What quantity is measured by a battery ra owf*t 4u, c0oklr1yd3ting given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electronsc ctktv7d2bjh( 5qc )6 flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative te bk7(jd6hvc25t) q ctcrminal. Explain.

When a flashlight is operf5sjtirl b,v : 4/aae4w/ea8nated, what is being used up: battery current, battery voltage, battery energy, battery power, or5 swblta8 /afne44/ae vri:,j battery resistance? Explain.

One terminal of a car battery is said to be connected toywfgn9eli 5x09, 1iy t “ground.” Since it is not really connected to the ground, whai9,1ig5e yw9ly0 tfxnt is meant by this expression?

When you turn on a water fau0kht*a stpm i14),r dgcet, the water usually flows immediately. You don’t have to wadtk4*,0t imp a1hg s)rit 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 battery?

Can a copper wire and an aluminum wire of the same length have nf3zzu:xtg09 h4 hfz)the same resistance? Explazhh t3) 94gfz:z0nxufin.

If the resistance of a small immersion heater (to heat water for tt9ft +0(1mpy jz l(hl:xe(eeqea or soup, Fig. 18–32) was increased, would it speed up or slow down the heyh(f(j l (l19tpeqx 0et :+emzating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a,qpck,cwk(f : 6 mtfc *:n6pc)(cj5lsv how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the great ,cc(j:s(cvkkl 6n6c5qfp t*fmwp):c est 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 lightbu+ u a;ao.eppz;f 2jkd f27d4ouy hu8)blb burns out?

Explain why lightbulbs almost always burn out just as they are td5/ch6prj3a x urned on and not after they have been on for some ti 6aj hdc/r53pxme.

Which draws more current, a /4uu/dbro-q*y ee-3v7 xym ic100-W lightbulb or a 75-W bulb? Which has the higher resiu /idevxm* e4--c3yubr7o yq/ stance?

Electric power is transferred ov2lvpznp) t:1hrkp 7l3er large distances at very high voltages. Explain how the high vollpz3)t lp1hvr7 kp: n2tage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to repl 5x*o3eoyi s/chwf 3zi.oxci;j3*ya ,ace this fuse with a 25-A fusx3o,c/ih53 os*3 wi *cxiayyz j.f o;ee?

When electric lights are operated on low-frequency acy 3m e)jv37tjp (say, 5 Hz), they flicker noticeably. Wet7m3 )pv3yj jhy?

Driven by ac power, the same electrons pass back and foa8ozb) np jmflk -n:-co,cg73 rth through your reading lamp over and ove ,co3 b: cf8kz-agopnlj)m -7nr again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element i-ommx cr4nzn-mu t+2t32otx8s o9 w p1n a toaster is made of Nichrome wire. Immediately after the toaster is turned on, is the curr sutoor 4ptt+9m2nxnc2zm - 8x m-1wo3ent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up iumey*no4/ u jrp:r5b0n a resistor? Explain.

Different lamps might have batterja8 eqkwp f:qjxnf r(3 4wc-n;1v:z-hies connected in either of the two arrangementsahwrjn- -fcw1:4:pzfqe3 jqk( ;n vx8 shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How;h;dl9 qwd2hx many electrons are flowing past any point in;xwd9hhql ;d 2 the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station chargeg-gv;cxy4 d .os a battery using a current of 6.7 A for 5.0 h. How much c-d4g x ocygv;.harge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes 5uj6g *ii.tyiif $1200\,Na^+$ 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 5k40w sdh do2lA?    $\Omega$

  What voltage will produce 0 u ,npq+umtcbic.zag .ons.u(/ 5y0h8.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 12q 8shenj,l0v n74 h8mj0-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 heating element with a resistance o9 9yg3v6zjxx pjtx1(z9u(o aa f $9.6-\Omega$.
(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 whose resistance is9umad1n76ji w *h* hnn $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmi4 gmt hg q/+f6rqrpu .x9x74cfssion line carrying 2800 A (Fig. 18–34). The line h7furt+fg9. 6 qhpqcx4x 4 /grmas $2.5\times10^{ -5}\;\Omega$ 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 k(igk36se -b u+vf:h.lj dx 1v240 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 thr9rq48q)(c w8ws,x2n pyb0xcs-xv * mbxg je4iough 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 whrnaq4 ..iit )b7)ry fwose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm inxfi+mwmxh1r ni8t)t :kk 7+ x1 diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in dikt/ 9zxu9:k qrameter, to ukr /txq9zk:9 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wir0157sy 1emefla k:jece have the same resistance as a tungsten wire of the same length? Give numerical detailae0e cke fy1s75mj :l1s.    mm

