What quantity is measured by a battery rating given ytif 4u3t; v5win ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons fzjfd gzr1 )a25low away from the negative terminal in the circuit. But witr) fzagdj25z 1hin the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being5dsz t +ghvbw+; 8,nwcd 1tea; used up: battery current, battery voltage, battery energy, c wtts ba1dg;v z+h,ed5+w8;n battery power, or battery resistance? Explain.

One terminal of a car battery is said to be8uzzu-oj( 8 ex connected to “ground.” Since it is not really connected to the ground, what is meant by this exu8z8zje(u-o x pression?

When you turn on a water faucet, thev.z 89 2qe c4gxbipg0s water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout2 i08qbc.9g g4 evxpsz. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and aheo+1c nbj 95 gys:l4wn aluminum wire of the same length have the same resistance? +j5 hl4 n c:1gbseyw9oExplain.

If the resistance of a small immersion heater (to heat wate izrf9vm4t:/mr for tea or soup, Fig. 18–32) was increased, would r:mz9/vitfm4 it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, ho3 ;cs4s*oj/ p,k8zqv xr9fbohw would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest4rkpbcqjvo9/f osh *s3 , z;x8 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 lighot/1k5) n2 vkbe eby3cl:h ld6tbulb burns out?

Explain why lightbulbs almost always burn out just a vtfz.,sny:mrm86q. r s they are turned on and not after they have been on for vs8 mn.qrtf,:mr y6 .zsome time.

Which draws more current, a 100-W ligh1:+9ex mfk3zu: kubiytbulb or a 75-W bulb? Which has the higher ku fzbi93 xe1:+:uykmresistance?

Electric power is transferred over largeeb o ol3qycd/ :e6pt3( distances at very high voltages. Explain how the high voltage reduces3 6dtyceo( /olqbe:3 p power losses in the transmission lines.

A 15-A fuse blows repeatedlkxux,ekwl v c49xlc+5v.f1m 0y. Why is it dangerous to replace this fuse with a 25-A fusc51 l9x 4xvkmxkwl+f,c.u0ev e?

When electric lights are operated on low-frequenlc-orjv p8g*p*-f hkb2vg 7-a cy ac (say, 5 Hz), they flicker noticeably. l2- 8fh p agopjr-ck bgv*-7v*Why?

Driven by ac power, the same electrons pass back and forth th uxq0eo42( yoj8y; qzvrough your reading lamp over and over again. Ejo y; u824ox(v0qzeyqxplain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately afterr)jxu8km0c*/n(rd(j hhw qg 5 the toaster is turned on, is the curren)u*jc(h8r n x0(rg/mw 5 djhqkt $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in e8k d+ rh k;qh6et)a* ,xqed*g1ux pq6a resistor? Explain.

Different lamps might have batteries connected in either of th nnh:cu, gj4z)e two arrangements showcun,j: nghz 4)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 elec6.ymvvttx3+0 (ro c eetrons are flowing past any point in the03.oyv+6(c xmv rete t wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5p 9xt7cav5gw/.0 h. How much charge/ cxw9t7avg5 p passes through the battery?    $ \times10^{ 5}\;C$

  What is the current inku t.6av p5mx6 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 lbo1:-* si npq7s hhu5current of 4.2 A?    $\Omega$

  What voltage will produce 0.s.h:.3 +t y fmn.jzzce25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A wivh 1p/51kgv ;;bnu: mxk3z bjhen plugged into 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 heatv rnxt cn8g0uqtyl72 +-n9l- zing 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 resistancfm q dmdkj20+6 fox1sxxz)r-6:o u-ok e is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc elx.0hfg1 4c 1e;rdwmwv/t*b vsectric transmission line carrying 2800 A (Fig. 18–34). The linrtd11v m0x; c*w/4 ghwvse.b fe 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 A at 2:cz4-rif :q.k aw mizf9bj; +t40 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 resisttzk 4h4 qiv3wysk8.8k or.
(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 wird2,-b )l 2x3ccumb6pm33o du/qjwawle whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper/jue +a nzx7bd2vey, . wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m okoce w- /o9xw/f aluminum wire 2.0 mm in diameter, to 20.0 m of cop c/ow-kx9/e woper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tuhc)lekny 8i,kfnuh*(t h 0o c n51i+2engsten wire of the same length? Give numerical details. e05k, 8( *fhukcye+it2i nlno ch1)nh   mm

