What quantity is measured by a battery ratg5j ofsu-t.y /ing given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit,ztv )nr* twv 0;ywk*m6 electrons flow away from the negative terminal in the circuit. But within the cell, electrons f mvw*tk;t60) vn ywzr*low to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battdafi2zk9 -db8u*ssl n5f7i s: ery voltage, ba8bsus: nda7fzi-fk5 is* l9 d2ttery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it pquqbz2:zto9 dc2adrpw.c6(ny ;x 57 is not really connected to the grod;n( tcqzda .o69p:qc b72 uz2yw5 pxrund, what is meant by this expression?

When you turn on a water faucet, the water usually flows 6,kg4rujs 6tx 4/j6aqd; h xqvn(nhv( immediately. You don’t have to 6naqd;4 vgnh,kt vxu4j shr(6/qx( 6jwait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same l*t:o5im y-p wqength have the same resistance?*q: - o5pwiytm Explain.

If the resistance of a small immersion tyzjd .(ypw0fc1tv 5m(l6a2m heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Ex2a0cmz (6y (t5vtdpfyl1m.w jplain.

If a rectangular solid made of carbon has sides of lengths*+za* 7zkv8zue6d qsddi;2 vd a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, *d6azzdv2 i7e q+*dz8kuv ds; (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lig m:6 e4zkl wxp*f6vy eyw+.*bchtbulb burns out?

Explain why lightbulbs almost always burn out 7 w a)t6v-*swv; pzvpwjust as they are turned on and not after they have been on z7)wp 6vw ;*wvp-svta for some time.

Which draws more current, a 100-W lightbe b-c9qo -wn*4t/kwlnx z 0ko,ulb or a 75-W bulb? Which has the higher n-tqkwzb/ooe c-x 40n w 9,k*lresistance?

Electric power is transferred over large distances at very u 8 xw8)/pqlwrhigh voltages. Explain how the high voltage reduces power losses in the wrw 8 l/8)quxptransmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with a 25kw6lc(kc 5fa+ ff e-+qnn/*by5iioi2-A wk5*f ci2nycb6qlfn+/f5( ie+ik-aofuse?

When electric lights are operated on )4 lyng9oyg,*n+k9 syp zd9vdlow-frequency ac (say, 5 Hz), they flicker noticeably. Wsy4v 9ggz9+dpndyo y)9,*lkn hy?

Driven by ac power, the same electrons pass back and forth through yo*3pd3 txo ygc4dh n0 r*7qe;ciur reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of electrong04 3o 3he *tnddc ip7rxc;q*ys.

The heating element in a toaster is made of Nich goth, qu ;v.23:k0 dor*l4pai0 tunubrome wire. Immediately after the toastkdn:otbl 4p.a0 uu; hvqo,t3 2*rgu0i er is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resip4 r6:tt/), ffiw:vt csuhzz8stor? Explain.

Different lamps might have batteries connected in eithj b)+bry gl-k5/xe/ cter of the two arrangements s-cj g5+ tb x/eb)l/kyrhown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire.0 7-k7sya mu aemq)wd/ How many electrons are flowing past any point quda s-7ky0e/mw7a) min the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a(i kq-g i wjd wm:.tmzp*2o.;z current of 6.7 A for 5.0 h. How much charge passes throuz-zj;2*( wkoqwmdp.gt m.i:igh the battery?    $ \times10^{ 5}\;C$

  What is the current i 5l-7 wgtwvt.tn amperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a curren6x3x41mbzb .dbr oy c8t of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A fufl7)zmu,7de1s) g s )k 8ycoof current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged in(o6p /4a2 ilhze -gagwto a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a resistancl6in;anaz-6(y: q x3n t5*wxagfcu 2re of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb who bcuqvm; ih y )s,m37yv84.pecjdof0* se resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmissia, g4slhx,*z upsp2+d on line carrying 2800 A (Fig. 18–34). Thx,d p4ssu+2p,hz lga*e line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.5f i4wy0x+ *oq+;t7l erv ch tz:yvu1i,0 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a resista.j4uott7 f)xor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m (d/o*h0zxco4 ad0 f b/lmpxq/l5;igplength of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.vplwltyc4)( z0wmh;i vs 3*-u,*k qwn5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of t2i f)eqg u1rib agbu2up9k+7(he resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. )fbriu7qk2( + u ugbe1ia2g9 p  

