What quantity is mea .ldz y)+cbxw/+c1tnu v:rff0sured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons w eeu:1siq5/g flow away from the negative terminal in the circuit. But within the ce i1:5 e/uwgesqll, electrons flow to the negative terminal. Explain.

When a flashlight is operated, wha6bq . btt u*ac8d9ix:st is being used up: battery current, battery voltage, battery energy, battery power, or battery resistance?tb:8i*cu9a .x6s q tdb Explain.

One terminal of a car battery is said to be cfj wa,s3;y5:rn p5trgxj -k n:3nyd 9nonnected to “ground.” Since it is not really connected x3g3 nnw ,pafy y: k:;njsjt9n5rd-r5to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Youtl yc/en,4 3cv don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the nylc c3e 4tv/,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 the same resist 4j 1lf 0 vonplzg30gdv+t*yxxqs2+ :qance qp*+ lsg4 1ol xzntvqj+vgxdf:30y02? Explain.

If the resistance of a small immersion heater (to heat water for tea or sodog-st3 dmi94 up, Fig. 18–32) was increased, would it speed up or slow down the heating progt-o 43s did9mcess? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and ccl4t83t ciq2/ :0b svfpv3jwssg/05a mhk6u 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistau jwvl kvgp3:cca/80 si s2 tbtf0q3/s4cm5 6hnce?

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 lightbulhkq1o va iudk* x/95)lb burns out?

Explain why lightbulbs almost always burn out just as they are yeil1 c2hcm/5 turned on and not after they have been on for somechl5me1/ i 2yc time.

Which draws more current, a 100-W lightcz zaj ;x514f 9g4n yykour5c+bulb or a 75-W bulb? Which has the higher resis95ck +a5 ru n4 41cfxygzyoj;ztance?

Electric power is transferred over large-t+ smq(km az* (ek,sj distances at very high voltages. Explain how the high voltage * (jqk zme,sast-(m +kreduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to repla(;crw* rtub( lw0(vkhp ,j)tpce this fuse with a 25-Ar(lkt ( tpr)w;u *jwb,c0hp (v fuse?

When electric lights are oxr5 9lp emkh (02gfaw2l2emp9perated on low-frequency ac (say, 5 Hz), they flicker noticeh k2g p awllm02m(9re5f9x2peably. Why?

Driven by ac power, the same electrons pass back and forth through your reading dco4w b(y bd*wz3f. ,olamp over andwyoo(f4,d3 b.c*d zwb over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is mavrt ru2; 5jyl+de of Nichrome wire. Immediately after the toaster is turned on,2rt yj+r ul5v; is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor8bxw;a9he (dx? Explain.

Different lamps might have batteries connected in either of the* a0 oqf(lm;rx; skt9w two arrangements shown *rq9ak(wms 0;t oxl;fin
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 asxkw(5n9/n ir ny point in the wire per second?wkin/x 9r(5sn    $ \times10^{18 }\;electrons/s$

  A service station charges a batteg vhuz6rrb 4.m)9q*tslp4q) s ry using a current of 6.7 A for 5.0 h. How much )hzrqs4. tp r*)gl9u6mb4sq vcharge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ifrd/*-f 5wzks c $1200\,Na^+$ 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 A? nv)m e7/utli1    $\Omega$

  What voltage will produce 0.25 Awvyuzbu1k 7, 6 1uz8oa of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plug.0tg6 o uyst9iged 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 hea-omifoz:zas (, lfo)- ting element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to)io ty ra8.ntg(s8c*eeu6)ws a bulb 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 transmissiob+sjxi(hhik *gmgrcn h4 7 8.;n line carrying 2800 A (Fig. 18–34). The(bci+hgr. jh;xg8nk 7ish4m* line 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 6j; 4yc 7eqke1f k49f2+ggarxf.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 currenm wr 15bo93k jfpiq. wyh(g00gt 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 lengthm q(umf-,wx(1t4y9hn - ejouu of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mmtvgwvf:s 3ibrd6 u+ 71 in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of alum k,tt1apy7nk(f;5ex i inum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 m5ki,a(xk7n yf t1 tp;em in diameter.   

