What quantity is measured by a battery rating given i yzl*k8tz4q0t6jao ,, -s jdsln ampere-hours $(A\cdot H)$ ?

When an electric cell is connecteypz-vx*s w,0 bd to a circuit, electrons flow away from the negative terminal in the circuit. But within w0-ypz,vsb x* the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery curv2m/q dd y+rjob8n -0krent, battery voltage, battery energy, battery power, or battery resistance? Expyq-/br+ d j0mvn o2kd8lain.

One terminal of a car battery is said to be connected to “grounzbu2oocgl5xlfp, 5 yr8( vd4 +d.” Since it is not really connected to the ground, what is merzv54 , gfblxuyol5p + 8o(d2cant by this expression?

When you turn on a water faucet, the water usd8 fl3e9ayv10cysw9t. g:wivually 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 a batygcv y:e9.1 0is d9t8fw al3wvtery?

Can a copper wire and an aluminum wire of the same lenzibn r gg:79d;gth have the same resistance? Expgn: bz9dgi7 ;rlain.

If the resistance of a smal+x chzv bki)03l immersion heater (to heat water for tea or soup, Fig. 18–3hzbkvc)+ 0xi 32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of l;-w1vae v*0a*ykophkengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest e0-1 vkapw*a yv *kho;resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lightbulb burns w k9-d52ofbpt out?

Explain why lightbulbs almost always burn out just as they are turned on and notmk 0gcl:f :0daw)hf-pyn 2vg; after they have been on for soyg m;paf)n-kf0:w: lgch v 2d0me time.

Which draws more current, a 100-W li0avpr)ahs869 t jtnv/ghtbulb or a 75-W bulb? Which has the higher resistancr)9 v6avpt8 hj0/n aste?

Electric power is transferred ov vh6flq-yj:8 fer large distances at very high voltages. Explain how the high v6q l8jy-h:ffv oltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replar(8ax ns)cuj4ce this fuse with a 25-A c )(48u xjanrsfuse?

When electric lights are operated on low-frequency ac (say, (v-h.mdpcu0 n s4qk q55 Hz), they flicker noticepuq nckh( .0qs45mv- dably. Why?

Driven by ac power, the same electrons pasfk69+dtr db -gs back and forth through your reading lamp over and over again.-k 9+ r6bdgftd Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately after th3fip r(pzyk6z 8dto .9e toaster is 86oit3 (9 r fd.pzyzkpturned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up inrvw0 1r ci*s -7be/yhl a resistor? Explain.

Different lamps might have batteries connected in either of the tw:/zp2u-c b+p5ddskdl o arrangements s l cu+/z5-: p2ddsbpkdhown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electzir- plg ialjs(j k,,/8i0 p6urons are flowing past any poinzpila(ri,k p isg-j8/ 0j6u, lt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h.e ron;zrv dc(: (li(;l How much charge passes through the batterz ;e c(inv(o; rdr:ll(y?    $ \times10^{ 5}\;C$

  What is the current in amp0-1 scv9h ;wk4tybccveres 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 audad5ilwm 9 /3 7iyk6p toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through a 9fr ivex4 1ruqn..h:b $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugge ob: + xmevz t0.6j .hnnskzz5ut-.w+wd 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 element with a resi48; k;:vti.inwwfs e7xb; jedstance 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 resistance is d0k598gy l7is-kd qo v$1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission lin4;jpbb/nwtjwdl( w*63 vh0v 5xs a9nde carrying 2800 A (Fig. 18–34). The bw(jsj/xh a5;dwn n *vwd t3 vl064b9pline 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+) 9krdvl qz)l.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 through a resist3hg2oe8l 12i rmq vos.or.
(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 whos18b7y q)rtizle resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of coppec5f8qw/v g(rl4mc 8ht2f * qsir wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wirrv e;t;fp4wi 5e 2.0 mm in diameter, to 20.0 m of pwrf 5t iv;e4;copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tuc i bo2r/1it6nngsten wire of the same length? Give nu1n b o/rc6i2itmerical details.    mm

