What quantity is measured by a battery rating given indsrw/dg9c) -o ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, ehxf:m,ug/,/dq;lzg:nnef4 g lectrons flow away from the negative terminal in the circuit. But within the cell, electr,fdn/mq g,4g xfhug:e;zl n :/ons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, batt-edx r g4+o+w nxkn7/xcbw+8k ery voltage, batterx/+n4 ex8+ogbc nrd+ ww-7 kkxy energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said8ox-j2b y9a is to be connected to “ground.” Since it is not really coiya28 -osj9x bnnected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Y, c50qpuo mrq:rt7mk:dh x91xou 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 tqp0qrkd:tc79m r ux5x 1,om h:he terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resistao w6s 2a b+6ufg2 jjv9fyqzim+g q)a.;nce? Explaif9y mj +z+o fq;6.ggjaua 2vq)si2w6bn.

If the resistance of a small immersion heater (to huowbrzx86eu0/xflpf )5 7ui .eat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Exprf 7)uf 56io/uxzb80 up. elwxlain.

If a rectangular solid made of carbon hq; -usst-x7th as sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so a7-;xt -usq htss 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 lightbulb burnsw7)n qy;ncx 0n out?

Explain why lightbulbs almost always burn out just as theku/ o9qocbfq,klxxv 8 p*+8:0(r :iqle;uopuy are turned on and not after they have bee :qopx;q c e0plxo/rfl(8v+ku8i9uo ,bku q*:n on for some time.

Which draws more current,ls2 e.7pwb)s4 o bk12 prd.fiw a 100-W lightbulb or a 75-W bulb? Which has the higher resistancw. efo217b kdsb4).lri pp2 swe?

Electric power is transferred over large distances at ver 6q )9qesp-o dsw6chv2y high voltages. Explain how the high voltage reduces power losses in the transmission lineq-s2)9 q v dw6p6hscoes.

A 15-A fuse blows repea 8ls,uw l8x pj6/ihmh6tedly. Why is it dangerous to replace this fuse with a 25-A f hx,6/mlspu i8j lwh86use?

When electric lights are operated on low-frequency ac (say, 5 p glfxk 5 *mzqv.xd37-Hz), they flicker noticq f7p*5dzl - k.3xvgmxeably. Why?

Driven by ac power, the same electrons pass back and forth throu2wjjqlv*d 27 wgh your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pas7*wjj vw q22lds of electrons.

The heating element in a toasf b*-lavqsom, 9/tak q2*y9t+nit/ nwter is made of Nichrome wire. Immediately after the toasterm9i2vn t9 awt*tb nylaq/k,*f s+-oq / is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explajiz6os i+buvy 1l -m (.mr4,bsin.

Different lamps might have batteries connected in either of the two arrangeylj.hz)x q9. uments shown in . 9lhuyj.xq)z
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 flvdf*kdwx/ l;y5r9 aj, owing past any point in the wire per second?flx9 ,v/ k;a w5dd*jyr    $ \times10^{18 }\;electrons/s$

  A service station charges a batteq,t,3 ( mrew:jbs 1jjery using a current of 6.7 A for 5.0 h. How much ch,( :ej, qtbr mwj3se1jarge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes i;sp cum wx4df6bq6d 06f $1200\,Na^+$ 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 toam6bp8f4mrp 4pster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current vu.hgf24d8 htyilj:- through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7mxt su5b.r 2 /m g1(nbf22lvug.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 dryer has a heating element with a w ahspcm 9, m5i--b/3igohg36h qn9m aresistance 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 connectedpvs g;j-w9l+ : 9c(j 3f kcfohhba9ml- to a bulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dcq8ivpdxv / ymlsq +0+5 electric transmission line carrying 2800 A (Fig. 18–34). The line has sq/ xyml8+qv i05dvp +$2.5\times10^{ -5}\;\Omega$ 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 24 j0tx5p/y:in x0 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 r4m315ifyzfzy-:mj+unqq y/j//pm o current 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 tui2d77hh qd0v4b0s rvwngsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length omii4d+t /m3 f+7ktem9ag-ew of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in diampgap( a9*+hw plo8(rw q:mip0eter, t0 rwlpahp:ip*m98pao(q( w + go 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wireb+vp 6l dnv.2i of the same length? Give numerical dli6p.vbdvn 2+ etails.    mm