  A certain copper wire has 78unlqw7lw qoad( jo)r n.)p;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 oq4tmtgo3j.u3z( yin .f a copper wire (originally at m t(3g. in3z o4yutq.j$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature mxk2dhg7ah i uwcq(j+r,;:b+ copper will have the same resistivity as tungsten doehudx+k,7g2( irj wq m+habc; :s at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about h3yl:3sulhe 0 $12\Omega$ 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 householnjx* fowp; d q53p c+f+);fqgpd no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carriespnjpcq3;++xf;f 5 )gf wp*dqo a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.wqm0yy+ tix 6i t:d70t) /wkv cm:ukf:0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistanck ):it yi/m6qc 7yuvtfktd :xmw 00:+we 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 have the same resistance. Ikd gds h/ b;jopi90.8tf one has twice the length of the other, what is the ratio of the diameter of the longer wire to the dh/0ib.p tdg9sj;o d 8kiameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V pfj q+y+g :g*p d7j epsx)e3 :u42esdxvower supply, and a current of 0.4212 A is precisely measured asv7 : :p x+2xj fsedeuj3d4)gg*q+ypet 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 conrs4 n0/g6femi sists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV0fe/n64 sgrmi 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 oej +a deawu f wyfc7n;:(*)a ;1o9uygof a resistance not change with temperature. For example, suppa1g7y aefduo*fou;wew)(n; ja9y + c: ose 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 design9 oxxas3y q,(ced to produce 3.3 kW of heat whenx(xoq93sa yc, connected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD play9ifac cz0 3t(jer that draws a maximum 0t39czj af(icof 320 mA of current?    W

  What is the maximum voltage that can be csy)8or 4d:e/ 3ld6nq3bzv qx applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current thro,npl0,)cogcs ugh, a 75-W lightbulb connected to its proper source s,,pn) 0ccolgvoltage 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 110 Wvz .:(-xuh- f+ qr+zrgahnxd lgm636e. 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 setijc,; ga2)fvg5k g 0kvtings: 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 in Eurpyk-huk88 )6k/ ju fueope, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 12 )kfk6yp 8eu /8kuuj-h0 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 power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is in ope kic)qt/06 ypbrat pbkicy6 0q)/tion for a 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 eo2-cjoriy)rzgrpe a0f*k vhu*y)6,)n1n 1 hdoes it cost to leave a 25-W porch light on day and night foro y *rhneg,p1 *kr 1uh)ifc z2o0 )jvear)6y-n a year? $\approx$    dollars

  An ordinary flashlight uses two D-cellc7h,y9bm dnqwwp(lw() w o4( .8wwndl 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turqyp4 ,()wd ohlc(lwwn m.nd ( bww8w79ned 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 storedi ik 5*ol:p,ah 3wdnj0 in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected t qa-s *zqcp4p4o 120 V as in Fig. 18–20, can be used without blowing a 15-A qa44q*s- pcz pfuse?    bulbs

  An extension cord made of two wires of dikob -wx +k4hjqt13 bn2ameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which drajkbqk42bnh-+ towx 1 3ws 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 12,000 V to a h+a8ehx0+.t rc z ut)oi6lc: zfactory through wires with oheat0)thz. l r6u+czc + :8xitotal 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 y(na2 uu c 7f;xdd,kht7c wm*,A. At what rate must cooling water pass over the coils if the water tempery7;t7,(2 xdfc n,*adhkmcwuu ature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to hw6o)ni wf;noo(jbv3 9eat a cup of water for coffee or tea. If the heater can heat 120 mL of water from 2f boow )6ijo9w;(n3 vn5$^{\circ}\,C$ 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 in .iueziig- *1yfph y6: a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peaz9xs razl//i5-d63 kofcd-vh k value 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 ok.:uh )a w) vt,erlo +k:fe;wnf 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 alternatvd2;iy5k i ylpzy 6-h*ing current in a 1500-W device is 5.4 A. What is the rms voltagd 5p*vziy k2-hyyli 6;e across it?    V (Round to the nearest integer)

  An 1800-W arc welder is conn uwrd7y(acf3 5ected 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 adca 8p:b8*ndgkh m/i;qh(v,q 3.0-hp pump connected t*8 /gq ,(in:pd;cbh8dmhka vqo a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to o p,f71logg /za $240-V_{rms}$ 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 currenti i6d7fxi-ljtq )v x7: 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-diammh9 m t*t.o;;e,8 x g3ybvvlzwr3rr*xeter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed3 38hr*ew,tz*vbmrr;go vy .mxxlt9; 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 a jt89dmvfz1f)n7bwc5 +x,vumf2;ehm tmosphere, $He^{2+}$ 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 t:*kintv y 2d7rhe 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 

