What quantity is measured by a battery rating given in ampere-hf sh8kiub )np:wk2) my7k1ry:ours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, 8c7ke 7fcfydj;hpitz 4ds a *,2,)lhy electrons flow away from the negative terminal in the circuit. But within the cell, electrons fhz8cfldfkaed2,j7y *s4hi 7),c p yt;low to the negative terminal. Explain.

When a flashlight is operated, jl91gwa3c 0z fzk5e 1arre 4k9what is being used up: battery current, battery voltage, battery energy, battery powak99lerzc afrg54 0wkjz1 31e er, or battery resistance? Explain.

One terminal of a car battery is said to be connected kb6mw.u0v8 j )nikd/q to “ground.” Since it is not really connected to86ik. kqjv)db u0 n/wm the ground, what is meant by this expression?

When you turn on a water faucet, th5xll4omyhu 2k,:( z- y)vu vzbe water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Il bzku4)y -ml o2, 5hv(uvyx:zs the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an alumi3c9 -x s+jdshvnum wire of the same length have the same resistance?sdj-3xhv9c+s Explain.

If the resistance of a 2f)lmn r z; ku,rqy60zsmall immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, 0q;rk 26 ,fn ulyz)mrzwould it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of leng kmm vcss)k,(eh51 fckq;a3 g;ths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a5s) v,k(e c3hc q;mfkamsk 1g;) 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 ligh/h(v*4 8v t zt fl;/q7rhuyhvhtbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned on and ssd8kut*;zxnvr ;) a7not after they have been on for some time.zsn) ;v;td*8uxkrsa7

Which draws more current, a 100-W lightbwmgubx c r0-7ky00;-mjk.u4p ras -+-ewgyymulb or a 75-W bulb? Which has the higher rexw4-y r e;-u jmwgu-bm gpkam-yy0 .sk07+c0rsistance?

Electric power is transferred over large distance5 espcrtbi 01 i)sqdm3h 5*of3s at very high voltages. Explain 5t 0hr) 3*eb fd3mqic 1s5oipshow the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to repz6 (bgb+9ay lelace this fuse with a 25-6(leb9z b+yg aA fuse?

When electric lights are operated on low-frequency ac (sayt7ejhsgq z8-, rjs((8 xnj7ed, 5 Hz), they flicker gs z(jej8j(d-,r7t xh 7nqe8snoticeably. Why?

Driven by ac power, the samk- shts0j0 de,e electrons pass back and forth through your reading lamp over and o-h0 ,estkj sd0ver again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made o1*p6b d osxt/lf Nichrome wire. Immediately after the t*bp 6lx /sd1tooaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explain. -acrcj/f )ws.

Different lamps might have batteries connected in either of the two arrangemiu am,95rhj5j,,quvxd3 o kg0ents so5j3i,kgdj,u5 0mqu v a9r ,hxhown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in5 bt r y b9,ro,+nybhf3vj1)fb a wire. How many electrons are flowing past any point in the wioy,rfj b,vrb1th f35 ) 9bynb+re per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. 8*j1pdlv6,4owe ;; vxdd q5o5zuiqr oHow muchq 51oz pd w8; oodv6eql*uri4d vx5;j, charge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes gjet:fay5s m s/ts-z,:7y4-+l lpq jsc l5nx6if $1200\,Na^+$ 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 *7m,r ic/wbmgc.px m4 4.2 A?    $\Omega$

  What voltage will produce 0.25+ lqcod/z pi b6 8ryk*vrtg2-5 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a w bsktm/)y3yqw+ , ft)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 y0 x:u7x8 f vv1p jcm/sdwe/bf azu27(myb9o7resistance 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 resistancgggm , 5nccl;5 1qqbu+e is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line c,5e xnfh v3m3yarrying 2800 A (Fig. 18–34). The line hasxmen 5f3hv3y, $2.5\times10^{ -5}\;\Omega$ 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 nujbey+k lynp8s( cj6k*6h;; z) z.hyA 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 curreox*f psbd9 ,72)k/plr1hk x nq-bf*aznt 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 length of tungsten wire whose resistance is :i,q5udian ;83ujxgp $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire j;5 wa;w,rhig rmt4+ek r(xm.1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wbwb.oyljw3 ul30 a39 jire 2.0 mm in diameter, to 20.0 m lj 33wy3la.wj9u 0bo bof copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistanc 7ep1zht)pgcj fe/1 7 rnd8ok1e as a tungsten wire of the same 7gez1dc)njpko/11f pet87h r length? Give numerical details.    mm

