What quantity is meas* ;qy ;fux8mslured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electez zbij03d,3 erons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal, d303z beiejz. Explain.

When a flashlight is operated, what is being used up: battery current, battery (zs(frzu6 eg 9voltage, bs9 r (ezfg(6uzattery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to 6 un o5p1nfs9)m9t olvt*(akc be connected to “ground.” Since it is not really connected to the ground, what is meannka59sno* t6 )muf t1lc(9pvot by this expression?

When you turn on a water faucet, the water usually flows immediat,xn p:e/x/po tely. 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 ynt /p: /xe,xopou connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length hatdjud/i7)3irv2t e:o ve the same resistance? Explau7t/td j2 dir 3o)ei:vin.

If the resistance of a small immersion heater (to heat wa/0.tugl)i wm nter for tea or soup, Fig. 18–32) was increased, would it speed up or slow down thg. i)nw mlt0/ue heating process? Explain.

If a rectangular solid made of carbon has sides of lengz m/ s799 im;zfo+fjxyths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, +fmjz oz yx9s;7m9/fi (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 lightbulb bua;c58i 0aq r jwzcx;wf;q-k/ urns out?

Explain why lightbulbs almost()t,7g mbsij l9q 8mvt always burn out just as they are turned on and not after they have been on for s)m (7ivg lt9qt,jm8sb ome time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? W,gy h6vhj,ez x-b9 v47k f;qathich has the higher resis6jthhk 4-yqe7 azv x;,v ,bgf9tance?

Electric power is transferred over large distances ats v sjeem13,8i very high voltages. Explain how the high voltage reduces power losses in the tra,3ses i8e1m jvnsmission lines.

A 15-A fuse blows repeatedly. Why is it dangerxigo- *6 w7bzoous to replace this fuse with a 25 7g6*oowx -bzi-A fuse?

When electric lights are operated on low-frequency a+ ya;)-bk1 syhyrh:q xc (say, 5 Hz), they flicker q1r );ayh :h-+ ksbyxynoticeably. Why?

Driven by ac power, the same electrons pass back t6w 8nt n 1jiq(zyp,e jt fnxd602x26gand forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of electronx6jj8t0e n q ,gt2nwyp2i6 dxfz1tn6(s.

The heating element in a e,)a5jp;*ga ki8 eedtbwo 91rm x1 vg:toaster is made of Nichrome wire. Immediately after the toaster is turned on, is the currenvaa e59, *oiej 1dtgr w;:xmke)8b pg1t $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor?4c s8xkz1ieod::hv(f 1 l 03vr bdj7nn Explain.

Different lamps might have batteries connected in either of the two vfc. +j-qtp*marrangements shownjc*pvf.+ mt-q in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows bc*f wqgxh*(a 6nd1 j.lol c ,tc+y;k)in a wire. How many electrons are flowing past any point in the wire per secondn w(c,c l +1l6yq.x*t jgoca dk;b*hf)?    $ \times10^{18 }\;electrons/s$

  A service station charges a bat qw4vt/e,fj 159eraff -+d whptery using a current of 6.7 A for 5.0 h. How much charge passes throa4e vf1hwr fq9+-t 5df/,wep jugh the battery?    $ \times10^{ 5}\;C$

  What is the current in amy5b6/kw 2 nbv6(sbwh lperes 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 produces acck4 vb.)g5 rmqshr.ymx:38z current of 4.2 A?    $\Omega$

  What voltage will produce 0. k:g,ftuvk26zdc oqvqkftn;l 01x ,*(25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7tlr fbsae4vy- b/u 5;vxf2/:d.5 A when plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dr*i.8++ 5wpdn 7oifeqg(z yd xoyer 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 4eskzsmy29e 5rg8 4qhbulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc eled 4b2o*sne jt0ctric transmission line carrying 2800 A (Fig. 18–34). Te 0nodtbj4 2s*he 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 drf8rcj)19 *vaq z5rg z9wf lv+iaws 6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a resistor.6u s)mkto3 v(f
(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-m3cq1m 2et 509q( ukhb*jwovqa length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of coppn ,gsfgxc45 .ser 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 diamenmg:v7vnd 3z.:wkpv 3 ter, to 20.0 m of copper wire 2:zvn 33dkgwvmnp7 .v :.5 mm in diameter.   

