What quantity is measur ry;u y(ix9om5ed by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow a717f mui tmy1* o;2jthhxoz 1away from the negative terminal in the circuit. But with;*1umixt12 mz afot1hyj o77hin the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, whak9fl;ctzq* 54w7m4tkkd9cba t is being used up: battery current, battery voltage, battery energy, battery power, or bat wcq9 b49zfk m4lkt* ac;ktd75tery resistance? Explain.

One terminal of a car battery is said to be con+x/82n qoh ccm rxu+odoa5y. :nected to “ground.” Since it is not reah cnro a8mxx2dq.o+ 5o cy+/:ully connected to the ground, what is meant by this expression?

When you turn on a water faucet, the 3bji8-mqcla 0water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to tm08qij- bcl a3he spout. Why not? Is the 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 resistp u p);bb j*z3iix/ (te.wzg3haneixu(.p;* zb/3wj3zi )pbh g tce? Explain.

If the resistance of a small immersion heater (to heat watw.5a4v fcg4 oy**4:hco qob4pdx5 ddler for tea or soup, Fig. 18–32) was increased, would it speed up or sh:o4oxl4w4*ac d4g*c pbyfqdov d5 5 .low down the heating process? Explain.

If a rectangular solid made of carbon has sides of le7.3kpmahmd.:vnah:w5l rre 0f/ q 2r ungths a, 2a, and 3a, how would you connect the wires frop :.wh0qr2u 5 markde fmhlv. a:73/nrm a battery so as to obtain (a) the least resistance, (b) the greatest resistance?

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

What happens when a lightbulb burn /yl);ampfd a;s out?

Explain why lightbulbs almost bevtkh,2s+ .z gu:+.pg: c sfialways burn out just as they are turned on and not after they have been on for sometszk.esgvp ic:hgu,2.:f + +b time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the high/-lph)txz n497 e kliher resiszkhnxilt9h4-) l /pe7tance?

Electric power is transferred 8+r4/0qycdom bjsn:v over large distances at very high voltages. Explain how the high vo+jndoy:c /rs04 v8b qmltage reduces power losses in the transmission lines.

A 15-A fuse blows repb()a hbv9 m(;dpnas7j eatedly. Why is it dangerous to replace this fuse with a 25-(9n7(v)b;aj sbda mphA fuse?

When electric lights are opeo7) vgg0zo+52elu:n6 upqqx qrated on low-frequency ac (say, 5 Hz), they flicker noticeabl625q +uo:lx 7q0ogqpzeg)vuny. Why?

Driven by ac power, the sa:y h5yg 2l kx;o0mw:cxme electrons pass back and forth through your reading lamyl w5gok;xc::mh y x20p over and 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 made of Nichrome wire. Immediate7b*qz m;1 f vn+e*vrwbly after the toaster is turr;7b v* n bq*w1vezm+fned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resist ,o.w x)ko 65mj ;am76jnsbywtor? Explain.

Different lamps might have batterieshtogq: lae 0 +z8)q,z(fy v1ila+dy670shtjt connected in either of the two arrangements shown in8fl hysiezayt7, d0v0gt tj6+ )h+qaq :1zo (l
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A f+8gbp a t du6hg62so8)r;t gxblows in a wire. How many electrons are flowing past any point in the wire ) rp;8tdb8b26guhgg at6so+x per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usooz3(( ddg6 pdf x33pk qm1i1sing a current of 6.7 A for 5.0 h. How much charge passes through the b1qi ppd3mo313d6ozg xfdk ( s(attery?    $ \times10^{ 5}\;C$

  What is the current in amperes 0wzwbv7.;i.q hc m za-if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a t 1tle 7n*rpd( cv/fcc.oaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current *o f7j87chzt uthrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged j+5pbn/o)k-l hpi2ct2fm + huinto 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 elemenp- 7cfrfr6:g xdp l)x0t with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resistanxuy6nuxx - --mce 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 carrying 2800 i)mwr)c v4 *fp sqv+0eox9 +ldA (Fig. 18–34). Th0+)cfpoxeq4vw*sr9 imd )l v +e 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 draws6()yt yoy (k:wn9p4tc a+to tv 6.50 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 resistor.9orf kxlf2 8b86s5w ah
(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 resistk:rh;/ 4aj kndance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length s-wrg( :k p6teur,2i bof copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 1gcwz2+7 nycl3n-n sb:0.0 m of aluminum wire 2.0 mm in diamete+s 3z c:by7gnn-cw nl2r, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper 43c b.m0acyp cwire have the same resistance as a tungsten wire of the same length? Give numeric04.b3y m cccpaal details.    mm