  A certain copper wire has a resistth57iyiwk8z7u n q;g-yg m: p.m/ffe:ance 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 ,9l,i 1ztt ,qrp x0fkicr1kk(copper wire (originally atl91p1 x, fii,z r(0 kkrkt,qct $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungstewim y5jlx o4*fz*px23 n doe xf opzy3lmjiw24*x5* s at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has5q +hzbo h5wzxl-nx53 a resistance 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. bejwqbihn j 0;v; 6 rkbz9t3skq.4 syl+:.lu 26-m length of household no. 14 copper wire (uselsvb9:h6kyjs.q. iw 4zbr .j0ne;; bu 3t lqk+d in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carge yqf o q5w*ip.l)3.wbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (F5.*3g.wloe yiqf pqw) ig. 18–35). Determine 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 78 lf7uqkq m68o)cbcwice the length of the other, what is the ratio of the di u)lfqk87 obq687ccbm ameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a pr:y xf)0zkqc2:-)qd oc4 b4pdlqf m7ocecision 10.00-V power supply, and a curreno xfk)7cd2m c4::)f q 4bqcdoz0pql-yt of 0.4212 A is 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 coppe(o,enlqf m6nze9fr2 v.af;+rr followed by 5.0 m of aluminum, both of dia,n;m avfrol (. zf2rn9fqe 6+emeter 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 resisn6onip a7ikf n3-*f ,duu .gho6. jg-stance not change with tempera7o6a ojis*ig. unpunn k ,g-f-6 dhf3.ture. 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 prc+ll p k9a2:csoduce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of t 2cllp:kacs9+ he element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD plac2azpq4a. fi.lfn,b *w :v ;mdyer that draws a maximumc:f zw2i..vfd abq;,m 4la*pn of 320 mA of current?    W

  What is the maximum voltage that can be applied acrpla t6*eed3o. oss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and currentfb7x 8ywqpj7;jz) n* q through, a 75-W lightbulb connected to its proper source voltage xf*qbj7qz;8w)py n7jof 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. :blgwtf nu34z q-5lf. 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 settings: 85 2 lkhxqj mjz:,z f8xb5;8tdvil2 d8j10 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, whf 9+ sbbz*m: ezty3wn4ere electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V bznme3*f+ y9t4swb:z(assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use iu . uncd5,2w9ealc ox;n the morning if it is in operatic2 l ,95;eodcunxua.w on 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 porch light on ;9ddv6jdv-o qndqg o60;si, tjf*s-gday and night for a year?jq6 s-jidqd;;o6 d,d9v on0g-gvtf s* $\approx$    dollars

  An ordinary flashlight uses two D-cefo h+my/.8 )vcs *fu jjwqtw/3ll 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 ff3wvw t8) j c*uhqo/s.j+/mymA 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 energy storx mcp.ftv q (nj:g((0wed 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 rx )2oy-l 7ylqfy78uy 120 V as in Fig. 18–20, can be used without blowiylr2y8uq l-fy)77 xoyng a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copj6bvy(6qn- f acmb0-b,io( vcper wire) and of length 2.7 m (9 ft) is connected to an electric heater c 6-ocb 6mfj-ivvq anby0b(,(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 factory 1wac fdl)mv/sb4m * j;through wires with total resistaf 4cm)d;1svwj*am/ lbnce $3.0\Omega$ 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 t 6p)id7svtgnsk +.i 6go a 240-V line is 17.5 A. At what rate must cooling water pass over the .s)+igng dpt66 siv7kcoils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can beqg 7y 5o9oz-* ldsyml+ used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water from 25y qgl9ol5yzosd+7-* m$^{\circ}\,C$ 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 currca9j (fjxu 5y/; 8fgduent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value arty9a3(fd6htcr fjwn1/zj0 uhz+ - n78atz-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 tfs d +y fy4t.(l,svt6whe $120-V_{rms}$ 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 alt*i yfwf 4gxe w7+dn: 3wm7/kbgernating current in a 1500-W device is 5.4 A. What is the rms volf gwgx:fw 3+e7mny kbi* 7/4dwtage across it?    V (Round to the nearest integer)

