What quantity is measured by m0j x3fbpy0 4ka battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected,4j8)2hcmurzfl5-xhr 2glja to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negativr-j8, 4lzja 2f hmh5g2cruxl )e terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battero/r+/ td-jj szy voltage, battery ene o/r/jj+-stzdrgy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to b4eln u6rqe;3ae connected to “ground.” Since it is not really connecte; uner3l4qa6e d to the ground, what is meant by this expression?

When you turn on a water faucet, the water uhaus5m9:gq1iac4i+ner y w0/sually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thr1 e: aa0g u9iniwq +hcms54/ying true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same epytr: if w i,xpk78 sljb/+dij.n:.0length have the same resistance? j/kjiwp b i, s0rif:ylx7..e n8t:dp+Explain.

If the resistance of a small immersion heater (to heax8* 9uyw02 heyzbami( t water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Explbaziuhw 0 (*x9e8myy2ain.

If a rectangular solid made of carbonyzqdjd x;u;58 has sides of lengths a, 2a, and 3a, how would you connect the wires from a bad;y xq;z ud85jttery 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 lightbulb 9ngcm6s*n 2pbburns out?

Explain why lightbulbs almost lck68qw0u- nil;n yd2u/b 0 fbalways burn out just as they are turned on and not after they have been on for some ty/ bqn lwbu 6dcli;-028nf0ku ime.

Which draws more current3(1cffm np -8vbpav qka1y(5y, a 100-W lightbulb or a 75-W bulb? Which has the higher resistance?1k5 yv- qm aa(p 8vf13ybcf(pn

Electric power is transferred over large distances at veryh /tj4) kije p+dj +9un gqc5s.7n*hqv high voltages. Explain how the high voltage reduces p)tni/hsc54 q*qu.jjgn+ p+7 kdhj9e vower losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replacp 0jrj c2dlp(ce f,7;ee this fuse with a 25-A fupjej0 ( 7f cdp,ecrl;2se?

When electric lights are operu, 1a*bpvaw+nated on low-frequency ac (say, 5 Hz), they flicker not+v* b1n,wuaap iceably. Why?

Driven by ac power, the same electrons pvxjegqi* 9* 5dass back and forth through your reading lamp over and over again. Explain why the l giq*e59v*dxj ight stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately after thumv zcfv r(yo9q3/* fk-r79cre toaster isrq ru/-*9 cffkc7 9y or(vvz3m turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in hpheau-mab57 )qbn9: qc7zo4 pm w, m9a resistor? Explain.

Different lamps might have ox)jfk ;g2aet+w:rw9 y0ev ntc 0v6v5 batteries connected in either of the two arrangements shown in +;kv)x 0v y w9f 0ng2:6evct atrjeow5
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electroa k*9wyt,r-h r0dch 0 *wkwe+jns are flowing past any poi cr e,jwt00aw*k hw+*dhy9k-rnt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usijta- t6+s q4vcf6; .5iauvinc ng a current of 6.7 A for 5.0 h. How much charge passes through c 6cq65-uatjt+f .vav i i;4nsthe battery?    $ \times10^{ 5}\;C$

  What is the current in ampere1zbb8 kvk/ l1m) p1x 8dov0roes 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 a currza7i: hb8 s3jjsa;; aia3 a2mhent of 4.2 A?    $\Omega$

  What voltage will produce q.rb bw/(stt3uxgku3*xr0 9( fz c el20.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged inz;u )yu m6q/ ,rlrxn,kto 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 w xucujbmtq p6h ( 0cidu1/5f9:ith 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 who-ajmjv5o0c : zse resistance 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 2)y s mlg1mo cdd8j.v0*800 A (Fig. 18–34). The lin1 0. yvjgd)sc8*dmmole 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 V5tkm3ba s(-om .
(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 hxh wl7yf, z7vtn 24h.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 lej n/ l-5nso2i 22bon+bauf oa/ngth of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m len )x* jh ue ,l0esngznq)v2ib65gth of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m *j; d9ij/azkwzdmf)al+)bydc+o/-cof aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter.ia)+ob /acz9ydjmdfj+/ zl dwc*)-k ;   

