What quantity is measured by a battery7,-;htumx sh8*lnwd5yl4f lq rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from d;y*rz) gxlc9 the negative terminal in the circuit.xyr)9*g zlc ;d But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery curre, oa) kktf*jpdv2v 4v.nt, battery voltage, battery energy, battery power, or battery resista,fvt k.vd a4kpov j*2)nce? Explain.

One terminal of a car battery is said to be connected to “gx 6: 6eyz-)v7 7vw*tqgdt1 csoe+viekround.” Since it is not really connected to the ground, what is meant 6+e7 tex*kq)vv g 6e-ziod:v7s1wtyc by this expression?

When you turn on a water faucet, the water usually flows immedqp*kf bc1t9fa*rack; 6(j0 gc(s0lz o iately. You don’t have to wait for water to flow fk9*a faq01f6*(kb;j z(cs0cpocrgl t rom 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 . tcj mm0.s8 ln/jk ys-xt2sjoaf20r:of the same length have the same resistance? Explain.t 8myfj/.j:2st-00nr.sjoma 2 lk cxs

If the resistance of a small immersion heater (to heat water for tea ,2ngg rk7nm1v or soup, Fig. 18–32) was increased, would nm 7kv1rn,g 2git speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon ha/euwzbfud2 5 (s sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest wz2b/ d5e( ufuresistance?

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 burnsp)ay a7 )5j9jpgz8 0k*vo ybsr out?

Explain why lightbulbs almost always burg35 xmaw ydt:8 c22t/dlpyq g2n out just as they are turned on and not after they have been on fo 8 2/t:agw ldy53q2ydp xctg2mr some time.

Which draws more current, a 100-W lightbul*v m)1be.s jt).viyivsh35 d)exnx;qb or a 75-W bulb? Which has the higher ry veds5hvm j qinb) v1)xs.3.;t*xi)eesistance?

Electric power is transferred over large distanetv .g a7bvk. lfk5*8yces at very high voltages. Explain how the high voltage revgfle t.5* .k7 b8vyakduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse witnuyh5fc( (epcu+ )bk+h a 25-A fuse 5(pyncubc(k+h) u f+e?

When electric lights are operated on low-frequency ac (say, 5 Hz),s q/ *+7ab ilx:cluxx83;rlli they flicker not+8q7sil c:axill* u;l3x rb/xiceably. Why?

Driven by ac power, the same electrons pass back and forth througrkimm7+ j/l.-- m kpbdh your reading lamp over and over again. Explain why the light stays lit instead of go./lj+--kpd7mmi m brking out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediai zuc-l//x 5(rbfx lt:tely after the toaster is turned on, f(xt -:urz5bxl//i lc is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in 5)tt6 tjz)8wj 0hb zbza resistor? Explain.

Different lamps might have batteri8 iev-yp;; 9k4sneakza eo .79ntfbq6es connected in either of the two arrangements sf6;p7yk.e 9qz an8vi n b o9ea-k4ste;hown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. c9bb ts5d1*: q/isssjHow many electrons are flowing past any point in the wire per secbcs ts/dq5: bj1s i*9sond?    $ \times10^{18 }\;electrons/s$

  A service station charges a batte9wqcud rue-d8; 7 dh)zry using a current of 6.7 A for 5.0 h. How much charge passes through the batte7qeczu d- ; wuddr9h)8ry?    $ \times10^{ 5}\;C$

  What is the current in amperes ifvssvo/w6+er xoopad4 6zlvm, 75p p2+ $1200\,Na^+$ 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 curren)a 7 sa5xu,ku 9psvl6.ziwz2jj tc 0k1t of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current througm9 -roo+tznc+5:r,m rhe *y ouh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V lineg8.e r8m,q+tl5wwu xy.
(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 resistanc,, cfhq j -xf,dn5 /-ozwco3g.y2hglb e 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 whose resistancea5nn z+o: eao p69uhh8 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 2800d9:u zw7y+ufw,f d+m x/-xyk9y)q cat A (Fig. 18–34). The line fxw) uyu 9azyf:-d+xt 7+ mdkwqy9/c, 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 24w/h+hy f11b/ o2 lt mbzrqx/.s0 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 v,ksqe8t6zx4 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 resistance i hf-3(oaxin o*l8qte4 /cfu8 lib; 3khs $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of cakf8izapd9 9t*) .akkopper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resisto a3 5t ohc83vu85.w s vbph/bg5x:xudance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wic8xoox 5h :dhgu 8ps535abvbu/vw 3 .tre 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same res4t/k)tj5p,q)mzqjzt/ bvn jg+1 i. zjistance as a tungsten wire of the same length? Give numeric/,4)5z+jbktjtjmz t 1vgnqzj).qp /ial details.    mm

