What quantity is measured by a battery rating given in 31ucyq9 yno 5zg3gxt)l4ts0 kampere-hours $(A\cdot H)$ ?

When an electric cell is connected ttk5q8 -a0ebok+6u 0d+uyfbyk: lamqqn(id . 3 o a circuit, electrons flow away from the negative te-a( 0 ot+ qk0 mbuk.:i6da8flk ednyb+uq q3y5rminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, 6pbsbmsa,). -5fsxdn battery voltage, bap xa5f db snsbm6.s-,)ttery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is sai ,fvu*jt*hx6,ij evj477hxht d to be connected to “ground.” Since it is not really conn u4 fj t,jh 7*6v,ihx7*xvjtehected to the ground, what is meant by this expression?

When you turn on a water fauc:yw9fs 7yb4qqlr306)goj lbzet, 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 :) bqb3gswf967oylyrz4j0lq a battery?

Can a copper wire and an aluminum wire of the same lfk-. 5asdv5c iy24cyzength have the same resistance?5vyy sa2cdizf-45 c.k Explain.

If the resistance of a small im5k-4- k6rjt*pku;td v,ib+g fu8o+q lkecwe0mersion heater (to heat water for tea or soup, Fig. 18–32) was increa80 wu +e rkbp-t5k-,kt6l c+dkvjq; iof4 *ugesed, would it speed up or slow down the heating process? Explain.

If a rectangular solid mcak z14tao 3s)ade of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from ka)sz 3a14o cta 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 lightbulqqz(k idnyli2d)0x5* qp1w6p b burns out?

Explain why lightbulbs almost al5t)duu0 sxil6 ways burn out just as they are turned on and not after they have been on for some time.0uxstl d)65 ui

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has c.cqyn *im+ b vdwcs-xh ytq:94+8 hl,the higher resc :vs t+4wl+c,d yi.8y9q*cqmbhn -hx istance?

Electric power is transferred over large distances at very high vo b49.t od.c.0hgw qkylltages. Explain how the high voltage reduces power losses i 4dlcqw.9yot h. gk.0bn the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with a9wzangd8h+jgnyi6 s/ 4pyzx 5v 2;-zy 25- +y6nw/5dv8 y pjy49nzzxgg2-ih za;sA fuse?

When electric lights are operated on lov r 9e4o pl*;(pbdfnvn1lne,:w-frequency ac (say, 5 Hz), they flicker noticeably. Wblep(fv *r n en1o:p,vn9;dl4hy?

Driven by ac power, the same el ,qfvyfg* t6k,ectrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the q6f*tk,fvg y ,first pass of electrons.

The heating element in /x n21o67l;f 6 rs5quymnqeqga toaster is made of Nichrome wire. Immediately after the toafxrlo ng2517q y 6/q6uqmn;esster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistoodr0g- bs8p1 682qgz)cl6ie;hkbu-uu vf :hfr? Explain.

Different lamps might have bikx51 k,+ qqjhatteries connected in either of the two arrangements q5,kih1 x+jqk shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrfsyl3 acq.9((y gv8ibons are flowing past any point ilifca.9qy(g s8 y 3(bvn the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a bm1 /(gr yl,bmbs+.qrzattery using a current of 6.7 A for 5.0 h. How much charge passes thryqbr.(1bz/ mrm l,+sg ough the battery?    $ \times10^{ 5}\;C$

  What is the current in arw ,)+t8+ka 8oztypbwmperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a currsn:f v1zap;y h)u*svy1g +7si o7vo)xent of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of cuq+taf5 0l sk-)6sgheprrent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A whenuec9up -r7sm. plugged into 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 dryer has a heating elemen-hwjy9e-iab1v aof + ,t 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 whosex tz)(ql o ivti4i4tng8l35v 7 resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric trays0gq0)8sd99 dvnl*qc k nuh2nsmission line carrying 2800 A (Fig. 18–34). The line hasyn *h)9s8c0 vg2s l uqn0d9dkq $2.5\times10^{ -5}\;\Omega$ 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 6d;bp itnav*6of: )d n6.50 A at 240 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 tuu* v)il; s3coqnzod2-7qq) ks d .o3dhrough 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 tungste( ipmf4 +:w*a+bahbd cn wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper w7i5 hhd+8bgeqz b,f 2yire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.yzjxrq2 5-q;pu8 5spu 0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of co5qz r;5-p s8jyxuup2qpper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter cvy:) ctyl z3w8a+ .jbbopper wire have the same resistance as a tungsten wire of the same length? Give numerical detailsc )byw8tb:ljay +.zv 3.    mm

