What quantity is measured by a battery rating given irkl.y n* yq+rbf7(oi. n ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, tmj :f7sfq6o1 electrons flow away from the negative terminal in the circuit. But within the cell, electrons flsff 76m1:jotq ow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: l9 8i3bj*nhs pc(o qb.battery current, battery voltage, battery energy, battery power, or battery r8cq (ib l9nbo3*j.phsesistance? Explain.

One terminal of a car battery is said to be cvj /.ddaf5eyu n2,/xjonnected to “ground.” Since it is noa/ un/y5,.jv d2 edjxft really connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You don’t +08mz8zeobr - vy (eungwi1w,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 to+uymewr(8-, 8 geniz0bz wv 1he terminals of a battery?

Can a copper wire and an aluminum wire of the same length haves t:+ 2 n;,nmludvozh o wme/f,z;y(2q the same resistancem2yhlnen :+/v 2ou,o,s;tqfz m w;z d(? Explain.

If the resistance of a small immersion heater (to heatrc feo8a2gg5bqc00sxow 9 h-a7my:l 6 mbv:2 w water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Explainvc w2 a l9 gxmymr:f0b5cb7go:0qo8-s2w h e6a.

If a rectangular solid made0xj ns0odnrt.o05a 2 c of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest res5n0c rnd a2xotsj.0o0istance?

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 burns outpx qnf4,kw7 )cvk1( kiel,,p5z-cuug?

Explain why lightbulbs almost always burn b:qemkz 59o jpa .iz*(out just as they are turned on and not after they have been on for some *:.jebz5azm(pk 9qo itime.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whichl s, c6uy)b;fw3pkfoozz npxj9 2g 6+* has the higher wcskz39x p6,6; fybf2*luz)onj o+g presistance?

Electric power is transfertgs-.o e lu eq567e:urred over large distances at very high voltages. Explain ho5u7 s -eg.oelq6ertu:w the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Who277qyfkwi,9 -p e+g ;hvk;illwqk ch2,bc;gy is it dangerous to replace this fuse with a 25-A fusc2; iefcb k9,2hw+q7lip,kholgqw v;-k 7g;ye?

When electric lights are kn u*1 en 83hvw,pm5hioperated on low-frequency ac (say, 5 Hz), they flicker noticeablym uewh* n1nvp5h i3,k8. Why?

Driven by ac power, the same electrons pass back and f(z8e: mj:)zx6p lvlo+q izt0 oorth through your reading lamp over and over again. Explain why the light stays lit ins(: ze 0 l:pimzvzl6x+ to)8jqotead of going out after the first pass of electrons.

The heating element in a toaster is made of Nim7t.hr vadp pc2 tv8/4chrome wire. Immediately after the toaster is turned on, is the curren2dp c path/v.v t487mrt $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in yh8r ctz7pb.6a resistor? Explain.

Different lamps might have batteries connected in either of the two arrangeme7 w,a5idbb3ey+ v.mwz nts showne, 5wbwzdi+v73m ya.b 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 flowing pastw :1kn:5ae4trjt8 kq: eg khv wd6d(1u any point in the wire per second?ww4t:81uh ::dn6qk r 5(akvtdeekg j1    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a curre1frw008o ni vjpj2m0ww w4*glnt of 6.7 A for 5.0 h. How much charge passes ri040mgw lo*j01pw2wv8j w fnthrough the battery?    $ \times10^{ 5}\;C$

  What is the current in lifx;x9+unge7zp a 7+ (x. lgdok.5xjamperes 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 pro)hc 9)7/rtihnzou+dvz)v7t b cue1r(z1q 7hx duces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current -q1gb1 wh.(ys-w 3e3gm pbmztthrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 1 5t /y0 bwd,f-uarnh)b20-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 hcmgg//x (+mpotm .swd1, bclz)p:bd7eating 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 wgdy )nf(v8ji 9wa xp5,hose 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 lineq2rs06ulyg 3w carrying 2800 A (Fig. 18–34). The line has62 0qwryug 3sl $2.5\times10^{ -5}\;\Omega$ 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 6.5-3w opg wuxury/ y*5 k58mv8bn0 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a yqfu v kzkv i.z;+94d6bs8fg4 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 ld;m p :w ch8qkluq76o(ength of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of nj(k .jh*ogb (a 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 in df. iy4/epmy 4fiameter, to 20.0 m of copper wire 2.5 mm in diame4i epf. myyf4/ter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tun 4neibz c-d9/lgsten wire of the same length? Give numerical details.d-4i n9/czble    mm

