What quantity is measured by a battery ratinh2sj5nb/v+w b v9w9gqg given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow af 8t6(1puumkte ew(9 mway from the negative tere(tmk1u(peu6 9 8t wfmminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is ow8bl; ; s; /e01f(jkorocz oblperated, what is being used up: battery current, battery voltage, battery energy, battery power, or o(b8sb;zo;k;frowc / j10ell battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sinceomcd+g;pgmt1 o01*5ut u 8zjo it is not really cop8joztotmo01u;5d+*c ug 1m gnnected to the ground, what is meant by this expression?

When you turn on a water faucet6gp0iz ycsp7. , the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why ngpi 67z0psy .cot? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum nd .r6aav t9n3wire of the same length have the same resistance? Expt96nanda 3 r.vlain.

If the resistance of a small immersion heater (to heat water p;)ws t y)4nctfor tea or soup, Fig. 18–32) was increased, would it speed up or slow down the hescpt;tw4)ny ) ating process? Explain.

If a rectangular solid made of carbon has sides of lengt0fdxmo: *oz 2ig4of+ ohs a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the leamg:4x*d 0zffo io oo2+st 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 lightbuf, ictyo bqxrpu7)1)1ya :io 7lb burns out?

Explain why lightbulbs almost always burn out just as they are turned on angi4ql fjy17xk 6x s71ad not a1lq7gi7k4axsf1 j yx6 fter they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whdgmky(mgcg:w* 8 qt, 5-g 9o/-w zxpjtich has the higher resistc qmw,5g(- dx *p:8ggzgjtok9m t /-ywance?

Electric power is transferred over largrrd. s b1q+ba4e distances at very high voltages. Explain how the high voltage reducer r d4b+s1.bqas power losses in the transmission lines.

A 15-A fuse blows repeatjy9 w.tb . wj*zn*lx31mb ;/4vssfpuyedly. Why is it dangerous to replace this fuse with a 25-A f 3 w/sm9sjfb;u zlp4n.*x.bv1jwyyt* use?

When electric lights are operated on low-frequency ac (say, 5 Hz), theymspgptz.g u3l5nn81muz2 *n4 flicker noticeablyzg*mgs5n3mp18 .uunz l tn42p . Why?

Driven by ac power, the same electbcpy** v6 )i9mjmyvsc(1.d r*qqi0ga s+ fyp,rons pass back and forth through your reading lamp over andy 9pp*m*jr 0.)6av+yq dgysfm1qcbcs ,*v ii( 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 maxl4 f0h4jd ueq;thju/ p66,-x hhml3x de of Nichrome wire. Immediately after the toaster xp elxjx;hu4 h- tm/40hl6d3 ufq,hj6 is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Exp2)k mn4y4bn ).rq dyoslain.

Different lamps might have batteries connected in either of the two ar1pykb. akj1f9i 9gwn hzz.tr6t9t ;2krangements s2k1 w1z 6g9i ;ht.t9k9.jz frpa ykntbhown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flokh rw0v2-r(*ol0obh b ajmwj6cl,30 cwing past any point in the wire per sb c0v3hw(oro*lk, ch2wjm j lrb-6a00econd?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usin 3 6sb+ci4j17qq9 uu*dsmd cing a current of 6.7 A for 5.0 h. How much charge pacqn+jd6*di73u b is4 us9 1qcmsses through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperel,, 5h c.; cwlcqx8nwms 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 ofqbq pp1t54;*k u: +su7zc9 fn+czzgql a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of cu6cyk) *10 *3f3chr 2:ib ti wm+4nxbzmsdhqndrrent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.w 7y xh6/2tusv5 A when plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a resistancerpihx uli(tz/f. 9z1 tu:1l6 q 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 resistanve ejmnsobwh rq7wc 27 1*(fk9n12 m5swez-p,ce is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc elv9b )1(ibsj9wvl sdx1n0y c(jectric transmission line carrying 2800 A (Fig. 18–34). The j( ixnw9vscb(bv9l)sjd 101 yline 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 d7pdr p.otf3(ag3t3t dmaqdu47j5+sh raws 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 )llk nj1,/ypn.izlz; 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 v mjm2relq;mh275:xaa 1.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of wp)cd(6*ieac a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the res40q7qx*dcezt:h 1vhruq i7 i7istance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter.hr 7h *q4v 7z0i ut:dqe1qi7cx   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten withi 7 hf3jgct*1 t:34zr1tui sre of the same length? Give numerical deta3z rjut31 *h4tt1: 7gichsit fils.    mm