  A certain copper wire has a resista lp/f -:c +qi56xx(mgjjew)wwnce 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 coppbi am b34 l;np1c())eaogmoo0er wire (originally at p 0gb3cba1nloa(4o mm;) eo)i$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungsten dnk6udglk,2) z o bfkl5z*ff 2929kf l* g6ln2,5kfduzzf) k oboes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of0 m-h2r+t 0 tzw.xokcc 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 copper wd) ocer5r a *6b1it*ld hh6ec0ire (used in 15-A circuits). The wire*h c redl*o0c6h )aie516rtbd has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of 5ee;u yv l0jhlgd icei(1:(de ;(qpk)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 for current tich(le 1vjke: eu( ; lqdd50egp(;iy)hat 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 oa8rzu jlxoc42 erm.9rp6c+h8ne has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter we6 jl8omz8+x2 curra .h4c9rpire? $\approx$    (retain three decimal places)

  A length of aluminum kqex2919tam4 oi v6m cwire is connected to a precision 10.00-V power supply, and a current of 0.4212 A is p xe9ct46 movki a9q21mrecisely 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 copp1r*aw 99p wdnixd r+2fer followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltagerr92w9 1 n fdai+w*dxp difference 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 of a resistanzr zjv 23ki kep;b09;m-os7 fvce not change i0 9p rv ;ovme-2k3j7;zzfskb with temperature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed v)r ilkjiu/13to produce 3.3 kW of heat when connected to a 240-V sourcr /i3jivu1l )ke. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumpdjagoo-h02* aq2 j-lption of a 3.0-V portable CD player that draws a maximum of 320 mA of cu j02jodqhaoa-g p -*l2rrent?    W

  What is the maximum voltage that can be applied a/d0pv9fsaa * fcross a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resisoh1:beoi.b 1a 2m-rs 2lls 5j.xz jp7btance of, and current through, a 75-W lightbulb connected to its proper source vosz obb j .-xl7 .2:seoml1pi1r jhba25ltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank hea56s;y4c pamkg ter is rated at 110 W. 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 hasf-qa(el+e j q8gb,z-ukw ,p1o two settings: 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 lightbulb in Europe, where electrici+0oo +o:u *fclhwymmk 0tle54ty is delivered to homes at 240 V. If you use the lightbulb in the Uokmmol f54:yo0wct*u 0h+l+e nited 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 power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if ioj.z1l jp14.o cz8uput is in operation for a total of up u84.j .zjolco 1p1z15 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 ix-vdkr91z 7gjc 9jmum3, gfm+ w;h5kht cost to leave a 25-W porch light on day and night for a year? + rkvhmw j;kzhj 9 dm-fuc xm1gg,7539$\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in *6*xw6odlb sf; l ,9 twj4oxxsseries as in Fig. 18–4b (Fi d66wl,stsol j bwx;f x*x9o4*g. 18–36). 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 a 12-gskasji d )lmnd;,yr wxj9c 1qkew 9*;0)1pl-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be use qe*8; sgfm4bsd withose m4b qg8fs*;ut blowing a 15-A fuse?    bulbs

  An extension cord made of twihjlj* 25*vk48 h qpmz3vpqj4o wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.lq3h4 2v p5j*m8jpi z4kj*hvq7 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 cord?    W

  A power station delivers 620 kW of power at 12,00 clmjnz (;t9i50 V to a factory through wires with total resistancem;(jnz tlc95i $3.0\Omega$ 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 elecc- d:ffuo rp2+tromagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperatu-o: fpfd+2ruc re is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be urs t/k59.ojqoxf(y, ssed in a car to heat a cup of water for coffee or tea. y k(oft.osx9s, r5/jqIf the heater can heat 120 mL of water 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 currenba*nys ttll246 ra+0sa 5dsd(t in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, i3ybni e;i 4bp31e+6uo 4m7gi8anfowcs 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 of the fh usqhj c*s9wr:5 o/(2uhb1 c.fu d3j$120-V_{rms}$ 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 curre*fwv)ky1tl a0vy: e /znt in a 1500-W device is 5.4 A. What is the rms voltazfvyetl01k/v: * ) wyage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected tcuk *tn6w*/obo 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 p +ja8l)wqw -tpower dissipated by a 3.0-hp pump connectewaj)q t 8w+l-pd to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to :c,w :0ztjzjaaq vp,v/+ qmy0a $240-V_{rms}$ 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 current :p kmg:m -c/sgof $2.3\mu A$. 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-mA8-vle8, ope2l1det po6fy5jv current when 22.0 mV is applied to its v,12lepy5evl -6fp e8d8 ootjends. 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 thdt/y n;qc m(iqnql 3o2bms:),e 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 Eej.wmq owu*nz25m6 ,bvr hv 5)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 

