What quantity is measured by a ,8orp*tbjf 5g battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electroecoqh fa514 .ld7wxb* ns flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. q4ad ehc.5bw1fo x l7*Explain.

When a flashlight is oper3abvev;5 ns w7ated, what is being used up: battery current, battery voltage, battery energy, battery power, or vs7anvb; 53w ebattery resistance? Explain.

One terminal of a cakltbumu 9)h; *r battery is said to be connected to “ground.” Since it is not really connected to the ground, what isku9l)mh t ;u*b meant by this expression?

When you turn on a water faucet, the water usually flows immediat5h4;crvx9y 8vf l 5moeely. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the tery9;x oe845clf 5mhvrvminals of a battery?

Can a copper wire and an aluminum cwt0j s *h;0mzwire of the same length have the same resistance? Explainctj 0h0z *wm;s.

If the resistance of a smal96plty up ak4fz1l;x,l immersion heater (to heat water for tea or soup, Fig. ;xl4pkz9a u 61,t ylfp18–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and + (-8 vmnivu 9:hvtvqc2-o/8h vpllmk 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) thevph98m/ivqo tlkc- h(- u2l+vmv: vn8 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 bz)3nlywu87bcete0 b9 jflg1 4urns out?

Explain why lightbulbs almost always burn out just as they are turned on and notgfwansu/ p6- 5 after they have been on for some /5-uwf 6gnap stime.

Which draws more curtj;m8(jx0n pjbygk o 5y;m6 g8rent, a 100-W lightbulb or a 75-W bulb? Which has the higher r0pjjm ;ox8 y8gj n mt6b;k5y(gesistance?

Electric power is transferred over large distances at very hi+1yb dg z*ylfx)d(x,rgh voltages. Explain how the high voltage reduces power losses in the transmission linesy,zxy*d( g b)+l1x dfr.

A 15-A fuse blows repeatedly. Why is it dangerous to replach 85r*qssc4qa e this fuse with a 25-A fu5qsc8 q4* hrsase?

When electric lights ar zfa+dm4rk(3 t4jprvt;p+ p*fe operated on low-frequency ac (say, 5 Hz), they flicker noticeablyp4rzpkf(rvt;m34 fjt+ *a+pd. Why?

Driven by ac power, the same electrons pass back and forth through yo3a3tyh:oyh 7 nw iyz1d-7w+z+m:zo o,na sk4our reading lamp over and over again. Explain why the light stays lit instead of going out afterz+4 nzk 3izw+nyo h wma yh7ysdo 3ao:o,t7:-1 the first pass of electrons.

The heating element in a toaster is made of Nich)1t gl(7rs* c kc ,xh/8aubblsrome wire. Immediately after the toaster ix 7rhslkt/*c bul) sb g1,(ac8s turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resi-hetp75a2a.i pr+ l tnstor? Explain.

Different lamps might have batteries connected in either qnlgh3u+4*ip6 dibi4-wog5r of the two arrangements br43hii+w6l*-4d5 qpggiuon shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wiry58xk+)wsuc b3 f :fwre. How many electrons are flowing past any point in the wire pew:c5)x+s3u byf 8fwrkr second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a currenk xj izm0 jzoj mb9tijg(:xji()/:t21t of 6.7 A for 5.0 h. How much chz(mxi(jjt9ojkg:/2x j j:zii10m bt)arge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes t8zo9 ix k8r:oif $1200\,Na^+$ 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 to9)p9gphez8 bbaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will pr rq; fb5h7ky-es +th 0uap6t(boduce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A wh(2 hu4g +ih b-glquu;sen 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 d+wkt eq0jr)8 7o )m3be-l* bltfky-fxryer has a heating element 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 t 6oepntez;6 1a xj8nr-o 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 electric transmission line carrying 2800 A (Fig3vmzzrg* q9+lf+ ez j:. 18–34). The linjz z lzmv f:+39+erg*qe 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 6.58dtcv4l 53d12 n bdfin0 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 4owesy) 3 dl/5tuz3 fasv17 rycurrent 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 whx2z/6: u:*bprvzgpz7zyg ;vlz / l m3bose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm 1sfcyn vsv-uo95;9 g gin diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mma 0n(7nt:zc/ojs+ dy u in diameu y( /os0+tanz c7dj:nter, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire of7o )rvisvd-3 p the same length? Give nume3 o psr)i-vdv7rical details.    mm

