What quantity is measured by a battery rating givenbe0k/yzbk8jbr , u6u z:zjn-6 in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a cz4(z nprnll5; ircuit, electrons flow away from the negative terminal in the circuit.zl 5n r(p;4lnz But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: batt7c-me4q t+df0y)22y iza bfypery current, battery voltage, battery energy, battery power, or battery resisyb 2 a y fz)eqcd0t74f2-mpi+ytance? Explain.

One terminal of a car battdmoa/z a 25m)sery is said to be connected to “ground.” Since it is not really co)dm5/mzo2a asnnected to the ground, what is meant by this expression?

When you turn on a water 5-t9m 3gvp nbffaucet, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a batteryn5ftg93 b-vp m?

Can a copper wire and an aluminum wire of thmdhkqb.)7 rp 7e same length have the same resistance? Explain7 dkb)m pq7rh..

If the resistance of af,t wmo38cyl:0zv-a z small immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would i 0mow8 ct-3lvz:zya, ft speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides ofyef;4 yx0oec zh+z3 v.f7f 8gb lengths a, 2a, and 3a, how wou. eecbz; fgf3x+0o hy z4f7v8yld you connect 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 lirzyp8z6xnwafcl)/ 4zw/j;2 z ghtbulb burns out?

Explain why lightbulbs almost always burn out just as they;uepepldw5:u;m 9:m z are turned on and not after t ul:;5pm;wp udz9eem:hey have been on for some time.

Which draws more current, a 100-W lightbulbb,gqwotqak8g/4l i8 + or a 75-W bulb? Which has the higher resistagl+,4 t o8qaig k8/wbqnce?

Electric power is transferred over large distances atdh1yp1r9g0-nfps p( 6,fm xcw very high voltages. Explain how the high voltage reduces power losses in the transmisxfg rns1d1 6f,cp0-p9hmwp (y sion lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace2+j)3txhd4/hbn5 zey qj gp7/hnsq/q this fuse with a 25/bh / qxjp4tn hygjqzeqs73n +d 2)/5h-A fuse?

When electric lights are opbee7l:mq i-o-vs(d:c erated on low-frequency ac (say, 5 Hz), they flicker notic-mo -qslveced:i(7b :eably. Why?

Driven by ac power, the same electrons pass back and forth thclfgr uk. )k)+rough your reading lamp over and over again. Explain why the light stakuk.) )+frl gcys lit instead of going out after the first pass of electrons.

The heating element in a toaste*kb(4c qi+(-twe kfi5)re :vpzqw th*, odgo(r is made of Nichrome wire. Immediately after the toaster is zp* idig5 kwtweqf*bkoev+(r coh)t-4, :q(( turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explaigeo q/9i86g8*a dp qfgn.

Different lamps might have batteries connected in either ox4l:,pg0u lsevwv+ y42 xq5qwf the two arrangements sqlwl5,g+yp2: xqx v u4w4se0 vhown 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 flowing;j mz40gdpyy 8 past any point in the wire j4dym; g8 pzy0per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. How muw0/uaa2wz* huqo ,* zfch charge passes through q,0 ah au/* uwzzfw*2othe battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ifpm3/75ychh2 kwcpax 4mdm 0o/ $1200\,Na^+$ 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 produces a c,z-lg xwaa6l7akr c 99. a:iyourrent of 4.2 A?    $\Omega$

  What voltage will produce g4httvsj,+mle +m1zhi :4 r7uhl6)gf 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plula + x/wmy lc:xi0;-8w 3cedjzs :*oiy/hnb 7jgged 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 /jnqak;sg7a m ecb8 0*dryer 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 resi qhwc.3/bgqnqfo16k 7qs 8 z4ustance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 A (Fig. 18–3c8olfpt 1za r(z )*ew34). The line e)craz8 tz1(*o pwfl3 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 6.50mc-nj: ibaeb4i q4( )g 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 currena dg)ib 82 zksyj(pu, 6jbl+b-t of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungsten/u lund.;4yhd wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m leng*xtzn7 8yd,8 l p.md/qmy4qxrth of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of alu29*mf (27qqmftds (p)4mbwcalks - alminum wire 2.0 mm in diameter, to 20.0 m om*2ap4k2qml) q(wdsc b( lfsf -a79t mf copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance ao(rnsq 6-g/h8kq*ve6x n+pg yj, eh:ws a tungsten wire of the same lenx6- */njwqg6he:rneyq k h( pso+g8,vgth? Give numerical details.    mm

