What quantity is measured by a baln kjzptf4m/ynet d-6 w8 v.8*ttery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from the nik1()q a h-h*ihtk ( df)5ipevegative terminal in the circuit. But within the cell, electrons flow to the negativ fi1) ihhi)pk5v(kqt-h* ae(de terminal. Explain.

When a flashlight is operated, what is being used s/5w.1m. zhdqde .xpyup: battery current, battery voltage, battery energy, battery power, or battery resistance? Explaisdmx. . e.w/hdq 1ypz5n.

One terminal of a car battery is said to be connected to “ground.” Sinci-28r oux(a sbb7eme )e it is notiobs ra-e( )mu72b8ex really connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You dous9-q*u rfwq /n uw-kr2 6rj5xn’t have to wait for water to flow from the faucet vw*/r-xk 9rn-5 qqsrwufu 2uj 6alve 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 len)9w/w 3flshdh 7 asbv a.e/7ulgth have the same resistance? d/a ww73saue)bvs9f l7. l/ hhExplain.

If the resistance of a small ime e uj)7udc(*vtl e4y0mersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slj du()cy 0t4e*eel7vuow down the heating process? Explain.

If a rectangular solid made of carbon has sides ofy k hbk6q,.8;d n)zyj 3op:xnn lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistancp yhznk :;.qydb) ,6n8jnxk3 oe, (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 (;pv14hq-0 ag b5zxaji exd9c :z0a tslightbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned a .fh(-4 lqg uf,16wllt afga.on and not aftgw (aaqf -fg.thul, a6.1 fl4ler they have been on for some time.

Which draws more current, a 100-W lightbulb o;gll2 p kewg3(r a 75-W bulb? Which has the higher resista glw ke2g3;l(pnce?

Electric power is transferred over large distances at very hig s6m(7hbb81d nc0vm7iuf kpp9h voltages. Explain how the high voltage reduces power losses in the transmissic8 if7(umb9 h06b1p vkpn7dsm on lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with axv+- .j9gz; rn r0huts 25s.0 v+ j;xnuzg rrt9h--A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), td89a;e akgpq ld )z:;yb( ,lvjhey flicker ngp;q d9 k;a,jvl abd:ey(8)lzoticeably. Why?

Driven by ac power, the same electrons pass back an-wyqo;g6cj ultc+l-0 d forth through your reading lamp over and over again. Explain why the light stays lit instead o quyojct-6l+0 gc -lw;f going out after the first pass of electrons.

The heating element in a toaster atfpl)t:cgy0clw +s ,4xm10 bis made of Nichrome wire. Immediately after the toaststt 00)bxcp1:+ycf mall gw4 ,er is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? h v.4upb8e(; ;vx 6j gqwjvt8uExplain.

Different lamps might have batteries connected in either of the two arrangementv:( so-j-q) hqz87-athhx vtc s shown in o--(:- taqsvvzj 7xthq8 h) hc
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A fl(9sn dk q8v203txrj8 ww( kielows in a wire. How many electrons are flowing past any point in the wire per 2vdinr9j(x k(8sk 3l0t ew8qwsecond?    $ \times10^{18 }\;electrons/s$

  A service station chargxr/;+,/pno i l:ul vw68p r+hsz)o7w q,hn kgzes a battery using a current of 6.7 A for 5.0 h. How much charge passe oox+l zl/ip7 ,r; vs6k,q wnu:wn/rhg8) +zhps through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperhbuljzvip gk q1 /(r l53xc0i6;*7zwaes 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 V produce0iym 3o ljxbhsm6f3*2 s a current of 4.2 A?    $\Omega$

  What voltage will produce12 ctprx8dd, e 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A whj ;3-cboxfbnbeow-5a; r 6ee;en 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 wit/cc(b g (njth(h 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 resistance is by m:ftsr/1ocw4yymw2/vp/;1n qw 0b $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc 0h3rnga+)sj -du r3nuelectric transmission line carrying 2800 A (Fig. 18–34). The line hasrudnua s-g+n0)j 3r 3h $2.5\times10^{ -5}\;\Omega$ 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 dog *ul5a pjvn* s19kj-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 0.6ook n pjk8w8:4os0 r.y.y :emt0 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 whosem*q shjb++gz3 5z yf8w fwr/,c resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5--+pl hcn7fmuvk3,m m*m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in diame7r9zez.- e 1p0ytpkylter, to 20.0 m of copp r0lyze pytk7ez -9.1per wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as ) ynmqmp;5w n,a tungsten wire of the same m n5;,nmp qyw)length? Give numerical details.    mm

