familiari nf3795 DC circuits yeazell 58395 1 1 2 in series with 2 in parallel This print out should have 16 questions Multiple choice questions may continue on the next column or page nd all choices before answering 001 part 1 of 2 10 0 points You can obtain only four 20 resistors from the stockroom How can you achieve a resistance of 50 under these circumstances 1 1 in series with 3 in parallel 2 None of these 3 3 in series 4 2 in parallel 5 3 in parallel 6 2 in series 2 2 in series with 2 in parallel correct 7 1 in series with 3 in parallel 3 4 in parallel 4 2 in series 5 3 in parallel 6 4 in series 7 None of these 8 2 in parallel 9 3 in series Explanation 8 4 in parallel correct 9 4 in series Explanation Placing 4 resistors of the same value in parallel will quarter the original individual resistance 1 Req 1 R 1 R 1 R 1 R 4 R Four parallel resistors Req 5 R 4 20 4 003 10 0 points After a 6 67 resistor is connected across a battery with a 0 23 internal resistance the electric potential between the physical battery terminals is 12 V What is the rated emf of the battery Let R 20 Placing two resistors of the same size in par allel halves the original individual resistance 1 Rnew 1 R 1 R 2 R Thus we need Req R R R 2 Correct answer 12 4138 V Explanation Two resistors in series with two parallel resis tors Req 20 20 50 20 2 Let R 6 67 r 0 23 V 12 V and 002 part 2 of 2 10 0 points What can you do if you need a 5 resistor is given by The current drawn by the external resistor I V R 12 V 6 67 1 7991 A familiari nf3795 DC circuits yeazell 58395 2 Ohm s law is V I R A good rule of thumb is to eliminate junc tions connected by zero resistance R1 R2 R3 c R4 The output voltage is reduced by the inter nal resistance of the battery by a d V E I r so the electromotive force is E V I r 12 4138 V 12 V 1 7991 A 0 23 the equivalent resistance The parallel connection of R1 and R2 gives 004 10 0 points Four resistors are connected as shown in the gure 1 2 7 4 a 91 V 53 6 8 S1 R2 R1 R1 R2 1 R12 R12 1 R1 1 R2 R1 R2 R1 R2 21 47 21 47 14 5147 R12 R3 Find the resistance between points a and b R4 c d c d b b Correct answer 37 8222 Explanation R1 R3 R2 R4 a EB S1 Let R1 21 R2 47 R3 53 R4 86 EB 91 V and The series connection of R12 and R3 gives the equivalent resistance a a R123 R12 R3 14 5147 53 67 5147 R123 R4 b b b familiari nf3795 DC circuits yeazell 58395 3 The parallel connection of R123 and R4 gives the equivalent resistance 1 Rab Rab R4 R123 R123 R4 1 R123 1 R4 R123 R4 R123 R4 67 5147 86 67 5147 86 37 8222 or combining the above steps the equivalent resistance is Rab R3 R4 cid 19 R3 R4 cid 18 R1 R2 R1 R2 R1 R2 R1 R2 21 47 21 47 cid 20 21 47 21 47 37 8222 53 86 cid 21 53 86 005 part 1 of 2 10 0 points series Two identical light bulbs A and B are con nected in series to a constant voltage source Suppose a wire is connected across bulb B as shown A E B Bulb A 1 will burn more brightly correct 2 will burn less brightly 3 will burn as brightly as before 4 will go out Explanation Because the wire is added in parallel to light bulb B the equivalent resistance now becomes just the resistance of light bulb A Since the resistance dropped the current had to increase which means that light bulb A will get brighter 006 part 2 of 2 10 0 points and bulb B 1 will burn as brightly as before 2 will burn more brightly 3 will burn less brightly 4 will go out correct Explanation Since the wire is the path of zero resistance all the current will ow through the wire and none will ow through light bulb B With no current to light the light bulb bulb B will go out 007 10 0 points Consider resistors R1 and R2 connected in R1 R2 and in parallel R1 R2 E E to a source of emf E that has no internal resistance How does the power dissipated by the resis tors in these two cases compare 1 It is greater for the series connection 2 It is di erent for each connection but one familiari nf3795 DC circuits yeazell 58395 4 must know the values of R1 and R2 to know which is greater 1 Bulb A is the brightest B is next bright est and C is the least brightest 3 It is greater for the parallel connection correct 2 None of these is correct 4 It is the same for both connections 3 Bulb B and C are equally bright and P E 2 Req nection is nection is 5 It is di erent for each connection but one must know the values of E to know which is greater Explanation The power dissipated by the resistors is The equivalent resistance for a series con The equivalent resistance for a parallel con Rs R1 R2 Rp R1 R2 R1 R2 Regardless of the values of R1 and R2 Rp Rs so more power is dissipated in the parallel connection Assume the battery is ideal it has no in ternal resistance and connecting wires have no resistance Unlike most real bulbs the re sistances of the bulbs in the questions below do not change as the current through them changes Three identical bulbs are in the cir cuit as shown below in the gure The switch S is initially closed S C A E B each is brighter than A 4 Bulb A is the brightest and B and C are equally bright correct 5 All bulbs are equally bright Explanation Bulb B and C are connected parallel they have the same potential di erence thus they are equally bright IA IB IC so A the brighter than B and C 009 part 2 of 5 10 0 points Which of the following correctly ranks the current owing through the bulbs 1 Bulb B and C have the same current and each has more current than A 2 Bulb A has the largest current and C has 3 Bulb A has the largest current and B and C have the same current correct 4 None of these is correct 5 All bulbs have the same current owing through them Explanation As mentioned …