  A certain copper wire has a resipc xe)nqzx kc9ettf5s6+/0u2 stance 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 temp z))k:hw5y;g ggvgq7tag(s ken; r5d8r0 co g3erature of a copper wire (originally at5w:r geyrc3gqn)7(td 5 gkgo z;g0v8k)agh ; s $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungsr.vv r u9ea5s7ver/dlx2. tun t5p 7c*ten doesepsrv t/c5v .2ralretduu.x *v9n75 7 at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistanue:mpj o )n0 f7vo3ni4ce 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 cop;x pt9sd:c -w6bwtqb* per wire (used in 15-A :dt*xb9qbc; 6ts-wp wcircuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cjyz ,6rrpeg82 m, 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 p2j6egp,yz8r r asses 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 e p( apff/. cj/m9suh4; -y3iuskts/kone has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of ty9; s4tjuus-(f h kf c/ /kemap/.isp3he shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power sae:bi56z b,ov6yk9m u)nffa3 ekl -w6upply, and a current of 0.4212 A is precisely measu kab:lnevby6om kw3ezu6,f6fi 5)9-ared 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 follo ff,o mauc 8. j119iknfw,vg*nwed by 5.0 m of aluminum, both of diameter 1.0 n 1kgcivf,19,*f8 m ufaonjw.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 impo.v f4c2ss qb ig*kd+vk z)ek9q/fwi4 zu.+b o5rtant that the value of a resistance not change with temperature. Fu9qdg/4k.q.i5is+ 2k*+ b4 z cwvkbfsv)e zofor 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 3.7/- h 0if .xq3bewqned9,we:)eu qull3 kW of heat when connected to weqf q-x d7,ube 9wq /eue0)3i ll:n.ha 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player t, .1 xwwx)u m4ubky2qvhat draws a maxi,km vu2 wb )u4qxwx1y.mum of 320 mA of current?    W

  What is the maximum voltage that can be ap)i6 yz/0swo odplied 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 lightbu 385obifsslu7svy; - plb connected to its prop- l5sfs7;uso38pvbyier 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 110 W. Calcuc)b5 z*ozno-slate
(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 settings: 850 W and 9.fp7tq dgo6u*lsy)e1250 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 homes w:8 v2x ,rdfpuat 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it ,wpv ux2:fd8 rbe 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 201otezew,/ 0 xn ,ytomhe j,r550-W toaster use in the morning if it is in operation for a total of 15 min?yoo,00t/re mzh1e,xjtnwe2, 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-yyi39q 8 g d5y*dtrle)W porch light on day and night for a yeard8lygq3 yd yi)*9 er5t? $\approx$    dollars

