What quantity is measured by a battery rating given in amper:2v*b7m5u+4iioh- 1uxep -pdf xw pjf e-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow awayx* aqx+a),aue from the negative terminal in the circuit. But within the cell, elec eqx,a +*)uxaatrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: bid:+*oi2* 0 yqir x0 rbyzt8olattery current, battery voltage, battery energy, battery power, or battery i02i:0b rrqx lyd i*yot+o*z 8resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it is ng-f: zeiqs +-w 9wbqi6e)f5hvot really connected to the ground, what is meant by t+seqf )bi9wig fwq- - e65hvz:his expression?

When you turn on a water faucet, the water usually flows immediately. You don’t g3x /gxah7xhm-at -2nhave to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing tm 2 x7x hgax-/ahn3t-grue 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 reswe vm zb 1p,zj, o,kcwv6,w9e4istance? Expla,vmep 9 z1,4ekwz v wjbc6,wo,in.

If the resistance of a small immersion heahe/:*oqfakzr3 h5+*o 0cq *-8f nl)peucam riter (to heat water for tea or soup, Fig. 18–32) was ilfc azhr o/f05:i*p3e q )8**rkhc uam q+neo-ncreased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon f p:.1rw s-cazhas 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 resistance?f az: 1cwpsr.-

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 sjfyxm:rws2- (5 5i/at/jlihburns out?

Explain why lightbulbs almost alw1i4mmya0jy; 4t3jw q idxc ;a6ays burn out just as they are turned on and not after they have been on fwj 1;i6 m0m xita3acy ;y4jq4dor some time.

Which draws more current, a 1i6r;;xefrs: a 00-W lightbulb or a 75-W bulb? Which has the higher resistaf6;r s ie;axr:nce?

Electric power is transferred over large distances at vlr7h h4 dabk.cq/jx3 yg-5btu 2 06jfvery high voltages. Explain how the high voltage reduceg b4 3l7 thd -qj. 52y06xcar/uhkfbjvs power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with p(a mod ab;h7bgqc 1+0zx:1eya 25-A fus:qdab exhoam+ypzbg;c1 (1 07e?

When electric lights are operated eqtwgqhg) :s en1w1.nwi3 kxmwk-1wq9u, s/: on low-frequency ac (say, 5 Hz), they flicker noticeably. Why/wuis:h -qkkg1:m,. 1qewxnwe sg ) 1t3n9wq w?

Driven by ac power, the same electrons pass back a:ke+:psur(0ro lst; c nd forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of electrons.o:ep t0k +u(rcr ;sls:

The heating element in a toaster is made of Nichrome wire. Immediatwm; z,kq)e1bh ely after the toaste k,1w;ze qmh)br is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a r m754ibbbx 1+pck gps9esistor? Explain.

Different lamps might have batteries connectedx, t-;rbjkio7k*wte3 in either of the two arrangementsji -etbo3rxtk*,7 ; wk 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 electrons az4a2 +h )q:x3fr z;timo- rdtcre flowing past any point dz q3rzx)o;f:m4 ht+ -i2atcr in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.6t60j-ql bu3row,j93nle d ea0 h. How much charge passes through the bat6 9,jjdro0- e q363nwe blltuatery?    $ \times10^{ 5}\;C$

  What is the current in 8n ninj 2u 1:uu/zjj7tamperes 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 o1e:ne0.,cniwgaf1or3s 3i k s- ha1hm f a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of xq.el21rc e.o current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7iglf*g49uov+alaf vbndx)u6h ; ox( o,rc;9 -.5 A when 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 element with a resistan2g7ft9cd.s a ebq, 5thce 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 rtqo07;+9m ds;8 t uwepy1lpl xesistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmiss1v 9o2yd3oexzz. z,duion line carrying 2800 A (Fig. 18–34). The lde1 v u2oz.9ozz3dx,yine 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 240 V. *xt6 v:pi 3+d ulvg;ak
(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 o1 0 pg86uzmflsf 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 anot*a5r(*- cguz: g /o mey;vg 1.00-m length 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 1bj 0 *+hzlk9ms.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resis+zm b/g tjtc;fm vt+40oo27nn tance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of cjcmnv;otgtfmz7b to n/ 04+ +2opper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wibt vt8i z3(*ejre of the same length? Gt iv83 b*tj(zeive numerical details.    mm