  A certain copper wire haj4bks (umye:rme27 x4 s 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 tdi uc f3m-sj(ea ;jh sffb,*l xt9f30,o raise the temperature of a copper wire (originally at a ej,c(j0-u ,*3s3;9ftsdbfi mh ffxl$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as t ar q7sl49vpg6ungsten d4 lqp7s arv96goes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistancebvk3iph+-3ds 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 -eam+o .eybn,+u) xcv of household no. 14 copper wire (used in 15-A circuits). The wire hasaxemcvu ,o.yben-+) + diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths(r 6oe ioybv(uw,7zauu0h +;d 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Dih7(o; (0z, +b rywduuae6ouvetermine 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 q4h6w *xesqq9has twice the length of the other, what is the ratio of thehq e *69xw4qsq 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 10.0po zz.6(pi 8)c/4h7c w1 midurylo0am0-V power supply, and a current of 0.4212 A is precisely measure6 idi c1m8 .uh0moalc )zp7w4y(z p/ord 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 yb ime09z.wkye/+ 3qw3xzz38aa , gel5.0 m of aluminum, both of diz30m +qw/ile3ew3yz,9bax8z a y.gk eameter 1.0 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 important that the vab/mepem) xudof+-c5; lue of a resistance not change with tem ex+/upmd5 f;eb-ocm) perature. 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 designed to produce 3.3 kW of wmkhkqe69u ym+4a ptc2hb9,5 heat when connected to a 240-V source. What must be the resistance of the element? 9wpb mck ,6umhqa 9et54hy +k2   $\Omega$

  What is the maximum pnpt0k,c/z13g6 hftr t ower consumption of a 3.0-V portable CD player that draws a maximumzth /c0tgrk3t1pn6 ,f of 320 mA of current?    W

  What is the maximum voltage that cg52hq52tt;:n5 ek5cv1 lwa gyxxqqd 0 an 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 1ig4m+o3,bonvyy t+ rlightbulb connected to i,4tm+v13n +bgoryi yo ts 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 at 11iv :u/w (rf9: a duzyp6xv.vu30 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 j1z p*az rgs62ohs;s0 two settings: 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 lightbut*pd 99kmefa;n,rten6x0 k 4f lb in Europe, 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 120-V bulbs? [Hint: assume roughly th,m 4e6d;kt9pkre0 x9nfa*ftn at 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 h:qs7:f33+byi 1535hr n ofdyqznegc in operation for a tfqcib:e g7ory s 5h n53+d3z3y:h1 fqnotal 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 potxn:7-9gckedd ag*p-rch light on day and n9:x kcp-a-*edng dtg7ight for a year? $\approx$    dollars

  An ordinary flashlight uses two 8yq8 4 vcj,aesD-cell 1.5-V batteries connected in series as in Fig. 18j 4veac8 y8,sq–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 amount of energy stor kd/n2haol.5rk: hf(we ,-pxbed in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 0e.rkv*qz9nm 18–20, can be used without br*9 vq0nemk.z lowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper w uc1a.jvrv 0ob,c6 pa9ire) and of length 2.7 m (9 ft) is connected to an electric hea0.b9aor1,u jcpa vc6 vter which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power alv a- 7.aeryha68c2h et 12,000 V to a factory through wires with total resisa6ayhr a2hee8-vlc7.tance $3.0\Omega$ 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 ixjeq3l ; g6t,,:qm:1u yteyrxs 17.5 A. At what rate must cooling water pass over the coils i gtq6e ljy,,;y:m1xxtu:e 3qrf the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater canzr3gz(-61/1y jtynmi 6mvbmv be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water f-jrn16z 6mz3t v/imv 1b mgyy(rom 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 heaj2wu8nr;tovxh*o5i 5: q -in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is,d3lfhg od92y, xrhn7 180 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 resistance of the gi d6 ;nx-sb,vp znn6ja8d8 m0$120-V_{rms}$ 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 :yd.)u7u-j tdl 3ejje -nwk ,h1500-W device is 5.4 A. What is th.h l)unu-ej3:ktwjd ,7ej -d ye rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected s3.y- 2c 5nb rxirlmt8mv,3gx 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 instd*qaq 2zk bd 35rk(r51p g6r; dnovdg.antaneous power dissipated by a 3.0-hp pump connectezd r gdgdr531 pqd(koqvrnb;a5k62 .*d to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected t2(8 +.nw:bp3 vqi tojvlc dra0o a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a ticfqylgj.n:5 e(r 4dc3ny 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 w56 ;s+7scwdq :jfl0,n dz+.wrpnvmk 9u wju z*ire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift :jsunw,undv5 ;r0k w6 m+7p z9.dj+ *szwqlcf 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 xzjkjs 0e2,rqd7o3 3 2nofb/jw(j.x f 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 

