What quantity is measured by a battery rating given in9ovcdv39zh y. ampere-hours $(A\cdot H)$ ?

When an electric cell is connect)s3dk(. funxl-a6.o;f v l+dwl ;lt3 b gz(evged to a circuit, electrons flow away from the negative terminal in the circuit. But within the;+3.(x z(sldnflgav k-lewvb6f.3o ) ;u dtgl cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used q-af3:i rwm gf47j ci+up: battery current, battery voliij-: cr4qg+ 3wfma7f tage, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.8i jaqp ilhwp70.;-*vbg (xz lyvi3u0” Since it is not really connecig q l3. p;l-*aivjp0i 7(hwbz0uy8xvted to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immedtvywj /m:d5-5qo 5mm c8qql6k iately. You don’t have to wait for water to flow from the faucet v:t/ovq6 qcjyq8k d5mml5 w- m5alve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resisydjd7s/kxq 8qwzcntgs45 ;3ye k ,;d2tance? Explain;5 dgddynj2,zkk; 4ecqw38 y/xt 7sqs.

If the resistance of a small immersion heater (to heat water for tea 4lbn( ejaalvk *6ua 6jzd9j ve 5op2.,or soup, Fig. 18–32) was increased, wouv94znlp526a,u . l*( d evjaak jeb6ojld it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of len7.w+) 8 rtkgxajahn:z gths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least r: ahn.+k7jwzx 8 trag)esistance, (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 lightbule1lgtscj (,pgt0kh+zpa4 1j 3b burns out?

Explain why lightbulbs almost always burn out just as they are turned on and*)z9s,.vll+8 acrcea gtl)gbh;(z rb not after thesh zz lgc(blv8 , rr* ;.gab)ae)9tl+cy have been on for some time.

Which draws more current8wrmo /22 u8r87tgjg jp5cgix , a 100-W lightbulb or a 75-W bulb? Which has the higher resis2o rwg rgc5 /xgi8tjpj7 u82m8tance?

Electric power is transferred over large distances at very high voltag+nmd3taqi l8 (es. Explain how the high voltage reduces power losses idn+3a(q8 mlitn the transmission lines.

A 15-A fuse blows repeatedly. Why is it dang xg+eqd/gr.+ .uqhp,*7x6kh xv 0hakcerous to replace this fuse with a 25-A x g* qkh+pq,xx7+ eukv/h0.ac ghr 6d.fuse?

When electric lights are operated on low-fre+mlmfvu , 4z)rquency ac (say, 5 Hz), they flicker not4fzm, )mrv +luiceably. Why?

Driven by ac power, the same elec;xsz38 dvo*ji() n77b z nclohtrons pass back and forth through your reading lamp over and over again. Explain why the light stayssv)nzh8b o37jni lco;zdx *(7 lit instead of going out after the first pass of electrons.

The heating element 8t, ts: u9lxmv1qc nr.in a toaster is made of Nichrome wire. Immediately after the toaster is turned on, is the xs vc,n 8.ut:1rmlq9t current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Eq6d mh h k0w8v2:d7kocxplain.

Different lamps might have batteries connected in either of the tb bcup 5ikx*+p;u-1ah8 r n*oywo arrangements shown 1kxro*bn+abp c;i5 y-8p*uhuin
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How m h +gapwe rpj08c -hvx6kg+*z8any electrons are flowing past any point in the wire peg phvac6jhwx- *88z ge+k p0+rr second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A e)dng( d 1c;42rp,/ qvzc m/rdpmzcg ,for 5.0 h. How much charge p2; cn/ cez,(gmvrp41g m dq,cpzr )/ddasses through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes 8(8 b-s0e yl0roejtpw 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 current of 4.2 dhf sbi wum;2mq0csdfvmib: (1*:01s A?    $\Omega$

  What voltage will produce 0.25 A of current through a 2s.6k 2almobj $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when rh,a zf v;z)k-zb1fyu0kr 3+fsh 0yc+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 heating element wibm3-f4ql4 kinwmz 1d9 th 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 whosed8.iwe il xj5r26 3uod resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmi)rmj* 66aklwpssion line carrying 2800 A (Fig. 18–34). Them)l6ja6rkw * p line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 Aznx )-oiio) *z at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a resistor. ;h0mndtc neii 2k/a u46ih*d0
(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 tungji21)qhgzm q i3m7. bep uk;h8sten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire y+:1i ,dlie sc1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire se-x3im ovv. nijd.6e m(5ms+2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diamet(xsni-mme +mie dv..s3vo56 jer.   