  A certain copper wire has 4k6b )2 apwc cscw9/vllhrd 89a resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wire (or s;k4+ -tux+fsysh+ hciginally at cxs; - y+f uskh4++sht$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will hatu;o35(d s pjh 0o7cyfve the same resistivity as tungsten does atf ;y3u h s5oocp7(0dtj $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistan o(5yrh ix.ozp5n5r5j/cuv1 ;;axaq ace of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m length of household no. 14 copper w47omnqvfp8f+idj;: . iyefn .ire (used in 15-A circuits). The wire has diameter 1.628 mqoy pn;+ f8.imfn: v4e.i7j dfm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, md+c 3nf+t k-eand 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35entc-f++m k d3). 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 hqnr ukb:*s ;o/5nmg.*z .ewgo ave the same resistance. If one has twice the length of the other, what is the ratio of the diameter of thenme *ubk:rwqz o;.go /sg5*.n longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected zd7zv-+,u9 bh m cvkh;to a precision 10.00-V power supply, and a current -;vhzhv +z cmd79,bkuof 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 followed c)vh sf+1bv ro7ua;, oby 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85+oa vos h ubr71);vfc, mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the value of a resistance not change3 p -l*v3knwaa)atbe7 with temperature.n3 *akab 73)wp-ela tv 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 pros -ge.)les *yf2rlm,pf p65dv7 a7 qemduce 3.3 kW of heat when connamdlm*epyf ep. 56 sl 7-,fv7rs)2gqeected 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 spx 2 6n53 l+.o(mveu+ p2trgd ylt6guCD player that draws a maximum of 320 mA of cu l+52y dtlgg6 us6vop. u+2nmpe(3r txrrent?    W

  What is the maximum voltage that can /zsp*txn -6 f )4zdqlrbe applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistxo*lrhy4;mi,t2dpu m6 7, gqc ance of, and current through, a 75-W lightbulb connected to its proper source voltage of 120 V. m,mc*hyt xpq,7l; id gou62r 4
   $\Omega$
   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. Calculate jdxhnb;pi qyx(r 4n7t/a2k,6
(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: 85x/b rxss 8f9h50 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 Europbsv 7+60k9z66+ btbs mf aavi:4fnmu me, where electricity is delivered to homes at 240 V. If you use the l: u +ab7b tv m0za sb96n46ffvkmmi6+sightbulb in the United States at 120 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 opera q5/bh*zv7k;s0o+o baob1oe ption for a total of 15 min? At a cost+obb*5 pe oqs1 ;7bv hzko/o0a 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 u;y 78) kszlxrzi*/ 8ej;glhskWh, what does it cost to leave a 25-W porch light on day and)zs78leh/s*;yu; 8l grzx jik night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V udnw2d x-f0(sbatteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on.uw(ds2fnx 0-d
(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 storx yn.:cnt, q(f74zgixed in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected93 emje*zo 8bs to 120 V as in Fig. 18–20, can be used without blowing a 18z9j osem*3be5-A fuse?    bulbs

  An extension cord made of tb- 0q-xxol )tawo 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-b0q)-xaltox in the cord?    W

  A power station delivers 620 kW of power at 12,000 V tol-pza up 6mi(4/o1 j8u.jskgh a factory through wires wuzp m4 k8(. gh-j6l1jousap/iith 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 electromawoy3 8s.q4 ccggnet connected to a 240-V line is 17.5 A. At what rate must cooling watg 8. cqs4wcoy3er pass 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 carfj8/m8 hkk : ,tvejo)a to heat a cup of water for coffee or tea. If the heater can heat 120 mL ofmev:8 ,kj) 8hj/katfo 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 curremn9lq r5q.kvtlf 6 s4 sdk2x0.nt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, .).fbevm4bf d;sx2pqis 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 of9rw9ldr f bz12 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 alter*m;h i;0cu azvnating current in a 1500-W device is 5.4 A. What is the rms volt uacm;i*hvz;0age across it?    V (Round to the nearest integer)

