What quantity is measured by a /ds5 oeh7l 6bubattery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a cirgh*jr u4i-oo1 cuit, electrons flow away from the negative terminal in the circuit. But within t*jog-u41hro i he cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is beingb7 05 ki whot8-rmwobg2:y1gu used up: battery current, battery voltage, battery energy, battery power, or 5y82 h o7giwr t-kbgo w:bm0u1battery resistance? Explain.

One terminal of a car ba msy(q. wg,l te8a/lc9n+v,d rttery is said to be connected to “ground.” Since it is no./vw( l9d ets,r8mncql, +yg at really connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. b9irmyry7-mza v48qv 48rgc j71q+ vvu2+wfnYou 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 thec2m 9z+a rr4y b+fgqi7n 4vv 7 8ym8jrvwuq1v- terminals of a battery?

Can a copper wire and an aluminum wire of t)nae3nm 65e0 ,kngtfche same length have the same resistanc3f n0nmnk tc,e6)g 5aee? Explain.

If the resistance of a small immersion 7d uyv(m dz3e:osd6y //d.jqmheater (to heat water for tea or soup, Fig.d7sum6y o:(d j /zvde3.yqm/ d 18–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of ca2u y:he o s:r*voig4+urbon has sides of lengths a, 2a, and 3a, how would you conyvs4: uuioe o+gh:*2 rnect the wires from a battery so as to 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 lightbulb burnsbwg ;tg;+ qj6a out?

Explain why lightbulbs almost always burn out just as they are a+na9/dwoak j2 2ixo*turned on and not after they have w /+ai22nkaax*9od oj been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has thehg, h k1pvxs1(3 h dandq*m8pq9e dsf3k-p)e+ higher resistap dgv3x+e (1 h )1h kpkhns8dm9pes-f*3q adq,nce?

Electric power is transferred over larg;:zoucge 00ly83 rt5-ulfch dhi*6 ate distances at very high voltages. Explain how the high volo06 id lchaghe8c0lrtyuuz t3:-5 ;* ftage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to relk8f7 4t w 1*obnpi(sdplace this fuse with a 25-A fus (oflds7bt1kw8 np4i* e?

When electric lights are operated on low-frequency ac (q.r,w*tc i( bc1o: ya*,ofwuosay, 5 Hz), they flicker notou (boi.1fq ,t*r*wca:o, cwyiceably. Why?

Driven by ac power, the same electrons pass back and:5dzxs xi 2g3o jtvt1 rxb9ozn71v2r 6 forth through your reading lamp over and over again. Explain why the light stays lit instead of going5or gvxi tbtjn 1d9rov63z1:x27 sz2 x out after the first pass of electrons.

The heating element in a toaster is made of Nich9:vl zjm5w( ,vgbsc3 vrome wire. Immediately after the toaster is turned on, is the currenl5,vs b 3zv:(jg9mw cvt $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Env3 uyxsggki+ok :hw 4y3 :+xf+g*g2x xplain.

Different lamps might hf i,b;aaj x 587fxw0etave batteries connected in either of the two arrangements show8;ae aj,5b70xift xf wn 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 wpzy2 hz: pv;: nmdx+gq8g82y5g(lshare flowing past any point in the wire per second?hg8 vpy(2gs28 mz:n hgl 5py ;:dwx+zq    $ \times10^{18 }\;electrons/s$

  A service station chargmj9 n9s,/b fqt25z6h:;odsrjb v o3bres a battery using a current of 6.7 A for 5.0 h. How much ch6:r,bmnjv3zh/ s ds;oj 5bqf 9brot29arge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current i5.kzuase ef2.m4 gl(i n 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 producespfd4mc.rin 1.e+i8 d/ t:xsyv a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current t+s mfxhq1ex:ak /xv* 2hrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggw3ee6sc md *9bed 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 h :r:robf*ld,fkm+1oj 7 d2go qeating 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 co8ctw bbq2 njw3n *.nt.4.bfiunnected to a bulb whose 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 ;;2q rg v.vw8xz qbl)oline carrying 2800 A (Fig. 18–34). Thwv );g8olqx . q2v;rbze 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 at 240 V. .p xf,9k 4xvnu
(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 vugsqf(ku-1 6 x0kmp/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 length of tungsten wird -xt u uwse(vid+):liw)l9d+ a0 sk.ke whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistansmc2uf q((gd0 k8ddn 5ce of a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio oi9 -.ioeqsrwjldht. w j4, ),2xas a/hf the resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of cil4 ht w /d9sj, srxoq-a.wajh,)2ie.opper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungwu7x8dreu8spvmr64 t 1. j0qlsten wire of the same length? w er1qrxjtlps08md6.u7 48vuGive numerical details.    mm

