What quantity is measured by a battery rating given in amp s1:z8 w8 nbvqe/dq1rcere-hours $(A\cdot H)$ ?

When an electric celldm m5:y1d1 6v0kdklu b is connected to a circuit, electrons flow away from the negative terminal in kd:5k0 1 yvd mmb1d6ulthe circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is op1 c6f:0.fdl7fsd ars gerated, what is being used up: battery current, battery voltage, battery energy, battery power, or battery r.dr7sl g60f:afcfd1sesistance? Explain.

One terminal of a car battery is said to be connected v.dprjvo/i 1eg8e8 w 4to “ground.” Since it is not really connected to the ground, what is meant by this expr 8gep1e4v.jd/vwi8 roession?

When you turn on a water faucet, the water usual i5evo4 x4fg l5 0dvgkvd1r-6hly flows immediately. You don’t have to wait for water to flow from the faucet0ldrioxvk6f545v1v4gh gd e- valve 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 resir(;pr)mf te5tw.8za ihsx1vvj 8-hcw; ;i) kmstance? Explai- 8wsa) 8p.c;xt5 h mi v(1r)wj;k v;emfhrzitn.

If the resistance of a small immersion heater (to heat water for tea or souzn4, 2ayxg2c dd- cw:m4g5 smwp, Fig. 18–32) was incream 2ydmn5:c zax,w4 sdw-c4g2gsed, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a,9,pnnr5 4sq)i d+o 3 rv3v,p.v.biletab0i p d how would ybeippnto+s)vr49, 3piv . l3inq.b5dv, ar0dou connect 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 lightbulheg7z5us oy o6ydl,)9 b burns out?

Explain why lightbulbs almost always burn out just as theyvp4mn5su1pi -sx2ff6l ssfl 2h95.bq are turned on and not after they have bn5suv m9 f224. s plplqfb1-fhix6s5 seen on for some time.

Which draws more current, a 100-W lightbulb ovz5,ch z*m/gqr a 75-W bulb? Which has the higher hv zqg5 mc,z*/resistance?

Electric power is trajf.fd 5 u:/vhjwwjww/ s7gi4kb0/ y, hnsferred over large distances at very high voltages. Explain how the high voltage rewjju bw h .k//jsdg,fh5w0y/vif: 7w4duces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this s,)b t; 4ao0h:icqk.8tti5t r+ghbp zfuse with a 25-A zo)4c 8t tbhb:kgt;5sipiq.a+h0 t r, fuse?

When electric lights are operated on lows:y ;w 8ay.btq ly9z3zr m7tf.-frequency ac (say, 5 Hz), they flicker noti qyt:mbwts3f 87;9.yz y.zralceably. Why?

Driven by ac power, the same electrons pass back and forth:o he+5 xmx+h(gb4/d wv-sfpy through your reading lamp over and over again. Explain why the light sfxvdgy:+ hws e4/ (hm+5x-opbtays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately af6+l cyrypy +ln ismz8w:7m1w2ter the toaster is turned on, is the curren+wy8cw zn1lms+ rlm 6y2ipy:7 t $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explai8er7ht . rgpsn mo9+3kn.

Different lamps might have batteries connected in ,8*nvg s 3 lttf.m(qdseither of the two arrangements sh,t qslg.*tsmdvn(3f8 own in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire.6081a o wfbtgl How many electrons are flowing past any point in the wire per seconbg8w ot0f 61ald?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery ur(2xo1;iuzpl2kiy8z(rt * ggsing a current of 6.7 A for 5.0 h. How much charge passes through thr ti;81y r 2*xggizo (uplz2(ke battery?    $ \times10^{ 5}\;C$

  What is the current in amp31nlnpz0nz,qvz/fr/+ro i, me +1l zl xy61d neres 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 6qn*:qm-2 0 qnzxr w0jqwd(hatqf/q(5ri c w9A?    $\Omega$

  What voltage will produce 0.:a6m:35d f fxog d 5r5q jqufio7o;/1a4goei k25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-l m t ox7q9r; hq3p+m88kczs(aV 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 elemenf s enwgpi5j/op5 *u uu9v;79nt 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 whoszjup(2nrvi-1 k76uzih-qcy iqn v2+ 1s w0 o(je 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 (Fig. 18–34 h:quv (im-gk7gxeu52 ). Th i:gmq( v xhueg7k-5u2e 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 hfowfyd3 t 6/7V.
(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 d;lh.(6 tq0e;,/bfi tyvqidrA 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 wire whosezy6ea4 wc:pepd3 s62 s; nm*y6zk.rqe resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in d ky+7 zs/pa6tk pk0yw7iameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance okbc- ;6lvix6 twwt,5af 10.0 m of aluminum wire 2.0 mm in diameter, t ikt-lbvt6xwc5aw6 ,; 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 a tungsten wivc5e). uvlr l94gf*in re of the same length? Give numerical details. glvf ir n.v)cul*459e    mm

