What quantity is measured by a b r q7xs ;2zzzud;n-us-attery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuitapf/d 4g52hk a, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the nek5 hp42a/dgfa gative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, bat3:cftb *bq+jge /as ye.wxi0q b2o:s3 tery voltage, battery energy, battery power, or batsbq ew afxoesybji0/g*+3ctb. :2:3qtery resistance? Explain.

One terminal of a car batteryg-; wv fyf-cm0,9q5io*8gj sib v g.ry is said to be connected to “ground.” Since it is not really connected to the grb-rq.jsoi y,c 0g* 5vyvig 9f;fg8w-m ound, what is meant by this expression?

When you turn on a water faucet, the watergg n*zwe h:r:4z) eh6:my wnz5 usually flows immediately. You don’t have to wait for water to flow fhe:zm5 * zh)nn4 g6regy:zw: wrom the faucet valve to the 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 thewxmen5x ;a9btz 8bw s:j/3j e6 same resistance? Explain.jex b /jb5ez:ws t9w8 mxn63a;

If the resistance of a small immersion heater (to heat wate7:p+tct9x a kxr for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the x :9tap 7xtck+heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, tqkb e447kr+sltar-. and 3a, how wouldbk-ta t+4.7r4r qs lek you connect the wires from 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)tzs2f:+jsj 8i h*x i(:qc*m*sf jy by56crjl burns out?

Explain why lightbulbs almost always burn out just as they arv8qe49qhct*ps s74h jwzm ta:(5(lwde turned on and not after they j4m974 vpd(zqtlc8h: q(5se hs w *wathave been on for some time.

Which draws more current, a 100-W 5vpv4 )b8s4xsowf0(7- y3.ygrxej/kkfpg pz lightbulb or a 75-W bulb? Which has the higher rekw-ypj(fo/pe.s3p875gb4rs 0z v4k yf gx)xvsistance?

Electric power is transferred over large distk54z +yfoxc,yboq 1*av 5v7giances at very high voltages. Explain how the high voltage reduces power losses in the transmissioyx v51i+4*by5gv7 oc,kfzoaqn lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse witlhmw 1lsbf92o:- g.m( aefv* ch a 25-Aosmmg:f-af2l (.wc 19v*h leb fuse?

When electric lights are operated on low-frgzd p ndd2;pme1x2u;; equency ac (say, 5 Hz), they flicker noticeably. Whg21;pdz eu x;2;pdmd ny?

Driven by ac power, the same electrons pass back and fyb 2d:mwi6r2,alxd)morth through your reading lamp over and over again. Explain wh,6w 2r :al dm)y2midxby the light stays lit instead of going out after the first pass of electrons.

The heating element in a gfwyba6 ol4*zf+4lx: toaster is made of Nichrome wire. Immediately after the toa*64wzx+ylbff a4g:lo ster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor?w z)( gwum)iu qr9tgz8b8dcc/l/7ni 7 Explain.

Different lamps might have batteries c/-x3af1:logpm wmpn /;kk+xv onnected in either of the two arrangements shown in 3 glmx ow+;n m:pka-1/pv kf/x
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many eleh*qa;m 4t hgxu7 zzw5l,-uvj -ctrons are flowing past any point in the wire per sec u-l4jah7 h-tzu*q wmzg;5vx,ond?    $ \times10^{18 }\;electrons/s$

  A service station chargenh9ke2av1sbibqtzy w +t+;1 yd)a2 y9 s a battery using a current of 6.7 A for 5.0 h. How much 1eti d;)nh21ybs bv2q+9ytaaw z9yk+charge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current /mxfu rdzmfhjwp6i3 *qq:)b d.5- +zein amperes 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 toaster if 120 c3r 2wzl0 z4n9xhx +ipV produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thr3h+- kvycm3c fough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V di) q ptf/9fn14plye 6line.
(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 eleme l9j0 m*5ke mffzkxz8;nt 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 conneukuw n8bm (mw6q 2jol-dm616 ycted to a bulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc elewd73/beuvtt9 o/5w yt ctric transmission line carrying 2800 A (Fig. 18–34). The line /dotv/9utbw e3ty w57has $2.5\times10^{ -5}\;\Omega$ 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 qaq0c gdxn(6.rj+r g8 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 curr5a9tt+u p3lhnent 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 tunw(,zzi vid+3x gsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diametere0 qp1 9dk2sdd9t:emk ?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of 2ems/bpby2n; the resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2;bpm /y eb2n2s.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the s-ptwks7i7 x: /(1dr 0otcn8)kq lw fsjame resistance as a tungsten wire of the same length? Give num)dw:/7cin8l1t sjk 7px- s0t kwfo(rqerical details.    mm