  Can a 2.5-mm-diameter coppebp4trf-g h/ 8un1 vok)r wire have the same resistance as a tungsten wire of the same length? Give numerical81/k)hp gvtuo-b n rf4 details.    mm

  A certain copper wire has u-xx*n) mj2tpgvpbz 3p7n 2+ta 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 tox3q8lstfi88j 63fnkg g079uq(j2 nxx dtae:p raise the temperature of a copper wire (originally at (g2tq 7fj8uk n njd9xp:ax 8 i36qxg8e f0s3lt$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivit0w t 5iu9+cbuiak*v2g 5q oeq1y as tungsten does1t5 cv i0qi2*9uoqb5uka g we+ at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance hiugzpr,kw/ .o pl, 31of 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 wire (usd ll6dhci1gsi :d--vq)av8 m+ ed in 15-A circuits). Thd :v8idl1g-c)v h6m aq l-+side wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made o8bje ipvlw08*+ ej4do f 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). Determine the resistance for current that passes through the solid0 +e8j ibpwoj*ev 84dl 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 osk t 5mntr,;m(ne has twice the length of the other,s;krn,tmm t(5 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 wy8awp38 0qk*tpnd 9da7t zns 6ire is connected to a precision 10.00-V power supply, and a current of 0.4212 A istwd8apzdp6 0 qak7s n* 9y8n3t 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 5.0 m of copper followmn6r rs7qrm-ov .w0) qed by 5.0 m of aluminum, 7q)v0o.w rrrn- m6msq 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 resistyz r;:t:isf s iib;6qb1.+l vjance not change with 1ys.v6qbjlbt;i; rs+fi: iz :temperature. 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 tm*z8n+ mq z.cutpuk d )v1,k:cpd)n izf7;yb5o produce 3.3 kW of heat when connected to)cuz8 t7nm+zp 5 .p z*d:,qdciu yknfbkv); m1 a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V po nl8zjd4gq; wp(7 sa 1prk0(ckrtable CD player that draws a maximum of 320 md; ql jpkz wcsnr8g((04kp1 7aA of current?    W

  What is the maximum voltage that can be applied across a - h6u3 uj+elnn4rfrw8$2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance otprr+ v7bzlj6+y,-ga f, and current through, a 75-W lightbulb connected to its proper source voltage jz+l-ra+vyg b7r 6t,p 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. Calcj(.1s mq nan,(yjw+esulate
(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 125e;o,0b/rx tdx0 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 delivere39bj-i0yhr :h)vcj, tg ;ycpld to homes at 240 V. If you use the lightbulb in the United States at 120 V (assgip-cyj) l cbty ;vh:9rjh 03,ume 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 does8o9 ;alrz:q zrka+5pu a 550-W toaster use in the morning if it is in operation for a total8r5 a+:r;kq zual zo9p 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 2r aznma9j -s-6nz 7+bx5-W porch light on day and night forz9 x+z 7snjnabm6-ra - a year? $\approx$    dollars

  An ordinary flashlight uses two Dt.*om3jcx wb +-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA wwc*.o 3b+m jxthen 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 amou/3hnt 7*n;in -cnkipgnt 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 120m.6u le lri, 1:olz7z dsnphg+t .c70b V as in Fig. 18–20, can be used without gr.lmpo 0tbunehl s,+1i.77:zdz lc6 blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wizbmnca 4*)a*i1 0 kecure) and of length 2.7 m (9 ft) is connebk4c*)cu0aim* za1 nected to an 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 to a factorydedv9u4 txe3lo7n- .d through wires with total resid d 7.4levexno9- tdu3stance $3.0\Omega$ 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 elrsqd45 l, 1sr pa36xogectromagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperatup5rd oar1x , g4sls36qre is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used :j;vh6;dk(j):dphp 6s9nl xh1 nnht vin a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL ofhs6tld;vn( jxhn69vk)::;dhp1 p njh 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 ab/w+ c b j2(ivsg07q+hkesfx7 $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 1r2miox ,jp zn//+ fk(kcyh,n480 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 resistancsvy)js4k 9izbs4cf an;.+;f*ly7 jzwe 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 alter/ b*wchl6mm1s0yz:n*imx 2pvnating current in a 1500-W device is 5.4 A. What is the rms *0v6mn2p z s/mh1mwbc:i*xyl voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected toj78 mfwqn(ra, ai7be 3 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 +.wh0h yqofj5s.3f sdby a 3.0-hp pump connected doq5s yh hf.jsw.0f3+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 a n*gf; d6k sjkc f/b,u7$240-V_{rms}$ 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*/yrbzx rj h,6 s4ql /t:s6sco 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 75-x+ :jt4s,f6nrvf k b5 jdy0xcx i8;uh0-mA current when 22.0 mV is u8ftx:x+x -j,cdj6s4rfbn ;hkviy 50 applied 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’jz8 +lb/y,xc vs 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 atmospho48*ir l7q ulkere, $He^{2+}$ 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 elec uhotyv20 k(obu5 ck dvbnxi6-,g0t 45tric 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. The action potential is detect6o1-3 y ot+clg evrrv8ed at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detetr368ycg vo vor+-1el cted 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 * si-cm+iixam2x*;x 6bxfm9r 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 chargim *2+s i9* 6mi;b xxxicmxrfa-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 potentih o, z j7/o:iqaqon1z2yn9y8pal, $Na^+$ 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,lsu6o-f m, mtav 61we 1.00 ampere-hour?    C

