What quantity is measured by a battery ratinx5k/i 5q/i7arpn. 4ox okl s:ug given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circ /i7s4 f/wt.dimme l2euit, electrons flow away from the negative terminal in the circuit. But within the cell, electrl4m /e m7is t2w.ie/dfons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, batted/p2cqn7 k-bfry voltage, battery energy, battery power, or battery resistance? E nf q72p-d/bckxplain.

One terminal of a car battery is said to be connected to “ground.” Since it isrflq-,p, ejg8*qwt b. not relf*g 8qetq,r-,p b.jwally connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You don’t d-t1 (cu/6acl7asl zdt;vw4qhave to wait for water to flow from the faucet valve to the spout. Why not? Is the same 4 (z1;c/-tcual7 wdl6dsvq atthing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same le5; )h36ejr6hnlcfgb q ngth have the same resistanc5glnr; 3h6f)ebhc6 jqe? Explain.

If the resistance of a small immersion heater (to heat watn d6fgopx35,j ( ekj7per for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heati5ejdn 6gk 3p(f,px oj7ng process? Explain.

If a rectangular solid made of carbon has sides owu5:pcbstx0v m)dga051o 3 haf lengths a, 2a, and 3a, how would you connect the wires from a battery so as to ouw t5p cs d5h)oabxmv:ag01 03btain (a) the least resistance, (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 lightbulb burnsyoe(h(dp hd *5ytbq; 8hc *9tw2mnm2a out?

Explain why lightbulbs almost always burn out just as they are turned on ziw3v7he k)0 qand not after they have been o7h zqv 3k)iew0n for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which+isab/a,ypm 3 has the higher res+3as/myi, pba istance?

Electric power is transferre/pk 1ldgbmtpvl*ix (lx0; c xn t16(7vd over large distances at very high voltages. Explain how the hig ;t1b/mkl l(x76(pv0txdcv xlpgi1 *nh voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeate wfkx5g0er.a:dly. Why is it dangerous to replace this fuse with a 25-A k0rg:wefx .a5 fuse?

When electric lights are operated on low-frequenc1+zsa5rr8kna*l,pqmz9lo- f y ac (say, 5 Hz), they flicker noticel k a8no9 ,frs+qp15rml z*z-aably. Why?

Driven by ac power, the sam5 ) o /hz3yena:, kda,62akiaqbivq5ye electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going ouq,k /a z oayv)yi2,3b k:5d ah5qaie6nt after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately afte az3n7; m l7 yztx5 ;l5zxsyeyn+-gd4ba o;3ghr the toaster is turned on, is thaz y;z5xes;lg3bng- ahn 5z 73o7 y; +mltx4dye current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a r42+5wk 0 hyb,,b uwtv zxn3wmxesistor? Explain.

Different lamps might have batteries connected in either of the two arrange-tp+s fk+hp 0ements showhtp0p skf+-+ en in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many eli0x79bg scgi4ectrons are flowing past any point in the wire i4s g09bc g7ixper second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A fo8fas-mvrlw0drk (j *f 4.d8oi r 5.0 h. How much charge passesw kj d.l-oaf4m r(f dsi08v*r8 through the battery?    $ \times10^{ 5}\;C$

  What is the current i, iwg)au0b0z in 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 hmp c(vq+t(6+f 0 cz+qip,hnha current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current throuc 4j(x;iy;nx0 vrreh *y6f5dlgh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line.gqaepsu2/v fyt;;e)sx .36y 7 kk9hzi
(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 dryerbv ixk x.-)nt5s l0i1u has a heating element with a resistance 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 whose resisr3+ju tf*2t5fvqyx e42 a6pqm tance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 A (Fig. 18 fl;xq/wn5lgkv;o 08o–34). The li 8v5loo/0 ;kq;l gxfnwne 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.)34gk-c9uc s3d rdv axxc5u3p 50 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 2fr4xfis )7d bzsg92r of 0.60 A through a resistor.
(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 length of tungsten wire w *m2te-qh wckwj44c8 r9dxto:hose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in d4j 8,4ay35m gimohbqe iameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of al sqma9,1b)rh.mje 8sruminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2 1hb,s9r)s ae.rm8jmq.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistaz 9y7 /syq+-ucytv3bj spws;4l3)n dance as a tungsten wire of the same npy/ sy j-c+u9)qsw tbd347yav; zsl3 length? Give numerical details.    mm

