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1 Exercises 341 Flow of Chrge (pge 681) potentil difference 1 Chrge flows when there is between the ends of conductor 2 Explin wht would hppen if Vn de Grff genertor chrged to high potentil ws connected to ground wire A surge of chrge would flow through the wire The flow would be brief becuse the sphere of the genertor would quickly rech common potentil with the ground 3 Explin how the sustined flow of chrge is nlogous to the flow of wter from higher reservoir to lower one, s shown in the illustrtion below Wter will flow in pipe tht connects the reservoirs only s long s difference in wter level exists, s shown in The flow of wter in the pipe, like the flow of chrge 342 (pge 682) Mtch ech phrse with the correct term or terms Terms my be used more thn once Phrse Terms d c b in the wire tht connects the Vn de Grff genertor to the ground, will cese when the pressures t the two ends re equl For the flow to be sustined, there must be suitble pump of some sort to mintin difference in wter levels, s shown in b Then there will be continul difference in wter pressures nd continul flow of wter The sme is true of electric current 4 the flow of electric chrge 5 prticles within solid conductor tht crry chrge through circuit 6 SI unit used to mesure electric current 7 equivlent to 1 coulomb of chrge per second 8 the net chrge in current-crrying wire mpere b zero c conduction electrons d electric current Conceptul Physics Reding nd Study Workbook 289

2 343 Voltge Sources (pge 683) 9 Wht is voltge source? something tht provides potentil difference 10 How do btteries nd genertors supply electricl energy? In bttery, chemicl rections occurring inside relese electricl energy In genertor, mechnicl energy is converted to electricl energy 11Is the following sentence true or flse? The potentil energy per coulomb of chrge vilble to electrons moving between the terminls of bttery or genertor is the voltge true 12Chrges flow through circuit becuse of n pplied voltge cross the circuit 344 Electric Resistnce (pge 684) 13Is the following sentence true or flse? The mount of chrge tht flows in circuit does not depend on the voltge provided by the voltge source flse 14Wht is electric resistnce? the resistnce tht conductor offers to the flow of chrge 15Circle the letter of ech sttement tht is true The resistnce of wire depends on the conductivity of the mteril used in the wire b The resistnce of wire does not depend on the thickness of the wire c Longer wires hve less resistnce thn short wires d Electric resistnce depends on the temperture of the wire 16 The resistnce of some mterils becomes zero t very low tempertures, phenomenon known s superconductivity 17 Electric resistnce is mesured in units clled ohms 345 Ohm s Lw (pge 685) resistnce 18 The reltionship mong current, voltge, nd is clled Ohm s lw 19 Stte Ohm s lw The current in circuit is directly proportionl to the voltge impressed cross the circuit, nd is inversely proportionl to the resistnce of the circuit 20 How cn you express Ohm s lw mthemticlly? current = voltge resistnce 290 Conceptul Physics Reding nd Study Workbook

3 21 Wht is the reltionship mong the units of mesurement for the three quntities relted by Ohm s lw? 1mpere =1 volt ohm 22 Wht re resistors? Resistors re elements in circuit tht re used to regulte current 346 Ohm s Lw nd Electric Shock (pges ) current 23 The dmging effects of electric shock re the result of pssing through the body 24 Is the following sentence true or flse? The resistnce of your body is much greter when you re soked with wter thn when your skin is dry flse 25 Explin why it is dngerous to hndle electric devices while tking bth If you re stnding brefoot in wet bthtub connected through its plumbing to the ground, the resistnce between you nd the ground is very smll Your overll resistnce is lowered so much tht the 120-volt potentil difference my produce hrmful current through your body 26 Is the following sentence true or flse? A bird perched on high-voltge wire is not shocked becuse there is not potentil difference between one prt of its body nd nother prt true 27 Wht is the purpose of the third prong on three-prong electric plug? The third prong is connected to the ground to prevent electric shock 347 Direct Current nd Alternting Current (pges ) 28 Circle the letter of ech sttement tht is true Direct current refers to chrge tht lwys flows in one direction b In DC circuit, electrons lwys move from the positive terminl towrd the negtive terminl c A bttery produces direct current d AC is current tht repetedly reverses direction 29 Circle the letter of the correct nswer A 60-hertz current mens tht the current equls 60 mperes b lterntes bck nd forth t 60 cycles per second c chnges direction once every 60 seconds d trvels t speed of 60 meters per second 30 Circle the letter of the correct nswer Wht is the stndrd voltge of AC in the United Sttes? 9 V b 12 V c V d V Conceptul Physics Reding nd Study Workbook 291