  A certain copper wirjlywf 8 z/6 dbybwt838e has a 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 wire (originally aytt f3(bho6w l n+;,wu87fogytf(f,y3y ;g n+w68 l7o otbhuwt $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the sam(u1+qen0k 8w:l r jcmae resistivity as tungsten does uw 1: 0 +clqk8n(jaremat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resist 3esx1jx-2j mxy-4knxance 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 fipdhtld16u:*a1v * tz.jk5alength of household no. 14 copper wire (used in 15-A circuits). The wire has diampv.katd1h* 5z:1*utfd i6ajleter 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, and o8pp: h yiot(*4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that o:yh( o8t*pippasses 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;9 ir, 1qym:ltycdz uq2rx n/: the length of the other, what is the ratio of the diameter of the longer wire to the diame91:u,ry q tni;rdz:y2l/ mx cqter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum v1,m6)ya jm ctwire is connected to a precision 10.00-V power supply, and a cucj 6mym ,)a1tvrrent 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 wiqeun0; ynhj5-5 ,n(otr y*253lq p4u lvjugrere consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is ,jh5r-3yn 2;pgl uq5* ouyjq t e( ul0en4r5nvplaced 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 not kpu i.xxrf8,y95d), yi zi1cnchange with temperature. For example, supp1y,r 5z x .cpf d9ynukiix8,i)ose 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 o;ckydsk( bv c 7o712q2h1ljaan electric oven is designed to produce 3.3 kW of heat when connected (da1 k ;skl12c yojhvq72 ocb7to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of:fjs .tu; fo3l-taxo4 a 3.0-V portable CD player that draws a maximum of 320 mA of curt4o aout-;f xjl3f.s: rent?    W

  What is the maximum voltage that can be applied acros:-xnf*dkks4sic m+x7 z3vh+j s a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a4koo u qzjc*jf)yg axejm.+- (14,k ad 75-W lightbulb connected to i z), o.j j-*1f4akxdkqc(+y ugoj4m aets proper source 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 is rated a i*t+ alirx8h1 va*zpzy8 d,;ut 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 sahx( m3l d7g4iettings: 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 delqvj eh vt:*v,koa59 m(ivered 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 willvj5ka qtvh(e:* ,om 9v 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 m4m33. 3y1khcemxa uz1gfd cd:orning if it is in operation for a totac. 1mzf3e1mda k 4gudy 3hcx3:l 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 4)0 pc( pk/zu61nqrw:s xg4d)ehczif. er-qgporch light on day and night for a y-fpsz0)g6 eq dpe4z1)cgn( :k hcx.riwr/u q4ear? $\approx$    dollars

  An ordinary flashlig/vyy1f) n8b+s y qkqgblxr/6* ht uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). vg) +1qr/b kxlbyn sf*/yq6y8 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 energy stored in a 12-Vuu; bk0 vvr 2yv rzhx4+)oh0i6, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, ca.kdy5zjpp6 7nty8i (kn be used withou 8dpk6.zy (kpnj7y5itt blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cgoai2nj b: p0a.o ms+8brw /)gm (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 power isbg/a2 o ba0+gwon.i r8mj:)s p dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wirqmw/q6/ uxz 9+vx-esi es witiw+ xse/vq6 ux m9/zq-h 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 wfs5*ncv61 0 b-rfqgebl h qc09hat rate must cooling water pass over the coils if the wate9nrh5 q -c1fqlfvc0bseb* 06g r 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 hea kjf/q0k dgl3:t a cup of water for coffee or tea. If the heater can heat 1qdk0g3/k fjl:20 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 cu z,o-ykvb).tkrrent 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 ao wuw 7j)/+5qblqi sa0ko8 .utcross 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 resistanc m/dn-8osf wv)y.o:dt e 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 1500-W device is 5i/a ;c b-j7sszqt*3t q.4 A. What is the rms voltage across it7qbqsasi*ttc- ;j z /3?    V (Round to the nearest integer)

