What quantity is measured by a battery rating gzex,: 6nk3cc niven in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a c,rvof *1xh8t n cb.zy0evli28ircuit, electrons flow away from the negativ2oeyzvfh8b.t8nvl, 0r x1c *ie terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is bein(pu p d-+wgo7,al 2ceh.hm*sd:k o x6ug used up: battery current, battery voltage, battery energy, battery power, or battery resistance? Explh6 d* o7 lekuch um:,.gw(sdap -po+2xain.

One terminal of a car battery is said to be conne3g 6m8qy947eeh h9xyjsg4ub( 4pv hagcted to “ground.” Since it is not really connected to the ground, what is m u(487 h4pye6jaqe9bv94hx shmyggg3eant by this expression?

When you turn on a water faucet, the wateen5q4 + rfg(ju(ra 5xpr 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 y+ u qj x(rpan4f(5gre5ou connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resistg d 5g)geo jwo(22ffq1f lb5h9ance?jfbh g5ol 12 f(5ge)f29q dgow Explain.

If the resistance of a small immersion heate 5jci;e2 x a)l8zp.q cuou0-e 1+friyhr (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Explay5)q ej;r pco-i8e2 cxhz a.10fu+ liuin.

If a rectangular solid made of carbon has )h m hdbv6,8dkp:s ,icsides of lengths a, 2a, and 3a, how would mh6, )hkpcvdd:s, b8iyou 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 o uogwzujcwk*tl6;98 5w0g6q yut?

Explain why lightbulbs almost always burn out juh o)/mkgw8qp8 ):izjn st as they are turned on and not after theo 8)n:khzw /i8)jgpqmy have been on for some time.

Which draws more current, a 100-W lightbulb ,nj kfgcg7;o 0or a 75-W bulb? Which has the higher resistan;j 0 no7gcfg,kce?

Electric power is transferred over large distances at vem t pg*4f0u;z k:la8zkeh 4wm*ry high voltages. Explain how the high voltakhk *plf*m8g440aut;z me z: wge reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerou,pfor m0 ex)g8wzt9j4s to replace this fuse with a 25-A fus ) gj0ze48fx,wm9 tproe?

When electric lights are operated on low-frequency ac 0ra/4 :;cs nudjxwzg-(say, 5 Hz), they flicker noticeably. Wa0guj n sz4-rc;x /w:dhy?

Driven by ac power, the same electrons pass back and fo k3kff 6tc5bm 6ikq9)hrth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the q mf69bk5 k3ck h6)tfifirst pass of electrons.

The heating element in a toaster is myn2h, nlj 5g+made of Nichrome wire. Immediately after the toaster is turned on, is the current lnmj,g +yh 25n$(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up inftjl c,c.d(n0 .g/r( gdq*y ji a resistor? Explain.

Different lamps might have batteries connected in eithbpp lzs-i9q 36o1 icd:er of the two arrangements sh:s p6ii1b9-z3q p ldcoown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowing past any poc nzi+f6 cu)jcj;5zy.int in th+ z fc)6ycij;ncz .uj5e wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5jm:sf xb rjl5: n-1h7 hzdrk05.0 h. How much charge pas10hls krf j5rnbd7:jmzh:5x - ses through the battery?    $ \times10^{ 5}\;C$

  What is the current in amper;q/(x4w sfkno es 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 15b5 pndjeyn8z )64bh;v ej0 qr20 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A ifyg * ,8zqdtch84mhh6v4-p p of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line+vz, qv6/:p wu5qzril .
(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 element with a resistance of1iqcn. od) ih5 e*lqfqw/w46 e $9.6-\Omega$.
(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 bu4nhx(9ae7db vhc;ys 3wat6 d+ lb 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 line carrying 2800 A (Fig. 6h34t8/;dx- vhfdlnn+ sq.j y.ed +nw5ht nty18–34). The line /.fnhvx4nt5 hs ;jn 8d6 -w3tyyen ++dthd.lqhas $2.5\times10^{ -5}\;\Omega$ 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 9ld37tsrpjg 0sh 09bf 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 cur7mj 0; y)rkih0pu bdm2-s d9surent 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 wire whose z guuj4drvzr) s35d+5resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 klvyj5z /pv-;zlw 5we:w7 2x0kv vig,mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wi8wemn2a i5zk4 re 2.0 mm in diameter, i 4n8z5ke2wamto 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance.p oigy qzx:g7(l ;jy +*yj6js as a tungsten wire of the same z6g.l; +iyo y (xj:*gysq7jj plength? Give numerical details.    mm

