What quantity is measured by a batte11sk2)ht(.nb kwa hfsry rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away frnwa43 ;ox8ep wom the negative terminal in the circuit. But within the cell, electrons flow to the negative epwa8 o;w x34nterminal. Explain.

When a flashlight is operh .8ji:j +f lscxhvzj8w*ts 3fu.y26 vated, what is being used up: battery current, battery voltage, battery energy, battery power, oril2*z+s .jwjf6sht v.3 : f8xjy c8vhu battery resistance? Explain.

One terminal of a car battery is said to be connected to “groundrpbp 1s0:9 mip1zhadxn -(e3 y.” Since it is not really connected sye3ixm- 9np(z:1a br pph0d1 to the ground, what is meant by this expression?

When you turn on a water faucet, the5s p+ vcdfjm;- water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Whpm+ j-sd ;vc5fy not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire andtwk)vu0 ul 2oj/pgw-3 an aluminum wire of the same length have the same resistance? Explainv 3u0jo 2/ tgup)-wlwk.

If the resistance of a small immersion heater (to heat water f 7e m0kmk2x7qdor tea or soup, Fig. 18–32) was increased, d7mex27k0kmq would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lzspz 1 htu.yyna8+ y5eag8l/4 engths a, 2a, and 3a, how would you connect 8g/elyy a u8.+4tap z5h1nzys the wires from a battery so as to obtain (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 bur2.g z)ov xgzd9tqy8fk s(on; )ns out?

Explain why lightbulbs almost always burn out just as they are tur7 efkq5mnd3sls1crw ;:x1gn)ned on and not after they have been on for some 5sc )grfn ;wdel11 s:nq7m x3ktime.

Which draws more current, a 100-W lightbulb or au fea0a-fhzj* -udtit3a) + 3r 75-W bulb? Which has the higher rejeh0+- fr*f3 3ia-az ta)tduu sistance?

Electric power is transfesso9g-.,45hq ihw la drred over large distances at very high voltages. Explain how the high voltage reduces power losses9- ah.4sdh sg, qo5liw in the transmission lines.

A 15-A fuse blows repeatedly. Wh2ikl:4baq+*mb6,46 i t ) i nriafljjzy is it dangerous to replace this fuse with a 256 6k:bimlqfblj , t42+zin)jaa4* iir-A fuse?

When electric lights are operate,hy-ao vsqxn ay (/.z2d on low-frequency ac (say, 5 Hz), they flicker 2(-/zy vha s nqyo,.xanoticeably. Why?

Driven by ac power, the same electrons pass back and forth through your re8 , mfewys gp.+su/ lj8lajf5.ading lamp over and over again. Explain why the light stays lit instead of going out after the flp,/+f8jsye g 8a.. sf 5lwmujirst pass of electrons.

The heating element in a toaster is made of Ni6.5-ps vad(/pztdmwa chrome wire. Immediately after the toaster is turned on, is th.wt5p- d/ vz pa6dmas(e current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Expla*msvrmgl( b ;1-fyw9a in.

Different lamps might have batteries connected in either of thmkx/8qrl+7qu;ht h/ eh d82 6eaf sts1e two arrangements showtr ha/ x hsq7q8d+se1ef/mtl;8k 6hu2 n in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are fl.vhm 5 h;ecp-r qr-we1owing past any point in the wir1h-e-mw ;ehv. prqr5 ce per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7(1of5 9 kwstih A for 5.0 h. How much charge passes through thsf ko5i(h w9t1e battery?    $ \times10^{ 5}\;C$

  What is the current in am6 sxt yvb)xb3/peres 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 qrpgkfg vid16*8vy/+m; 4ug r of a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will prod1w4 qrog b , 71+ysuoyptg99uwuce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line.w 9,yoson 37dn
(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 resistance of d f*+0+vxl*ccg kf6ev1uw cj3 $9.6-\Omega$.
(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 connectedwrp 3o(rgh8 rj1w43pb- 0 eica to a bulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electrie *2nv *z 7p.)cpssdutc transmission line carrying 2800 A (Fig. 18–34). The l2pcs)tpsvuz. *7ned *ine 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 6.50 Ax5ci(st g0v) g 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 of0, ru3;lti obq 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 wr9f4ddf+zf0 7s,is dz z1xf9a ire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of mi 49 ivv+j-gfa 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm , .hap( myvfgtc,m c4x j6z84rin diameter, to 20.0 m of copper wire 2.5 mm in d6af z 4h (x8mr,gvc.y tcpm4j,iameter.   

