What quantity is measured bcji40i) qdssv + .9qn6u; gtazy a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electron w avphh.-; dn4az(u+ful4r, rs flow away from the negative terminal in the circuit. But v fh (al.hzr ;-4n4uwdp,a +urwithin the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery c:k*;o gblt dj.urrent, battery voltage, battery energy, battery power, or ba*tk .j ;b:gldottery resistance? Explain.

One terminal of a car batv*3wge- iug 3q;/mbo3+bftgbtery is said to be connected to “ground.” Since it is not really connected to the gro-vo/3q iw bmgb; g+*3ftuegb 3und, what is meant by this expression?

When you turn on a water faul :am o+frm ww0x.e.egi40.e lcet, the water usually flows immediately. You 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 the terminals of a ba rgax0w4.:e e+ew.mf 0i l.lmottery?

Can a copper wire and an aluminulu 6c bn(xf7(xm wire of the same length have the same resistanc bu7clfx((6xn e? Explain.

If the resistance of a small immersion heater (to heat water for+/7 djkvbvnf j** m.qn tea or soup, Fig. 18–32) was increased, would it speed up b*j j+f 7k*n.dmqvv /nor slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, i;*qr ygg)yl2 2a, and 3a, how would yoyi q*y 2)lrgg;u 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 lightbulb burns out?edp0p 8jh :afi2hf 7:m .urnd4

Explain why lightbulbs almost always burn out just as they are turned on ands yn(5a;us:.yrsi4 :.j )uf rdz:iioa not ;.ajr )ufuayi(yzdn4ii: :ss 5.o:sr after they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has q8(( :lqmcfg v bf2a1mfx2n/nthe higher rvq 18(l x2 afnmfmf:q2bcg/(nesistance?

Electric power is transferred over large distances at very high voleo i nr:+jf;l8tages. Explain how the high voltage reduces power loss: i8l+j;n roefes in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replacelf i;1 /idc;cq-ta8au this fuse with a 25-A fu/i8 i;lcu-ft1cd aaq; se?

When electric lights are operated on low-frequency ac (m6n6(+a av rng- pavc3 wv7fj4say, 5 Hz), they flicker noj( cfp34w gvaaa7 rn 6+v6mvn-ticeably. Why?

Driven by ac power, the same electrons pass back and forth through your reading vvmaqtu3(a 1n4 r-xg9 lamp over and over again. Explain why the light stays lit in v9m31ga aq(ur-4vnxt stead of going out after the first pass of electrons.

The heating element in a toae 9rjll:30 yacster is made of Nichrome wire. Immediately after the toastreac lj3:l 09yer is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Expla q e.y24l-g.kmryelc u9qo*j2in.

Different lamps might have batteries connected in either of th8h uy*/gblk gq bt 3vz28vy85re two arrangements showb8 / z*28gtv53qluvgh ykr8b yn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. Howv rz ;yb98ij u9ft:kk- many electrons are flowing past any point in the wire 8:yi;tvuf z-br9jk k9per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A )v nne7sd0 *.n2fvvn w*(4eafh e,opz for 5.0 h. How much,odvn0se hzv2* )*p fvne a(n 47wen.f charge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes *yp8eb;45uci6ktt o hm *vh/ lif $1200\,Na^+$ 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--g6lu1ich6 ow1jk f(7rw7 ew ,aejz n a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 5 i okgyzdx/0g91cly9 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged isn 5m ux6xj+u0w phyozk0)n+c2r8/ybnto 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 d5ldjpwt 4e5 iy2,:f1we*uuujryer has a heating 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 buaa*.3z lfj9r) 1;dale 7jj ywhose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc elect 1qeqe1da: -fkr3a46bad xs9tric transmission line carrying 2800 A (Fig. 18–34). The line has d a3af:19q46a br-eqtk s dxe1$2.5\times10^{ -5}\;\Omega$ 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 djv,t 2 tj3kh3jal.28*tlkv v 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 resi0eu(4r *lvf 3rlzlfy u)+ij 7jstor.
(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-wnyq 62 rx6.fza qj8:hm length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m xsd 0g p9n)ehcif2e*3length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 1vh*k 2 /wtdo*t dlz/i2.0 mm in diametiv2tz/hok*t1 /wl d*der, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance -fh t5 lz 13h-5sjrzi e4rnmjlqj2 m3(as a tungsten wire of the1j4e l2jhq n -zt jzimh3sl55 3r-fr(m same length? Give numerical details.    mm