  A certain copper wire has a re5l8tf-6fqucz7 a9l+/hd 713 gijzk1 btyk mk esistance 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 tem6b orkj(q,f hs 61y4bwperature of a copper wire (originally at6kqrbh6, bf swyo1(j4 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as2k(4vwwlpwfj e 66n l+ tungsten dlejwl4n6f2w kwv( 6 +poes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of aboutpo zbmm(w 9:vrlg l9xy;7z q17 $12\Omega$ 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 bb y9v ml662hdcopper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A currlm69bhb y62 vdent.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cmrh5.w+tli6 9(kghsh l , and 4.0 cm, lyinh(hk6swi+ g.9thr l 5lg 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 has twice the lenz4nwc .7zsem f a.je0(gth of the other, what is the ratio of the diameter of afw.n7e s(0jz. mcz e4the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-j -o ar,i7rx1bV power supply, and a current of 0.4212 A is precisely measured at 20 x-rroi1b a,j7.0$^{\circ}\,C$. 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 by 5.cb+rqkaz gek : s2h6*(5.t.xnf-it jg0 m of aluminum, both of diameter q.2x*ft kr.btgna ejsc -(i:gk+5z6h1.0 mm. A voltage difference of 85 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 importy., 6f k8npp73y+py8m(q uxtru w oks/ant that the value of a resistance not change with temperature. Ff/wt,u3 n+yrpps 86kmx8 7.(yp ukoyqor 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 fbk. n.1bka48 y u i88awnq(xfto produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of 8f4anbfkwyk. ( ib1 8 8xaqn.uthe element?    $\Omega$

  What is the maximum power consumpwp p:.3gn (k fkv7v llag5)h)olu.uv; tion of a 3.0-V portable CD player that draws a maximum of 320 mA of curren o)vuv 5.g pkp a7fuk;nw.g(hll3v:l)t?    W

  What is the maximum voltage that can be app+ lt2f 9i9 zv,1ugzvblk*gw krb0 g)d.lied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 7;/f,6rl asz.e zndmw ha),c-v5-W lightbulb connected tr s.lmvnzh /dazf6awc-,)e;,o its proper source 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 at 11g.sjt(q.a xe9 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 tw8-q 8/ rx wi7eog.xwnawta. ci+n*9wxo settings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulbk+c .3p3y3ydm bpwx7:,c rad l 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 is proportional to power conc b :d,+37w.y3dkpa 3yxrp mclsumed.]    as bright

  How many kWh of energy does a 550-W toasternkudsc(oj.w8 8.x 1 yca)9npb use in the morning if it is in operation for a total of 15 min? At a cost opw yoacnbc.nu)d(xksj198.8 f $9.0\,cents/kWh$, 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 leavest qx7vvg:8dq a0,l)a a 25-W porch light on day a) tvq0s78:dqgla,v axnd night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected.rx5vl;; jstv7o*wy d in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA ;jowlryd75xs*v .v;twhen 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 enezqph/28ucq7lp ol:jh;-np (j rgy 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 pb.s j oo;s+o8120 V as in Fig. 18–20, can be used without blowing a 1ob.os op+;js85-A fuse?    bulbs