  Can a 2.5-mm-diameter co(:fv0va2pj xt pper wire have the same resistance as a tungsten wire of the same length? Give numerical detailtp2 :xjafvv (0s.    mm

  A certain copper wire has a ree p+a3,coh l6vtxxms/ x3:h2)qe p 8klc.h5qj sistance 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 raisa m-y8zj mzfxp/ -3l7me the temperature of a copper wire (originally at3- -ml/7jm z8mazfy px $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have t3pi*r2yn : shizs0o j3he same resistivity as tungsten does at i 3 i3zj0:*phys 2orns$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about .4( 3fetav1 kptnkp8o ++la kv$12\Omega$ 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 householdeb k dn,1+ab1a no. 14 copper wire (used in 15-A circuits). The wib+1, aaknb e1dre has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of leflkf9f )u *h*g)e yy-rngths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the shyr- fe fu*fyl9*)gk)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 hatbwrn:ov+ , 1sve the same resistance. If one has twice the length of the other, what is the ratio of the diameter of the l,t o1ns+rbvw :onger wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected-l xqyt:ys-,a to a precision 10.00-V power supply, and a current of 0.4212 A is preciselys-yty-a,: x ql 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 psu r-h3/y 6ce5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed acr/3cy6u-her sposs 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 res1fruxr:ht5 q (5mc9auwlo.b( istance not change with temperature. For erlm(h1wuc.urxaqb9 (:5o ft5xample, 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 ove( elksa *+ybkb ntexf)sm2)63n is designed to produce 3.3 kW of heat when connected to a 240-V source. Whatbsnal3 +*) etkb2ykx ms)(f6e must be the resistance of the element?    $\Omega$

  What is the maximum poaq*x+ v- l-z(hcu ecz o8;ogn8wer consumption of a 3.0-V portable CD player that draws a maximum (gl*e - uzohc-+ovza8x8n;q cof 320 mA of current?    W

  What is the maximum voltage th srn)lk4b dk7(at can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, ang72a 4)d+hw1yy, gc-mgh cba9hgs9 n id current through, a 75-W lightbulb connected to its properihw2)a-cha1gdmnghg7 y c9 gb ,y4 9+s 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,x ;hfhktf .d ,bkiz6m *80phn rated 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 twvq60t).+ apiq u ur5ndo settings: 850 W and 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 i8 b;ea6 e:dcihn Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 :aed;i 68ce bhV (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 power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning ifkckja,( 5 a gz/)kfi8b it is in operation for a f/k,a) gaz(c kj5kbi8total 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 por)d y9gjtx3 5 xh-n )ecwkk.8gvch light on day and n.gkxek 3 wt-hjdcyn )vg5x98)ight for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in sx:clv* l6 ng:byp8w 4ceries as in Fig. 18–4b (Fig.v 6p*:8lbwn4x:gcc yl 18–36). The bulb 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)wx un *s/mip5 stored 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. 18–20, can be zala / xsb9k6l3.3wimused without blowing a 15m bi3sax w/a 6zll3k9.-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire). o:(9zg4 spmyd fv 3fsn9fxw8 and of length 2.7 m (9 ft) is connected to an electric heater which dra3 (9f svw89o:ngp .xsm4 dfyfzws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,00j qs*14 t x*t2laqyt0x0 V to a factory through wires with 1 *a4tljq stxtyq*20x total 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 to a 240-V line is 17.5 A. At 3:o ; ciji/ekzwhat rate must cooling water pass over the coils if the water temperature is to rise by no/ oc;3z iij:ke more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for cof ueewwj3e ez;,uguwqq)1;/e :fee or tea. If the heater can heat 120 mL of water from 2u 3w:zue/we;j1 q qegew,)eu;5$^{\circ}\,C$ 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 jzuyj, 9g9f19cc(mv zmy7 wi8in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, 33p 92b 2 uz7zys*j5hibzq gcyis 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 tun6r:+mml 4cs he $120-V_{rms}$ 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.o82slx(nx jow n. +w7mx+o 6pm4 A. What is the rms voltage a+2(xxoj +mp6w x8.nowmn7 s locross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to pmzmpjm/w:a;*z k0 /t 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 dissipate, ovn7fwyj7ek8u5 q c9d by a 3.0-hp pump connected to a n5fe8ov7cw,q9uj7y k $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tofy, 1xhrx.v x5 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 currenteclu9nzykt sh57s 5, 8 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-mah 2k7a izgj77h1s;vf m-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the d fhja7k2i 71vs ;7agzhrift 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 theeeq-gt9) 0t tnz0)tqe Earth’s atmosphere, $He^{2+}$ 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 atmospvx .dhy2v9fh/q* 5s jkhere, $He^{2+}$ 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 electri k7i8 s)/gfbyxc field across 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. Thdc3wu:6a ; je) wxgw2re 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, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements :ura6wexdg3)j w;w2c needed instead of only one?)    m/s

