative At which position can the point charge q be placed now so that the net electrostatic force on it is zero Same equation as above but it s the other number found in the quadratic equation 14 531m Two spherical objects with a mass of 9 76kg each are placed at a distance of 1 24m apart How many electrons need to leave each object so that the net force between them becomes zero Fg Gm1m2 r2 FE kq1q2 r2 FE Fg total charge charge of electron how many electrons Fg 6 67E 11 9 762 1 242 4 12E 9 FE 4 12E 9 8 99E9 q2 1 242 q 8 39E 10 8 39E 10 1 6E 19 5 …