  A certain copper wire has a resistance of 3coh2bnhcxrb 9 a;9d ,$10.0\Omega$ 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 coptxbu: ,g4gk/ pper wire (originally atug:xg /k,p4 tb $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resi1xz.ff4osynglg.d 4c5 6xj9hstivity as tungsten does at z 6dlc nh..x1y4g jxgs o49f5f$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistansja )6zns q :r(ji3z3vce 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 copper5 n1:w (h9 use8dbi:ezreml7zncwo l1(g 9r9 z wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A currewned9l r1nz9 (9 csgr(wib:z e lm5 eho8uz:17nt.    V

  A rectangular solid made of carbon has sides of l 1zue boex-ki8 l7; uc,bhx(l,engths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fi xx ,1 lkcbozu-7;(e,eib8hlu g. 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 s0ox zh7uuht-of) z2-zame resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shzt0 zh fohu7xuz)- 2o-orter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisiokg; 7ya z+/vagn 10.00-V power supply, and a current of 0.4212 A is precisely measur;g 7 gavkaz+y/ed 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 ( s1-o+7r kufdjl63qck r-x ytconsists 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 placeu rtsdco- 6 kj rk7-qy(lx+31fd 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 valu2vfn 5c5sz/ wce of a resistance not change with temperature. For example, suppose you v2/c fcz55 wnsmade 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 b/wusxj( gz)b g9jo7/3.3 kW of heat when connected to a 240-V source. What must be the resistance of the ouwjz)bj7 b /sg9 (/xgelement?    $\Omega$

  What is the maximum power consumptiv3wdluf4*;r3 *q/-f( e rkvx q b.fzzjpat g37on of a 3.0-V portable CD player that draws a maximum of 320 k;a/z*pf gz(rvxb3vd*lur7e.qtwf34qf j 3-mA of current?    W

  What is the maximum voltagwye,g5j 05ep)-s mewz e 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 through, a 75-W ligh(lj k:02p9 xhpimo(p 5elvh6e 1mnj u1tbulb connected to its proper source voltage of 120 V. l lpmu :2h v 5eke0pin9h6m pjx11(jo(
   $\Omega$
   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 :6l6w+vgzyyxg3lri 5v p:v-x
(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 settinbmng .j/dy) pn/,l * *wtsszb.gs: 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 lightbulby i2ss mv0 k:129ud1-cligzze 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 i z:u1 sv2msed2kg1 c9z liyi0-s proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toastea+l 6w e.q(wlhr use in the morning if it is in operation for a total of 15 min? At a cost lhwqw(+l ea6. 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 leb)iz1dky*d c9w hlz/2 ave a 25-W porch light on day and night for ak)2yl h*d/1z 9zwcidb year? $\approx$    dollars

  An ordinary flashlight uses two D-cx3*ip.ib4ti6 whoz o, *qwr:7ir u+dhell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb dr7i r6pwt* oir w*i,dh :4hxz+ui. 3boqaws 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 energy storedw,l u(aqc98kp 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, 4ryb+vt* gt .0 iakorwhm. .2zcan be used without blowing a vtrhbtwg2 4 . +0.oayk.i*mrz 15-A fuse?    bulbs

  An extension cord madeufm;hiw 8* /th0upxr1 of two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected f*8i m;u/th 0wuxrh1pto 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 V to l,rwz4in5k7rhltbi:x- ) 6 tza factory through wires with totzl4t 6:t, - 7lwbin)5xizr khral 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 conppl8o ham x-j-,36 0oztf3 becnected to a 240-V line is 17.5 A. At what rate mustpa,fjp e6-3xlomo3h0 -8t zb c cooling water 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 in0 s+tl99yp f.h9lg f 01c2hwhehtde /f a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water from 25e p+heh glh 19d02f swf9t9l0tyh.fc/$^{\circ}\,C$ 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 cur+r*6 wwepyzbfwba979rent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 vm1ej/ lss mqzf (6+3lV, 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 od nlx:z 5k,/kvf 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 inpifs.4nf pw..xj l+;np.k9(z . grijg a 1500-W device is 5.4 A. What is the rms voltage acrosssfnig9jf .plz ..j;w4igr(pk .np. +x it?    V (Round to the nearest integer)

