What quantity is measured by a battery rating givenqpth e 5r)-a 96uujc xk.g19hs in ampere-hours $(A\cdot H)$ ?

When an electric cell is conng ui2g- /-bvbeected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electv/-bu bgeg-2irons flow to the negative terminal. Explain.

When a flashlight is operated, what is bec* b4byb:ou8ding used up: battery current, battery voltage, ba4 bb*bu yd:co8ttery energy, battery power, or battery resistance? Explain.

One terminal of a car : v1qglq(izxu ; y+y/obattery is said to be connected to “ground.” Since it is not really connected to the griozq(u +qx:1v ;/gyly ound, what is meant by this expression?

When you turn on a wat a pgh7y.*vy4 ga3h/bcer faucet, the water usually flows immediately. You don’t have to wait for wat3/pbg4h*vyhya a7 cg.er to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same len 4crzsg 5i. n7y9l+oungth have the same resistanly s9o rc4.uzg+7n n5ice? Explain.

If the resistance of a small immersion heater (to heat water fl7 bi;u8khs2mor tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Ebk 2;7h8 luimsxplain.

If a rectangular solid made of carbon has sides of lengths ai; js0jb9 j-3ce:axak eq:i-f, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) jjk 0scjf:-b9a3ie ;a-ix:e qthe 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 ligy5e wl oivuezg koa)m /*h0-54htbulb burns out?

Explain why lightbulbs almost always burn out (w)lybx i4v 5x(xkh9djust as they are turned on and not after they have been on fori(5dl)bk xxwxh9y( 4v some time.

Which draws more current0 6 p+ m7)ydu *wauo+sw/zfm.dkn61 clkshz5e, a 100-W lightbulb or a 75-W bulb? Which has the higher reeu f 5 p.hc6adsw+ z)dk/o* sm7w16zl+yk0nmusistance?

Electric power is transferre:fyrd g2: qto3d over large distances at very high voltages. Explain how the high voltage redy:qf:3 r2dot guces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with8w lr)mmvco51 n n.1ug a 25-ncm gmro 5u.l1)81vw nA fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz),(5a ,fjd;o8hjbohn zea84(xo they flicker noticeabhjx oe8j (ohod4(,fzn aba;8 5ly. Why?

Driven by ac power, the same electrons pass back and forth through your b s8f9h/yie:ce-2xjz g r7y j9)h;lxereading lamp xie /:e zge9-c;8y97)brshj2 fyhxlj over and 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 made of Nichrome wire. 4nuoae7 o)l*xgp- +t9u yf/c jImmediately after the toaster is turned on, is the curr)9/o7yx4utnj ceo *af- gpul+ent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in3xe+ciytfana y.ww0q - 8:s ;u a resistor? Explain.

Different lamps might have batteries connected in either of the two arrangfa5; 2 rw,,rmhc o yp*m47ailmements shown in2 ,,m p;lr5f4mmo ricaawh*y7
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 flowing past an:y1fj- loti8lhov d5f h4lh2* y point in thiv 5 ot*l:yf4dh-1fhll2j8 hoe wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a batteri .xzg0lo4o4u y using a current of 6.7 A for 5.0 h. How much chao404ozig.x l urge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in jw+b3 b)xt(auh9u3wg(d **x t;eagu samperes 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 produ: z2soj7wr0bp 4 r1cvhces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A .5si s9/1ye*bbam2uxwwwa3.uiu 0 y x of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged intox;6*pvf+ ca lkv1aj9k 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) klkw7zx igiy;8k8hz-*e gh-ryer 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 9he./wx .;riyfip9v n 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 transmissiy vysv q2b v*5j7*ubr0on line carrying 2800 A (Fig. 18–34). The*257q0yvvuby b r *sjv line 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 6.50 A at 240 V. z7aer5g *jd l:
(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 through a resistorbtjgpx r(jz1c/9u1ruyjcxqj8l6 + 11 gz:2 lg.
(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 ofja76w a bj31exapdwi 7/y8mt5 tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a h7:dt hjnb 5 (wwkyn-43.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.m hlk vsmt -ve5h*,+2c0 m of aluminum wire 2.0 mm in diamevmv2h+- le 5*skch mt,ter, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistanc/ .ducgdqnc94n 9rmjd5: 3agfe as a tungsten wire of the same leng g dcm3 d:.5dcfr n/9nuq4gja9th? Give numerical details.    mm