4 31 Will n pplince tht opertes on volts work when plugged into wll socket in the United Sttes? Explin your nswer Yes Applinces tht operte on 240 volts (such s electric stoves, ir conditioners, nd clothes dryers) cn operte on 120-volt AC line becuse most US electric service is three-wire: one wire t 120 volts positive, one wire t zero volts (neutrl), nd one wire t negtive 120 volts When the plus-120 wire is connected to the minus-120 wire, 240-volt jolt is produced 348 Converting AC to DC (pge 690) 32 The current in lptops nd cell phones is 33 With n AC-DC converter, you cn operte bttery-run device on AC insted of btteries 34 In ddition to trnsformer to lower the voltge, n AC-DC converter uses diode, which cts s one-wy vlve to llow electron flow in only one direction The digrms below show the effect of n AC DC converter on lternting current Mtch the letter of ech digrm to the correct description DC b c d c b d 35 Chrging nd dischrging of cpcitor provides continuous but bumpy current 36 Only hlf of ech cycle of AC psses through the diode, resulting in pulsting DC 37 The input to the diode is AC 38 By using pir of diodes, there re no gps in the current output 349 The Speed of Electrons in Circuit (pges ) 39 Circle the letter of ech sttement tht is true Energy is trnsported through connecting wires of circuit t nerly the speed of light b The electrons tht mke up n electric current trvel t the speed of light c The electric field inside current-crrying wire hs no effect on the motion of conduction electrons d The rndom therml motion of the electrons inside wire is wht produces current 40 Is the following sttement true or flse? A pulsting electric field cn trvel through circuit t nerly the speed of light true 292 Conceptul Physics Reding nd Study Workbook

5 41 Explin why current-crrying wires become hot Conduction electrons re ccelerted by the electric field Before the electrons cn gin pprecible speed, they bump into the nchored metllic ions in their pths nd trnsfer some of their kinetic energy to them This cuses the current-crrying wires to become hot 42 In current-crrying wire, collisions interrupt the motion of the electrons so tht their ctul drift speed, or net speed through the wire due to the field, is extremely low 43 In n AC circuit, do the conduction electrons mke ny net progress in single direction? Explin your nswer No; in single cycle the electrons drift tiny frction of centimeter in one direction, nd then the sme tiny distnce in the opposite direction 3410 The Source of Electrons in Circuit (pge 693) 44 The source of electrons in circuit is the conducting circuit mteril itself 45 When you plug lmp into n AC outlet, flows from the outlet into the lmp, not electrons 46 If 120 volts AC re impressed on lmp, then n verge of 120 joules of energy re dissipted by ech coulomb of chrge tht is mde to vibrte 47 When you turn on n electric lmp, wht two forms of energy re produced? het nd light 48 Explin wht hppens in your body when you re jolted by n AC electric shock 3411 Electric Power (pges ) 49 Define electric power Electric power is the rte t which electricl energy is converted into nother form such s mechnicl energy, het, or light 50 Electric power = current voltge 51 Express the eqution in Question 50 in terms of units 1 wtt = 1 mpere 1 volt 52 One kilowtt-hour is the mount of energy consumed in 1 hour t the rte of 1000 wtts 53 If the power nd voltge on lightbulb red 60 W, 120 V, how much current will flow through the bulb? I = P V = 60 W 120 V = 05 A energy When you re jolted by n AC electric shock, electrons do not come out of the wire nd through your body nd into the ground; energy does The energy simply cuses free electrons in your body to vibrte in unison Conceptul Physics Reding nd Study Workbook 293

DIRECT CURRENT CIRCUITS

DIRECT CURRENT CIRCUITS DRECT CURRENT CUTS ELECTRC POWER Consider the circuit shown in the Figure where bttery is connected to resistor R. A positive chrge dq will gin potentil energy s it moves from point to point b through