What quantity is measured by a battery rating given in ampere-hk8yue1y10yi r9wx(*nub*3t s s kducg(y) cv :ours $(A\cdot H)$ ?

When an electric cell is connected to a cir:kx9n gpvy .p6cuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative termg9p6ky :x.n vpinal. Explain.

When a flashlight is operated, what is being used up: battery current, fis+3jkut- jlut+0ib; 0b o5qhyv6k 0battery voltage, battery energy, battery power, or battery resistance? Explahj0tfu 0i i tk3+o5v k0-suljq+y b6;bin.

One terminal of a car battery is said to be connected to “ground.” Sinceh9o g zpdn;079exxsm+ ad.4ix it is not really connect9;+zsda4hipmdg .ex7o 0 nx 9xed to the ground, what is meant by this expression?

When you turn on a water faucet, the water usuallj t* 69o7amqb1s7 n8sdgmgi-5i x3 skly flows immediately. You don’t have to wait 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 obnx t8go q-1iljim3s*7s 6k79 dmga5sf a battery?

Can a copper wire and an aluminum wire of the same length have the same rfi or,-5xq3g (b dp-yoesistance?, 5p3ybido-xq fr-( go Explain.

If the resistance of a small immersion heater (to heat water fo ye 3jxj/ opy4 cvn*j5v sm+;8xkb68gor tea or soup, Fig. 18–32) wasp6vcy sk;5g+o vjo 4 8jx/b*ny3jxm8e increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengt f x:tik:/j-of oi 05u o;)rgf)xppdcv).whh0hs a, 2a, and 3a, how would you connect the wires from a battery so as i;)t: )ox:hv-r)/ oucwdxf .0ojki50hfppg fto 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 g 0s opu 18poppc86tt/lightbulb burns out?

Explain why lightbulb 6zz:p+ov1xe xemc d0f-,ar, )nkd8xbs almost always burn out just as they are turned on and not after : nf6z+c), ae1v -xxkdbp8xedorz 0,mthey have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whio-.t-:d bo,nr8q aem0j*m ca +y8y inoch has the highery c 8edr m+b8,n-0qj-ooaamyo :nti.* resistance?

Electric power is transferred over larg,5pae fojwv 8jj1k 43,*w- wio q4saewe distances at very high voltages. Explaie i3ks vow8, ,1aow 4jjw 5j*4wq-efpan how the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse k2qrp) py,v;r os**u swith a 25-*pps)skr;o uq, *2rvyA fuse?

When electric lights are operated on loiwn(r2;oyj b7w-frequency ac (say, 5 Hz), they flicker notice;i2onrjyw 7b( ably. Why?

Driven by ac power, the same electrons pass back and forth th uru16xup b3n4rough your reading lamp over and over againbur 136u pu4xn. Explain 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 after 9;syu dej,034fbqrfk r+a ,5(zcumm o the toaster is turned on, is the 0fm e(rbm f35;ks,dz9acyou+uq4j, rcurrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a rre 10fed 0 c2oq,i,vypesistor? Explain.

Different lamps might have batteries connecu7ey3-qdlr9c kr.l v5 ted in either of the two arrangements shown 5 yl3 v97urldc.k-qrein
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wir +l 5pio,8)gxhnso3vue. How many electrons are flowing past any point in the wire per se+ gun)olx i,v5 38spohcond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6d56 mmfzybr ;1.7 A for 5.0 h. How much charge passes through the battmd 1ym6;bz5r fery?    $ \times10^{ 5}\;C$

  What is the current in amperes i6hy/c/j2* klt2okln tdmlh5 :f $1200\,Na^+$ 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 current ol jd2 7lyx1kbo; rw*xa a:il7+f 4.2 A?    $\Omega$

  What voltage will produce 0.rffg3s2bt:r. 25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A whi w hti/ow,v5bun5r( 0en 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 as49g9h ine ug0 .mbh9v 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 whod,nf-7h yqe ;fse resistance 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 (Ffqph.. d-z6c y2swex*n: g 0cfig. 18–34). The linwzy0. -s cgpn.qfh2:e *c6 fdxe 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 ( 8b c; r(rxptk2+,nbia8sdsuA 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 throug3hlz6owub( t:v )j o9gh 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 wire1f xd5g1f1ek 1 hyo-k1l jkf(v whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper5sgp jo *u+tr- wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of alu cdz:xinz(w nrofc+h5:58 gk4minum wire 2.0 mm in diameter, to 20.0 m of copper czizh + rxnwd::4(nk5o5fgc8 wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance kh354sbvuy v1as a tungsten wire of the same length? Give numericahbuv 41yvk 53sl details.    mm