  A certain copper wire has a zjc3 d.6vex*l8jcwc7resistance 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 tywsu/ nm/vh4 0b+q+orhe temperature of a copper wire (originally at hwsb+o/vq0+/4y mrn u $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have th a h:j.rk7u8flwi44 mle same resistivity as tungsten does j4klilu8fw a.m:4 rh7at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of ajvw,t7 dw:;ow bout $12\Omega$ 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 lengthjm q -n,nwbu4tdl*jh: gop 8+; of household no. 14 copper wire (used in 15-A circuits). The wire has dil ;h4nunjojgtbpwd+,8:m * -qameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, y .pq+kwjo7hwk;2o emh xq150and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for currente+kmx.o 2yw ;hoq hq170jpw 5k 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 hc f ty-h1w5i4ty:q:z.lb mc3has twice the length of the other, what is the ratio of the diameter of the long tfcm3lz-5:h hy t.q1iwyc:b4 er wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a3:n xwoy8u *gl precision 10.00-V power supply, and a current of lxw*3o8:uyn g 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 followed by 5.0 m of al d wufbxyb1)b2d/jk a d/jz-+*uminum, both of diameter 1.0 mm. A voltage difference of 85 m*wja/y-f1bj2dkdb)x u/+d z bV 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 importa/fh/wacp0r g ,8xfnxb6u0e r: (q/thunt that the value of a resistance not change with tn r/ cxp6h/f x0,:tgu0e/hf wuar(qb8emperature. 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 dq 9m6.tbrv8 vey efp*0;xtv;yesigned to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the ele8vty mp0; xv6bt;req v* yef9.ment?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD p9 jjf 0/zb+s sid9qm6mlayer that draws a maximum o9/s60z +qfibj sm j9mdf 320 mA of current?    W

  What is the maximum voltage that can be ap9rc *e 3.t+o2 8.poagwbxqiakplied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resnys/xtr1+i 3.4 z+ffpu 2bpweistance of, and current through, a 75-W lightbulb connected to its proper source voltage of 122unt+fe w 1rx+bz p .siy43p/f0 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heatero20 1ue liqbv)jj,1c+qv7jij is rated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two set.;ocbh /+llscwk y:t7tings: 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 delivered to ho9v; ec u9uazce+/y hwyiqi3gpj/,69zmes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not c3c uy a/jwei,e9 u; ih+ 96y9/zpgczvqhange), 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 toasdcgiqx8/t bvbz-.*z5 ter use in the morning if it is in operation for a total ofb xzvdci/bt-q gz8 5.* 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 perxv a53pkst ) q;t0*+cii1m uqo kWh, what does it cost to leave a 25-W porch light on day and night for a year )sqti 1 k+c;o530*aqxtpmuiv ? $\approx$    dollars