  A certain copper wir (c(zco)g pgi d4v4i*ee has a resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wire bupx/bqz(/ra/7 g b51kk - jwo(originally at wu xqb/p r(7zab-1 o/k5bjk/g $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have theh)anle/ vd.8lm:-rzh same resistivity as tungsten dd8)-rh: azv/ ml lnh.eoes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a r,5 y()cgs eb7cc: ekdmesistance 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. 14 copper wirs 9dbkl z;)9txe (used in 15-A circuits). The wire has diameter 1.628 mm and carrd9lk x9s;b) tzies a 12-A current.    V

  A rectangular solid made of carbon has sides of lenh3k l)2b7uyd wgths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in 7k uy)hl3bw2 d
(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 s/xi/bxia. q:same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wa/x:/iq xs ib.ire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected okv 8gj a+-vqnzjn(0- to a precision 10.00-V power supply, and a current of 0.4212 A is pqog v-zaknjnv0(+j -8 recisely 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 5.0 m of coz ))bafhecc( ;9xvr(b+yuabm (k uy45pper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference ofce(c y;5uaam( bb zb4 fyx)( rh9v)k+u 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 thnixd b8nd 10 24v9gegbat the value of a resistance not change with temperature.bgb9ingvxed 24 n08d1 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 hea ee6+v9 p4yw9lwy4 u r6kukl.pt when ckl w6r9evueklwp. 9y+4 y6up4onnected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumpti py3 8euf7z0raon of a 3.0-V portable CD player that draws a maximum of 3eau rfzp8307y20 mA of current?    W

  What is the maximum voltage that can be applied acros0a 8x d.wbxw/qs a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 7lfjmpm9g* ;snca yr9j;5 c0jd13) *xrrrj1 v u5-W lightbulb connected to its proper source voltage of 12 9lj jsxj r*rr;u ad30*m;pm519f vycc )rn1gj0 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 /vpw:ka,u:)s (b,bi obtsx zi)cx 0+ r110 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*io 8 c;jeic0uings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is delivered to homoj 44ri tzl8; b1zq2gmes 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 bulbs12jbz8iqgz ;4orl4 mt ? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it c d 1 fqp52r6pxceabyrc67c*+ is in operation for a total of 15 min? At a cos 6 rp5creafcb cc27*pyq+ 61xdt 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 doesgd-u8zv a(c58smx b/p it cost to leave a 25-W porch light on day and night for b8xgd (as58 muz /-pcva year? $\approx$    dollars

  An ordinary flashlight keob ph3b ) g*bvi ),caln0/1cuses two D-cell 1.5-V batteries connected in series as in Figb*vk0o bgp b))ae,cn3 1lh/ic. 18–4b (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 ef3rghg03wq8 bj ( t)manergy 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 t( ht7jjdp2s,mugz n8 7o 120 V as in Fig. 18–20, can be used without blowing a 15-A fuse?sd7, hpgm82 jzjunt7(    bulbs

  An extension cord made of two wires of diameter 0.129 ciu/pa2ro-*( kf nx3v sm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How o3ruk- fsavn2/p( x *imuch power is dissipated in the cord?    W

  A power station delivers 620 kW okjdhu;sdy 4 )+f power at 12,000 V to a factory through wires with total resi)h4+ k s;ddjyustance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A. At whm+ 0b /3pi j(bs6bjji2xnmgk i*66v enat rate must cooling water pass over the coils if the water tebbm+/06s (n6 pji26im*kg nvj e 3bijxmperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in17 p*1lcob thnrxu )a0 a car to heat a cup of water for coffee or tea. Iflpn)*xcr 0uat hb71o1 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 cur4fe 5az9-sr rdrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose.7 ra+j4u6slmiw)4x7 mhrp gd peak 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 resistance of tmu .t9o 9v0savbv ; vjk;9wg2fhe $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 1500-W device is 5.4 A.evez4.wa6 jth z-u89)kq6c qw What is the rms voltage acroah9t)6vuz.ewc q ew -6zj qk84ss it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a x2 q.7pgeq)v,5 fsy bi$660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp pump conong/2xvxw( 4a))yuix-f nhb,nectewbvf4g-yx )xu ,na h2ixon(/)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 to a6dxk1oz)6m;.; rc x psk es+w-cc.ipr $240-V_{rms}$ 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 rr 7.qzsh .y;ja 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 m2 i4 vjr1lf1ueV is applied to its ends. Ilr ju21ifv14e f 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 atmospheredabnu 3 otu9)3, $He^{2+}$ 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 E*9mo x+l/ cnvxysg)k5 arth’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 accpz d/)gnwrpf u)/f//inf( ) vross 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 por1y o3ft;eg iqr 2z;c;tential 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 thetoz g r;1rif y;2c;eq3 electric 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 ovb*+(nj h;-lc w2m4h c0l)1vmqexyhalong the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capachwj40)-e xynmcvh cohv(; 2*+1mllqb itance; 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 poten.3ub+es ucdl ,x3ab u/tial, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there in 1.00 ampe*(6 1wnf tfnwjre-hour?    C