  Can a 2.5-mm-diameter copper wire opnl,r(3 fm+ fhave the same resistance as a tungsten wire of the same length? Give numerical details.rnom,p+l( f3f    mm

  A certain copper wire has a*f;wli j/ojod (i lvf6k+h60h 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 raisst 7/5qb9z dd0ff,b wqe the temperature of a copper wire (originally at b, f5 b7q0ftd9/qwsdz $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wi/eyms572 p6ivq:p3u dqvfc1nll have the same resistivity as tungsten does at nf7qvvy m d61q:pi52ps/e 3c u$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of:*uciv( apjlr 8w:u1geys+v 8iht 93z 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 dromym8k0xg+1 11 q xit5biyb,sj p along a 26-m length of household no. 14 copper wire (used in 15-A cb8qs,i b +0k jimgy1tmx5x1y1 ircuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has silul0 x:q 8f1atdes of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Detelq xf10:u t8alrmine 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 on/ mwki ;fec4j(omta-1e has twice the length of the other, what is the ratio of the dia(-4oj mi f;tmack e/w1meter 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-V power supp ir m 1r0wsiqj+rh ad/gs93ne. i0zp-/ly, and a current of 0 i1s /r.sre rp9/0di3hmjq-+ig a0wnz.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 co;1b naz(ohkyr+wh s..pper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage diff w;n(1rsy oah+zh. k.berence 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 i g;j7zox7ybkk h2.gp; mportant that the value of a resistance not change with temperature. For example, suppose jzpo.;27g 7bhxy; kgkyou 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 q gk-/uwn gp/a*e;-(fcu*cy edesigned to produce 3.3 kW of heat when connected to a 240-V source. What must be the resisc f/qguaey*wp-cn( -g/k*ue;tance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V porlq21o p+ -bmjqtable CD player that draws a maximum of bqo pjq2l1- +m320 mA of current?    W

  What is the maximum voltage that can be appliedhtm/ /f qurs haa*..)( 6ftdck across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current throuy*8lem.jnef ; gh, a 75-W lightbulb connected to its proper source voltage of 120 V.nylfme; j 8.*e
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rate0dgo:vwtg;tg, 0 bs*:tqm0 l yd 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 ha+ guxf7wi lt46vd3ci5e+/-id a:o d ans 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 electricity is deysem - jb)9mz3livered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance doe) js9bmmzy-3 es 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 if8i up02 wn2v7xunn dt4 it is in operation for a total of 15 min? At a cost o2pwt 47id0vunu8 nxn2 f $9.0\,cents/kWh$, 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 y1c8s6gu aim t))xo5wleave a 25-W porch light on day an)gxw5u)y cioa61 tm 8sd night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteu-:e9 hje m,okries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb de:mkje, 9u- horaws 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:+/lb u;8 dd-r zlcnbqdco8e4 of 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. 18–20, id() 1j m8j.dc du ,m:jel+jspcan be used without blowing u)+jmsm8djp(:j i,1 djl.ecd a 15-A fuse?    bulbs

  An extension cord made of twox1o 0w /ubf1fk wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is/1 kowfb1ufx0 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 powege ,s;8r(bvcer at 12,000 V to a factory through wires with totaserb g vec8;,(l resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A. At what c+ :szsd c,d)zrate must cooling water pass over the coidzd,c +s)zcs :ls 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 heq35nku, 8)cg*vykyx eat a cup of water for coffee or tea. If the y*3g, e kvn58kcux)qyheater 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 currebf,9nivos.5 gnt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 18 qzkiovq sg -74z*ht)b( eh:ha2dpm/. 0 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 of t:i gwuz4ug5fw .bat9)he $120-V_{rms}$ 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. Wh. wdo.wct8e3mat is the rwte o3..md 8wcms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected rqd(f+z ( 1m;phhaf :cto 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 dip:emu4, l6ut:*;8fubs hf ay kssipated by a 3.0-hp pump connectet ,s8p maku;fubl46 :f:hue y*d to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected txr3 yn ez/f a9,*u vw0h/vumc9o 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 curr5ro*ejfqq .1r1dn:v qent 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.du;x;8x.(emwa8xrk 0 txa)ql 0-mm-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speedxtr ;08x;d x( ekl8.aaq)w xmu 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 cmn-nd)2 e2p7zi5rnk’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 thetajwi0,oeu30 :cw q,k 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 