  A certain copper wire has a resistance o v)n oi2brv(i,f $10.0\Omega$ 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 havyh hi24s(f bd)e to raise the temperature of a copper wire (originally at sif) (2yb dh4h$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have t)flw+ct(l obdyf 7xj78u r 4v,he same resistivity as tungsten dc(,4 yb7 d)w ovl tulj+xr78ffoes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of 9 mpm/se,k 3xvabout $12\Omega$ 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 l6n3byubv/ aorod u-at;c- *f:; spk0length of household no. 14 copper wire (used in 15-A circuits). The w /onta kdu-*-;rao :3 ul;svb f06bcpyire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of )bvyk /5vocb .3j-ndn 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. 15 o3d-yj bnnk.v/ bv)c8–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. r ( 9vbaa7scfp5 oe3f(:uvyk1 If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diametbufe7 vp3 :1 ck9s(fyraa(ov5 er of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V po57o2fqr f g5zkwer supply, and a current of 0kr f5o5fz27qg.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 consists of 5.0 m of copdl+eha: o62clper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the complch+l: 2da6 oeosite 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;32zqie zben+dn 8s5v the value of a resistance not change withezdq+v bns;nez32 i5 8 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 ele t:+(a,fj24rlc ilpfl ctric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. j+fp ll4c:arl(f t2,iWhat must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of raik64t1s 8vmcj qx36w+;mxa a 3.0-V portable CD player that draws a maximumx r1+c6aws4j ;ik6xa8t 3vmqm of 320 mA of current?    W

  What is the maximum voltage that cad/gic ).4(ez 4of iqqyn be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current thrrhplm--046t9z ehxpg ough, a 75-W lightbulb connected to its proper sourg6x-zphh-9 4pte 0 mlrce 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. Cal5-h oppcg:(+nte q v oncm8y 3e;u44ycculate
(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: 8/bbl 5yw;;h alim0 1xz50 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 lightbu s xlqbv6*,.kplb 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 roughl .qp*,bsx vk6ly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is in ofyvrp3 (sst out .r1s-3p 37yzperatyrytr sz s1 ptou3fsv73(- 3.pion for 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 doquc+f 862 yeru e epgk8d1a4lw /1wqwi66ts1zes it cost to leave a 25-W porch light on day and /e ade611z68yis+e6qcq wgt4 rw8wlkup2 f1unight for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected inw 6mxx5 gu:-d*seu5fw series as in Fig. 18–4b (Fig. 18–36).5dfexs:6 wu-*5m ug xw The bulb 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 energy stored in ar/.t c3)hbyre 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 azx42/rdqe 32n9 jd0yp tqg1kfs in Fig. 18–20, can be used without blowin gn9kz2 dyqe r10x/j2dq4fp3 tg a 15-A fuse?    bulbs