  An extension cord made of two wiresn)vp kj1w2 +hh4u jp7u of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heaterp)pn4h+uvhk2 wjuj17 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 at 12,000 V to a 8skr fx- 4trxa:d; e5yfactory through wires with total resista8d5:e a ;xyrftrk4 -sxnce $3.0\Omega$ 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. A1d3cdt9 e65; ,jdu7pr8o rddquss l/wt what rate must cooling water pass over the coils if the d 9rcdds 1 tes u,35 8d7jwl6rqdp;/ouwater 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 a ye*6f;e ;sw:5yrrzly cup of water for coffee or tea. If the w;y ;lr *ye5fr:ey zs6heater 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 current in wxm;.tya58 rv a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is* 7 wb4pfrpd *k 1itm*xxz.4ln 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 st7h7jyf18l a 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 1509hfm*ou(t0 io 0-W device is 5.4 A. What is the rms vol mh* ooit(u0f9tage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connec5;b /l:xb v*+iyo77 tl ngagkwted 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 dissipatexbczr ti*0f 7t b.42jtd by a 3.0-hp pump connected to c2tfzjx7b4.b rtti0*a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to.i,k ta:jadzg/gr7 :m 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 carries a tiny current k lt0ul-)gel:o 3uy y)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 aby;nu* *q hs4k,ap r(l 750-mA current when 22.0 mV is applied to its ends. If the drift speed is*;,pry 4a*sb hn(klqu $ 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 Eartlc ;t bc26*jrrh’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 E6,aym,kl4ouy0ku6 juxll* p 5h;0jxkuf 7 1ucarth’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 acrner m32ad3 58fvl fllfva1+g3oss 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 pote d y8sdfrhj(((ntial 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. r8dds(y((jf h0063 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 potentialw d-93fn9yda- 6 2gtxo*qad bu 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 -f9 o2dxa wuna6*qytdg-3d9b]. 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 potentba +(0l*i e7o tl+v4zap9zooyial, $Na^+$ 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 t 2af5a2:,zmfbj)x; ecs c6 kfdhere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motor? s,3r0nv qyd,rl+hkyy7e a9f* $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the5st 6k)z0rzjvsflhl +3r g7a2 lights on. If 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 bs z367at2 j50rlrzhf)klvs+gattery 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 longv- am)gx25aq6:ay8kb3k ao *zv7qsp s . If it is made of iron, kax5:-sm sv va a)qa*3ybko7z p6q28gwhat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an obj42*pq:z kvllkwg21or ;4sob ro x) 2trl4 wo2vect is defined as the reciprocal of the resistance R;wl wbg*kl:; 22x12r )4 osok2ovtz r qopr4lv4 that 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. Supposehlqm) 1j2 *tkkb 40 haym*rci3 that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wil3 jmb2) 0c *kikh*m4ya qrt1hre, 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 househ(:bf5bpx ) yd- rk uur/vmr n3u+5f:llold 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 tw4psdegb8-an xo peb.+2u,dc 7o lengths are wrapped together side by side to make a thicker wire. How does the resistance+b b2ee87,x so-.daupng4c dp of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed fog.m1v p g7ag 9kd11.sp1.(gge ta(ap eeb;gr hr 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 does not become so hot as kgq +td3ndhs8.+ev 4j to start a fire. What diameter m ddj+q38.h kvg4e +stnust 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 equationwevz4 h 8 7yoqcr37:lux+byv; $I\,=\,1.80sin210t$, 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 per9h.ye a.gq2 zy second to the g yze.9h q2.yainterior. 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 /y :n:;aq,hda6hhzdw two different conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio o:;hnd:hdaw,za qh /y6f 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 vol z lr45enr,;niume $62\,m^3$ 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 hook ;see;pe:8 cxy5v1fve9 n2nyy ed 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 a6 wy2*fr z, 1r tejjve:d.szs3s its source of energy. Its mass is 1560 kg and it is powered by z w djz*j1.6fe s2s: rev3rty,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*qhcgf1 jx,,a9ti50ukuj j(rrh, *b l 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 b ;2tq/cocrvl)g-4qq1 l7fgv (Illinois) is designed to carry an 11-mA beam of proton-g 21vf bgq tcl7qr/4)v;lqcos 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 connecting cord is nur25x4 g kzdev) ki2qi1/it-copper wire with a diamet -kzdgi2v4x 512qe/)unitik r er 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 connected to 120 u8x.tac-e4v.owxk u 0V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total le.cxua8v4 -tu x.o wk0ength of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies frs2vbn;*t zjdffzo-s 7v9m35m fx3t .fom 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 pow ffv9s3 2x;z7.o*ftmfbm-d5snj 3tvzer 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 applickm2ubfg,4:st ations. Lightbulb B is rated atk g2 u4s:,fmbt 12 V and 40 W for 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 appliolm666* gxjqvances at 120 V, which draw 2250 Wm6 6 qvl*6oxgj 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 cagr aoa r*many)7d;qea.6 n o-zjwy:jc94g/ /m and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pip/r*ay.wnj9 re q n7-a:zo;4j gaoma)g6 d/caye?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doublenl51u bbe/6idl n9u)4xcx7bj s, by what factor does the power dissipated in the w1x u )bx 7j49uc6/b5ilnedb lnire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at tbwj :wnu+q4dy8uq ix;er/e1 (l,n - a0.20 A and 3.2 V. If its n8/,i1(juxql+n;bue :dw- e aw4rtyqresistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$