  Can a 2.5-mm-diameter copper wire have the same resistance as a tunt ili jzuhn3 )af.2)byo4y 5p5gsten wire of the s5ny a5i. juto)yiz3p4bflh2)ame length? Give numerical details.    mm

  A certain copper wire has a resis* 9h51pib(ught3c1a mcwdc + ztance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a q.f/b3; vw tk/.cozy. +ijr ezcopper wire (originally atko.zeyt/wcbzvqr 3.+ ;/. ifj $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have tlvx3(sf i8 vzm 0t 7xlqh9-3uf*oo (dzhe same resistivity as tungsten dzllfu 3*foo70tx(v -vm8hd 3i zx 9(qsoes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a ro1sd/ k 3sap8iiiv1:p esistance of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop a(7 /y krs;x/tbnuemp)long a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire y pnbr(es/ tx/km7)u;has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.7nj2vzw,l xqup8xd)- 0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the s x8w7luzqd- vnx),j2p olid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the ss tu433b:ed:*gc ewzq p wfi,5ame resistance. If one has twice the length of the other, what is the ratio ufzi5,3:tbw pgc3dqe e 4 *sw:of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V 2c+,p/empqx 85e sxbhpower supply, and a current of 0.4cq5 bxps, + peh8m/x2e212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copper followed by 5.0 m of d ;6lb b7w/nvwaluminum, both of diameter7 bvwdl /;w6bn 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the value of a resistajs 4ad1ko59xp*u / wionce not change with temperature. Fors /a94pj15oo*id xkwu example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to -,3e: pi sccarproduce 3.3 kW of heat when connected to a 240-,p se c3:cir-aV source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD ;dus: pp x.o kx1vjg0(player that draws a maximum of 320 mA of cuxp(; xok1pdsg 0 v:.ujrrent?    W

  What is the maximum voltage that can g(/ )xj8syfxt be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbul/33;d tg/ hudvx yrzx1b connected to r;1 /ydgz uxvdh xt/33its proper source voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is ax j14r +oc3 f7w.-etrcuqs (brated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and 1250u+ 0d+e rq 8hr7srtx6k W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricw*a*r) l1r4xlqsmn0o8wjt 3x ity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to powwljrq wlrox4*s3t8nm x*1a )0er consumed.]    as bright

  How many kWh of energy does a 550-W t unhc60 vhtqnv+w;tlpm4:.; b oaster use in the morning if it is in operation for aut;vwhnn;46q vp. : 0+hm tlbc total of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W porch light on df tq;.ma 7hi*lay anq*m ti ah.f;l7d night for a year? $\approx$    dollars

  An ordinary flashlighxb 8gihhyu71fr4squb )) n4i8aa9 z,ct uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulbzqyi x4 b9 4a1b,ufc8gih)h87ns)u ra draws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energy stozflky5(, rd,ge9e7 s ored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. ycw5jmg;v t 92+gd.q v18–20, can be used without blowing a 15-A fu wyqdm5g.v9g c+t vj;2se?    bulbs

  An extension cord made of two wse wx*f2 wvf p/d6;ar2czn8b/ ires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heaterwbe /xa2 c;v62/ f zwfr*nsdp8 which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kWy5 cz 1qn)s34 ck;1c+ vevsmbz of power at 12,000 V to a factory through wires with total resistkcq3+yszmv) vc51 sc4ebnz1; ance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected *+geo 1sb21rnh gg1qwto a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the wa r*go1hgbq 11 s2en+wgter temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can bu ij+x9a4de:6rwd* ju e used in a car to heat a cup of water for coffee or tea. If the heater ca*9j 6 : ej+rdxuuiwad4n heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current ihd+gtlp4wy 7 qqk7frn58v3l5 n a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak k(rkp u3- t478qqbux nvalue is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of theckp7y/q7 a -tr $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 1500-W device is 5.4 A.m k /dt+encdov/j91r7 What is the rms voltage across it? dnkcv+1 drot79em/ /j    V (Round to the nearest integer)

