What quantity is measured by a battery rating givefw5zw.p 7vkwq) 7(obrkx vy/j02mcm: n in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away fc )k 3q jtd4hb w,.m1 .f5qjjwj1j/ 8nxdp-elcrom the negative terminal in the circuit. But within the cell, electrons flow to the negqlj.cj .,c8ep1mb/ )j5 1d k-q jfw4nh3t dxwjative terminal. Explain.

When a flashlight is operated, what is bein 5fp-a/f 5 pephqkc57ag used up: battery current, battery voltage, battery energy, battery powepa e7p/c- fqf55a5p khr, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “grka-qj;lg c5 n.ound.” Since it is not really connected to the ground, wk;j.q a5-c nglhat is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Yos0q 3w7v bxb/il url:2u don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is th:/xr02 vbqb3 slli7uw e same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the5ls:5cd zmfn81 hfyb6 same length have the same resistance? Exdhns6y:fz8c1m 5lb 5 fplain.

If the resistance of a small immers r5kwg2bit2 6uion heater (to heat water for tea or soup, Fig. 18–32) was inc u56wgit 2kr2breased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, an . x49e 4mubpn*3dgtdhd 3a, how would you con.d*g4xpb3e u4hd m n9tnect 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 q;wphy,q qu/;)vz*aqu*7ccanh,6b1 sk 8td olightbulb burns out?

Explain why lightbulbs almost always mfs :a 1ardfg32xkkx99 qkl13burn out just as they are turned on and not aff gk13r 1d2q:a s99mak x3xflkter they have been on for some time.

Which draws more current, a 100-W lighta ww 8m)v **2mfec2h)yw cccw1bulb or a 75-W bulb? Which has the higher rescc2hmw*)w emw*a)1fcc8w y2 v istance?

Electric power is transferred over large distances at ver a9ffa:(3 xs x. qy 3-ynm)b9i/waqgka2d5qzuy high voltages. Explain how the high voltage reduces power losses x)ffqz(9 m39dw/ ay5sauyqbikn q32:.ax g-a in the transmission lines.

A 15-A fuse blows repeated:83k ginkze .vly. Why is it dangerous to replace this fuse with a 25-A fun g:ke8kvi z3.se?

When electric lights are operated on low-frequency ac (say, 5 Hz), the 2j2e1w/ +m k+dqfv s+ fvqsg8jhi,8qly flicker notiqs/+v2+d 8q1 g+8qh eijsmkj,2wlffv ceably. Why?

Driven by ac power, the same electrons pass back and forth through your reading bmq( gly3;4 /9osu qddlamp over and over again. Explain why the light stays lit instead of going out after the firdu;mg( o94/3qbq dyl sst pass of electrons.

The heating element in a toasfqr gzqi,6a7d tmo ah k;60**lter is made of Nichrome wire. Immediately after the toaster is turned on, izh*lfta76am0, oqg;r* q d6k is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a dm 2 l*6m./pmmhalm,g lhn*9cresistor? Explain.

Different lamps might have batteries connected in either of the two arrangeme362yywb7qzec )rpe u mghkjo,5.r( ,lnts shown in pjum25gb(). 6,eo,3z7kyylrrweh qc
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows 4a af5qe 3y ehyl m,m0kgw-d,0in a wire. How many electrons are flowing past any point in the wire pq 53f0yae lad ,wh-4kg,0mmyeer second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current o358a yyr 4hy eo*qpj*df 6.7 A for 5.0 h. How much charge passes thyrohp* 3y4 8*ajye d5qrough the battery?    $ \times10^{ 5}\;C$

  What is the current in awbsjw +v .;t6y.i v5s:ezlqcr; 3eb4fmperes 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 o0fg2lpvc- oa.f a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through 7 qyj:it6*zvxztyjzli n8.i q n-1z-.a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged intod sf4.+x-cujc ,9va op 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 uqxv g 9x5dv8w 40ppf9dryer 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 to a bulb whose t m+baq- ,72ebo a lw*/ot lk h;i;og.8d7iwyoresistance 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 carry9 es)mku x)mw8mbco 3,ing 2800 A (Fig. 18–34). The lin)8ums)3c ,wmb9eomk xe 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 6.6(kqkzptq,i)mj-mmf9; 3v sco aq 9r .50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A throug) z73thb*0qx8gpc.(i *ts nm3whf**v y lds puh 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 wi;u(p)ifz 9apj0vtj3 a wto +7pre whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3bef+j;9f7p yh tr/wq(1 +m azcft1n ;u.5-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 wireg,rt 87b5 ryio we-*nt 2.0 mm in diameter, to 2bgo758t-t*riwyn r ,e0.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tunu/5 b7kicl cr4:k s31k0rcvve gsten wire of trvci7s u5ekvl b0k :r/c41ck3 he same length? Give numerical details.    mm