  A certain copper wire has a04.)ty*gyb3 i 88u e boyvd9 xi6 ugxwoy;ag/z 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 of a copper w)1eftf vs-pj4 l0cfx-. (nqiqe +d- gvire (originally at gc4ep0e+dq--ff.sj vv nqt1li( )-x f$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the samljx jyt5c o1n87d;u 8eq2qnn;rdt y(bp39 u: ee resistivity as tungsten dojc7nx 8uy:nu385 ; nqp;ybdot(el9 j2qetd1 res at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistq(,va6gaf1o,g) ww2dplw i,mance 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 n;;h3t pdpdz f x19gc;no. 14 copper wire (used in 15-A circnt91c xhg;3f pd;d ;pzuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon h rkl: 9ciwwnpclt,( +tg.m/ 0uas sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–3wnt0 u,gmtwc9 llki: c. (pr/+5). 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 s:0lzw+3m3cuz )zv whr4:adu +c1vrbone has twice the length of the other, what is the ratio of the dz z:3 ca+cr4u1u:m zd bw)3rh 0lwvsv+iameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-1f8 oa w9 iu 3z(w4jzf80aneyuV power supply, and a current of 0.4212 A is precisely measu a1( 4o8f wzijeunzw903fya8 ured 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 5.0 m of copper +6* yc 6q43l/ k8lqrwlode+sco6fecj followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage differ *8wco6jrqlsc oe4+ekf 3 l6y/+qcl6d ence 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 important that the value o kbve8m306,mu;h kds of a resistance not change with temperature. For example, suppose you made a 0,v6u8ksod; bkemmh 3$4.70-k\Omega$ 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 8renlr ow9b.. k4 u43eoeyor8kW of heat when connected to a 240-V source. What must be the resistance of the element? r88rbr93 ykon4ule.e e.o 4 ow   $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws s(eoc yn+m4*+ ;h fnoba maximum of 32 b;+*4cfneom +nshoy(0 mA of current?    W

  What is the maximum voltage that can be ape,nqg9k bj0- of +f5swplied 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-r 0.6qo (dkndo3ogq z lightbulb connected to its06(oqr- gzqnoo d3d.k 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 110 W. Ct+.1bp iwiqp3pzp.p*alculate
(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 iv,q,,i(vn o/ag6w juW 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, wh: itx iql1s a*ia+tp+:ere 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 bri:*ii1q+a s atpi:x t+lght 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 toaster use in p:/l+ iwphd1f the morning if it is in operation for a total of 15:1p+fiwpl/d h 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 q4aupgxf/kd h5 k3s54to leave a 25-W porch light on day akf 3kd 4 /gps4qa5hux5nd night for a year? $\approx$    dollars

  An ordinary flashlight uses te3 +z:nubx01gzu 4xp p; jt*siwo D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb dr ux4g*p p sebiu+j0xzn:t13; zaws 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 stored in a p( 1 uipl wb/g8iv)f8k12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V asn*slkvpth*a vs - :2:s in Fig. 18–20, can be used without blowinst2sv-:h* :*s lnpakv g a 15-A fuse?    bulbs

  An extension cord made of two wires of dip5m3g9w . wlmiameter 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 the corpl9w.g5i mwm 3d?    W