  A certain copper wire h /1; h rawcg0r,3f+dayxyaul:as a resistance 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 copper wire (origipjv.+ac k; i/.mpn,ginally at .pajk, mi;vp/+n.gic $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resis1j1ei yrop1-3xpl d bq hj5 +i3ikh7dbl9*u3qtivity as tungsten d3qbdeij-l 3kphi+lj*up yi317xo1 r h9b1q d5oes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistazj nn-iqk+*ro e/y7m4nce 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 along a 26-m length of household no. 14 copp*520rp.s/uhb dehi ai0 pi-vz1v d;pcer wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A c 0zd ch*5 1i.pvb viihudap0s;-/r 2epurrent.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm,:v9q dc*m ho;nu q2nm/ and 4.0 cm, lying along the x, y, n vqhqo/*d c mn;mu:29and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid 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 hap,dd ts*uo- 3b4c+ csbve the same resistance. If one has twice the length of the other, what is the ratio of the diambtu dos3-pb, 4ccds*+eter 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 power supply 7 (vff200l-djzx yalv5fcpr9, and a current of 0.4212 A is precisely measjcv0ldrvz fy0fa (l9 p57 -x2fured 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 c9ci4vtyxjs9p( .+m atonsists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage differencj 9t 9 y4scx.pam+t(vie 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 vaaahia00 xf o4)lue of a resistance not change with temperature. For example, suppose you maxo0f0h ia4a)ade 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 ove uio +1*u fr+tmdnutk.)y, 7oln is designed to produce 3.3 kW of heat when connected to a 240-V sor+*)o u,uflynmit1t.dok7 +uurce. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws a,q0z(5jy h3azkw8b sk maximum5w83ahbk k q zzj(,ys0 of 320 mA of current?    W

  What is the maximum voltage tha ub8jgvakc (z 0e8t/v4t can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current thrga0w1ui ,ho8q9rgv 1lough, a 75-W lightbulb connected to its proper sol0aqhg81 gow,1 u9ivrurce 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 rated at 11valf v*cld; 7)1*wjlse 5e c:5gc9w xa0 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 andbmvy 7++m nw2l sdx(-x 1250 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 electricity imhou+yeft )8u0-imi:4 bhyr(3g 5b yhs 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 yfe +5u ro(bhy )mgi b3u h:t04iyhm8-to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is in opera8y31(a ux, j,2kvukt:n9 xci/yaq dtytion for a total of kxy9yq8juix2vna,(c ty d: uta,3/1 k15 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 o1kx- /tckcd7c,xi k/fo*hw) on day ak1txd//cccx-ko ko) h7f,w*ind night for a year? $\approx$    dollars

  An ordinary flashlight uses w ja e/5/.hmcrqg 7ff:two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turn7wf mf a5qr.:jeh/g/ced 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 stored in a 12-V p x*v3c/ 51)wfa-6vqslggdtt, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be used wios(zie9c-ms ( thout blowing a 1ec(s(m 9oszi -5-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm d) n3/: akfw0a tgu6tk(no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on kfkuwn/ 3a60 g)ttad:a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wires/0 qzk sx* t503wp*fcux h. ck3dqd5wa with du5 c*0saw50f kkx hwc3 tz*/3dq.pxqtotal resistance $3.0\Omega$ 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 tm nf*19o.bb) ;xyew eko a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water n 1)xfe9.;mobbe *kwytemperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used fg6yj.jr/ k*g in a car to heat a cup of water for coffee or te.krgy / *j6gfja. If the heater can 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 currentpx5bi11ihpff k: b. o/ in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, nf: .4qztaob8 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 ov0q9lw6vv u9t f the $120-V_{rms}$ 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 deviw8p2q b- v+.d(prc ntlce is 5.4 A. What is the rms voltager2(+ncvb pw t.dql8-p across it?    V (Round to the nearest integer)