  A certain copper wire has a resistance ohbvfl h,oa 8*5f:7gs k v7uye(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 have to raise the temperature of a c/8g a:bn bxg6 d5ujw7yopper wire (originally at j/xggnyb6b5d8 uwa :7$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the saab 1m(gjb)ws 0me resistivity as tungsten does awg0j(ba) bs1m t $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb haskh5e hqyoab e)m;)k l, 9u32lb a 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 length of household no. 14 *ksmi jk n)8z+copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and car*n+z) kik8s mjries a 12-A current.    V

  A rectangular solid made of carbon has s4 3((jzehfvi yides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectiy 3 zv4ehjf((ively (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 the same resigx2l*4x dyqnb kew2(2stance. If one has twice the length of the other, what is the ratio of the diameter of the longer wirxkglx(y2b4ne2* qw d2e to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precik ,kq: n3dz0*kir s*ulsion 10.00-V power supply, and a current of 0.4212 A is precisely measu,r0*d*:l3k ks uqnkizred 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 followed by 5.0 m of alumbz9 so9uy )5afinum, both of diameter 1.0 mm. A voltage differ )foubsy 59z9aence 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 resistance notuwb jul1k 5q/m-:og)m change with jm u q-):ko/blw5m1gu 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 g++vvbiyez *no;1a6e designed to produce 3.3 kW of heat when coni ven;+eab6 ov1zyg+ *nected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power fh 8z/a0;;nkx q ddqp1consumption of a 3.0-V portable CD player that draws a maximum oz pqk n; 1/df;aq0dxh8f 320 mA of current?    W

  What is the maximum voltage that can be applied acrogfju),x .l.+ak839o mih0b eut;h t kvss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lig* gzqti,q4yc+qb/hz5 ycbv7l) i w,o;htbulb connected to its proper source voltage of 1; hv,g)bz47*z,qyc + ilcbt5qyoqw/i20 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 110c3b8e/c (+a m qzs8ocs 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 W. en) 6;wvs2wpqs73 s xq
(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 q6).qiiyn5a/)a agoi;4znj melectricity 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 roughly that brightn)a.qin 64q/j)zy;ma oi g5ina ess is proportional to power consumed.]    as bright

  How many kWh of energy dvelg d,p37+w +-vgx3tjv( c jboes a 550-W toaster use in the morning if it is in operation for a total o+gx le v gp,v(w tj+3jb37-cdvf 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 oa1kgv i+lc: k3* 9gfndoes it cost to leave a 25-W porch light on day angi1+ g39fkn:*ock lvad night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V bat8 zgve dbq1i-,rr5 eq9teries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on. 1q bqr5 de9-8gz, revi
(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 w- 42d)gm:ivt wxls r5stored 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, caqd8ihz:ss2; x n be used with:q;ixd8 hzs 2sout blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diamet)e:q,l2 4 vmojpeif.68 lmwlper 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws)l6ep4l.j m:lo weim2, vfpq8 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 12,000 V to a factory ,new2.slbu o1through wires lu1 ,2o w.besnwith 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 k;*2w 9f0k em-qg0 ,zkc sbgn,b3cxer A. At what rate must cooling water pass over the coils if 0sg9 zwkgkrm*-f, k0eeqn2 xb cb;c,3the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water foq -: qas) (igg9e aviwka(c10hr coffee or tea. If thek0q -g g) aq:sai vhwcai((91e 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 current2;uhvg 1o ;io74msa ho 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, is acrosmo/.ba2 , eyiwoni -f6w zf;0iu: vz9ms 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 s, r9(lt0g wgpof 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. W1i,)3x*dz fck*d-)sy ;iwmllzf r/ 6s jmjs7ahat is the rms voltage acros-y6i1rsf)jlj 7)d/;d lz fsizkxmc,a*m3w * ss it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected tox p+g-z+ :zzfb 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 i0;m fa6 yyyms0nstantaneous power dissipated by a 3.0-hp pump connected to m6ya0s;y 0fm ya $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecteh zv-*prpn,m;1x, uz.ed t;,vyadxo:d to a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a tiny current of6s6tlt+fv fiu4cl( g * $2.3\mu A$. 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 wh2agl0tv/ s6v nen 22.0 mV is applied to i2/6ats 0v gnvlts 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 atmosph e;zd0 )x lve -s7oeq.4rtx-yrere, $He^{2+}$ 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 atmosphewd+ *-6uie bq3sn+.jye d :pekre, $He^{2+}$ 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 axo)hzkzk (jsu(q6+ x nvvvfx; 27 3evt ym;ir1r4n 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 actionf/a o) tan5k- bh:4q3mx6e o9/tifpbz 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, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why 6e/tfkb )/bf9ap o5nqhmixzoa34 -t:are two measurements needed instead of only one?)    m/s