  A certain copper wire has kg1t:g:9zf9on 2o s feez3d-aa 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 raise the temperature of a copper wp cdyqht-x0 .cp25 w4zire (originally at qx-dyp h25tw 04zcpc .$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will hav)plzway7 cw t,k2 *z.te the same resistivity as tungsten dwaz l.7kpz*c,)y tt2woes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a 2( kj; iw5 * 5codjz +wlon+hcfltw+f*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 housekb*ipiu bv9s,18ql 3hb4 +jwphold no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 13*q4jh v +i1p, iuwb b8kslbp92-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm.jopf 4y;4n+xtz*g6 w+u zlld, 2.0 cm, and 4.0 cm, lying along the x, y, a;fdllnz44p t*zu xo+ +.g6yjwnd 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 the same resistance. If one has twice the lengthj4cnbq djq . ,u a.9fw.;( 3+nkhpdukp of the other, what.9u.n;pcfqdkjq u3n( 4+d. ,hw pkabj is the ratio of the diameter 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 supply, andem/c rt3m wit+1nn64v a current of 0.4212 1+tn/n3 tm4erm wicv6A 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 yl7w;rhuza s s/0s*:dte.r 9km of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wirel as;z7res ry9* wdk 0/sh:ut..
(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 uqic4u h28w / )yatv +gfg2/ivis important that the value of a resistance not change with temperature. For example, suppose yougaviyv/+q22fcw /guthi48 )u made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an ele;e5 lk*e2 2f ohcp+wywi8qz 3vctric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resizf8 2hlcp+3w i2o* e5qkwe v;ystance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD playerl.7*j6pt ( /u pf vks6qxpq,vd that draws a maximum t, k6psj.dfq vvpx6p7/u(*lq of 320 mA of current?    W

  What is the maximum voltage )6/ ysc oq6hqdy rw-(vthat 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 light 43u+n 1vvvdcvbulb connected to its proper source voltage ofv v+nd1cvv3 4u 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. Ccuz i:y* n2544dtx-4i cpbufmalculate
(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. engi,ukb:ln77 edy,s,klp . 1
(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 r11y( h2n jkwmEurope, where electricity is delivered to homes at 240 V. If yj( wyk2n1hr1m ou 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 brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is inwt1pvn4a.ot8 z) b1tzkb e-+, d6 jtks operation 1a-)w618zpnsbttte tz. bk +,4d ojvk for a total of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W pcv0.rudp qs)ws :6zpb7rivz/u+: (aeorch light on day and6 ezsupv uprc ia:d0 z.rw:+7/ sbvq)( night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in ser)0y*dn albg)1cqc,gsta26 xm ies as in Fig. 18–4b gq*l,6 )das10yb cxa2mt cgn)(Fig. 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 enj.vi:e f7 q4rcergy 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 toin my;a9 lfzgh+0b9) g 120 V as in Fig. 18–20, can be used without blowing a 15-A fuse? +zg0f 99myhbinalg; )   bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 cd *lez0 lzv*c8o6sim)gy6q*bbme, e+opper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is mg06lemec) bv*ie *d8qz, +*sb6ly zodissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wiresm o/olu is8pd1+(q2b c with total resiu/1 +plq(s2o 8doibm cstance $3.0\Omega$ 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 l5vus.+: cq+b cqps:fdine is 17.5 A. At what rate must cooling water pass over the coils if the water temper5sb cv.qp+:q:+u ds cfature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used34b t:60rvppa itbw +x in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water from ti+p 0rbp 4:6v3bxtaw25$^{\circ}\,C$ 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 curr k uylk(i:-:ayclj e99ent 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, i0- shbkwch)a)a y57b ps 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 ofh8wt5bne: m+) kz-l9goh0kig )gw 0lo 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 isa ;fp(.p bebn9p g dlw+(4*di q-mjj(g 5.4 A. What is the rms v l-ibjj g p (wd;.dm e((+pq9p*f4nagboltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is conn:s mqzd+:b8r sb0suu(ected to 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 instantaneoh/1sa 0qg fiw,us power dissipated by a 3.0-hp pump connected tog0/,q1 fiwsah a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to :/ hzpr pz;c8l+t e f/:ihpy;da $240-V_{rms}$ 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 coppe2q bqt;tc6pg(r wire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carua9 -/mgp in4vs.x c,pcr,7chries a 750-mA current when 22.0 mV is applied to its ends. If the dgavnp.,s,c -m/ 4uhi crcp79x rift 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 atmospherenahet 6ku5)6 l, $He^{2+}$ 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 atmosph9f vrue92+)eechg7j jksh; 0here, $He^{2+}$ 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 ele wcmrf +7w1g89g a6juk w67fkactric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potential is detecte-b6ig he+ 8py jowoh(;d at a point 3je8;oh 6-+p wob i(ygh.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 are two measurements needed instead of only one?)    m/s