  Can a 2.5-mm-diameter copper wire have th)c/+qn( iyg u1ga d8ohe same resistance as a tungsten wire of the same length? Give numerg)cna y1/qid8u +( ghoical details.    mm

  A certain copper wire has a resistance cx2 x6/vl;tovb 5g7i y.b7jqyqo k9h*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 (origigucf. 6v5/ qvqnally at . gqcfv5vu6/q$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperatuslf4f hs z43v.q89ntopz/ ,trre copper will have the same resistivity as tungsten does 8n qz 4ztshvrs 49pto,. ff/3lat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resifcbp.13vg41x0 -n;pasrmjyb stance 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 househfe22exwz jfx , +b-*qoold no. 14 copper wire (used in 15-A circuits). The wire has diamebf *+ eo-2jx2 ,qwzexfter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.y(np3gt ua6:s 0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for curren:(tg aupy s36nt 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 htx)i 4yujajm v-k(.s/g b-wu(as twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorjx wg().itub4myu(k/s - -vajter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisionkzwm(:lm(m6dd y v70 k 10.00-V power supply, and a cukm7 d((6lwd zmvyk:m0rrent of 0.4212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copper folh(qu xjw( royya0n3 )+lowed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the(w+yujq 0 ax3yr)n(h o 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 ugv9bk7ts7+pjq*g 0kis important that the value of a resistance not change with temg9k gjpv*u7 +bkq0t7sperature. 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 3.3 kW w ysv1k,z4x+o4t;6/t my i 0 i5vtwjojj5 bb/sof heat when co 5t0/ /w i4bm45vo 1+wtxb;yosjizs tjy,jkv6 nnected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power c zg jwo)m+8z6ae(9 zrconsumption of a 3.0-V portable CD player that draws a maximum6wz zaoz 98rem+c(jg) of 320 mA of current?    W

  What is the maximum voltage that can bes-gl:1z)nstt+ ny:ky f9x+i r applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, an flcks b -w gyr72,.(ynrka;1td current through, a 75-W lightbulb connected to its proper source voltage of 120 V. r2ys1 .(k tkn-a, ;7cglrywfb
   $\Omega$
   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 W. Cal)x1x o t-+fl4pm5vrl kculate
(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: 8z3n * luq9efaj.*zg e850 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 Europe, where electricity is deliveretd8; (q t73tppnqjsl2 d to homes at 240 V. If you use the lightbulb in the United States at 128tsqt7;3 l2q j tp(pdn0 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 ;zf yl q+soinrr:l(k +k8:3iioperation foil+s:r;kf i3nq 8o kr(i+ ylz:r 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 does it cost to leave a a*ew iwkp o.d(zk /n3525-W porch light on day and night w5/k(p edkaz*w o.i3nfor a year? $\approx$    dollars

  An ordinary flashlight uses two D-ceo hcen01 i*xu3ll 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turnhc 0 ie1*nuox3ed 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 1/w0hgk* 6h.axg4jn l mhedi( (2-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 rcnkd ,of2p j70fbh:pu 0r(0z, can be used without blowing rbpd0,(pk j0rnff :7z0c ou2ha 15-A fuse?    bulbs

  An extension cord made of m-fh( //d+uqold jg, qtwo wires of diameter 0.129 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 the corj(l+q o// ,udqhg md-fd?    W

  A power station delivers 620 kW of power at 12,000 V to a factt*n q:g oav65 jb:4 aq:v5 i2v:nnnlsuory through wires woa6ij: nt4 *5v: gnqv:nbqa 5vsl :2nuith 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 electroma;o+5uc j6isgg gnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more than c +ujg;ig6 o5s7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water fj(ank+co9a 7+( d nekr;sgpo f- uw3p3or coffee orpokea3(f; o 3u7rcn (-wksjp an9++dg tea. 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 cu :,zov/)1musrz2xhto rrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose 2t*(w z 4m9rc(bqcposc 0r5id peak 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 resistancefq xyqt+5*5pn gu :0fc 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 alternating current in a 1500-W0o,po g(uh 3zq device is 5.4 A. What is the rmsoh3g 0q( ,uzop voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected tb) cmkqds+:p *gz)k)p o 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 conl/wgo.:0 e nnh li /y;(y m;s5s ..flo/coytjknectes.:m o y5lwghkojny c .i/e;; (sln to/fy0.l/d to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a p-)ond ie hno8e8jg7 8$240-V_{rms}$ 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 wiry:txivf2 6jx/ e carries 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-dqr **uwg 9)l+yxqcf j3iameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed is w xcuf9)l y+qjrg3**q $ 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 atmosplctb8-w 9zhh(jlx*v. here, $He^{2+}$ 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 atmosphthlm/ht. 8q5 lere, $He^{2+}$ 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(q5wy7 z4orks c 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. The action potential ,)htlr 9t lcd6sf-v(l(5ds mois detected at a point 3.40 cm down the axon 0.005tl(ohv5l-cdm, 6srf9l ( s)td2 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much enefz,uo3l g5;n*p4b dr bg 4d3iorgy is required to transmit 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 axon capacitance; see Section 17–4 *du5zflbdoo gb n433;, gipr9]. 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 poteno5iqefjp 80zy3x*hc *wh 9 ;natial, $Na^+$ 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 s* (f1trnf ivt:is* ,gampere-hour?    C