  Estimate how much energy8u:ufv pc2i,a is required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axf2:8v u,upcaion 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 potenmq4gi8 y ty*7v.-c tuetial, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there in 1.00 ampere-ho6 kcb xvkf:y-erc7ria8 l*( ;xur?    C

  What is the average current drawn by a 1.0-hp 120-V mo8 o9)3qmv7dl ohaua5itor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If fck )m7 f6 l4rd;ucri1each of the two headlights uses 40 W and each of the two taillid lc;r rc1ufmi)64 7fkghts 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 long. If i )v ;l fy5swaq8afzw yf0:x.3xt is made of iron, what )fq w0v:aw x3 axff.8yz5yl;smust its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recipro+ j)frlakc1n7cal of the resistance R; th)jfk71rl+ ac nat 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 power. Suppose that insteadtup i)llu8 n*;67mftu 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-diamef8pu7m6iut nll)u *; tter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.-g j6d:hnuc)v 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 halp+ u l63 u6j*qt4umtzvf and the two lengths are wrapped together side by side to make a thicker wire. How does the res4 u 6j+tmu*3tzu6lvqpistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is desipo45mi/avjv k n6/xb.gned 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 ih o k k8t.s9:9hse3isot does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum currents3sh:e9sk.89otkh io of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is gi-j/8/hp3mp tgn6 pge0*cgbob ven 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% efficiency delivers 950 W of energy perv (5ln1zikd3vq b*nx;(.fq xx second to the interdv ;vznx( fxqxq.(*1kn3 5libior. 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 of the same material. One condy hgr-n1e 8ah/uctor is twice as long and twice the diameter of the second. What isnhe/8ryg1 - ah 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 room of +l9xu o(t/qr, zq jat3volume $62\,m^3$ 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 hookesl65 ( 2,hinp;m;hi5qrf2za uyx :li ld to a 240-V 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 s /m:pet;lyyqi9z m 8+jyb/x (ctorage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries,:9c8/;itb m/elyy(qxy pj zm+ 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 resist(om )ehq(y+) rlux,hz ance 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 (Illinb;(.p9ur7jbwyx p fofyw17e* ;x6idpois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of ligi1rjb y bx;.o7f fppw;(96d e uyx7wp*ht ($ 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 2283zzht/8//ahw oobytjmp np /8sb z 460-V ac. The connecting cord is copper wire with a diameter of 1.628 mm.hz t/z /p ybb4oo6a8 88pjzm /sn3/wth
(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 12d. -b3c zia.wo0 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total le .c- wbd.zo3iangth of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, theoqrp :tn)ebk9:3 9zke system 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%. By wern pto39bkzke) 9:q: hat 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 applic1undt jsq upt7i4 .xw)n2e ylo:96. tpations. Lightbulb B is rated at 12 V and 40 W for auto1u6d4ils7w )u:j. ptnt2 9tqe .nypxomotive 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 s k0(2bqmes0b( y0h(jeed: ld cm is used to connect a set of appliances at 120 V, which draw 2250 W of power tey mq00hle ebk s0 jd(bd((s:2otal.
(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 diameter of 5.00 vltk58s4gj.l rdr17:mf(g; yug 1x qkcm (Fig. 18–3rt4ulg sglgd71mvyj5k(rfx; : 8qk.1 7). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so th2vnakrhofmvj *kye )60a 32g/at its length doubles, by what factor does the power dissipated in the wir23a hm0an)k2 e *vjrfvy/og6ke change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashligh9bnm i eoaw*e,9+y e+lg)q 3lxt bulb operates at 0.20 A and 3.2 V. If its r 9y eobi9x+q3l, g+*me)w naelesistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$