  A certain copper wire has 8s,bwr v,s/yja 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 wireq.sp1.una)m pkf;k:c (originally at qp). ; 1np:fakc.ksmu$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistiv+ hhu9:/ / so(vu)/ fyefca trqog)mw1ity as tungsten drq a 1m h:gys+toho /e)fc(u) w/9fv/uoes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistanc(j6rj-kmwxx b8 i2mnun 6q68ibr-d; le 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. bdirv9yu+be780n9fl 7ne; ufyn)r;x;f;k dy14 copper wire (used in 15-A circuits). The wire ha;y)9reifb9yxd; f7 dynve;rf;nb+ 8kn0u l7 u s diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid madeut2d..b s yne0 of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine u.ebyd.ts0n2the 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 thelsxso+ 0a m hq )),8x2xwes-el same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter w ,s-xwqmx)2e xsl 0as)+hloe 8ire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, andl , k+6z/vexsz a current of 0.4212 A is precisely measured /vse,zxz6 lk+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 foc6z1f0 y ztzx5noqz/1llowed by 5.0 m of aluminum, both of diameter 1.6 5q xzzfnzy0 c1oz/t10 mm. A voltage difference 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 imp -*c :z(u hqtwe;qwg/jortant that the value of a resistance not change with temperature. For example, suppose you m/ w h*g ez(uq;tjwq-:cade 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 desi(kv tm 4p8kt8kgned to produce 3.3 kW of heat when connected to a 240-V source. What mu8 m(k8kp4vt ktst be the resistance of the element?    $\Omega$

  What is the maximum power con5fwjzgb p y8ig,( 9kfe 5poay+*maf;-sumption of a 3.0-V portable CD player that draws a maximum of 320 mA o9+ oam f8pg w gfz5pfbe,yk-a*(ji5y;f current?    W

  What is the maximum voltage that can be 3 mz)a2m d0ony1dfq 2zapplied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-i *x,vu1 9q/ejb*w7oi w*08jcldjsrd W lightbulb connected to its proper sour o 7*19uqdscx*ve*l ,j/wib w0 ijdr8jce 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 i1r6*yap89kjd(y2e/wucq ru fio 6w 1qs 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 setting tsm5nf;i5m an , g38a,aq*zrns: 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 2t*q wvv.n-20a/thvgx (s phrEurope, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W hn-a( r v t.2 2q/vp*wxtgh0sv120-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 fra:b. ) (-jsm ,7ukungrb1ne the morning if it is in operation fornfg:krj(n rub-mb )s7 .1ea,u 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 porch lkfy +jdr; *zf3ight on day and nigdf *jy+k;f z3rht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V byondt 4 qd()w(jg-4vhatteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb dra(d4ohvn4g) wyt( qjd-ws 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 z;9c,fm z96o*t+ y2jcvu,qctn b*bxe energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulb/*mwm2uh 3qv ls, connected to 120 V as in Fig. 18–20, can be used withouu3* 2mmlq/ hvwt blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.1290v sy 4bzrhpwg *6jz/p)y)+kj cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which dra/z 6ywj *0)ksb4g pzy p+v)jrhws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 ah*l45z;qmwqqg4 ;jdog +z )v kW of power at 12,000 V to a factory through wires with ;aw4 5q+4;oh)l zqmgqj vg z*dtotal 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 e+vlsh;08ods. At what rate must cooling water pass over the coils if the water temperature is to rise by no mohlo;80s vds+ere than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup0 p.- 1aqxuuw+dt,eepcwlbj*+g o 83 b73 jgtp of water for coffee or tea. If the heate+ l3tguu 8pgqpdw1 t-b,*j7pwa b3o0cj.e+ exr 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 in aei 4i7i(+ wbmb9ntq4o)at2tu $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is pjekl+cpw hsl- ;3)xi6qn n0d )hbz-5180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistancl-uauvcm kmw0.zng73 agv r 7;,cg;;67c v xgie 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 0kop 0egnx( tbyx(3 k61500-W device is 5.4 A. What is the rms (np( 0 xt6bg3kyxeko 0voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to v5,eamh )8fqh3hw7r ga $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneousxozb60twevvarza 5r2l u hwyw4 *au. 7+w27 7t power dissipated by a 3.0-hp pump connecteda 2 lv5 0wry 6a uzv4ww+h*2ztwex7.7otar7ub 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 a ir:8 vc5up34u6 yw2dja5s ds k$240-V_{rms}$ 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 cop csdw5r+. 0lrqs9d.m(oq zgd;per 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 carries a 750-mA current whebuo cw+0rw6+on 22.0 mV is applied to its ends.cowr 60bo+u +w 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 atmosphere dq:hq too*-l4i*i,cb, $He^{2+}$ 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 Etsll:(s:d ,m lg9k ma5arth’s atmosphere, $He^{2+}$ 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 electrisz qrtpd+p8 xgs31k7d8(ar7 ;bhbok/c field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulate*bsr5qj4 *bki3;lhaix 427 pxe2sh zid with an electric pulse. The action 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. Whaabi4p s *7eh5ihbz 3 rx s*ql24x2;jikt 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 requ e 5x2j255gltat4ea o :r*kybiired 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 Section 17–9]. What minimum average power 2l25 xa*4goteya: rbjkt5e5iis required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potenz 1,pq7tbawz s (f v637 ;ghla7uzz(sztial, $Na^+$ 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 am ig 2y3.t ;7nzcw4lxqhi+4cc wpere-hour?    C

