What quantity is measured by a x6m+w hn-acc.battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electro8;39f r,ecpfwr 2cfa gns flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative tefcga, p rr;9wfcf28 e3rminal. Explain.

When a flashlight is operated, what i200g qajbrs2f7 v p9dks being used up: battery current, battery voltage, battery energy, battery power, or battery resist7 sjkrbq2v0 p0a2f9 gdance? Explain.

One terminal of a car battery is said to be co,ari, p (l*riennected to “ground.” Since it is not really connected to the ground, w,p*ea ri lr,i(hat is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Yo* diig-1brsu(7y(j9u -.pp oyzsv7 vqu don’t have to wait for water to flow from the faucet valve *7( y-u9osip jy(7dbsq gpvi. r1zv-uto 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 sa6hgz ziyubj)yi3fehp . ;z(8x e5k:n: me resistance? Exez:f g z; )ihb:ejz65ip83yh. x(nyu kplain.

If the resistance of a small immersion heater (to heat water for tea op a-cf4wcu;a*zz +s ,ets4g:or soup, Fig. 18–32) was increasede g:*f4,; pzcatz-saw+c 4uso, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon hagay24,q qs+n7 yu4;l byi3jiwa( ,d uvx9k.nqs sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to ob32vdq9iuq s.ibw+n,,7xa 4 kl4 y ygy njqu;a(tain (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 lightbucx ei f2z19gzn dw8ft7c00b5ylb burns out?

Explain why lightbulbs almost always burn out just as they are,wxzt -v:(bj t turned on and not after they have been on for some timextt wj:,v( b-z.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which hasr w5,nxgg.lvl tfl *(/ the higher resir.xtnv*5l gw/l fl (g,stance?

Electric power is transferred oveu+y35 apaekut8 b 11ohr large distances at very high voltages. Explain how the high voltage ou5ea 8u1 1h+tbayk3p reduces power losses in the transmission lines.

A 15-A fuse blows repeated ;/ambr1/em83uy* /ituuy q )3uqzjgmly. Why is it dangerous to replace this fuse with a 25q8*ie3ub/j3my/g;a1z m) m uqur/ty u-A fuse?

When electric lights are operated on low-frequeuu8x8 m5s0fq x9 vz6 uv* haux9u /q.7vg*wkucncy ac (say, 5 Hz), they flicker noticeakxx9huv7/uz8s 9 vwxf 0q *.uvmc 658guq* uaubly. Why?

Driven by ac power, the same electrons pass back and forth through your readiqw :,ne au/mr8ng lamp over and over again. Explain why the light ae,:n ruq/w8mstays lit instead of going out after the first pass of electrons.

The heating element in a toaq7ek:7npenfm: y )2tv wii,+;,c camhster is made of Nichrome wire. Immediately after the toaste t 7 ,y:vik;ie :hpc2,qfnwce7n) +mmar is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistmj;14qk m;3iqfost e 7or? Explain.

Different lamps might have batteries connected in either of the two arrangements5)tmwrr01sz1v rccgbp6n9o - show-r nrb s5v6rgp1 19oz )mwct0cn 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 ,c 9zdb fgvn: iv71dh4are flowing past any point in the,iv f:dhgzb714cd n v9 wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a batte52k+uov+l,5u4d 6cn zfvpw.su+yon z(l 5 ele ry using a current of 6.7 A for 5.0 h. How much charge passes throughuvou nen2+ kezl65slucwdy , l o 5p+.f4(zv+5 the battery?    $ \times10^{ 5}\;C$

  What is the current lyvlaq /+e-v)uc r73jin 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 pr5zxza(ycy is) 7czxd3;qm ,:aoduces a current of 4.2 A?    $\Omega$

  What voltage will produce 0p4j su59-c8rh syo4a z.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.57xrn;q /fud143fdmx wf/2 oir A when 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 heati 0 b 2y(;dzsol/hjo8zma2tya 8*xn v8sng 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 whoseh lu o1(ws3+*nk)ni ui 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 (Figk+p64o2s v2pzcq5wfqin c 20 t. 18–34). Thpcsfqtwv +no02 2q 46z 2cp5kie 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 A az.:ky8j q/a apcgre +7t 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 ah6ouv p76b.sh- wqj )i current of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m les/pl1oy g:l akcy fl49h99ly .f.9xdmngth of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistanz9 cw)p9 cwqw r+/ar5owm-2xzce of a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of to +vk ev;zb/9uqm s7d9he resistance of 10.0 m of aluminum wire 2.0 mm in diameter, tuqvo7+ke99 z;svdm /b o 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as.qiz-,; hs+jk vo:kvp a tungsten wire of the same length? Give numeric.-vpo, ;:zks+ivjq khal details.    mm