  A certain copper wire has a 1u t(r2x qxnojh. /qokt7,) * kkm96go6mqngsresistance 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 haveq 1t/6u3+fc k:f ow/nor tilzu) dt2z+ to raise the temperature of a copper wire (originally at ud)c26l+:nz1tktftrq/ f /+o3zwou i $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperatl0dxjcjdi: ae2* /;d hure copper will have the same resistivity as tungsten does ch/;:el j jx2dd*i0 daat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance ofseg4;h i6nvqe6vo 7d0 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. 14 pvi1 k x;.*)cs eavhj8copper wire (used in 15-A circuits). The wire has diameter 1.628 mm anxc.e)v 1jvishakp 8;*d carries a 12-A current.    V

  A rectangular solid made ofc62z q7:m bejb 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). Determin276mc:bj b eqze 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 has tb rkivq4 vsv90(z02zvwice the length of the 4 k2sv9 v0b0zqirzvv(other, 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 cq k+5 xct5rvgm ,f2jh9onnected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measured at fvcq +rx5hj5 gt9,km2 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 cope xx7zj5s0 pfp;0 g1h+*iqqepper followed by 5.0 m of aluminum; xh 0fqeqep +j1sxg z*5pp07i, both of diameter 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 value of a resista ,9(zg sj8ctdh1(f lwsnce not change with temperature. For examplfh,tds8g j((sl9 c1zwe, 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 toyb/*fldu m28sw ps j;; produce 3.3 kW of heat when connected to a 240-V source. What must be tj d*2;;ws8/pyumsb f lhe resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD pl)t.k8 7ihafa6 iyw*pa ayer that draws a maxi)hka8*ap t.wy faii67 mum of 320 mA of current?    W

  What is the maximum voltage that can be applied across ay a r8s i7;966pustskm $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistanceuoe a3 tq791p9was a8u of, and current through, a 75-W lightbulb connected to its proper source u9tq9o wp 3u 7a81asaevoltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank he, w hzz)k(sq8iater is rated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two sett8-igtmt2l(d v ings: 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+fmot3gxtix 0j/7s ,m2.9bc m /gzwoqb in Europe, where electricity is delivered to homes at 240 V. If you use the light9o mt fcsq3g+o iwzx t./0jg/27xm,mbbulb 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 550-9lyj2:d obq1iyw31fin ;w q,)zfn7ecW toaster use in the morning if it is in operayfiz 723e bcln) of9jniw,1 d;1qyw :qtion for 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 xz5bgsu 7l i4i7mu,;gporch light on day and night for imu47ixu7 5; sbg,zgl a year? $\approx$    dollars

  An ordinary flashlight uses two D- e4kffx5mrh-61q +w vicell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). Tfqk1 mv-x+f rw4e56hihe 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 energx4v 7v7xzam;f9 j2aj(3xtvg8o 6m mwdy 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 in Fig. 18–20, can be used wiy agukh+7qwa ku +p(qe00 /gz2thout blowing aaa q zwgqu(+ pk/he70y+kg20u 15-A fuse?    bulbs

  An extension cord made of two wires of diamete h4w tlwg085xx o*p0hdr 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 1x05pht8d0gwo4 xhw l*20-V line. How much power is dissipated in the cord?    W