  What is the magnitude of the electric field across an eejso3/57rxv 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 +85q tzdh3pawpotential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is t3 dw5 qh+z8pa0.0063 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 ondfe2cl* b)q t/e action potential along the axon of Example 18–15. [Hint: the energy to tdq)btc l/e*2 fransmit 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 potential,yk +gh a:i -e-)anxb1c $Na^+$ 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 ar9;ygf)s /se6i lsmjg-e there in 1.00 ampere-hour?    C

  What is the average current drawn fw0,9s e kulmjmt,f3xrq4 m/-by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car wz hzo+hu g*mlh5v/,r *ith the lights on. If each of the two headlighth or ,5*huzvmg+ hlz/*s uses 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 5blpunb4htqp)u5 *pzz ( ta *0long. If it is made of iron, what must its *b(nhp0* t5tp5b u zp4 uaqlz)diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recidpgp:blg8* 7wprocal of the resistance R; that is,bw lgd8:g7*pp $G\,=\,1/R$. 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 inste 2 2q9dqxmtg6kad of using high-voltage lines to supply the po62q9g ktmd2qxwer, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househoh6k7:sp g*v noyd9wa.ld 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 1*axry.(0vemc6rnan lengths are wrapped together side by r*xe .1n6narma (y0cv 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 is 0mg+ygark4rocb 0 u-5 designed for 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it does nk.r:x.* oplu 5b zcz4rb a8.xaot become so hot as to start a fire. What diameter must a copper wire be ifuoarx *.klbp5x 8rz.b:a4 cz. it is to carry 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 +rwu +vbhvlz,. 4+sak given by 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% efficuk3uq+uax 1b ,iency delivers 950 W of energy per second to t1,kb+qua x3uu he 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 conductors made ol.(ysu rgs6-9-r, om 9yopfjh f 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 rel99yo,6 jo gsl-u(sy f.prmrh -ative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is u3iedde l)vw :* n.tlv1sed 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-n7of7yza:4l c k86cq aV source.
(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 uk3-c*vxj,qggnky e +505 vq xstorage batteries as its source of energy. Its mass*+n 35kyuv- cqvg qkjx,e0g 5x 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 resistan zrl7 k.nm/ij1ce 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* zwf mah/lckw w--r )em3y+5a (Illinois) is designed to carry an 11-mA beam of protons tfkme-r h)-mc 5aw/z+ a*yw l3wraveling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. Thenoqzg0fei9p, t+z x53 connecting cord is copper wire with a diameter of oxitgzn eq3,f +p0 95z1.628 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 conne wa - )jxlcr*;sdf.bydp8*,bqcted to 120 V. The heating element is a coil of Nichrome wire. Whenf-qc; rd)slpd,j ax b*8*y wb. uncoiled, the wire has 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 aboutd i)gnec2 ,fcr4((at h 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 headltn,ca(4c()r idef 2hg ight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household8ogb c4ye ,rp9e.hdk5a- ef4v6(qkso applications. Lightbulb B is rated at 12 V and 40 W for automotive ac s8aeb6h(44,pe9 v-oyd k5e .of rgqkpplications.
(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 nt 9fus8tx 08puy1y8t 120 V, which draw 2250 W of power totaltyfu8 t8ny 19p0u xs8t.
(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 outside diametez0z njs/b),c3e h. * nqsti0iar of 5.00 cm n0es z*q.a,s30ht/n jcziib) (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformgn r0n2r)x 4n fuymv39ly so that its length doubles, by what factor)yg3xrn20v4f m unr9n does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A an izagc8dw 9y:s(eu( /ld 3.2 V. If its resis(a l/ gs8w(iz:ye cdu9tance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$