  What is the average current drawn by a 1.0-hp 12 .lx/wg 9w:etz4* kagt0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with t.e;jkpb2iq g z971-edcd)x pqtx dw 8:he lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, fo2q9gj1de t wpexd7-c.p8bq ikxdz ) ;:r 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 iswf)m us3,ttdztpp* 57 5.4 m long. If it is made of iron, what must its di*5wt)7t tmf pz,pud s3ameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of thei:1m 5thnekm zl(mq9f ,,mzt , resistance R; qz,tif,,n l9: mmme1mt5z h( kthat 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 ofkd2bp, jb3 (x0 vkk:dn8g.urg fx7 2ll using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming0vdl(u8pgg3 kjn2r x: bdk2,7lbf x.k 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. nea8pj2i0h f:kio 2c;5mvh z;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 zngh*ws tizl3p /7qq5qb6ra 11 dw: +7 rzcxn1cut in half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the5zh7 x6tc pq+*w1ar qs/iz11wgbnz3q:d l7rn original wire?

  A 1200-W hair dryer is designedvo kef3kk-o74ap(vg/t v4zjx 4 4 9hri hxxb+8 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 does not become so hoe/j- b) -anpy;s niq9yt as to start a fire. What diameter must a copper wire be if y 9 sja e-y;qnbi/n)-pit 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 givef7u si wo)9(ycs0p, oen 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 per se 6)ivc/(zr dqvcond to the i)v(6vi zqcr d/nterior. 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 sov 7px4 2njhv1ame material. One conductor ihnv71o 2px4 jvs twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat ,qm8ne ;eimyjyh l t8zmh)3 (+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 hook(lno3l nv ei;zch27;qed 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 storage batteries as its solbv7 9hzz8b +s3 jxe-aurce of energy. Its mass is 1560 kg and it is powered by 24 bse-3 h xjzvz l98a7b+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 lightbu+)*ex * bmanuux,gla( lb 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 Fermilab (Illinois) is designed to carry an 11-mAlbq *cm-a*0drg (iiw. beam of protons traveling at ver0-bcmiaq*d r.*gl( iwy 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 conxi3 vu l+yoi.0necting cord is copper wire with a dii3iyxvu. o l0+ameter 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(qs- tr f58eje:5otep 7stg(o rated at 95 W when connected to 120 V. The heating element-5qere8sf7et ( t5 (so:pt jog is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the systcpk/v((vrgezy)3+5nivs9uy 0 rn)ln11 w czi em 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 what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assumee yc(n5v v3ig0ln1) z+w (r)sk icnzvpuy9r1/ the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Ligq9g u sey35t(0s5.jox+nfipkj2 x u,hhtbulb B is rated at 12 V and 40 sio29g x5+n(503ejq.,ujkxs htupf yW 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 diameter 0.259 cco;9agrpr ql) t uj2og2z7;4 ym is used to connect a set of appliances at 120 V, who27p;q uajg;)ycr2lt 4 o9zgr ich 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 diametevmhcvkd7 o+hc5i is)+c. ,,fv r of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this 7) h,5ikdio vvmhsc+.c,+fv cpipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doulb+ckb h .0oq1bles, by what factor does the power dissb o0+b1kqc lh.ipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb opera (4wny:g e)hkvtes at 0.20 A and 3.2 V. If itgv wn4e)k: yh(s resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$