  What is the average curreny q9/78d( j+akc nwww)s,hesu7,p+ wf: nomay t drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the t0lv,+o2 q q8s tqb1clrwo headlights uses 40 W and each of the two taillights 6 W, for a total of 0q,81co tl+ qrsbq2 vl92 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 *vka;+dy5kezu*y n b ;m long. If it is made of iron, whayev * adnzk;kyb *5u;+t must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the hauf. an* dk(gk3j( 2fn2.ocwos) d9 ireciprocal of the resistance R;.aa2(9 dw u njg.kf*o)2sfncki (d3o h that is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Suppose that instead of using m; azr+f1-y wtu1 ap7phigh-voltage lines to supply thtam z+p 1y;r7 pa-1wfue 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 about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW he95n4eygxmd)p)hx n d7 ater $3.0 h/day$ (“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 length :ckz s )g+zw21gbob.ss are wrapped together side by side to make a thicker wire. How does the resistance of this new combinationsw. 2 zzbg:koc)+sgb1 compare to the resistance of the original wire?

  A 1200-W hair dryer is designed q8plc xl9ou ,o a/oz6b+-gt)j 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 / nxcfo9xs5z8it does not become so hot as to start a fire. What diameter must a co/95 on8fxsxcz pper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is g h9ih3xcfhpy39t;u4 l iven by the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running tjg-99e w a go9eiofti)wu2g p (7k5j5at 65% efficiency delivers 950 W of energy per second to the iitpgeg5 otweuk 9 7a(99-gjfj 5 o)iw2nterior. 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 qem; 7/c;h/ zumcc-vutwo different 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 tr/u ze mc/ h;;cu-mv7qcansformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volume acwq(- 1rca/ + 85hyeyz ;gtemwj3ds4$62\,m^3$ 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 sourceodyr6 of 9s:;e.
(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 souru 4(9anix,bxk.v1kbh ce of energy. Its mass is 1560 kg and it is pow k(uabxxvi9h4n. 1 b,kered 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 lightlx5p 5sy tgglno;; ce1.y1 )kibulb 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 desig n1zqb8,l + f;fmxlub5ned to carry an 11-mA beam of protons traveling at very n,m;bub58 fzf+l1q nl xearly 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 eje++l0:tmbglkgjxb, /x 5y2 12 A at 220-V ac. The connecting cord is copper wire with a diameter of 1.628 mm. x gejjl 05+2:/mgklx + ytbb,e
(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 conm2vtjzek m 8 ag/6)s5xnected to 120 V. The heating element is a coiljx) 6gemk85m/avts z2 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:pxz9vo5oug b k;/cz/ about 12 V when the car is off to about 13.8 V when the car is on and the charging system is /9bov:o5;xkzpugz / c 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 applicatix rdeu8y )g((fons. Lightbulb B is rated at 12 V and 40 W for e(dy)fxu g(8 rautomotive 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 8ia;a2fhdt2 ju)5fnl connect a set of appliances at 120 V, n)f aujit h2af5;d2 8lwhich 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 inside diameterb:oy3zy s-9cqefamz **7tlucd 99p * f of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). Whyq b 9of*tc9l *c *mzfz3a d-e7s9pyu:at is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so t lhx02hwwu.vn*n sa1 8hat its length doubles, by what facton8sxhn *2 vw u.wah01lr does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight 4-ar cfd b -m vrl,yb,j2zt:n1bulb operates at 0.20 A and 3.2 V. If its resistancbmlyvd1 bz4a-c:frt2-n,, rje at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$