  What is the average currrl kyi3oo)r6w nd b*2448krs yent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leavei;nl5 j7h06d mp.ks gus a car with the lights on. If each of the two headlights uses 40 W and each of the two taillihn du smg;56i .0jlpk7ghts 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 g;*jc2 f/x+kxi:se:v6pmx.a zn p1ug is 5.4 m long. If it is made of iron, what must ivs x m1kp./ pize;g*a + x:fgjcxu26n:ts diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recip2b*oy w4d bc;mrocal of the resistance R; thaw ;c2*mobbdy 4t 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 insdr f6km),8ld ltead 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 tkl ) rl,mdf8d6he 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 1.8-kW heat 6 0lhys8urh 3xbuqh)x2x k 38x-f8dqaer $3.0 h/day$ (“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 a zu::zh5a+ w9knx5eqa +c pdih.x/2e83l efdand the two lengths are wrapped together side by side to make a thicker 5x: qhkhilef32.8 xzaa+w+ z9da d/n5epuce: wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is dbm c ku)esbn490z al4*h1mmb+esigned 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 t gyd1m;ja(d: not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum a1; (tygdjdm: current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equat0f.dhu7bg f n : q)oj ;b.vt62+rgination $I\,=\,1.80sin210t$, 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 dem+7d bsrdn 01klivers 950 W of energy per second to the interior. Fibd1 7n rmds0k+nd
(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 m i6f lc3q+7zi-sh6gk0.q eitnaterial. One conductor e k.chnfqg l63s+ zt76i0iiq-is 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 a ro:u lf0::0p2d dtcsa bvom 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 i(.7 y7mwk x;zlzxn9ga 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 aaiul xwerxta v ,(74u/3/7xums its source of energy. Its mass is 1560 kg and it is powered brul/3 ex 7a (a7vu /iu4txwx,my 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 lightbulb has a resistanx*d+bu;8 qhvmv7 b9dace 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 cw j2 rp9gn(f64ho7 kzrarry an 11-mA beam of proton4h wj2p7kz(r ofgn69rs 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 1l.ovpk zrf3 a5ar:1l.2 A at 220-V ac. The connecting cord is copper wire with a diameter ozlof lvk:a..p31 rr a5f 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 when connected to 120 V. The heating elehi8 9n* m2hq+g /hdwicment is a coil of Ni m8i2 *h/+ dwqh9ncgihchrome 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 abow+omae9t26 gqs 6 k4subzw/t .ut 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 13t/wmaseo 2g9+sb6 u .4 tqwz6k.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for hou,zk4wysyw,-1 ra0/ rp1iguoz sehold applications. Lightbulb B is rated at 12 V-g i o 0yr4/zpzuwk,a,s ry1w1 and 40 W 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 coan18c*yr((bq 3o wqng v;w0kcnnect a set of appliances at 120 V, which draw 2250 W of powkaq0g1(y bn ccwrq*8ov n ;3(wer 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 insiv;9j ak5nn:,y1ytig u de diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 1jngyk,yvaut;15 ni :98–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length dnapj z4m 9)2v2 gfo1ycoubles, by what factor doecyv42noa9 j m2g1 pz)fs 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 Ajijufp3/t i(cr ,n7l 5 and 3.2 V. If its res ctf5jni/37(ui,lp rjistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$