  A power station delivee aj t*86i -plsqix(p0rs 620 kW of power at 12,000 V to a factory through wires with total resispjx86e* pli( iq -a0tstance $3.0\Omega$ 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 conneb dkjx p+b*,)z )rhlf0cted to a 240-V line is 17.5 A. At what rate must cooling water pass over thezrkl)fhbx *d,+0pjb ) coils if the water 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 heat (1*rwz -k;)t.q /wu veib kh ivtb0vf9a cup of water for coffee or tea. If the heater can heat 120 mL of water0vb -i vfi*kktz w.h breqw/uvt;1)(9 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 cuav(*s4u fz 5 hrqvf6chz*uzm(a; h9g3rrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value iv lzz*+kl9)b:wgwu z -s 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 lfbqw ;-kw. ;e jx(1nuthe $120-V_{rms}$ 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 alterna7rj c k**9gkb*j ig5oiting current in a 1500-W device is 5.4 A. What is the rms voltagg9jrijb*5kk oc*7gi * e across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected tox,sp9 5u+ -o32ccnnc qas6sie 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 instantaneousf5 :l:wcdl.8vbm-a bj power dissipated by a 3.0-hp pump connected. : fwlbd :85v-lacbmj to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected 4.z o25m0s wji 6kn5+ikkk obwto 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 tiny currenkf/g-no t be*v,.9mi xt 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 52 dj3h2iiwoy) ( nxtkmV is akji2o dw hn2t53 y(x)ipplied to its ends. If the drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmo:dp2vq j jbr,2sphere, $He^{2+}$ 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 E6z tqz .xpw4a7arth’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,/ajy1x6 jsy j 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 electric pulse. Tt oc/.5br 14qd1h c wgv:onk w)2.q 4d-qupvlehe 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. What is the speed of the electric pulse along the /)1v- bvo5ocqkt2wq 4d .1:che4uqnd wgp rl.axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmi73;+5 l3iq6 peacn+qr km vbmkt one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by chargiqki3c375 km++ra ;m n6lpqvbe ng 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 potential,1v-y ui v0pwebc9u*,p $Na^+$ 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 ampeqk(av8we b+y50:cl h1 yoass wnt;g0 4re-hour?    C

  What is the average curreni lc ou02l/*sct drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the dbx3lc9vq ebn:mi0ya; u, - :clights 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 12-V battery last if it bel9 ud:c 0ax,-:nqcv3ib ym;is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-Vt/k13q1zpyymzrk - ,um2fun., 1500-W heater is 5.4 m long. If it is made of iron, what must its diamet 11k- tuyf /2r y,3nk.mzumzqper be?    $ \times10^{ -4}\;m$

  The conductance G of an object is define3if9;wmpo17cc b7y u7p jx2gbd as the reciprocal of the resistance R; tcw37cbxo ;pjy7m9 72f1 ugipbhat 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 ox/7w6hd67rp9c h s22 albrybof 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 h62ap6 owb 9l7c rhrbsx2d/y7. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househol h2c3 x2a 0cwg 7u+b5nhpouj6td uses 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 two lengths are wran1qm74e smx0ncz,j1 i pped together side by side te7scm nmx z0qn1 ij4,1o make a thicker 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 11gs2fnfj60243 9rzikl * w mlnw7 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 sor1v2d;iev,--e 2qgqxnm/xas *wrkc 8 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 meter of length qs--a2vmxv w;ic2rnk8 qe* ed,/x1rg?    $ \times10^{ -3}\;m$

  Suppose a current is given by t9dr v 2kz-a,+x/u .wfaapgas 2he 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 devx/(ml36sekq .x8whv livers 950 W of energy per second to the i6mv ehvkwql x(8x .3/snterior. 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 v6i;yn5 t c,yomaterial. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in t6ci v ;ynot,5yhe first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used pi q(hcuq( /6:uois.8vkdr )m to 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 240-V .; )sp50 tu2n9clw:qdngwyipe:z7ylsource.
(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 source of e .c*tywr(m8h9ygr. figp+uegz/. t: gnergy. Its mass is 1560 kg and it is powered by 24 batteries, each trtrf(ge i:8 uh .y.9 *cyggwm.z/+ pg12 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 lightcjpgq c9/.y z7bulb 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 (Illinoy ;5qih3 .kcx2fi x,rois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed oxx3,qh;r cki2. fy5oif 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 wire w5xng7v oi:2 nhgo2 ;koicro/)ith a diameter of 1.ki o5h2ngrconv gxo/ ):i72;o 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 when connected to 120 V. The heat3g2el 3k a;ww9wa bt9eing element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. Whlw; ba29e3wagk39wt eat is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when d rn :,vbq4cr6kx:pl7 the car is off to abo:dbqr7x :rvln4c k,p6ut 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 resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb B i0-reirfi48kc4 .e od rs rated at 12 V and 40 W for automotive applicationseecr4ro0 f.i48-kr d i.
(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-cjr. l6jgg+w appliances at 120 V, which draw 2250 W of power totajgr+j6c. gw-l l.
(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 diameterlm5xxpdg q:/* of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of thisml xdp/x :5*qg pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doubl .mauqcts 3bp*2hf* 8qes, by what fmb*p*sqfhuqc3 a. t82 actor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used d iq3x.-a(uwckbt* 2* / kkyxein a flashlight bulb operates at 0.20 A and 3.2 V. If its r *a*xkk3bcu t2-qky /x(e. iwdesistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$