  A certain copper wire has a resistance8 i ;x33olqwq1xkmv s9 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 co yrc* p*f4yb*fzgfe7 .pper wire (originally atcgy.z 4fb*r *e p*f7yf $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper w3eokbk,xxupo8v26 cxn-dt0-awmg ,c 2j6 -q gill have the same resistivity as tungsten does at vp6t 0x8xme ,6-3n2dxua b2kkco gco-,qw g-j$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a r -dnq2 2vgdw 5loj a2s/ qsj.2j;m3weqesistance 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 ,5h; gk /0nqobr2rhpqq 9 (xtd26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and cthg0qd nqx9q,5/rp ( bk2h ro;arries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengthsb+ifeaz9f(g7, zx7zop f t(3e 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resffze,7f+ p7x(z9t(gzi e a3obistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one has twice the ls+hu9 xlqw a1dqt gi ;k4h0m((ength of the other,q1+l0xwha 94gqu(dthi;k s m( what is the ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is js-c ;uq 7k.o-oi5lpoconnected to a precision 10.00-V power supply, and a current of 0.4212 A ocs--7uio5lpk jq; .ois 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 5.09df7 e/a7veg ; q)yhqc m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed acq79da)v7e f;eycqhg/ ross 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 thes h.f.t)ts3sxpi7a n , value of a resistance not change with tempnf)attis px h7.3,ss.erature. 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 desagrn),l5z hf1 ,,bedo igned to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the db,gn r,a5l1ezfh,) oelement?    $\Omega$

  What is the maximum power consumption of a 3.0-V portabm0 ijmwx1da) n(2.wql (. dkrdle CD player that draws a maximum of 32w(a.kdd 1rxm d.jmiw )qnl20(0 mA of current?    W

  What is the maximum voltage that canskr3,9p /4; t xkavbbo 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 lightbulb connec6 6ivf lz+0y g/8vtnbited to its proper source vlfv6z v/it06iy8 gn+boltage 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 rated3nydt: 7spc*qjso kf);l5v0 r 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 sett/5 :hqvvnl, yfwj,c.7* s4 v3v frkxmjings: 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 lightbul,4zq 5 4f3qgnmv-a wyzb in Europe, where electricity is delivered to homes at 240 V.f,ay4v4 w n5 zmq3q-gz 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 that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use itzp*z+k;o /oq 8 zesu3n the morning if it is in operation for a total oftoeo;p /*zzq8k+3 suz 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 po/4u.b c0r,84p9ks b xd ptplekrch light on day and night for a ye0cd8 b pe.rs4p4bptl9 kxu/ k,ar? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connectedd3vl a25(afb g2*3wjtqh. sum in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA whena2h *2t.(5 wa 3uqgbd3mjfvsl 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 am7zt(r/ ftn ;ym:xlgpnj6 g9v5ount 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 lightbulbs, connected to 120 V as iy-z3 i-jeq-n,qssvwhb78 a m*n Fig. 18–20, can be used withouq i- 8ssymzwan-eh,v 7j*- q3bt blowing a 15-A fuse?    bulbs

  An extension cord made of two wi km2ms.f pawlewf/(8-c pa;g 9res of diameter 0.129 cm (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 liea/;pmg fam sp 9wk(l8 2cw.f-ne. How much power is dissipated in the cord?    W

  A power station deli, csjsp,a/dmdq 99n j3vers 620 kW of power at 12,000 V to a factory through wires with total resista9j cddass9m3 ,pj,/qnnce $3.0\Omega$ 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 1xo/0)bo+yc e ih5xf7irj 3 jw37.5 A. At what rate must cooling water pass over the coils if the water temperature is to ri r7yio3 wj/e35hxfjx+b0oi )cse by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be usd.ojxd ss2 31ra7qq3aed in a car to heat a cup of water for coffee or tea.qd2 3rd. 3x7sjq1aaos If 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(iajig 1 /klp;xg-nd4 in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peakna+2z9xs; rdlt(,g23b nz vcf value is 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 resistasv l6 9w-z+jxince 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 dev: niqvvicx.nf :*r8z5j6m uf5ice is 5.4 A. What is the rms voltage across it? rjmfxu.*in :8 vi6q5 cf5:vnz    V (Round to the nearest integer)