  An 1800-W arc welder is 8oxkq) ajd98jp2.joo*qt( fhconnected 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 di *je2 tmxs:9)bu9zlg3a0z ahna/3wf x ssipated by a 3.0-hp pump connected 3za ea:l9u2w / axtmhj3xn9s b)*f z0gto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectedt,w*xet8i2n oq3nb; y 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 carries a tiny t+urqi4 b3g3hcurrent 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 wh3oylqgv / *mp5a); tsqen 22.0 mV is applied to its ends. If the drif3/sva p;mg5 )yqq*ltot 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 Ear v* p97xetei.jpd1e/ cth’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 Earth’s atmosphere,rpa/05qq y 9 f6ripduz)tad 5+ $He^{2+}$ 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 fieldu5q nk*d:xs,b qzl::: bv uzk9 across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potentomsidawh13 6 3);gmj42waypwial 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 pulse along the axon? (Why are two measurements needed h3is3 w)m46;12yj opaagm wdwinstead of only one?)    m/s

  Estimate how much energy is required tobgg:us s ( 44v6y/eq-k ubd:/ lrz/hwd 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 17–9]. What minimum average powhvlyweuq du6 -4b/s k:(g4z/ r:sbg /der is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potenteb dox05),e o -:h2sf4do2z oywro0 fxial, $Na^+$ 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-mmjw:f 1es5-1 yu8i;j ydhxc-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motoi3m h5ykr0 ia9 k;ep6oylu,c,- olen 1 +/kgcgr? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the twov6 uq sbldgdjf2ky3.:r82h4c1j y ; pc headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W,6lfp 4rq.gdu2yjby2khc1j: d8s3 ;v c 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 kskn2ioli4 ;tbzp 6:+ it is made of iron, what must its :t;s bi+nzk4l6kp2 iodiameter be?    $ \times10^{ -4}\;m$

  The conductance G of an obhsr*g ;f9d4yn;b5 rr :ac9r zrject is defined as the reciprocal of the resistance R; that in r:9;dbfha;5zrrgc9rr*sy4 s, $G\,=\,1/R$. 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 using high,- (tr( l oy1ri;+wdydvgti 5z-voltage linetydr(v-5 oitzi ,1w+lg yr;d (s to 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 househ+ist7dqw: yzj lgyc.a/r :4 0zold 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 gq5cv1:z ( :ytp+ zz2f9dh lhethe two lengths are wrapped together side by side to make a thicker wire. Hzylqh :fpz+(c dz9:v2get51h ow does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is7pfpb,+dp6px in-emxirs * 7 2 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 sonx hdpww, q j;o 1gpb2.n652cy it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a mapd6 2chqy,51 .p wgwn2 ;xonjbximum 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 ek q(i zq,-uz2c a+anu y zdf4m52p9w,wquation $I\,=\,1.80sin210t$, 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 6 a2wvjg *t06dx0szcm W of energy per second to the interior. Finwjx czad0*6 gs 6t02vmd
(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 sameqz z7 +c *3tw.bh,lmat material. One conductor is twicetzb hwt7 q aml+z,3*.c as long 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 hea:he7x) cilhrk i+xm.5t a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V source. swr4 w-g7y/8v : 3xcnkh ai3le
(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 uhz w omjyosm.:i71+l(se of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batterwm7j(lm o ihy+sz.1o: ies, 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-ubx oq50l *z(duyk-pdvvt1-mw 0k6z 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 qka z51j7u ,xzbeam of protons traveliq ,1ju7azxz k5ng 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 Ahhrwi5 s2z9ws-r7u8 n at 220-V ac. The connecting cord is copper wire with a diameter of 7s52n r-s9 h 8hwruizw1.628 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 yn sbq*p47 d)r4cf:ot95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When un *p q4nr47:of)ytbdsc coiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, th+gs )wddzo) d82 rdw q)m/cx;ge system voltage varies from about 12 V when the car is off to abd m2+wcg/qdxdzog;r )ds )) w8out 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 1ietb-+75 vyosj*dd2c 20 V and 40 W for household applications. Lightbulb B is rated at 12b dv*j27 cds +ty-e5io 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 u4jwa8,f n1xme sed to connect a set of appliances at 120 V, which draw 2250 W of poweew, mn81a4 jfxr total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and a (u0r..zwrvf 06imj.r m v,nmvn outside diameter of 5.00 cm (Fig. 18–37).wzi6nmf . mrv0,jr0(um .rv.v What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistanceo, 3n;b vjj0uo R is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hoob;jon v,o0j 3uked up to the same voltage source?

  A tungsten filament used in a fla3c3t3 a -zw+58x3hzc ztn hfvoshlight bulb operates at 0.20 A and 3.2 V. If its w35hx 3 t3czz83-t zv a+ohfcnresistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$