  A certain copper wire has a resisxx-r :s p vxm+hp+4f8jtance 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 temperatqsq4wt6 3d0vd9 v: uweure of a copper wire (originally attq90dqd u4 wv: v6w3se $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature co2d6rq 4eigg(h pper will have the same resistivity as tungsten do e4r6gigd2 q(hes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a+gt v5 jqea;/dzoa:9 +zqwu-t resistance 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 lzi0gz,6fh hp-ength of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm a0zigpf h 6-,hznd carries a 12-A current.    V

  A rectangular solid made of,dh8.drt g-wx-*kcqq carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lyickt d.*8ghxdq-w r- q,ng along the x, y, and z axes, respectively (Fig. 18–35). 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 thub5:op(yf7ifgo7 r .jr- .cj c6zhh6se same resistance. If one has twice the length of the other, what is theyzj5cfcifh6. 6o h ugb-rs :j(.7po7r ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wo f 28c/1 hrnpudbu9xvv6i 27kire is connected to a precision 10.00-V power supply, and a 8ud7 c6or np21 bvkvf2x /hu9icurrent of 0.4212 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 copper 8u,g -jc q 6eeguwudf7-*.lfj followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference o 6lc ujje-g.w 8fg,u*u7fd-q ef 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 imco ,i7w)k ,s94dcbtqhl 2ffl7portant that the value of a resistance not changei,fdk,27 h) 4c bw 79ftlcoqsl 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+8y(z *kf(i wnmi.lupien/( to produce 3.3 kW of heat when connected tfvpn i8u((z/ iy(+lme. wkn*i o a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V porr 4eaxdx ollr8l ;p70.table CD player that draws a maximum of 320 mA of currentr xr;8 7 .l0l4aopxdel?    W

  What is the maximum volta+7ki* u7rxvy/pn e jzny2b6.e7cy* a dge that can be applied 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 lightbulb co-) ;im :mgas7/ zhk q2hx5mgiannected to its proper sourcehk zam/2qsm5:-i) gg;xh 7aim 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 z/6f 2ojukx gen9*6i b8hrg3yis 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 has two settings: 850 W and 1250 ,l dlcmf;qx5 8W.
(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, wh2*-izj u5 xz8bs5 qd.ptyqsq3ere 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 brightz5 qp5bjy3.qts2siu*-8z x dq 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 morninsughw t6sonc42t /g(. g if it is in operation for a total of 15 min? At a cost of nt wggo./t6(24hussc $9.0\,cents/kWh$, 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 itkl3ifw/5c /v3 gvxazv5s 9n/z cost to leave a 25-W porch light on day and night nz/lzk3a/g9vv3w xfcv5is 5/for a year? $\approx$    dollars

  An ordinary flashlight ga kxzgc27d2:arj 66u uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). T jg a7dx662zacg2 ku:rhe 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 en n.deo6s/or*ln, u(v(dq3 onv1/gqvuergy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbp4 ,mxced1, e jq.xs2ppyzn()ulbs, connected to 120 V as in Fig. 18–20, can be used without blowing y42sxe,p, dzqje)x np.1p (mc a 15-A fuse?    bulbs