  What is the average a0w13jq bwom 1current drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the 5c pn9v2v2zn4hz a9kxfn c5v*lights on. If each of the two headlights usesfvvxcz 9h2k9 vnn5p2* n 4z5ca 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? 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.lsw .kms 0gyszo*99jk8-k w6a If it is made of iron, what must its dia ka -y6z9g *9wwkjms.l8ksso0 meter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of tyq45;. * sz8hsekxtt ngnd7m .he resistance R; thatxstne .7sq4 . z8h5kmygnd; *t 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 about 10 MW of power. Suppose that instead of uas7mty*h38*qwd :ntx sing 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 thesyqx* m7ht tdw8*a3:n 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-kW heatetj9pcgg.iv ofp 6l,e*4)v0jn r $3.0 h/day$ (“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 together sidq)m sh2+hjl ;te by side to make a thicker wire. How does the resistance of s)2hqm+ j;h tlthis new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 1d r.v2:o 4(gh7zdm-.dt nm2edpou.plma v2 ,x17 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 beco-znv db)v0v86c3 ap okme so hot as to start a fire. What diameter must a copper wire be if it is to carry a man0pd3a -)zcvb vv8k6oximum current 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 equationzfwb*p)gdz1q 6w5 tdd:+9f- d wqpmr: $I\,=\,1.80sin210t$, 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% ;x8yn f e,tpz6efficiency delivers 950 W of energy per second to6ztp; nxye, 8f 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 the same material. One condu 5 st:tek:q:i3e7eu muctor is twice as long and twice the diameter of theek:eitm s3tu7: eq:u5 second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to hea b6-y9sb g3yqat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V soury9pwj8;cdz8q o6y.z pf ob8b immo;4*ce.
(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 batterizg6as. udcv3*t4k h9 7c sx qgs8l0*xues as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each.9gl7c 3xctvs80* uu*zkxhqag6 s 4d s 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 :pmef3iu,( bja 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 to carry an 11-mA be(nm /xp5 n;ow,0mlili ed2/pyam of protons traveling at very neld/p0xn pw52e,m y (;imlo /inarly 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 h 4 79o(a*ijcxqixv1scord is copper wire with a diaoaiq xihc*17(vj9 s 4xmeter 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 when connec46fiw:aeo u:g* g7g lpted to 120 V. The heating element is a coil of Nichrome wire. When uncoile epug7 g*:ilag f64w:od, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V e6ox6q 8la2tk 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 constat qlako2 xe866nt.    % increase

  Lightbulb A is rated at 120 V angj15uc jk v3n+9:ykygqv-l;e g5ez0rd 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applications9 kk e5lq-:;n 03egjgrvc5vyzug+1yj.
(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 ap9 55ncfft e2,5 y /hixopc;mstpliances at 120 V, which dr /n s5,yxpm9hf2fi 5;cc5teot aw 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 and an outside diameter of 5zlra,7d 5cquw *5jw,5gh(l liq :;+gw ugn5ft.00 cm (Fig. 18–37). What is the resistau,fww5:dcg r(+z thll,iq 7ngg q*; 5jal5 wu5nce of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that it,gz y7l) mklhaest 0/.zc;6les length doubles, by whatlha70s lme/lyz.t, c)g;ezk6 factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operjl4/uh ,-w5+ fqan 7qbq k:f(+ zfhges0fmc1a ates at 0.20 A and 3.2 V. If im+kfa+g n1j:lqbcf fzu(f- / w0qeas4q7,hh 5ts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$