  A certain copper wire has a 5wyf p9v6ecm0 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 ewt 8-hf;x:tv raise the temperature of a copper wire (originally at ft-hwx; :te 8v$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempe .8zdnzto9au1rature copper will have the same resistivity as tungsten doeuz9dan t z1.o8s at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistaad8o/vcr,f - vnce 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 ao.6rg ma,0n:ova d 9ax 26-m length of household no. 14 copper wire (used in 15-A circuits). The wirexo m6g:.,av d0rnao9a has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths l:xy,t+ 1c1ud8aj8hplg0t o d1.0 cm, 2.0 cm, and 4.0 cm, lying alo djt8y1dato+gp ,1 0:h8xl uclng the x, y, and 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 have the same resistance. If one has twice the leng*gvw /b)gz 0ri t2o sqg-. fle)a*/qamth of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter wig)atg l.0q/2*i-wvsf/ag)e mrbzq* ore? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.06fczu;zqkt eeb-+d9 )0-V power supply, and a current of 0.4212 A is preczbud-ez+)9;6 ectfk q isely 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 consi d;vjtl/d6/d 0ixeq1ists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the compitvi/jx0d1 l6q ed/d;osite 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 importan9c b;mnsu, xx;t that the value of a resistance not change wi;n9muxsb,xc ; th temperature. For 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 produce /*ms 0z9el.rj n.qwtl 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the 0r *n lje.zlw/qm.s9t element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable6dlae92ksv r (rpxkrw1(2y g3 CD player that draws a maximum of 322plg9we s1r2yv(d3 6(rk xakr 0 mA of current?    W

  What is the maximum voltage that can be applied across a29s8z i9-udvogdrvh ; $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and curre,g )f+kx ep q:::lukvrnt through, a 75-W lightbulb connected to its proper sourcur x):elv:f ,kkq+g p:e 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 vx4jw svn3u3 3 u9(q(sx eftz8cu u-s1at 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 andv5oa)ro0l,1 ri tbj n- 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 is delivered to homes at qc j 6n3kj 22mvumd,u, i6ypg1240 V. If you use the lightbulb in the United States at 120 V (yujc, 66id 1vp2nm32,mujq kgassume 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 t1z4leq i*hlhg.z+vo(m 5+s ) gtbs(vuse in the morning if it is in operation for a total of 15 (vhe+1g .t5i 4s*oz lbtmzshqv lg)+(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 lig 7rqqpqytk2g) 4x:up, i c5ms*u1fr7fht on day and uk mqp 4: 2ftusqxgyi, rq51*fc7p)7rnight for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connr 8v dy(:j9b85zz3g1xxwq3bsi ,ixgm ew/j6fected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 v8 xjz3i iy/ w grqs3(gz6wb:b5xe1 89jxfdm,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 s-jctp rja 0xf)5sjw)s k0zoz b9:bj;6tored 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 used w+ 3sl 4h7gr/b lbzek-cithout blowing a 15 c l ebh/s4-+73rzlkgb-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129qxsa4sl.k ;p6o ig *c4 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in k 64;qx* cs. poagl4sithe cord?    W

  A power station delivers 620 kW of po cesel-j iq1+,wer at 12,000 V to a factory through wires wejcs-iq ,l1+ eith 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 10g.gbqd+du twhat rate must cooling water pass g+qtb 1u.0ddg over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat )f2rd uqb: quoqdc3;ax:a.ds. ozq6 7 a cup of water for coffee or tea. If th2ax:ofasqrd7ddb uq6 ;u .z)q.:c3qoe 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 currquh20 qjq+l8 niu4g3hent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak v k7 qiiz9w7(vvalue 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 resistan *4;lhzo rax ksx1c+-uce of 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 alter58/wro4zjrvorc )d d 0nating current in a 1500-W device is 5.4 A. What is the rms voltage ro w)d0rvcz8 o/ 5rjd4across it?    V (Round to the nearest integer)