  A certain copper wire has a resistance ik om(pl(9cb3vn);rr 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 tempera+co5o 2.s8:y hsm amfwture of a copper wire (originally at cs2 y fw.:+sh o8oam5m$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have thehrvg/s8t nm wi:1 8ge)5y cgx7 same resistivity as tungsten does at c8n ygwgt)v1x :ri/ 58m7e shg$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a re7viyr5 i;;)fhd ndbwos /z2/ vsistance 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 l/03*ltdlzkd bvr8tu 8v fi/b:ength of household no. 14 copper wire (used in 15-A circuits). Th/fktrvlbld / d:83tbi 0*8uvz e wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of leng0/izw*z4g vyqths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine i *g4wy v/q0zzthe 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.nl96.4i p 8vxun h3ac)qkl 4x-cufq6q If one has twice the length of the other, what is the ratiq8n )6nk6 xv.pu hq4lfcc49xq a3iu-lo of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminumzyd38r17,) ac ugtome wire is connected to a precision 10.00-V power supply, and a curreduey3o8 a1 ,7cg)zmrtnt 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 conzd9i0jok92 9g1 iacptsists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire. i to1a99j9gip kzcd0 2
(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 resm sv z5/aa4e8zistance not change with e 45m/8aazszv temperature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is dewy7 .0bdi3g tnsigned to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistan.7wb03di tgy nce of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that drapepmf38xu; bzs0l *i jf).wv )k(m 5euws a maximum ofs k*xf);) 0p uiu.jz 5fe3wmlpvm eb8( 320 mA of current?    W

  What is the maximum voltage that can )riflo8p i/c d +/,q+a.npmgp be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the re6ra: 4a)fdr;e l9 lkf-2qnpwusistance of, and current through, a 75-W lightbulb connected to its proper sour:- f6 re n94lkru);ldfapw2aqce 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 110 W. Calcul p,6;ftjsbn9 tate
(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: 8n:l67 9+ yk;k:gjhqnkgjy -pw50 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 delivered to homes atr+c q.n0 : vnzxu ax(q(h qoq,8bkmo99 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance doe,q.9qn8 cz0ou xok+9rqn (vmhbxq (:as 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 toaste.t8sdm sli4gkb y-73yno * it4r use in the morning if it is in operation for a total of 15 min? At a cost o i73ml84dbyist g st *k.o-4ynf $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W porch lig sr /gym1ts)4q:xan .v8,d hltht on day and night for a year? rmtd1 ,hst axy:glv.q)/8n4s$\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries fsw ,+ gu q9/dob*av2mconnected in series as in Fig. 18–4b (Fig. 18–36). The bulb da o9mf2w*sv q+bu, g/draws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of en aq obrf.gy4fp- qhue9 ;3n8s6ergy 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 be used witg tyigl-+9)k wk--c, ariako) hou )9rty gaok-kg wl)--i+ic,a kt blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wi9 xa4oi) rrjk1re) and of length 2.7 m (9 ft) is connected to9 4a)1krrjxio an electric 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 at 12,000)2mvipb5blsd3h u8 x a-0p4im V to a factory through wires with total rex8m silv0bihp -)25 4u3 mabpdsistance $3.0\Omega$ 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 connzvp ku(/6c)icected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water tei u/6 k(pvzc)cmperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater cg 1w9lvb*z;f oan be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of watwgb v;9zf 1ol*er 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 cym-n2z bo4c. iurrent 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, isp ff/g v3m2o3u,v u2dp:t* wohsdr18m 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 kw,o v,wl8 loqzucbuo 1x.1iq ju**8;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 croqc 0( n42x: hcy x sxkrof3 :keg*;n,qqb3m6urrent in a 1500-W device is 5.4 A. What is the rms voltag*sk xc3xr4 m f,k6qr:gxhcq q(e:;20oby no3ne across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connec(4yr)c* i hvy td.t o).ov)dwyted 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 ap6b)cxfsn fz5/m ,*qpump connected to a sc/)a*x ,6fqb mfzp5n$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tokq-d1i0 owxix:e b83c 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 cak (g6uqe huo;nv vr73esyej lc- )/0f(rries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current w fe*2nv8il(ushen 22.0 mV is applied to its ends. If the dr2es f*8l(i vunift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmosph50az*lc8aaikr(i 5y c9sd7 vlere, $He^{2+}$ 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 n:8tdewi 4r:i vh ee*8vy2 s3uatmosphere, $He^{2+}$ 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 membrantdo d y5/4)9naj, yggb32sz cre $ 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 is deu5yde ogm9m- x66fga-g +xwa1r64roetected 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 pulse along the axon? (Wh-uy5grr6a- ewog fdoxg6 mx+1m4e 96 ay are two measurements needed instead of only one?)    m/s