  A certain copper wire has a resistag1j:1lc)n 77;wk;1dh 0x nq awokph ucnce 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 temperatuztx0 va tky;/1q.tl0 bre of a copper wire (originally at axz1y vt0q;btt.0k/l $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempx*xqowfgue2;w1uhv 2+ 6iv* e erature copper will have the same resistivity as tungsten does at +2iwo2e e;vqgx**fuwux 61 vh$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resis4l-)r 1e9 3+drcsmwjv z 0tqqftance 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.m.xlnh.zmd ( h8 .mou5 14 copper wire (used in 15-A circuil dxmuh.mo5zhm .n(8.ts). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon5s o (wsga.(z cbb:vl5;r)b mwljo(3v has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying v(:swgzvc.swol(j ma;5l b3r5(ob b)along 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 hjt p1p i7x-jo,y* ,qysg b92nxas twice the length of the other, what is the ratio of the diameter of the loptj b,7os21j x,q9yxin-y pg*nger wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is conn oh vmb:,/ xxvt dk3z )vplo0l7j57f0zected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measured at j l0xzpdv 377kt ):v0xzfom5/obv hl, 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 amf0jiswe8q.l yr; -5copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite we8wq- ij;s0maf l.y5 rire.
(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 resistancelxxr;9,oh .qp not change with temperature. For exampl9 rph,xl.; qxoe, 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 of heat whn l,3u5rsxf0 cen connected to a 240-V source. What mustc5nsx ruf,0l3 be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws av n--)4jxqf s w82cx:xh0hqxm maximum of 320 mA of current? 0xw 2q8xcj-vh h)x:4sxf q-nm   W

  What is the maximum voltrr6u4z/n0 pwqjq; k i)age that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current throug -iar36s x*uw2gqoe9ph, bei8h, a 75-W lightbulb connected to its proper source voltage of 120 ge*ip ,wae6o3r 829u bsqxi h-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 1171m mc-rn zaw,0 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: 8yywb7)wwfk7jp v xm+p )p*/.g50 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 lightbucow 7 1ia1z e7oe5uq3olb in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb 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 is7eqc1uow3e 5o7o 1za i proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster usesv(aw2tgtla 3-bqj4*k4/8 lyuo zby7 in the morning if it is in operation for a total of 15 m(2 *vul/-a 3wg8as74k4yb tbz l jyoqtin? 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 a8s7b 4ackgcp)-pjm1 zu83zuz 25-W porch light on day acpuam8cz4 8bz k3g1pz suj )-7nd night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V battey3fskyju l+3 oul o1brzp6av8i)/xz75) viv ( ries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when tula)yuf pl3vzsi8jvr )v571k 6o (o + iu3xzyb/rned 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 oly3x4v v,no7c qr2weig. -nr*ktp( i 3f energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can 2j y1- oo4jl+zr4wcabto+ y +pbe used withoutl-y +o p4 2oyro+w+zjja 14ctb blowing a 15-A fuse?    bulbs

  An extension cord made of two wig 3(xgy.8urz f) gy6(lhqvs*tm bke 6.res of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electrigg)e *86q(s y3f.y h6vg(kr tlzmu.xbc heater which draws 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 ucidhiy 3 nsej07.z *q jf)*/cat 12,000 V to a factory through wires wjic7u0*s zn e q/cj3.hd)yfi *ith 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 dmxd.2wl)0 9ry4rjf kA. At what rate must cooling water pass over the coils if the water temperature is to rise by no more thank2jr fdxm)y 0w 4dl9.r 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for c.f+kyyp36 nqadx fq)gd t-(f8 offee or tea. If the heater can d(x3+qy n8p)6-tf.dkg yfa qf 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 c*yx by 5eb/q7yurrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is3 l0u( q:lxhpun ;l,dy 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 q 575xujpmaj (1r .:i cbhzdr: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 asi)1 pa 8 1fhk+8uabux 1500-W device is 5.4 A. What is the rms voltage acisbh +1 u)8p8k1au fxaross it?    V (Round to the nearest integer)