  Can a 2.5-mm-diameter cyo jc0q2vc61d8mjqu 9opper wire have the same resistance as a tungsten wire of the same length? Give numerical detai09 uo1mcydj q8vc62qjls.    mm

  A certain copper wire 9+xfhpw slb *1,a w;erhas 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 (0c l5ns bn;1s qedl00f9b-bxworiginally atbs09w5elq0-dbnnf ; x bl0sc1 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will hele z 4ib x,f.x-iw.7bave the same resistivity as tungsten d..i4 b-l e 7,bzxwefixoes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance o:oq.h7p/.b1 rdyxb*tx 6 kjycf 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 len i asbv j8m0. ;d3lm64lkqq3ecgth of household no. 14 copper wire (used in 15-A circuits). The wire has diameteljdcq 3lvm6k;8a40i. eq 3bmsr 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.2ss:h v 0vm6wr0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determinwh:sm r2vs 60ve 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 theo 4sk2jp0ep rxa-y5 i6 same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longerajri5sy ep -k6o2 0x4p wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power)*arxsdh2/bl6 6d8 ,fwpwikn supply, and a current of 0.4212 A is precisely measured xprwblh)2dk*i 8 6an wf/6,sdat 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 followede:oa :gx1zq/ n by 5.0 m of aluminum, both of diameter 1:en/oq g1 xz:a.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 iws 2*+ jzzhog:*t e)sns important that the value of a resistance not change wi2e*sn g)+j*swz:h tzo th 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 2;4 m lot5ai7whsgf*d an electric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. Whftwh;l5o7s*a dgm i42at must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3 a,)t.i5 etvx2ho;ufk.0-V portable CD player that draws a maximum of 320;f5etu2ki ,xvo.a )ht mA of current?    W

  What is the maximum voltage that can be applied across9b vz9qn5cnd(o( 4t mo a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance/ 45vm)dlzcac jvo8 (a of, and current through, a 75-W lightbulb connected to a4)l8ocvmaz(/j cd 5vits proper 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 ratjge*dw7p+mau 7x( jq2ed at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W an ;z t5c tm)41a-sdkbsed 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 inl *uxh-whm7a-oy.+.l zqh 9 cf Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how b9 .z hxau+hcwl m lhf*-o.q7y-right 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 in the morning ife zpm:3,uh8u1 7k w7dlfwpg,facm,:g it is in operation for a total of 15 min? At a c ldu, feuwkzgp,,8pgf :17whm c7:am3ost 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 leavgow1mep ; . t 16lwuq6jchm+k5e a 25-W porch light on day and night fo mkgt .hl1c pweuw6jmq+61o;5 r a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in s x9bxv4bt;+ 1e2kfb6a0ue apj eries as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA wh+ ak4;be92b1ajvb 0 extufxp6en 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 amoh6wv sq*t k7-tunt 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 in Fi-upwrg3goif 2nl48+g g. 18–20, can be used without blowi3nw 2ro4gu+glfig 8 -png a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire) fnyfscv 5s2 r97b7m6 cand of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in 5 rs sbvync97m27ffc6 the cord?    W