  Estimate how much energy is requiy jt c6.z9afhr*ta o,9red to transmit one action potential along the axon of 69 t . ahazoc*,ft9jyrExample 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 for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential, *cb yh91( degi/ujjl5-8*wbzu m 8dllez/(ok$Na^+$ 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;o r .bd82qsk)a/oc nl-hour?    C

  What is the average curren 5xo)nh()x pqmud 1r5c* ouq3wt drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally lewsz27 sople*zx .a5r 2aves a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights as5*p22z7eo rxwz.l s 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. If it is made of i*j 55etcubygb * 1xq-oron, what mustt -y1x5u5* b*jg qecob its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the-vkqk8uue ,9 q koz4o6 resistance R; that u ok9,4 k6kvue-ozqq8is, $G\,=\,1/R$. 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 usintxu /ruhx p;2 )vdx,1dh id9d+g high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-dih 9dv2u)+rx; ,i hu1ddxt p/dxameter 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 househop:s0yl5(( 2 dpchh bjmld 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 le/qw8o:j;ouj,b ;lq 9 wft/ jyrngths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resi/8/y ;jo wq;u fblo9jq w:rjt,stance of the original wire?

  A 1200-W hair dryer is -rr2a z7p,nwgy+/o: wkn2htj designed for 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 o 7iozsrk9vp a1u9d y*6 +b++g6xnaz xbecome so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W96 z dp+uriaavxg1zx *kon +ob69sy7+ of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equation ih0d t6id1v,v39j;nvv wqm8 y$I\,=\,1.80sin210t$, 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 -kvl;c (f -h-(gj6 owa8s priy65% efficiency delivers 950 W of energy per second to the interiakc-r wjpl(( yo-hi -v;8fg6sor. 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 j 2bf*e muprl;ondi3ou:w ::4 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 of the power transform f;i:lu nr*pwd:o:j4e2bou3m ed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volu p q--jv;wnl8nme $62\,m^3$ 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 source. ipb6n*22si l3 b/gzaz jp 7f8t
(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 battm+gtrtr:;b2i -uxwq :eries as its source of energy. Its mass is 1560 kg and it is powered by 24 battgt+m wu2q rb-i: rt;x:eries, 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 resistance o9w(fy q a c9y;heyrn67f $12\Omega$ 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 h. y7h tl1hj)m( zh*kf+zvdn:beam of protons travelinz lfzh1vmh.j* n h:hdty+k()7g 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 connes m,,gd ctbaq6*slx.)cting cord is copper wire wisq ,,gcbx tmdl.a)6*sth a 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 rated ati4j qfvk h:nnnlm9/ef++x ( y5 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, t+hqy 9x/nefijnkn +f (v 5m:4lhe 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 abobt75eh s azy 8,ivc8o0ut 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the heac,8bie578o hat0zys v dlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applfm:n jn)d0 j1;kgiko(ications. Lightbulb B is rated at 12 V and 40 Wfj:nmj io1 g;)(n0 kdk 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 applianmbd*ea co4)m )ces at 120 V, which draw 2250 W of power t am)co *4b)demotal.
(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-1jf35 nm vrxwfrskee72, yz,k,r v+u of 5.00 cm (Fig. 18–37). What is the res2v f+n5x ,k ,w13syrjr- kzuv7eemf,r istance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uqbxo. zf bf)6kh y:etm:te4.zx74w *iniformly so that its length doubles, by what factor does the power dissipated in the wirtiff 6.eh:4)qze. z bw4*bmxy7xo tk:e change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 4w h *hos9nvk5c5rs6s(zlyu9 A and 3.2 V. If its resistan *c(osk5ru9ls5h94w nh6yv z sce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$