  An extension cord made of two wires of dxg0 q( rf6lc7piameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draw6prg (7cf0lxqs 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 12,0g :pzzn03u ,yu+hxim7 00 V to a factory through wires wihu uznx0iy:+ m3 gpz7,th total 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 8fd:nm;v-fz*y 0lkmt bg0gl9.iu + pgwhat rate must cooling water pass over the coils if the wdgpmkz0f lg-y9 f gbn:+i* 8.tvl mu;0ater temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater tgfht4 .2oob/,y ts 8lcan be used in a car to heat a cup of water for coffee or tea. If thfyt,t tgb4 oho/.l 28se 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 currev9*b,psq h6)ev cr*qhnt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value i,gzez65fb(ovm7bl z - lt+pv0s 180 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 resistamhh ,t)9y9 jj,hmm q*x -u 2:ijr9gx68wiusnmnce 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 iza e *rl z(q5+uy7ax(fn a 1500-W device is 5.4 A. What is the rms v(q (*xz7y +lfrue aa5zoltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to blhxw3*iq0dy.y-eh. 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 maxi7g :3wqjlgrg/ mum instantaneous power dissipated by a 3.0-hp pump connected to a 3qg:wjlg/rg 7$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tovz , fh )wanal 9oi+*b uc*bntsey;05) 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 curren01b)-pinw cz3wb hr. dt of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when5pwio lvjq h+;j; w,b8ru7tq9 22.0 mV is applied to its ends. If the drift speed isjvq;u, lwr 7i+w9q8bth5 j ;po $ 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 atmosph/ursb,ld lr/ y.j2wj *ere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’s atma+m )/eio7uthosphere, $He^{2+}$ 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 field3bjbfyjxt rhy6 04v1c(dgm;( 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 pokgib2m* (uak6r ei4b ytr2w+8tential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential g4+kt2* ube 8ar 2iibyrk(m6 wis 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 a776a v33lrphfcsi(rtransmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the en7c l7apav6ifrrsh3( 3ergy 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 potentihci8q9jk, 0raal, $Na^+$ 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 v2 7o(jskxrudfv3b69there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp b:ads zr d( ;glp/,pf8120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentall /ay(w2rop6 tqy leaves a car with the lights on. If each of the two headlights uses 40 W and each of the two taillight w2atoq 6/pry(s 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-Vko4 4 kzpx+h+4el igs 3lz31sx, 1500-W heater is 5.4 m long. If it is made of iron, what mu3 k+ zsoepz1l44 xsix3+lkgh4st its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is define34al dc 3td-n35r1hf6x,k4hzqy-jnjwtzax7 d as the reciprocal of the resistance R; khwnj a4t d ja-xx3hz4 yn6tzr-17d3f5q,l c3that 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 M w0gp)d ic-mwu-g:w9 sW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 1c w:)0wgugdm-ipw 9-s0 cents per kWh.    dollars per hour per meter

  (a) A particular household uses at;x f 9y-ea .-wnxfk0q 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 together side b; i0o(o/ grso.bwa re;y side to make a thicker wire. How does the resistance of this new cro;iso ;go(./ be0 rwaombination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. l;wts h:(mmtb( 34kkz
(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 not bec9,jnr cajajh9h8 31vvome so hot as to start a fire. What diameter must a hn9 jjv3aarh1 ,c89vj 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 of length?    $ \times10^{ -3}\;m$

  Suppose a current ish4 0) o2(,x cwcv,xy(lmjq jc (r,unfnr u9+zj 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% efu 6;cxy r/1:-cpc 5psen: sxkaficiency delivers 950 W of energy per second to the interior. Fi6cn51-p spcxck/a ::ru; xe synd
(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 tw0 --ct rn du/likukz0,o different conductors made of the same material. One conductor is twice as l,-n0 cku rkt-/l zid0uong and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a 3- 0cdsg e0xiubszu 36z87ol droom 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 source2g n jzc qgbl f1,ry6(r3.lb/f.
(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 batterievbbi+ym 3)wz2kg3 - uzs as its source of energy. Its mass is 1560 kg and it is powered byy+zukg-2mz ib33 vb)w 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 resistance3t kg+9vmei8e 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 carom 7d92q 4rgiu f16qpdry an 11-mA beam of protons traveling at very n9gqpd m67ru4qfo1id 2early 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 copper aes: my 4(0b8 ( ,hzmj.xbncodwire witm,m8b:jbo0 en xhya(s c.4 (dzh a diameter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. The heatii0ab.3jjw,kd/s+, h2gcclnq ng element is a coil of Nichrome wire. When uncoiled, the h,s. 3,+ bjkida0 cn/w2jq cglwire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system lnu/ ,e7bo9e:uanii ; voltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15 / el:7;e9,uannbio ui%. 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 1pu7l+h 17y) zqoa f6kbars+ a:20 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applications. z1+phy+ 6s aulbf kaa:)r 7qo7
(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 uhiump3l6q9 ; jsed to connect a set of appliances at 120 V, which draw 2250 W of power hq3 ujml9i6p ;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 /e6fg33gxvwqdiameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is3 6g/qve3wgxf the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretczuorsx2p utgl*7sh3 p :0rs6)hed uniformly so that its length doubles, by what factor does the power dissipated in the wire *2t0susl:)ps x go6p r3r7h zuchange, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flasccu ,jr4qalqr43k d1 .hlight bulb operates at 0.20 A and 3.2 V. If its resi,dc jc3 rluqa14q. 4krstance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$