  What is the magnitude of tw;fwvn j4wpb c 4i061ehe electric 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 witu e0c 5qbg;rf+ 9wubj0h 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 fro50bru jcewfg;bu +0q9m 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 transmit one (c0,q5 lh0smkxxb+)ku1 z y g+mnj4d oaction potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon ca +0xs h+1j5qk cm() ,dbkgn xymuo0lz4pacitance; 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 pot 8y7 n puh79mxr5ut cn5d6bp*nential, $Na^+$ 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 am vpcj, z37pyy)pere-hour?    C

  What is the average current drawn bq ;n bx.of,-qsko 2ax+y a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two h 5e+kl esib5yfnr 8i:gb x-77oeadlights uses 40 W and each of the two t y n5xle7 fi-e io8+sbb57g:rkaillights 6 W, for a total of 92 W, how long will a fresh 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 5.4 m long. If it is made s(g3,wetu.) )0iwp , ,oxev9qmrfsm nof iron, what must its diameter b(,m.n,m)i,wgs storp e9x)3ev u w fq0e?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined asiksw/m/2kce 9e3 ( gxt the reciprocal of the resistance R; t(tew c3/ 2/mskg9k xiehat is, $G\,=\,1/R$. 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 ablr oc5n5:s i3fout 10 MW of 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 energy lost to heat per hour pe3s 55 :nrcfoilr meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.zasyb3:lt q qpa68p 5,i y8,iu8-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 lengths are jj,hdfe+3 +q5ncql*c wrapped together side by side +ln*c,j5 fjq qh +dc3eto make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed fod toml89sxr5l v27xs2 dq*.bzr 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 musqhx f cr0 --92cppjbk.t be thick enough 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 ofhq 9.rc-p c0kx2f-pjb 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 ewi b 5 eyo4n)a*sn .q/muu o5r6i:ztp7quation $I\,=\,1.80sin210t$, 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% efficiency delivers 950 W of energy per see i9t 8ein+v,iqd7yf6 cond to the interior. Find 6tvife,+d 9in q8y7e i
(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 same material. One co o+ dim:ktc2v-3/qzme9,fxe.xwg (i j nductor is twice as long and twice the diameter of the second. What is the ratio of the power tr/x3cemvj,:i.-ikxq fzdw +t o92e mg(ansformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of*e+d7km g7wbm a ,y/nq 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 hookev vmix9qpj/;a i 4a7a -a0uah.d 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 ofyqn 6 n0l:y0tnnlwbr6e0sg08 energy. Its mass is 1560 kg and it e0ys:r0nn00 ql tn 6yg6n8blw 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 lightbur .0nqew.guv 1lb has a 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 (Illinois) is designed tq cfuqdqab -md6:*b*4 o carry an 11-mA beam of protons traveling at ver d-c4b*qqd6 :a*qbm fuy 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 u, +: m(ozzylvis copper wire with ,v+(zuly m: oza diameter of 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 95 W e/ddb(pgd 9okqfujy 681e0u .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. Wh0ufdq8o g 6y d.1b kpj/de9e(uat is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the systek2h:z(i k 5u*uav zy;u,nt ce;m voltage varies from about 12 V when the car is off to abi2*ue c;zk h yn(uk,v:zua;5 tout 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 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),:3lx ) 1bz u3fvlkds tr4zqldvx.u9 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for aubq) drll.du,)9: uzltf33 kx4xvszv1tomotive 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 conne7lvyy:ge cp(a4 3yb 7hy kwd(9u/ qke9ct a set of appliances at 120 V, which dg cy yk9eh(7au :qdywv3k bp y74(e9/lraw 2250 W of power 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 a vs5 . p)1ctg)kq uz68p9selsbd h,dn)nd an outside diameter of 5.00 cm (Fd69 zsdpt1 ,e)u)sp5shb.vgl8cq)k n ig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretc 2r l* r-3tkak9ivvy1hhed uniformly so that its length doubles, by what factor dovyla tk 9kv-ri2 13*hres the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament use*ze-)nk0 /i f,8otffvicfz 4ld in a flashlight bulb operates at 0.20 A and 3.2 V. If its resistantz,vz-ic0 48 f)ilef/k ff *once at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$