  An 1800-W arc welder is cond-z uc;*r 7ums;girmkxa 09exi5i1m+ nected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp pump connectbx)24j gsjxy)cz uw *kk yp3/4ed to a 3k uy2)px c) */kgswxb4j4 yzj$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected i /xgwjla w40*to a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a :6 .,yctf uyhzs19izu tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a+oyydcoc(m2lm uneq b2r )2*o3iw 8l5 750-mA current when 22.0 mV is applied to its ends. If the drift speed is by352du c)w*2loy+2 mc e(oli 8nmorq$ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmosp mouvjw:s:8ki;r/g + ehere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’s atmo;.g pni-92tgf aal, ulsphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electric field a-w-9hsb-kh egaf+ sm-cross an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potential is detectemtxw 4hih2kcu ; ;1b-kd at a point 3.40 cm down the4k-w; b2;kt xu hihcm1 axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to t7y089 jpqfs 2jom mb3k,wxy q+ransmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored80s 2xb f7+m j3k,qomyj ypw9q by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentikv0 2u+n5bmrkui w c;9al, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there in 1.00 amg7i wh)xwm0m2m)i e (fpere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V mof6dj8g:y j v:ftor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lightskgh,. 6 6r xolbgd*f7p on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at.rfkhgo*7xp 6 lg bd,6 $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 m r2djqgy )m 6be5v4hj 3+lxho3 long. If it is made of iron, whay 4+) g3qjvh e53drohm2x6jb lt must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprjjmr,1t g+tt( sg1m/9zz f1z tocal of the resistance R; that isg9 m1jj/,+ gr1(tzzts fz1 mtt, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW ohgny k(8u8es .jmjr5gc 92pn 5s 8iyj1f power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energkrhp5yg j1nu88 cg .98ij(nes s jym25y lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heater ,mzw6 k 4b x1h.j-yzvce w6zr.s1sle6$3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are wrapped u: p6yin bex:,together side by side to make a thicky: ,i:ebxu6n per wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed ede;ib,w/a9 wi6hxc,yt4q 62 ztza:v for 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it dr.28 r osf1njfoes not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no moresfrf8njo 1 .2r than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current isr )4u9h;njh nv2 b+axgicy/3a given by the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficienczh d1h o4e1 *c)u)rkqty delivers 950 W of energy per second to the interohe z1r 1u td4hc*)k)qior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conduq +o/ia:j;y4jx tg i0kctors made of the same material. One conductor is twice as long and o iay4gq: kt0i/+; xjjtwice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used todd3p9q : -5ymbkmv9x a heat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-)co gjv61 tl7omkqh.+V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its source of ebuuyt90/hqp; nergy. Its mass is 1560 kg and it is powered by 24 batterie0b;u9p/ t hquys, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has a9az*mv x- 7es- uxfv*g resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Il 8b;jy jvh2bs4linois) is designed to carry an 11-mA beam of protons travelinvs b8;bjy42hjg at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. ; 2d yuzdff+7jv.4fmaThe connecting cord is copper wire with a diameter of 1.628 fmjy fzafud4d ;2. +7vmm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W whenqsx5c7rc*b c0 f 1w6eq connected to 120 V. The heating element is asx05*bqec1cq7fw6 c r coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from abouyl ;j9.yg3gjgq(mpy:v j 7npsq /ie96 t 12 V when the car is off to about 13.8 V when the car is on and tggvj ;m ny3l:p699jepyq s/y.g7i (qj he charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 3 bc14tbe8*+n qh(m. sroj n*r3zerip120 V and 40 W for household applications. Lightbulb B is 8hcireqb n ( 3+rop41 t*jn*3bm esz.rrated at 12 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to con8s wd3.(u,us, imyoep snk zco-t ;x);nect a set of appliances at 120 V, which draw 2250 W of zu.3xp,ne , yd;(smiw ussko;-8t) ocpower total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3hxlz6a l p +;k6*l-hnc.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resil c-6hkn px* a;z+lh6lstance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that f r33jb u,(icuits length doubles, by what factor does the power dissip3b3cr ui,j fu(ated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flasw e:hvs6k7we eg9+ /mthlight bulb operates at 0.20 A and 3.2 V. If its resista+w vmse/w 9h g6:t7keence at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$