  An 1800-W arc welder is c 3wq4eyf+f x k do;88+tqahsk6onnected 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 dissi8 vif svr a(0(iyc.4ix1f4bv npated by a 3.0-hp pump connected to a na f(syvb(8riv. 0ix4ci14v f $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecte+ 4pxci 87u 59nvsgqaad 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 tiny current . eq r1ofes8 uk8bi92zga fb.:x xmi(-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-diamete(p f: 6zggrw2ur wire carries a 750-mA current when 22.0 mV is applied to its endw:gz p fr2g(u6s. If the drift speed is $ 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 atmospher(,kv+uv wz y r:yomo7:e, $He^{2+}$ 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 atmoq em571bb uhw(sphere, $He^{2+}$ 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 across an axon measyh3sa-7 yiptoz - /(mbrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated i);uhr2n4k bjwith an electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, tkhub2; )n j4irhe 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 transmit one action potentialpjcnrcs(bdf7 drt27u6/ 7x5te9r ,n m along the axon of Example 18–157 /6sn pnurtt7m2r 9j5dbfcdxrc e(,7 . [Hint: the energy to transmit one pulse is equivalent to the energy stored 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 potenfr 0b. (vb;p:caw(adine9c 3k tial, $Na^+$ 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 ampere-houcbn6by5r s7q:ds q/i*r?    C

  What is the average current drawn by a 1.0-hp 6oc 0djgzhhz,df61 k*cncy1: 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of76y d )jo7/.ndnve5 maa5f0 yyoe0ngf the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fra 750)dnyo7 of /e0ad e.56nfmyyjgvnesh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.45kfgz x o,+mn4oi8*z5ncrxg * m long. If it is made of iron, what mustz+c 8oogf5ri**z kx n mx5,4ng its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of 2*q.2qm bdbe* l)wzerg/ksxn +xv)x p0:fx9ethe resistance R; that il22s/pqb 9e+fxv. q edxx*z )xwb)gn0m* :kers, $G\,=\,1/R$. 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 of power. Suppose that instead of-7 a.znzwn xy0 using high-voltage lines to supply the -n.azyw x7nz0 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 energy 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-k z3m.1 pmpt*xu.2wto pW heater $3.0 h/day$ (“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 togettbl ay hy/mmf1;*dx0 5her side by side to make a thicker wire. How does the resistance of this new combination compl*x0;y1/mh5b tmay fd are to the resistance of the original wire?

  A 1200-W hair dryer i ; i*b883kzij*fgbayyx v7n t,s designed 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 zmi z9oksj*7) k/ja1 kenough so it does 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 more than 1.8 W of heat per meter of lengthj j s/)1ikozz k7a*9km?    $ \times10^{ -3}\;m$

  Suppose a current is given hy d00edg1/ yfi (wt7wby 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% efficiencye1gh+8vl kt:gb/+ *c g4blybw delivers 950 W of energy per second tbc/*vb 4bl :y kglg+h8 t1g+ewo the interior. 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 conductors made of thev +i, nl2sa6fy same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of th2 , alyifvns+6e power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is xor 3 )hbgcb.(f6x wm:s;o 5frused to 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 hookegjklxo)-. a1fd to a 240-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 ofqrri.o/p;;( 3 7xkslozn g al+ energy. Its mass is 1560 kg and it is powered by 24 batteries, each 12 Vrqllzop;( a +;nxi gr/ s.k73o, $95A\cdot h$. 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 a resis7y-en9q sty7 ntance 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 (Illinois) is de 1eq1e:zth7u psigned to carry an 11-mA beam of protons traveling1heuze:17tq p 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(o ht ejjk6/a6e (7 8vkrxgt)p p8+nik ac. The connecting cord is copper wire with a diameter o (ke pkart+n8g8te hvx/jj)i p6k(76of 1.628 mm.
(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 3ss ezl(rz3,4ou4 uom95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wi4r4z,smsl(uz o3uo3 e re?    $ \times10^{ -4}\;m$

  In an automobile, the sy4yi;gz bu2zdv ) v44b 2ontd)kstem voltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered t)gt4 zub24iob 2kv 4n;)dzydvo 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 ae kt . )okbxm;p-ht15ya-xvb z+hl9n+t 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 xmaehp 9vt1 )+-k. btkon; y- hlx5+zbW 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 diamets + ./)h yomhqvr5h8yher 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of powe shyrqoh8v+5/ hh ).ymr 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 3.00 cm and an outside diameter e )nlr(4fx0e*m8fk: wtgf0fsof 5.00 cm (Fig. 18–37). What is4 flsn8wffrt*0()0eexf:m gk the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is sujn6woj1,i 8p om2k*n tretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it rema mpoi1* n68n wjkuo,j2ins hooked up to the same voltage source?

  A tungsten filament used in a fedi*h tai8h nlxqhf2yet( bk-559 87h lashlight bulb operates at 0.20 A and 3.2 V. If its resikh82hhetynabii8exlt (57 fq95-dh *stance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$