  An 1800-W arc welder is cowvwm;7sedr2* nnected 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 insta0 ,kbmuj/m-dgp5vey5-5z tdc *d jrp5ntaneous power dissipated by a 3.0-hp pump connected to pejb5jm k,dm5 z/-c ruv0g- dyp55d*t a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to ac+kdmw8ud3x z7h;b + q $240-V_{rms}$ 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 current n+va y; uhij; ko3q gy+tbz856of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire bya*2qrrl(wm7uj ,; tcarries a 750-mA current when 22.0 mV is applied to its ends. If the drift spelj2,qtm;w*by 7raru(ed 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 atmospwk:2:c;9v0r7 pq 3c luoozij ghere, $He^{2+}$ 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 atmosphjfe8 ekhs2;6z wt w szwn/)0s,ere, $He^{2+}$ 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 across an axon membran j bj0err40bx1e $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electri8xxco45 :w dt)rl dj8(afrxj- c 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 is 0.0063 s. What is the speed of the electric )j5xx ralo(cd-f8td w j4r8:x pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is reqq*y3 d5 yvr(d ;*knfl /+tpzskuired 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 17–9k drk *pf/5yyl*;zq(+3s nvd t]. 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 poten d/ys4 1rfecr0tial, $Na^+$ 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 ampere-houyo9/ ct*5tn ;ng8qzk 4mopfc*r?    C

  What is the average current drawn by a 1.tx0ucs0a il51e2q -9gsy bpim*t/ q:s0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. 9 qk7w1mnz8yie)d 8u 2f.rjniIf each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at ny .nqk98721zfu mw8irij) ed $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, m:z tz*9m81dbf*8/we3lnhneg*ise y n2m o g91500-W heater is 5.4 m long. If it is made of iron, whe819lhyestne** zmw 2z : om /n3idm*9ngfgb8at must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of anm;re cv3i oyuz5sgz35+ mvv. 3 object is defined as the reciprocal of the resistance R; that 3.y;veo+v zm5vcug zsimr 53 3is, $G\,=\,1/R$. 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 y uq esv:h-gxj.)om):07a h hhusing high-voltage lines ) y - x:h0qhh.jhs:)gum7evo ato supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househol mv :wla5 8i)/ho;7,wjoimpn xf. c1vad 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 h z;2p;d3 7uhgoi ul5q,8mfznualf and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the rehgu7qml8,;z 5 dpnu 2i 3fouz;sistance of the original wire?

  A 1200-W hair dryer is designed forhlp,b 9r37y gy 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it ,ug0(vcia m1f dd/ rw6)fr:ocw4 98fdmy b 0zldoes not become so hot as to start a fire. What diameter 0r )lu1f 6b94(/cm:iad wrdvfd0 cozgfy,m 8wmust a copper wire be if it is to carry a maximum 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 equat of8 )hw-kx4 /9xl rb,vyqjq9hion $I\,=\,1.80sin210t$, 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 energyyc d:e dumisg8oji y85yv 9):9kt +h n,ia37be per second to theg9v edaui8d,9h+y5o y 8sy i:)c3jkitmbn: 7e 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 4 kb-hcbxd2/77ycy nvmaterial. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relatvy2h bkcx4 yn7cd7-/bive to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is usezvgy/9xtt* nz o5gc6 6d to heat 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 hooke, 3koo nusd,,pd 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 of e.pwker z 2 :e2.3odlepnergy. Its mass is 1560 kg and it is powered e2pe.po3 :re.z l2wdkby 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 82xu 7/ oqyvyia 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 l95:jx7jag rm 59hmlf.1cusd designed to carry an 11-mA beam of protons traveling at ml51 gh75 msj.rajf cuxdl9:9 very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting co7;2b jihk mo:7w* ecgyrd is copper wire with a h 772ewgim*joc :kyb ;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 r xtrqy,5 2y g0emm-k 4+c 8umptnv8b7oated at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 mo-58n2ut xem0k r+t c7 4 mg,pmv8qyyb. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about qp*8we/ v /dls12 V when the car is off to about 13.8 V when the*8q //vsd wepl 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 h 4 zxn(.6. yxsdkz+fib;0xmmyousehold applications. Lightbulb B is rated at 12 V and 40 W for auto;.izmkx(y.zm bds n+ x0 4fy6xmotive 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 app7;6l mtkkl0klur s.j9 liances at 120 V, which draw 2250 W of power tkk 0 7l;uj6llt .k9smrotal.
(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 anjxso i;qdo wk+o,.2 w)d an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 1o;)dijw x oowk, .+2sq0.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R t5 l r5+rh w*7jgiwt:mis stretched uniformly so that its length doubles, by what factor does the power dissipated in th:ti jwmh 7l5r5t+w* rge wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament u1 op.pb3* cxscsed in a flashlight bulb operates at 0.20 A and 3.2 V. If its resistance at 20b x .os3c1*pcp$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$