  An extension cord madjgt*,sa33f nie of two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which dr s, gtijna33f*aws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 z 7.p,hgn9gn gkW of power at 12,000 V to a factory through wires with total res .79hg,ngp zgnistance $3.0\Omega$ 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 conne*hdztw4lq*a /aia8 /og(9mj vcted to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more 4/mgla(i9/d*qv zhjawta 8*o than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to hea9,pg7 nl/p7v jsbolrx, h3s/mt a cup of water for coffee or tea. If the heater can heat 120 mL of wans9r /p/mlxgo,v j 7slhp7b,3ter from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current ir31a0 nj86 m rptke;srn 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 ace5;q d-r,yph lfcet+ 1ross 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 resistakn1-(d,nwpkylfrpspjrm7v1 18x *ad7t0 f9qnce 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-W device is 5.4 A.d*w8hjn*ls a/ )po)93ekebt l What is the ob lenj* h9s k8d)lpwate *)3/rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a .8-h6k uaabem$660-V_{rms}$ 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 kf;5mq8qqs3 1u 0ltui.0-hp pump connected s3q uqqkli0 81u; tfm5to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected7dv d.q jzd,g8 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 0/m95kqh gwddn( mz :dcarries 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-diamed e0vw-h8 z/mcter wire carries a 750-mA current when 22.0 mV is appl0 v em8wcd/hz-ied 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 the Earth’s atw+w+15::zjgbnqso 4 xms9 a o ,b1veigmosphere, $He^{2+}$ 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’sv gfcw 0y 8lg.zw+9 6aw:94cjlm r(pii 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 e 7y9x2rpd ;gx vn/mnloz/y:+ olectric field 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 potential i;i h i6l qc1 * bzitp4t(hj4z0ncno7n7s detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential i n t;zh* 4hnz67n0qijct ibi(1lcp 4o7s 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 tjkb*( +g*avsmhz;mt5o transmit one action potential along the axon of Exa *v*( m+amz5sgjhtb k;mple 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 potx* aqndk(u.x( .b0k( xpgj y,aential, $Na^+$ 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 ::g3 g: vmclyp7r8o:n/ mkiqjthere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motor? a9; zknlm8e)mgo8c .f $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If eac;68 xzie8 owmgh of the two headlights uses 40 W and each of the two ta88mioew;x6z g illights 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. l4 gym ub5n.mgl9c*dn5e 3sr94 m long. If it is made of iron, what m mlyes3lmn9bcr gdg4 u*5.n 59ust its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is define+ywb0t 0kbr wo,t-hp82e y 7k.s+xx xkd as the reciprocal of the resistance R; thkptbey0x+wxb8o 2tw+ -k r.s 7k0xhy,at is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power2a) x0 (4i3 kcrivno dvg.(hmlyuo3 t:. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a.nrxyl m(a2di(o vv4)ocugt 0k3:i3h 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 usesqlih2c8x/ 9q/im:4)o n )nmrw(g vd qo 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 lengths are wra7 qf/z8bl,;st5id nv xpped together side byqntib;8z 7xdvs,/f5 l side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer bwe(gc/ggv y* eb:h+* is 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 eno26 c(j6agxoa9k0imw zugh so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry9 o(gwaim c62k6xj0az a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by+3:w(yjityu9gj qr4c y. ca3k the 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 delivauflgvh :,2qxhg:fp; w 3 du:be7j81 bers 950 W of energy per second to the interior. Findgwd:x: 8pa3,bqjf u f:7uv;heh1g b2l
(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 same wrg jzir92/dy i yn5m;fd5nw9(cdi*0material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the ff ir iwnjrdcdn*;d/i z5 9w20y5 9(ygmirst relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volum4xxrq9q(477 yhgp njxe $62\,m^3$ 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.- l)sc f ymy2 fmcqnt ty(n;.4g;o8l0f
(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 styg sh6wyqj7 /2e(0z1jo- pbhoorage batteries as its source of energy. Its mass is 1560 kg a 6 pg/ze (-q17 osoyhhwy02jbjnd 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 resista hjx4rr;4f nuuup5 e(,nce 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 designef*sk uk/ca -d li)ri6cu/4s7zd to carry an 11-mA beam of protons traveling at vei/7iu *rcsc)au6kl4k/ -s fd zry nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord is co, uw7lh ux g5n2:e)mhz)bi9f bpper wire with a diameter of 1.u9 7mxf25ilb nhgu)h,zbew:)628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected tyuo(l75+snn rcy yl(/n8+p ido 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire han ( l+cny ndy5/i(7lsp yru8+os 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 about 1e)nb autd7 iia; n3t;h.1 e4i2fd: jau2 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;ndne)te j h3.a7ba1fuia2 i:u4i;td 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 120 V and 40 W for household applications. Li9i.zacfxe1 / :g+r0 ous tkrk6ghtbulb B is rated at 12 V and 40/10ti9re au .ocs 6gf+:rkx zk W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at .bqmc ((p c3im120 V, whic(cbqm3 . ipmc(h 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.;sea +m3 4050umq z)noaq plqf00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance o qqzqa)4p;mem0+ 0snuo35 aflf 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniffkqm2 bmg;.nc(r4(h x -fk0yqd.r c.jft 8d2 oormly so that its length doubles, by what fac- bxm;4d c ktf(2r johm.r.fygqn(k dqfc08.2tor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashligs ;qzs2oj6 v*kht bulb operates at 0.20 A and 3.2 V. If its resistance ojqkvz 6;*s2s at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$