  An 1800-W arc welder nn oe:6g krkb90r*tfen +.qy0rxm5-a is connected 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 3.0-hp /i imjsm8s:tqoriq: 3hjw - )u*3g7mgpump connected w7* jjst8/s3 q:3mi)mi-:guhqmigro to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connec-zxbv5( n m+bdwe;lb 4hp9n:sted to 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 tinyo((o3 eyjrk2cju e2bk50*hgk 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-mb)nwcruel4vzks; ;3 iq0h,vuc-8 -cdA current when 22.0 mV is applied to its ends. Ifc-v;kv ,uqd4 8b e )-3nlshczc;ruw0i 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 atmp.pap,e2c1,mxg rwv 5 osphere, $He^{2+}$ 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 atmospher h1u/mv8zzy )zv :.fsfe, $He^{2+}$ 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 memsa51+5y,v) vy eajtwxbrane $ 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 pobj f8t6wq9z-mtj29f lfgy6 n+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 requiredjz2ly q69w bf-69fnt m gft8+j is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to tran:zdaw :)x 0t/ moqc)uasmit one action potential along the axon of Example 18–15. [Hint: the energy a/oqm))da ::0 utwzcxto transmit one pulse is equivalent to the energy stored by charging 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 pot,v6u aw+kdb7b, pb5os ential, $Na^+$ 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 1.0.d 0oy4.g wzc-h(fof w0 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motor6uc*:bvzhkr gq c-2r (qf)hq8? $(1 hp\,=\,746\,W.)$    A

  A person accidentalld5k6 w*t4fy( t0vbsyqh bw lo0*h od);y leaves a car with the lights 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 125)yv4wbhbwl6ofdq00d yo; ts k* h*t(-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 5.4i/z guu- 6wlvn,ta2 7t m long. If it is made of iron, what must its diameter b u ,-utna/ivt6glzw27e?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the re dlb4: /z6,wvpao hvdgf35ie 8ciprocal of the resistance R; that 6p,/i fe bh:vdol g83dawv5z4is, $G\,=\,1/R$. 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 v*tl.dv+mebd) im -+epower. Suppose that instead 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,lem -e+vib v*d+md ).t 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 1.8kx:/4e hs5czdo 9* jks1a q4cr-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 wra( e0k9x1ece8 vohwcx.pped together side by side to make a thicker wire. How doesxe e(9vewo8 ckh0 x1c. the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is des fi(ii+:dl6vow: wmzs 74:rp vigned 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 mug +9h:cj wsi6kst 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 andks6i:g 9j+whc produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the e /ao-)mlui euk4e 8kd1quation $I\,=\,1.80sin210t$, 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 energy9 5 xzxtoo*0uy per second to xxu 05ot9z *oythe 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 digjgg(k0b:gezu9g/ . u fferent 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 powz/. g9ekg0g (ugj:ubger transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is xna)8 pdma4 :yused 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-V2(zrc pni;+ tlxrt*3nopp;9w 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 batteritvxigm * km* -anz2.*ues as its source of energy. Its mass is 1560 kg and it ig-kt*z*vm2umn .a *x is powered by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightqu-ugtrcl 8*dli3 01 lbulb has a resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is designed to carry an 11-gtvwn m43:f: tmA beam of protons vtmn:f:t3w g4traveling 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 12 A at 220-V ac. The connecting c ,.t b r,qf4m,cnvkwvkipv8)yde9de3f*8 zo (ord is copper wire with a dief kt3c4zmq d,,e wy po )b8f .kv*n8v,rd9(viameter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connect* 1(ef/amud pu j.kx;jed to 120 V. The heating element is a coil of Nichromjupjmd1ua ; e*k /f(.xe 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 voltagewi*k;s/ j:e7ilpe 7k e 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 percentp* e/;:ki7e7lksi jew age 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 fm8h1qmy.b:r c;shz -m3lgw u7k4yec;or household applications. Lightbulb B is rated at 12 V and 40 W for automotive applications. ;c hme8y43:-qm1 bks7.zy uc w hrmg;l
(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 diamet8-k5n*td yf+ w4jzycser 0.259 cm is used to connect a set of appliances at 120 V, which d k48zyc5fwdn+y- ts* jraw 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 diameter of 3.00 cm and an outside diamek snzt mq4*;odatm8 4+ter of 5.00 cm (Fig. 18–37). What is the a;n ks tz4m+8*dm4otq resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doubles, by 5 ;vzw-,xh xjbwhat factor does the power dissipated in the wire change, assuming it rw;5x-jxzv,h b emains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.sl c kno vr zme843n-wp;(j3j42 V. If its resistance at 20 jjcr3on4 8;ve4l-n mz3wk(sp$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$