  A certain copper wire has afb5n b:d rzj-oy1a;22g2eh: xkpsew. resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature om3 d)5lj oxf7og..fp df a copper wire (originally at g)3 ffd7ojlop..mxd 5 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper bf ol k)) 2st9q/u1istwill have the same resistivity as tungsten does 1)q )o29fis /tubksltat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of ab8pix :fk z+2+egiu 7y okwad3mhi( /,kfvn9i9out $12\Omega$ 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 droky/j7yu jl)+ up along a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire hasy/lku+ju) yj7 diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made ofb 0j sdank9+ *wltukso/)s*f9 carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance fo k/sfn+lu**o)9t0wsj a9skd br 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 resistanc6o)4;q h lcpbhe. 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 shor )6qhc4h; plobter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precip ht4cm wk bqn/2q92 02yw,;xm:qqcqlsion 10.00-V power supply, and a current of 0.4212 Aymw4l2 qtbqqhc2/ :pxmwk0q 9 ,q n;c2 is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.bo ),esf mq,z181sc ee0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference obfqe, 18 1 e)mzscs,eof 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 impfato 7p1e wb0/ortant that the value of a resistance not change with tempeo b0w1e/f7patrature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to produce 3.3 kWl shii5l75c cphd2a lt 7-2ri) of heat when connected to a 240-V source. What must be the resistance oh2 dt5ca-sh7lic rl )lpi752 if the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable 7f7axn7ws7g (7thsbg CD player that draws a maximum( 7hst7awf s7xgg77 nb of 320 mA of current?    W

  What is the maximum voltage that can be a-k 3: y0efuzziaxi 8u:pplied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resis3 ga 1kwp 0;0/sdfxb371ae lbp qx4ozctance of, and current through, a 75-W lightbulb connected to its proper source voltagaz; bd oc01 q ls3k0/71pbpaex g3fw4xe 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 6ud favi *0/ldW. 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: 850 W anbrx;3m) mg q6ntud+u65 sms. ed 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 to4jqgf;6,zfr u 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 pow uf;f4,j6rz qger consumed.]    as bright

  How many kWh of energy does a 550-W toaster use -vyt2m gjpp.lm1 4 9 v(-;ezoo,csa9myb:h tq in the morning if it is in operation ( qjsl;yvm.t-ohyt cog v-m:m,1 bz2p9pae9 4for a total of 15 min? 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 a 25-W porch light ogd +c,nq;udc -n day and night for a u d-qd;+ccng, year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V bat kdwwh .6a*kx:teries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 x:dkw *kaw.h6mA 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 sxv ws-1t:c7-tgmyhp8w6i)i 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. 1)hex iwcm t 1hdx. mm.78y:(3yakajb/8–20, can be used withbt.y7k mi xm3aw8: .(e m/ )hydxachj1out blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diamey87y)c, a.pg s: q xc9z0wfn; u/bggplter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in tq0/,u np:xysf8 y9wcp )al;gg z7cg .bhe cord?    W

  A power station delivers 620 kW of power at 1g2 pxa1 /kigyft8x6b/rw 9jd9k(cpi9 2,000 V to a factory through wires with total resistanktdf(19 j 829/pxy /bgpwiaci 9xk r6gce $3.0\Omega$ 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 els-,fc y4wjc p2 s5ydk24ec:a sectromagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the watwsd yp4j:, 5 cea2scyc4 fk-2ser 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 cup of wa z7 pryrf z,)(ct++mv/exi7r d1vytp9ter for coffee or tea. If the heater can heat 120 mL of w ,r rext+z 1i f7ycv(m/9t7d) vryp+zpater 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 cn;m7c52imna -* o,s upcgmip-urrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is fy47taxcyw(qhl kx +6-h6.vptkpd x(m 0a9j 2180 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 ofc;)s :0zscj 4ljmchxn.z0 fr; 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 vdo6i2q18-uhdufl *i8 gx e4t in a 1500-W device is 5.4 A. What is the rt-1v8*8i delx4o6f udiqg2 uh ms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecte5g,bx ;clp8 rxd 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 inr tyn+x:()hd+rn:ve 0cj2a6y4 te ht,dgu*p xstantaneous power dissipated by a 3.0-hp pump connected ,vdgt6unyhht:( r xrja++02 :ee x cy)ntpd*4to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected;yk v/r)p4 wh+ky,df q 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 coprh1:9br1/a)jnji f)3bpn9u t nle4j yper wire carries 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-dv)9 55tafetjuh /a 5)ri:r gomA current when 22.0 mV is applied to its ends. If the drift speedg je :uv)f/dtira ro)95h5 5at 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 Ex5oi lbk3 bb082ulm hhp1m6b8 arth’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 * 4ez/zlhlt7g:cgi : xatmosphere, $He^{2+}$ 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 memh cgi4sk78ja a* iqb,)brane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated wi62 5c3olx-qavco;ded 46r1u )m lgc hvth an electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later c16 rl2ocq5v ;do64glc- uxa h3mv)ed. 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 instead of only one?)    m/s