  An 1800-W arc welder /bxl 2jca)s/qgd0k ;his connected 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 connec4xbqdvk80hgqnml:*z /hy5ida 9te/ : te:n8 m/e9 xhlk0zv4*/yd tqba5ghd q: id to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected3qti esxgvf8 *cu ;);l 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 carre i zjy*mo8k; 96m5rnxies a 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 -+o sd9h pscps0tw.u9750-mA current when 22.0 mV is applied to its ends. If the +p p9c.ustw-0ssohd9 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 /baz2 g ekcbciw() a8.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 hy()lr+gx yr +q4bes;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 the electric 0zzm+ io ue8:cfield 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 o06*ogyr s h(y.nzf8delectric 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, the time required ihsy 8 dg(ofo.06nyrz*s 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 h .avtbrbu9 00required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one 9b0rv ta0 bu.hpulse 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 potential, sllnx /k33rjh3*j )wj$Na^+$ 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 idjyzo)4 4 vwb0n 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120yn* a hx7qj q-bcs*wc+7wf -d--V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a cut(x od+khy8gh 7kn3 x b-44phar with the lights on. If each of the two headlights uses 40 W u h+ x(n g4bdh38k 4yxh7okt-pand 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 $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-nc zfx 3e.oe 25/xoti(k)u0nsW heater is 5.4 m long. If it is made of iron,sec.tunk( oen 53x x/)fi zo20 what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of dm7i *m4 lx zl1ori90nthe resistance R; that is,4i*m1 0m o7l 9drixnzl $G\,=\,1/R$. 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 highm b4g9erx d fxmc45l+8c8eb;b-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-mf g8e4x5m;b49l8 bcedxcb +rdiameter 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 1.8hn::2l, bqk uzh.jy pz/ow l3.-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 haltp4.t buofq(58 (ub kvf and the two lengths are wrapped together side by sif((4bbkpvttq58u uo.de to 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 for 1epvxy ,l z(f:3c5bp.a17 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 mus y mrt 7snmox,7-yk-3ft 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 oo -3x7m-rfms7 nktyy,f 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 e2xml1 0e kcr mcl*/-(r gv,o-;zt ;vljr-hcajquation $I\,=\,1.80sin210t$, 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 asgzihi0g( 09 it 65% efficiency delivers 950 W of energy per second to the intz 09ghi is(g0ierior. 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 conductorc;cya,98b ut z:op, w;y/lc fqs made of the same material. One conductor is twice as long and twice the diameter of the second. What is the rati;cl,fzy, wya9 c 8bctqpuo/;:o of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of *zqz frjnh2 52volume $62\,m^3$ 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-Vqs:bs nh3cr6, 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 vec bkv6y+ :zo8jx9fv: qhicle makes use of storage batteries as its source of energy. I:cx qo+v9jz :8 vb6kyfts 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 resk( 5yhijb ic37n4cb/c1 amso+ istance 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 dej dso z-t2xf(,lt(y pz5 fd5xy-6kf 2hsigned to carry an 11-mA beam of 5h( yd(sk26xdofl ytxt--2 zfpjz 5,fprotons traveling 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. The connectwu +xju(9 :kzping cord is copper wire with a di+9xu:(kjuw pzameter 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 Ws5yidb + 3yq(q 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 3d 5s b(qy+qyithe wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltv ff36e 4. td1ac-pkoqage 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 to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains c4-foq1p3kdva6cef t. onstant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household anmvzp24n6u3 egx v7aj +g85-zropej1 pplications. Lightbulb B is rated at 12 V and 40 W 82x4j1 -vnp ag+eno7vuzepgrz5 6m 3jfor 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 set of applianfn8tu vu eq* 5ki2/lh*ces at 120 V, which draw 2250 W of power uf k5 qtne*u2l/i8vh*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 in,k kt -5vuo3lc+7i oxuside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the reso vt ixk-o5, +l37kcuuistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lengt5nusg:h9e 2 s0 +mrd ;esub9rch doubles, by what factor does the power dis;sed rugh bru+ e9ms92:05sncsipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates 3:rz;cx fy-sl4 u7-e ilowsg;at 0.20 A and 3.2 V. If its resistag7u -zfwsx4eylrlos; -:i ;c3 nce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$