  At a point high in the Earth2qd +o- lag-2y yvx kow1e9bm3’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 electric field acrosu-ytfaf 75iq zu 4w(i(s 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 :(yy8ohe se/q is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the elect sye(y8:/heqoric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potential along the o( 25nuui6 sstaxon 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 pous(iotn6u s2 5wer is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential, :lkv j v2/esfgh df*;z x+w/;z$Na^+$ 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 ampevvc ze xr2-a,og4y+h8re-hour?    C

  What is the average current dra;vj4n svr 6zveq01 v(awn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each ofcgn)t/4myyxvc/ dpt 3)((w z omk zxo;j--ti3 the two headlights uses 40dky3 p)4og3m)c x oc -min(y/txzt /tjzv(-;w W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater ismt v6h)zid ihj-s m-8( 5.4 m long. If it is made of iron, what must its diameter bi-)m(6 md z jth8-hsive?    $ \times10^{ -4}\;m$

  The conductance G of an object iswyv2mqcs0qiidw s4)n7cqe8 1k l n1. p6k+ao* defined as the reciprocal of the resistance R; thakmcpn2 iqv a418 yq7 )ilds0 sk 6.wq+o1cen*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 uj te6 , uj86xigr/ ydyz;ye- d+t)cb5ysing 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 enyct8e yj)eiu/bdg5 66y+zd j;t-x yr,ergy 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 1u1 3y/ohsmuh+)r(hw p .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 tw0;,uohqfflmw o.u c )1o lengths are wrapped together side by side to make a thu w)1om ;fqo. c,l0uhficker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 119orxvge(; 1-+hjdzue7 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 hot as1gqg i6-0( ivjyy p,ic to star(g1vqyc yipj6-, i gi0t 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 givenectxv9n0/ l5b 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 se1 wdbs4i kg8r5cond to the inte8ik 5s rg1wbd4rior. 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 - jawx3jj pdb(9l cax7)ll2;lmaterial. One conductor is twice as long and twice the diameter of the second. What is the rati jx)7 2 wlpl (xjajald9c3;-blo of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of ny9itzok nk-fi1b0 r:/p 4 9vqvolume $62\,m^3$ 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 souuq+4lw,7 /go p)/uahrz.q o lcrce.
(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 batterie2lipjm;ch0xtqq5u ux)j2 .sb n 0,1vus as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 12qj, i;)1chpu jm2 ux x2ln50sqtb.0uv 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 resistan9m+h +q5hyxmmce 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 toumtby-67 f v0tj78zsn carry an 11-mA beb 8 t0fstn- 67u7jmzyvam of protons 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 connect-8qim )(h0qwwu(oomd ing cord is copper wire with - (qo8mi(wdq u0)h wmoa diameter 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(p+1jb4 yf p o;wbkwx/ 95 W when connected to 120 V. The heating element 1pbbwj ;p(w/k+4fxy ois 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 system voltu6e*d ol 1w ;1ox8zjriage 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? Assume the headlight resist6iw;jxe rl1o81*o zud ance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for hous1reds c*9w fs3ehold applications. Lightbulb B is rated at 12 V and 40 W9fc s*rw31se d 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 cm is used to connect a se n, 1)ro, m/8qvjit 5th0klsbkt of appliances at 120 V, which draw 2250 W of power tot )v5b10kjt rslho m,ik8qn/,tal.
(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 di d++v2pqm* 3+df zqak .0rgqroameter of 5.00 cm (Fig. 18–37). What is thezg+ 2.qm +*q+o03krdva rpfqd resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length 81kz /8ghu a.edo 3lr4kg-nundoubles, by what factor doeg1u/e .- 3 lo8ukg4zkdr8annh s 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 operates at 0.20 A and 3.2 V eeplm*hk n9. cao;s)(. If its resistance at 2e.kma)sepnhc;o *l9(0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$