  An ordinary flashlight uses two D-ce14iah3s3mgcxcj7y 7cll 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36 1xcs4c yi7 jha73cg3m). 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 amountkpnrm.9,1erh4) mwq9-0hajxc j2uu h2+n tw m 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 idqsv:pydc+ -zs-w5 4i zm )k/cn Fig. 18–20, can be used without bci)cq w 4+d-p/v dz s:kyzms-5lowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129gv5glb9,uitt4l g p-* cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to -vtg*p ,g il4ub9lgt5an electric heater 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 at 12,000 V m)d+bg 5*rt *vyopd6z to a factory through wires wro6m ybd+*z5 )*ptdvgith total resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A. At what rl yb cs ,:* ;.zhbysu4zdpk+f-ate must cooling water pass over the coils if the wateryy *bsd fchusb,lk. :z;z4p+- temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in 8;8a zuxo7 fua5tzt/m a car to heat a cup of water for coffee f/ mut uzo ;88a5azt7xor tea. 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 in 3h*u 1457w kpku qr5vojlq*kva $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, iz7 ejg.ksr:1 m fyju19s 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 t:vv;jb i 1aqwi,7by,il-3es00z vuduhe $120-V_{rms}$ 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 ibxehmh44y . i ;b:m q/hca0u2quqww: 0n a 1500-W device is 5.4 A. What is the rms vo4e0ixhm :: 2h .caw;qmqhu/0b4ybwuqltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecj.-tge)pe kfa 9wd)n +jx2b* rted 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 by a 3.baaii v6mlmgtu7p 76) 2c-; bz0-hp pump connected to - pvac)ilm2m6z;gt 67bbiau7 a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected w:b rbwfgaw53 ;,,fxjto 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 currentzzh42xd( p.l e 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 cur(1h z;s hjqdn)yg1f;(wnvf m2rent when 22.0 mV is applied to its ends. If the drift spee(hn ; zsqyf1(gv n ;jmw1h)fd2d 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:xzvj7*l/ f qh zak7q/sphere, $He^{2+}$ 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 atmo+(jp45z dp2jo*rfg 3mgq6hz zsphere, $He^{2+}$ 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 ee.5/ usb.f7hytyc4 j membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electrbrjnf72g /npdst+01 oic pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When1b onsfgnp+j/2rt7 0 d 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 requu xp 2er,+ui:fired to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17– ue+puf: xr,i29]. 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 potentiaty+w(ary1,d+g yc. jll, $Na^+$ 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 ary, eiya5zq89ue there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-pgrgtwm )l v d,o;78+whp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the mugbmv3.4c9;ylgk n. 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 ivym u.n;4l3 ck .ggb9mf it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element sw+v++fp0 -.w7j 8kay alowr dof a 110-V, 1500-W heater is 5.4 m long. If it is made of iron,+jdy kww0a alf o-7rws.8v++ p what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an objecsoj3kd7el 3i; *p7 jkmk- rs*v+nli8bt is defined as the reciprocal of the resistance R; 8 k*p;bd * sjmr7 jkl+i-no3vse ki7l3that 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 i9j-tqf) h;wsd 7n;arz p6 c(ttnstead 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 electricity is abot(n pzf;96 t;ha- cdswqtr)j7ut 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW he z8z6c/7skj2iw o7mxf, ixl*bater $3.0 h/day$ (“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 wraf7 h7 j.rfl7 kiach6wx1oj;m3pped together side by side to make a thicker wire. How does the resistance of this;oj7ka 7c16. mh 3 wiffjhlxr7 new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 Vkiw xba5-in :+ ldhura8 6ri41.
(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 mutmew0 id h839n9 ;rzrghb y34vst be thick enough 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 more0evg3brm r9i n 48zwt;yhd93h than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equationh rc453eyqi*, +v mqrn $I\,=\,1.80sin210t$, 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 secow x1r4r0ps05fn cu 4 op*hm*ornd to41s cofrh * x5*o0wr0pp rnm4u the interior. 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 differen4a0iu1xg7gw( ouizk 9t conductors 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 first relgkz1aw70 (ou9 xui4giative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of voc5i)g 4d/z+7x5nv;w n ysmpgolume $62\,m^3$ 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 *je6-snv+x79pwac oej 9 ts-r240-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 batteri4 )g x+ ie+5tstfxuo9jes as its source of energy. Its mass is 1560 kg and it is powered t954t+xx uoi )sfgje+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 lightbulb has a resist2fz em ,p3zm-do7qpml95ktl6 ance 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 cd/ wg/vb.f*t s2lh0ll.* t5qypl c1sgarry an 11-mA beam of protons traveling at very neas*t5pdh*tl fl sgbq// g. yl10lvcw2. rly 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 connecting cordn/t2 8bb/xqjw 9yvy2 g z:qom: is copper wire with a diameter of 1.tjvyq/ o qy:x8b2mgzb92nw/: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. Tu f xnwa.x6s71he heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What i .6nu 7x1wfasxs the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system v wubr/y4xvrar 53jn;4oltage 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 chan;5br w4nau4x jr/vr3yges 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 applicatj t*4 g5y/bxq8soi(z tions. Lightbulb B is rated at 12 V and 40 W foqxgy 5s 8/jo4(b*tzit r 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 set of applian uc/ocl,j 9j/jces at 120 V, j /j9jc,ocul/ which draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an insye gd4imuv0p.hk7 :/y:pvx(w ide diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of thisuv hekx/.:p 0i 4ywp7(:vgy md pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stret-zf/3k5i 03faliqswj c -v(y mched uniformly so that its length doubles, by what factor does the power dissipated in the3 f0viqw-5zs yl f-mac(/3k ij 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 anwy+kzctr740 w en)bnzk6 gp7.d 3.2 V. If its re4wyczkp7 +7k0g. rt6)n bnzwesistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$