  An 1800-W arc welder is con,cte9p8vq4+ cjm , ivznected 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 conne,xsp+riql7 k1f 7-k zhi6 f,emcted to kif lr76e,7+qifshx1-,mzk p a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectep9 ik9x16 i.*hp bcdlvd 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 carrie7bsjn 9vk0rv 4 h18ylgs 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 carr )q6kp:cc/vnnies a 750-mA current when 22.0 mV is applied to its ends. If the drift speed qcn6)kn:c / vpis $ 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 atmospherlcd :g1)bu2at87ufu te, $He^{2+}$ 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 ozajy26.w:i x 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 field acj6c-4dyhse :yo.i) adross an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated withx8me 6 lhnl9g, an electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulationmllg h ,89ex6n, 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 action poten1u38df,m vr6nms5twn tial 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 17–9]. What minimum average power is required for3sm6v8 t5rfm d,w1nn u $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentif+qf+6unqeojlc .3w4 p hv;6 ial, $Na^+$ 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 there1x:s(bc-1 jmni9i1*nulsn t v in 1.00 ampere-hour?    C

  What is the average current drawn by a 117i/7mmy g:wp ;gyasp e g/ewwd(a*4 f.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car(6bj vo g 3v4o/3j;q2tnto: gbnarg f9 with the lights on. If each of the two headlights uses 40 W and each of t2 3vvgf(jg6nra3n9oo jqo4bgt:;b /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 hef t tvh+-c-m/mater is 5.4 m long. If it is made of iron,t m -h+-tvc/mf what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reu f6*ou -d-fgociprocal of the resistance R; thato6*gf fou-d- u 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 oq r)jbr8a. ej,(7swsyf power. Suppose that instead of using high-voltage lines to supply the power, the pa,eq8 sb. jwrs() y7rjower is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househoqfnia zv 76vfv ,:e-fe+yhi75ld 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 lengths ary+5 yl)-pxbo hy:lc c:e wrapped together side by side to make a thicyhyy p:l 5c-+)oxlb:cker 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 16 8mt .pkixowg6:lj +y oq9)vw17 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 9ru8icq)of 1ythick 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 cuf u981yrociq) rrent 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 thersp (7sv;3 wvd equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of energy ped9c oxg,c+ zp*e1-5nbd9aueer second to the interior.*ucg-1 e5dcxeznpoa9 b9 e+ ,d 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 matertj uv9i 6v6*lkial. One conductor is twice as long6*jkvit lu69v and twice the diameter of the 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 heat a room of voluq 8aq3z:hqh18r:a.dy/x6 w9mf cl tndme $62\,m^3$ 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 2)leu03qk pd6o 40-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 ob21jg* fr4 vvbatteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, eac o1jvf4* bvr2gh 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 hassrvxv 1;6r/ pd 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 to carry an 11-mA jp1cc/fc4(i g beam of protons traveling at very nearly 4c (c1jg /fpcithe 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 dri5tz)g2g1 dptaws 12 A at 220-V ac. The connecting cord is copper wire with a diameter g z5gp2dt1 it)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 whenvg 1i/8r ojff6(rz+kc connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total g1rfz+ v6rf /j k(o8iclength 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 when the car is off zej,k 0c rxt ff.8yh),to about t f cyx0jz, )h,efk8.r13.8 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 120 V and 40 W for household applilv ,ccae2stti0+h0 m 5cations. Lightbulb B is rated at 12 V and 40 W for automotive applicatcehat5i0s v+m2,0cl tions.
(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 vj t xx41(*)z:ay evetpi,j1m v r+jc,cm is used to connect a set of appliances at 120 V, which draw 225eyv jjx4e( cm z )j+x vrvpta*1,:t,1i0 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 ins,/ smci0ev; 0ny,hkw)6: yacdfa ,vsjide diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is thnc,vejf;yy,ck, mdaw6i a/v: )0sh0s e resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doubl 8 b x2czz5k8ek4ljt3aes, by what factor doe3kj b4 ztczkel85 ax82s 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 op2 xb/ljudui ap7y 9z(0erates at 0.20 A and 3.2 V. If its resistance atd02b uyzl/jia( 79upx 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$