  An 1800-W arc welder is connectom(ba.g67uigx-1 j q aed 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 - yukr t0p.8bqby a 3.0-hp pump connected to a 0tuk8q by-p. r$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to)a e k6fcq6yco0lajc.b6c68m 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 coa 9bme(7dy:q1i8b td -byu l-zpper 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 when 22.0 mV is s-fg -cxje,1m applied to its ends. If the drift spee-m xfsg1,je -cd 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 Earthgtg,5(0/b.hl ub as gq’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 

  At a point high in the Earth’s 6zoeqx:. *wo :bi4ita 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 across an axon membjlhv0kns cc/nh 1jr 1tsz-).0rane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an08m6z5zgmz l:inzknro) fuh 3rebv1g2 :/* k n electric pulse. The action potential is detected at a point 3.40 cm down the a8ku k2n:imz e5 1hzg0/robv:6z3lz)m ngr *fnxon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit z9se z:,pnjl ozc )ohat;9u1 ,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 S,pcnz,ej)z;lotz 9 :s1o uh9a ection 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 potentio:yiqlg r ) mp)8:z4soal, $Na^+$ 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 arvy g j*c a .4cc:+8artazu3oa3e there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120b x+4gb7dek x0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the db aihcgr9-y3 kwtxl196 mj29lights on. If each of the two headlights uses 40 W and each of the 9 629dr3i 1lh-tyb9mawjxkgc 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 is 5.4 m longd1n1nbs6(hdds0yd*z ug vb-,. If it is made of iron, what1dhzbgsund y db(d10-nv,*6 s must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined ase3oo0 .3uegaxgq*m1fe( u g-k the reciprocal of the resistance R; that i- um31 kxee q. ueoa0ggo3f*(gs, $G\,=\,1/R$. 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 instewjhy (l;)1d 5ncfp/joad 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 to heat per hour per meter. Assume the cost of electricic;yojhn5(j)p1w f dl/ ty is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household us +qabtfc: 8le0/dq* lzes a 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the t qz4hg407kb zyiixi70e yc82 rwo lengths are wrapped together side by side to make a thicker wire. How 04k7 4zciyqg87 0zy ir 2bhixedoes the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. ikuo/ 2u.tlfdxu()gps 6, v8m
(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 e0yf,q q5 cbnzpax.*4cnough so it does not become so hot as to start 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 metfnabp cq.xz*5y4,0 cqer of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equation lnxhxs*a dp.5hs)4 /s ewli-g*hw) 8k$I\,=\,1.80sin210t$, 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 per7/sp00bdy b-xdpb(do second to the interior. p bsxop/y(db0d 7-d0b 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 c6.,txtbp r (wpt*a. xqonductors 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 fir.,(* brwt atqtxp .x6pst relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heak wjju6d:ei-l/ uw:/ mt 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 9xrymjqh;*cz*: qe cdw6 i:1 va 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 vehicla;t 04 l bgj(w7;on2i) z-b cuqbspg8ee makes use of storage batteries as its source of energy. Its mass is 1560 kg and itc 70bgw;ibp2lou gnjq;-e)(tz s4a8b 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 lightbulbb0 h 8ggx2)m54c*srbf( wefe w 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-mA be (-ml4j3 q6: bfeaplzqam of protons traveling at very nearly thea 3-6lzqje( b :qmlp4f 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 t/c qnxoor5w:7x4t(a majbe4.y a30b ac. The connecting cord is copper wire with a di 5o(x0rtjn4xe43t7awacoqmb/:ay . bameter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W wmv 67u ;npw,wonvvy- tn0a 63r6grwn2hen connected to 120 V. The heating element is nm 0wn6wgnyu,6;vwtran 7- v3p6v2roa 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 voltage varies from about 12 V when the carg8o;:g57db-avxr jp w 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 res7-rv j :;5 8axgobdpgwistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W bxvdf2agy14 i/*-gbj for household applications. Lightbulb B is rated at 12 V and 40 W fvgixy/ j24bb1 -* dagfor 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 usz/ pooasi5or-71i 6um ed to connect a set of appliances at 120 V, which draw 2250 W of power ti o6u1- sir7p ao5omz/otal.
(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 7a n+1 l eicn:ey99upkwqcn6o4 zkc5 8inside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What isczin c7+a l8eoe6 p9:1k4 k95uyqwnnc the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lefgai3:z3v x*w29dl r nngth doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the sa3izwgx an:vf 9l2r*3dme voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 V. Ifnoko(uz7pi* 6si+s:e . znzop, a4zj9 its resistance at 2aj. *o (p96,z upkoz+i7on4ns: esizz0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$