  An ordinary flashlight oynk -pj ,9.p +wnd9q4x afwz(uses two D-cell 1.5-V batteries connected in series as in Fig. pw 9x p,n9ad4 jfz-w (ko.+qny18–4b (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 amoun; mb4-yl jfn*3wn5m0.q fxo gnt 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 lightmwo e/7,y* rjnbulbs, connected to 120 V as in Fig. 18–20, can be used without blowij*meyr7 no/,w ng a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm n+9 3.pax 0 h y3dp55hbx8h*1smo gqnjn-fycb (no. 16 copper 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 powdcnxnx9+jhay qnmop8bb5 s y3 1fgh-5p3 *.0h er is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through j fkw/+(9ni .dep,wz7awja0ywires with total resistan7f/j,+ k znwi9w epad.jyw0 a(ce $3.0\Omega$ 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 connzy0cdvl1(mf fn o9v (6ected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water to(9 zd1l(vyv6fc0f nm emperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be us 2rmx; tl73t iphrph2,ed in a car to heat a cup of water for coffee or tea. If 732r;ptp l r xm2ithh,the heater can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current :4r40k a o,i .zig5krf2fuwy +k6vi3bqzny:din 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 across a sxci7 .q;m +hy$330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistancefod74 r5q,+r+h b5awlff f3 6v.mfibh 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 in a 1f+tq*tb5 pdsd: z v13ln m(o:f500-W device is 5.4 A. What is the rms vofb:*5tn :ofqsz3 d(l+p vd1tmltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectedxb0pakx.von5: -n -ruuy e v7n a8ia3rl) j*b- 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 instantaneousl t.8/s vqsz u)+f4aqpt5nxh;*rarv1 power dissipated by a 3.0-hp pump connected rqs+xn4ap;sva5 u) hr*l8q /tvt z1f.to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to fli2 wc,ls l+jt s/f ik/s/,4u,jp/qx 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 cgj+tx* bkp 6, srj5l5e:w6wi oarries 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 carries a 750- y6u9nyi8jj i),:zbgqg5 c4uj)frg 0fmA current when 22.0 mV is applied t,z4 )8ugnqi5 jjygf0cu6 rf:ib )9jygo its 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 at7;on*vbtv 5i5d5wcyi5ftx ;mmosphere, $He^{2+}$ 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 a9hhv,)vr9wzdp k w0 c 2tu5aq:.j zly1tmosphere, $He^{2+}$ 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 acntvr pz2w/2, vross 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 3 e* l8dakp3*l2vaef qis 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 thevqlp *a3l2*3 8kdeefa 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 transm :sec- f0s qle-s,an7kkqv)f9it one action potential along the axon of Example 18–15. [Hint: the energy to transmit on-esk:a7n fs,q)lfv9- e qcks0e 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 potej+fjn wav78x-ntial, $Na^+$ 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 in5q yqtus /tk:+ 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 12nsc ;xk2c5c g5bc4wb 90-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the ,rx.xe * rqk.cb3 ksnvm2d 1sq9,qhk :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-V9k.,rqbq1ev h k3xsm2x,c:q *k. ndrs 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 longduidhcg/cq g1l q*we )l5s6 x,u,u---diaa9l. If it is made of iron, what must its diameta d,6lqg,duc-u -uhe-/1qls9* ) wi5c gaild xer be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined a lz-vz897nxgqax2 xl8s the reciprocal of the resistance R; t-x8z8lzxa7l nq9v2g x hat 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 txyh9;t.me5vxrzf;lx /v-3ij, j4zfrhat 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 t.xyir fmtl/zhx 9j,v ze; v-f53jxr; 4o 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 1.8-kW heater 2/h rj/)l t*tar cea)h$3.0 h/day$ (“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 -h+xli/f zs63icvr6r together side by side to make a thicker wire. How does the resistance of3f6zl+hxr/-cr6s ivi this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is desigby- g16tk/)hcyi ct-n k5xoiv bic +39ned 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 do/r3var jhycp)*sza; -es not become so hot as to start a fire. What diametea*/s - y ;3)arjpcrzhvr 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 given by the equationq8l;d6 9txrr 5buyn-5q/.lpsx(zb e r $I\,=\,1.80sin210t$, 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 en:6dd6xo +u vgf l:jsiv.s ;2lwergy per second to the i oi::js+g 2s6;6vwvlxf dlu .dnterior. 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 c8goh5j nf3c87jze-e different conductors 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 relative to the secon-3 z o88ecj j5ghc7nfed? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volumeqyq9 .h+ysdzxk w,+1 mv6z l.t $62\,m^3$ 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 d+ 2mz*odbpk6 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 storage batteries asl9iggke2.ol9 its source of energy. Its mass is 1560 ge2.iklglo99kg 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 res2xtet ed c2 onxdik7)vw.p+ia;r-..listance 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 designe1u ushq,vij h0gp81u16f v yg5d to carry an 11-mA beam of proto h phfvg j85uquv01gy6 ui,11sns traveling 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. The connecting cor 7vn zwvrw7k91d is copper wire with a diameter of 1.6 wzv 7k7r19wnv28 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 r ihqpw3 j ag6dltd2.59ated at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire ha 26h5d9gqwjt d.ip3als a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the systwmlvfh r g+:+)b)v0 shs u(qhc-s tl+)em voltage varies from about 12 V when the car is off to about 13.8 V when the car is on and tubh h )r s+ llwmv( t)+scvq0gf-):s+hhe charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb 35h vdun-cou2 B is rated at 12 V and 40 ou-h vundc2 35W for automotive 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 diameteqe.+g(q abi2ro4 1b0dqd(g em+,ysp zr 0.259 cm is used to connect a set of appliances at 120 V, whichem qq 2ro(d+s(gd ig1q4y0,b.bp z a+e draw 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 outside diameter of 5.00zbugo3 :t-d *30dr zrd cm (Fig. 18–37). What is the resis o-0ur3 zdg:tb zrd*3dtance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length d0 w9yv 98uzxgzoubles, by what facxv8 g0 ywuzz99tor 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 opermwz4em -5uy;xates at 0.20 A and 3.2 V. If its resis5; zmux4 my-ewtance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$