  Estimate how much energy is required to transmit one actiotmfb9sm e-;gn)9e* swn 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])fmb9- w *ssne;t 9emg. 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 potybhjgc.o j-)l)1 s3f eential, $Na^+$ 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 tcg( srnzljr8g*r7 c73 here in 1.00 ampere-hour?    C

  What is the average current drawn by a-dej8 /3ivpz9,ot;awk c 84y+uqvf he 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leay51y;my9(,x0etptu6o krbsg+fa+ h r sq8a m* ves a car with the lights on. If each of the two headlights uses tykay e81;(q osx 6s,r9h50mf*tumyg+prb a+ 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 $95A\cdot h$? 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 m8gr2 zlz0 zj :4s1gvcoade of iron, what must its diameter be? 48vg1jz2 or0cz g:lsz    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the5.c1rmc xt2 yh reciprocal of the resistance R; that ist mhcrc 2yx.15, $G\,=\,1/R$. 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 b;q hnkw9b-6 1 xsvh7d10 MW of power. Suppose 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 wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per-h wdhxb nvb76q;9s1 k kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW rm8 )zw1p*brvheater $3.0 h/day$ (“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 d0; hwdnjp, m2c2lz k0lengths are wrapped together side by side to make a thicker wire. How does the resistance ,dn 2m 0zl ckwdpj2h;0of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for7 zuj +z1t*t:fr1e2deuk+r* fzsk7 bd8 pa.q c 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 l7jq3ob/7z* o iu+qgn flrg+/so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more+3r /gnlo*zjqbi /g+ouf q7l7 than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the4c6ewc2s+; mjf ( wpln equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of energy per second tqewh-87 x g9rpgprc:/;+ubhto the interior. Fin prcqb/w9e th:x+ gp;7r8hg-ud
(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 g8+fgd r,md7btwo 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 transformed in the first relativfmg8,bd+r 7gde to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is use qobq 1v mqktkbx;.*..d 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 hooked to a 240-V source.sbm(3m 64bqych+v4ii
(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 batc)yxau,s 19tjio fozy,if d2 3gz :7w9teries as its source of energy. Its mass is 1560 kg o2, 7ujg1f:to,zcf9 )ay9w3i zis dyxand it is powered by 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 resioc y1qf)ez)5o stance 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 hc vk+cbg-45*)fvgrr beam of protons traveling at very nearly tccrkr) bvg+ f5*v4gh -he 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 copper ,aiw522id b rswire with a diameter of2s5,d2 waibi r 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 rwonb ts7y.lo-u4u4rs :8j zk 3ated 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 m. What issk4:-uw ytz8 ljob4ou7.sn3 r the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltanme fyx7mv3;6 ge varies from 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 power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the hf73nm ;ymv 6xeeadlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb hhj/)a yg)8ceB iyj8a) / hhge)cs rated at 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+eb3 awueg)k 9)apg q, used to connect a set of appliances at 120 Vwq u pgab)9a,k+ege3), which draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm 2wau j 1bst/jxhm r2v(i y nw1l9,kz(mt(kr28 and an outside diameter of 5.00 cm (Fig. 18–37). What is the rwsb/k y9krhal2 11mi,( (j2w( znt 8j2tmxuvresistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that ap0qse3fw8ii/ b4 se7o3 u fp,its length doubles, by what factor does the power dissipated in the wire change, assuming epubp,0 8sfowq337i /f4i easit remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.2kstg vszb.t k,jl*90 50 A and 3.2 V. If its resistance at 20stt*.9 ,gs0 bkzjvkl5 $^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$