  Estimate how much energy is required to transmit**/3hk5w pb p(a8mgy z(nb xaj one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axo( x5(yp ba*nk8z/abwg jh*p3 mn 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 potential, +b.. gf.s* 3.tpxlvdsrhx ;r x$Na^+$ 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 ther63 djw6nezdvndh80p .za z2r2z06k rre in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motor*/c p+2bs 8aqyowi-tf? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two hzbyx 1hu 8v0uw 9 rcy/-r-5yfzeadlights 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 iszu9-uz 1wfyr c/y5r-hvyx 0b8 rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 157l9 f ;u9vk,l;sxo.vus dz78zixi; ce 00-W heater is 5.4 m long. If it is made of iron, what must its diam,kx u 7s e8cxz l9s9fli v;z.d;;7iovueter be?    $ \times10^{ -4}\;m$

  The conductance G of an object*dhj7 ez+hr 6khw;er 1 is defined as the reciprocal of the resistance R; that is, jk1w+ 67h d;erezh*r h$G\,=\,1/R$. 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 using d4/penvx5l8 n 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 energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents 5 4nnxepvd /8lper kWh.    dollars per hour per meter

  (a) A particular househoh nf9o47, yvvx.z)i* p++vj 5zhyc/fnv j3qva ld uses a 1.8-kW 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 l4 wyge 0u+a:yo7*bkh lc xa/ kmhg8u+-engths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to thexugaw0uo 8gkek bh*: ayh/l+ cy7-4m+ resistance of the original wire?

  A 1200-W hair dryer is despy(t5 cx(k7 rjigned 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 does not becomaa*r)vn 0);r.fk;td:7a4 c jpkp no;jiw9ece e so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum c4)rftacp w;;)e7k9;* 0or paj:jncdane. i kvurrent of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equ nb ,ln7-tax(pio93 moation $I\,=\,1.80sin210t$, 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,p;ngw crh+k3kilso;ycg. 6 1 65% efficiency delivers 950 W of energy per second to the interior. ygw+n3,hc;1 6i.ksgc;lpk or 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 the saenh5y t/ojh+s1*-tfof- zbk:bj 0:e qme material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the s- -*j/byfh+bot0nt :1e5 qhe o:jzks fecond? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of v46a a2nr0xao yew a;8uiri v(7olume $62\,m^3$ 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 80mb;nn,1s;i a+yt 3ue yrngu 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 batterie1) haly if1di:mut (.ms as its source of energy. Its 1fm:m)iyti .1 lhd au(mass is 1560 kg and it is powered by 24 batteries, 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 a resista1 0qw o2xei(xdnce 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 designed to carry97*ohnk+6w i mb: dxzg an 11-mA beam of protons traveling dk w go+6 nh7:*bmx9ziat 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. The connecting cord is copper wi -;,fr6kki6o;tuzbb5hw.wkmsuf --pre with a diameter of 1.628 mms.wi-fop ;566r uf, kuz-b mkhbwk-;t.
(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 h,l0g p*- 9shvzoa)hg95 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 thoglhpv z -*0,ha)g9 she wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is e)8ec:+nusa m off to about 13.8 V when the + ame)8esnuc:car is on and the 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 120 h*+4jq4j;r9dne7 jp0ugpi9ux+j l onV and 40 W for household applications. Lightbulb B is rated at 12 p r ++dh x90j7 9jjj;*uiqn4ng4olpeuV 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 connect a s57h0dg 7t7jzz(ud; oaneufyc5v 72wpet of appliances at 120 V, which draw 2250 W of powervn(t2o57fd7u ;y zwph570ceuazg dj7 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 drp3eiu;ji) (7wv b0wf la/a+aiameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of /f 3 v;p rwualb (aeij0i+aw7)this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly s/ )oog rqm1*sso that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage s /sg1) *smooqrource?

  A tungsten filament used in a flashlight bulb v7cvt4y :,o.lq key: ujo3ck3operates at 0.20 A and 3.2 V. If its resistance at 20ky : okcuo7:e4 qjv3y ,3.vltc$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$