  An 1800-W arc welder is cja *sv hj;m+w(jh0 s r(d2 f*pr6w/cejonnected 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 instantaneous power dissipated by a 3.0-hp jq7/ryr f (rgjinz)c:,ewz,1xp czt0f t);r5pump connected ;nxcr5p(z)gzc j0zy1, j:r7rqw)frtt/ ef,ito a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectm,6k y, :gbrsmkt(mb7ed 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 ca; *8s.a3iqf hmc:gzv brries 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-diag:/ o5tpg- vrthqg l*7meter wire carries a 750-mA current when 22.0 mV is applied to its g*h:5gvqg port7t-/ lends. 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 (tul;kd1 tb4ratmosphere, $He^{2+}$ 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 atlr7 u-2 jen-xtmosphere, $He^{2+}$ 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 a2mkt1u.g.fw8n tay4 h6foq + the electric 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 u06,whjwc9jx )+w59u nuwtgr+ a/ 14z kafozfelectric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is deu u4a hk/wnf5gwzr0jx+1,a uo 9+6 )cwj9twz ftected 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 t*gdg amkm4l t b-7oiu9(;wzz0 o transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored b kdzagm4 g-z; 0tb9 ol*mwiu7(y 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 pot- d ii1q-hihriun5:lg 2c;q- zential, $Na^+$ 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 ampe bg*(z7 g u16kyr:hbio8ali.ere-hour?    C

  What is the average current drawn by a 1.0-hp 120-kitj 70ow59mgc9 .rt mV motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car wdmr bt)y.2w -rith the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh yrm)w 2.bdt-r 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. hw wd/+*k ej.zIf it is made of iron, what must its di ze h+*ww.d/jkameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined aq :eiz x1*as9c tuo6uy7o4;vk: utxs .s the reciprocal of the resistance R; that9*uco:qsyoe:at s xui7 zv1x4 6;ku.t 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 using190hr(uiftx o high-voltage 1tr0(i9fu xo hlines 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 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8uzt sci.pgvlx7od+1 b/)/en1-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 t4:nut gy-jo)a.* h /:vgyrfv wogether side by side to make a thicker wire. How does-h:yw/n 4: vtrv*fo uy.a g)jg the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 1w5 yc,t+deeev*r +v4y17 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 eno w hk2kll8v72+7loy qri 1fmu-ugh so it does not become so hot as to starl +m iho2-7vf 2r8lyulkkq7w1t a 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 given by the equatihowq;r-: lim 5on $I\,=\,1.80sin210t$, 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 tjkk l6tz-iij) a+u34950 W of energy per second to the inte-)4iku+zjtk6 3 iltj arior. 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 condl,v7t q,/jh :ff tw3jyuctor is twice as long and twice the diameter of the second. What is the r fl, wtjt7jqyv:h f,/3atio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used t,84x6a*j 6dd0vs0,oifi*o nnnkfr f u o heat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 24/f*ldr nxhg))0-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 ssiv,tj ;u 7guuso57cc0a g1z:torage batteries as its source of energy. Its mass is 1560 kgo: u 1gsscziu7,;t 7ja5cgu v0 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 light gqz8obo45 dg9f mc llkf(39k)bulb has 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 Fermiz21eaqdk icxs(*;qf: lab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of kq2q(1a*:isz; e dxfc 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 wirnv( q*qowh2 qk,byb5m-6sr4z e with a diameter of 1.6voybq, -( 6 mh4*qnbkrz52qws28 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 hefdak9/md:v s/9u3or rating element is a coil of Nichrome wire. When unco9mak3u: fdor/drv /s 9iled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the/a * j1qsv)pqp system voltage varies from about 12 V when the car is off to about 13.8 V when the car is on aqvq sp /)1*pjand the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W f+uc5n; b zl0jeor household applications. Lightbulb B is rated at 12 V and 40 W for automotive applications. +5ejn l;cuzb0
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at 120o 8 daj3) 1/)zvyjyygq V, which draw 2250 W of power tot8jjyyy/)z )oaq1vgd 3al.
(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.jt+dy1l gl;o 1nsb; e aabnj/t))/2 bp00 cm (Fig. 18–37). What is the resistance of 10.0 m of th +jladt1)2); /na;1l bpgo s/jenytbbis pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretche(oyp( rls0e7d d uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assumingpyr( e 7s(lod0 it remains hooked up to the same voltage source?

  A tungsten filament usto9s5;oky xb1t ;ps6yed in a flashlight bulb operates at 0.20 A and 3.2 V. If its rpt16k;oys9 ;5xyo tsbesistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$