  Estimate how much energy qg(7bv+3n ect 4ooat 2is 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 axon capacitance; see Sectiog vt2oq a t+n4eo(3bc7n 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 poten)x 0vtvojq:qv,p89ad7bo w1 j tial, $Na^+$ 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 therexr9rlj sza1; .5rq9nr0c85uj beh wc/ in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0/ g/ 6+2 ms+q/t)itnub/tmpyf2w x uec-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of ogw4ooi0q vn99b bid2:hk5v7the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V batternoo bbg0:9 kwd95iv24 o7qhv iy 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 heatuq*2fe zbzgayi x;,8 2er is 5.4 m long. If it is made of iron, , yez2*ia gu2b8 ;xqfzwhat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an ob/v*pek2 -u w0i)w hcvnject is defined as the reciprocal of the resistance R; thaihve0- w2cvu p)/*kn wt 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 instead of using high8mz6jqd x/h5kw5 gvfzepq 9 :,-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 k5:wmzv x,pg6ez h5 fj8/9qdqhour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househ0ps)uka4p6c rx/4 +ban)qiwc old 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 lengh: g (cbg9cfvv2nug0p nj/5h ;ths are wrapped together side by side to make a thicker wij9hnnvg 50c2g f/(vh ub :p;cgre. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer isv r*zlbau ),y54tdth+ 9aylt8 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 thickvou5iv :0fz* u enough so it does not become so hot as to start a0u5 vuvoiz:f * fire. What diameter must a 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 is 46k0zo0sq)n0nqzq k rgiven 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% efficin3mf)z96tpu9(tc 4n/ srqdre +idj e. ency delivers 950 W of energy per second to the interior. /i qc.r)ee3rztdnp (sujtf6+4nd m99 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 cond hd:lt k;ju5/d /rx6lquctors made of 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 relativqj://lulxr d dh;k65t e to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a roomk75kc r0edh j p0;xi;n 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 s srhv.x5eysoi::rn*/u td9 ;d x;rkf 1ource.
(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 batteries as i,+)4jg tj( 1uex vb vmi23k2slfrk x+dts source of energy.x1 +ukj224kvlvsd+i (x )f3 gm, terjb Its mass 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 hasw6;hnu( ,ur xy a resistance 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 desi ik,sn5(td jt.gned to carry an 11-mA beam of protons traveling at very nearlyd, .(jit5tskn 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 ise1u(2vk pr2*1daoc et copper wire with a diaa1euo2vp *1ed( t2r ckmeter 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 mx6y6lhbuw2m: f/c9d connected to 120 V. The heating element is a coil of Nichrome wire. When u:6c /myud6bh9 l2fwxmncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the sys:kvok -sz jj t0i27b5stem 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 diszkvb07-k5s2 :tj ijofference 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 ac+w0f b6npi dw frbo4b/r(a8az2 tk 72nd 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automorcw2kb tz (b +/in8frw4p76oda2b f0ative applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a e fwqpax)kej *5hj-.xt2u q2+set of appliances at 120 V, which dra+5hexajwqkj2 *t.up- ef2x q)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 outsid e0op3i;9+oux*14pw yva dhyte diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of u +p1hx;a o ov3wti*ye94dy0p this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R i6-sb0w u0lhr hlr.1 fis stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same volta01lrr0iw .lsf b 6hh-uge source?

  A tungsten filament used in a flashlight bulb operates atkl -o5 fg-uf.*j1 ipbf 0.20 A and 3.2 V. If its resistancef ulo-1p*ffigj .- kb5 at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$