  A power station delivers 6wq.k ge+ k6sez l;y-l*20 kW of power at 12,000 V to a factory through wires with total resistan ke+;llyqg* -ze6.wskce $3.0\Omega$ 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 con6f 4pn d58ak.t l( fgcht ,3vtqj(jm)jnected to a 240-V line is 17.5 A. At what rate must cooling water pass over5c (mgktqn63 flt),j4dah 8. ftpv( jj 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 in a car to heat a c hlke bz,j0;*lhd8zkxs 9.4)fq4v r mlup of water for coffee or tea. If the heater can heat 120 mL of water from 2f4v k4 ).blzlhz8 kh,9 dmq s;*rxjel05$^{\circ}\,C$ 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 iec :sg88y gxk5n 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 hv d :6rx(cld9i34fcsacross 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 resistancejf7m qm(7( x9q.wlznb 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 1500-a2a*z*5c +rv-avt3+ kgps j,g 6 o uvb:l)hjqzW device is 5.4 A. What is the rmphv + vz,l*aogc szj)3k2v5a6g ur : -j+atq*bs voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecte9 5zh4skqc f(qd 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 dissva esn7 pw/q*7ipated by a 3.0-hp pump connected 7/qwspan7ve* to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connect1-t sijlxf lp)u42gn:ed 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 vfu0 8mw2 o7j3j.zcsbu8e k;k 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 winnho9 ;gc6og l rw+(,sre carries a 750-mA current when 22.0 mV is appl6oocnlr ,;s+wn( g9g hied to its ends. If the drift 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 thetw 26 ti7hkp1a Earth’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 Ear-aqpckm .jb62owh 0f.th’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 across an axon membrang3vey) kuzdpk32o q yf35,y4p e $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. Thd-xv-jcg2tdo ft6yq oipwb:5r) 8 08qe action potential is detected at a point 3.40 cm down the axon 0.0052 s latec:8 ptq f)q0ot8ri- 5d-6w yob2 xvjgdr. 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 wfy)zj94ajts9q6c mp q -7 )notransmit 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 aver ) jqf9 7jnt46sw-omy qp)azc9age power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potesi(m k5aroea( z/3a f21h )jeoi f*u.sy)upp2 ntial, $Na^+$ 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 a*trk7bzn z dk; 69(cod vk,pj8mpere-hour?    C

  What is the average current drawn by a 1.ikry ):/ iq2d-yy2exrla 38la0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a cuiizmc7- g9y; ar with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total ;7- uyicgmi9zof 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*db5gof ,) ep)qt6l uu is made of iron, what must its diameter be? ud u)b*6q)fl t,o5gpe    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the r+;h tl tfuu g85xns:d/eciprocal of the resistance R; that is,+ uhuglf:5 ;/x8ntd st $G\,=\,1/R$. 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 ad/2 -y5uk0a)ck krnk using high-voltage lines to supply the power, the power is delivered at 120 V. Ancdky u2k a/-r5a)kk0ssuming 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 household uses a 1.8-kWt cusyi0z0x/ - 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 tweh,*6) bo ngeho lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination comp* n)h,6gheobeare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 6:b9 h5esa 17uudt5b: veumux 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 enz: u sn4zs67wh envb(1ough 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 than 1.8 W of heat per meter bu:n74hzzv 6 swns(1e of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by th: 5cp fvh nbx) x aev1uuk;l;8*,kln3ze 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 40/w axxlq2kxu( 5o;zotg al8 per second to the inq /x xgt8w(5l2;kua4oal x0o zterior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors made;kfv1jw a 7+jb 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 relawbf ;+ v17akjjtive to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is7a a/p. x mspw8.m5l+vvds1hw used 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 syh e rnx9x7xcu21c)v1ource.
(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 batte5fwl)o+jrvvwr pzk j*g24f d9()co :bries as its source of energy. Its mass is 156b5(l rwp*j) 9c2ofz go)f k4v +jd:rwv0 kg and 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 lightbukru jmhe4)rqxsi*;(*h1k a- 0n b+ azglb has a 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 Fermilabrrh7x;ei-ifh +dh,2 a (Illinois) is designed to carry an 11-mA beam of protons traveling at ver7hi2ie -f,hd+ ra;hxry 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 22*zu-xkx8yo 7f x0q;hd0-V ac. The connecting cord is copper wire with a diameter of 1.628q-7fu;*oxkd 80yx zhx 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 V. Tqfq:d7le qk1l(u. t3hhe heating element is a coil of Nichrome wire. When uncoiled, the wir:hl f eqk3d1t. (u7lqqe has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage 8t *adebh7 r8ivaries 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%. bh8 7tda*eri8By 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 (fkh3y9x+* 8dzzp c 8rtd5fbhat 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive d (c88kdbt9f +p5z zyxhfrh3* 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 appliances r: e8huk88g-ny m+1kmjo u qv+at 120 V, which draw 2250g 8mkyuejr + um+88:ovkn- q1h 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 insidr*9 b r ;(*nfoxgdc.kfe diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.bxok(**fg ;9rrcnf d.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uz7/ -y j-bt2cu8ujmdsd,i8fzniformly so that its length doubles, by what factor does the power dissipated in the wizdu8-ujjb 8fs yd c7mit2-,z /re change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in agfno)l; x o-u.zmf2* g/u+slgk8fpg/lb16ut flashlight bulb operates at 0.20 A and 3.2 V. If ito .2ousl*lbf6g/t+lg/ -1 )k;gmu zffu8ngpxs resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$