  What is the magnitude of the electric field acr 9/7 wzib7c9y(xkthg )ojx0bgoss 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. 3mz) b 9w ;y,wg4jhkm()gjnnc The action potential 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, tgwbm y4khzm n3,jn(w); g)9jc he 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 requi3s ,m ka,5zv30uubxag 5engbt*3bl1gred to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is5 aas 3gbzn*kx30bgm31 ubue,v ,t l5g 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 pot7(rx3 s2w(7fu znf qypential, $Na^+$ 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 1.0 - ocgb lnqvy-.4-0hsilzja )ww0k(h- 0 ampere-hour?    C

  What is the average current drawn by au(l l c,gkr7q4fh5s34 x m+tof 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the l8 3hu 0b2) h lw/-ylvr8-vqr)xlejgpkights on. If each of the two headlights uses 40 W and eachejv)rqp /3l v 0-8x )wg-ll28urbykhh 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, 150i:ihw uhdb 9)l40c 2al.fk) r:lrqh sko7e.f (0-W heater is 5.4 m long. If it is made of iron, whath:(lae04wh uoir. )hk2 q)kl.dci 7:brfs f9 l must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an ob7kvq zs6u 12xbject is defined as the reciprocal of the resistance R; th2u1qkx7bz6s vat 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 .y/ ph6d yqi/v8fjj(q+:g qjw 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 vp.fqyq/q6jy:gjw i (/h8d j+ 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 householdi1 ef++0fg q ypm5sp.i uses a 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are wrapped toi r--+p3ihi8 dau fai8gether side by sid3i puf+h iii8-ara8d-e 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 ia6erq2pf47 nk+c) pyak 8y v.ps 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 e-*x * c ogpg2s hhhr/geol:)8nnough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carryoxlgc *p:ho2hh- n*sg e8/)gr 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 thegq 9yi;btm 1v x aks7/-;d-sjc 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 t42q83rt ,bax j0fazc notx20c4,8ja zn faq r3b the interior. 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 conducthv )n. ebxsi;-6vkku 5ors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio k)e hs.bnux5vki v-;6of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to he1p9ckjha 0iftx.szk f r:+0-eat 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 rb/t;(o/v h chzlt jxs8)m4*zsource.
(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 stor:p()* pbbdmpk age batteries as its source of energy. Its mass d):p(kb*mbp p is 1560 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 lightbulb has a resistiwy;x1s( 5iv dance 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 n tqsxqfo.s/y+8 f ;x611-mA beam of protons traveling at very nearly the speed of lixtf n;s8sq/.o q+6fx yght ($ 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.bfb*5s8 ml2e3cfrqcg;a6g1s The connecting cord is copper wire with a diameter of 1.628f ;gb ss1e5rfmq2gal63c* bc8 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 o 6 .8*+jxyry5tclbz, qyhl8 z.mbvi 6120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the rvb qzz8ht*ylib .6c6,l.ymjo y85+ xdiameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the sys:iv d0z vu 5jpq.;3hfdtem voltage varies from about 12 V when the car is off to aboutuvj .f p ;izqvdd5h03: 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 120 V and 40 W for household applications. Lightbulbqjr29,* zi elx B is rated at 12 V and 40 W for automotive azi2,l*xqer 9 jpplications.
(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 appliance 97 jb.g2c6w n/j,qka k)ktaccs at 120 V, which dra bwk kq nc7/.9 c26gaktaj,jc)w 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 and an 1: cl uggq)dlj4/yc99ms + gqusmyup i --fh8*outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of gc9g mqihp dfyc-m*g s 89j)/s y4qu u1ul+l:-this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched yo/, op. me)te:og.ah uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the saoyg ,p. .)aoeethm o/:me voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 Vhd1r1 ozsx7cn:rn g) *. If its r)n*o nh :sgc 1r71zrxdesistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$