  A power station delivers 620 kW of power at 12,000 V 7;(5yrro cl2h zx2umcto a factory through wires with total resistarlr25cmhzx7yo;u2 c( nce $3.0\Omega$ 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 2406c,n9y/ cez59lmhc1e a3 j b2kf 1nat btw1t;m-V line is 17.5 A. At what rate must cooling wate, hy9mb 31t29canzn b/ c5flt;t6wea k11 mjcer pass over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used/b hxwm. k3d50rpxy.z in a car to heat a cup of water for coffee or tea. If the heater can heat 120 m /hz.3m05dr ykpb.wxx L 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 cu-eyndxkc j;t +igo jur48*:p4 rrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, -s.q xg5bi5) ,3zyemz2lzh y sis 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 the rc f rk/7 .yl7sf sp:+bpr6h .xnjr4:e$120-V_{rms}$ 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 ar35xwac g/b8,swbbt . 1500-W device is 5.4 A. What is the rms vol bwg8r .s5,t wb/ab3cxtage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is9:ia7ges/a2x a*ptj e 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 instantaneoxhnn9 o66xe3uwdee 60 us power dissipated by a 3.0-hp pump connecteu0 n3h exd9ene 6wo66xd to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connec uiwgr a60- ulgdv;: (fs.9qewted 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 carriesx -1ea8 n50wu9k 2j7tjlavqsw3zfe6 , em7j ru 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 750-mA current w/xgcyey 1d5 3mbeylk38* 5zzt hen 22.0 mV is applied to its endsk xzb3y5*eyg8z3c letm1d5/y. 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 theu3ve ayaal+ **xnubl5v 8okl i:/w3d7 Earth’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 

  At a point high in tlm/tt3 vs 2nc4he Earth’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 elect5m 5 n)g 5i59kgrurvgi. xx- g7iqcyw) yk/b1eric 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 poten 1ti.(0 g2f(hvzby.+rzywck o tial 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 spg2..+( 0zri1voh yfy kwt(b zceed 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 trans3p/zux 1rzn v;mit one action potential along the axon of Example 18vz; 1/pzxurn3 –15. [Hint: the energy to 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 potentiaf3ue;t2df 4fu;ba-,0e hbfq;xm0j d ml, $Na^+$ 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 the 4ipov ojs(7/hre in 1.00 ampere-hour?    C

  What is the average current drawn by*/9i-p6a h llkm5gxaw:/zkyq 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 two hemam) svw26e t-adlights uses 40 sm)2 twmv-e6aW and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it 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 m long. If it i/ r n0b+ih7qkgs made of iron, w+qhi0rk7n b/ ghat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciproj )8vnw y(byk;cal of the resistance R; yb(wk8j; n)yvthat 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 requiresg otuhd4y og/;y3ji+7 about 10 MW of power. 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, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per3o yjhty+; gugoi47/d kWh.    dollars per hour per meter

  (a) A particular household us 6hom0/m;8qx6 ylilepes a 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut ijw).pi 9:f1gunawp7 i n half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the origi p7)w.91 gipuwf:niaj nal wire?

  A 1200-W hair dryer is design8vp m0hg a0u3eed 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 not become so hot as to sn* kc1f w.y3w .c)bjistart a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter oj*3k.w 1 ynibwfs. cc)f length?    $ \times10^{ -3}\;m$

  Suppose a current is given awc+h6ezc 2 6hby 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 at 65% efficiency delivers 950 W of energoh 3gb4a5 si.cy per second to the interi35.gb h ciaos4or. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors made of the same material. O5ai *vq9vt,w -h6fe qxne conductor is twice as long and twice the diameter of the seconvwxav ,95h* ft-qeiq6d. 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 room of u4 .w7iv1f 9bhaa/d8 ymol.ftvolume $62\,m^3$ 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 sol6ogcu b*0g2 asr7nx6jwc:) furce.
(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 sou 09fj2eahv )corce of energy. Its mass is 1560 k fc9o0jv)eh2ag and it 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 lightbulb has a resistaqaj2zu(n1t0f9wzw 0 vnce 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 (sh) a*k/r60uzkwypfa -r:x1 aIllinois) is designed to carry an 11-mA beam of protons traveling at very nearuhars6)ykxw z a *f:pa-0/rk1ly 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 cord isxqm9j ag 2i+niq8u:o, copper wire with a diameter of 8mx2noi, +u:jq 9qagi1.628 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 x(: ua-edwnmr3 i-ofl+g*x+xin4y7t 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When iu--ra*x+ lt3n +wf:4i7(mog xnx deyuncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the2wh u4ak5oz t dx0rc7, system voltage 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 th2wdhx,k7o4 ca 0 rtzu5e 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 ap2 zferp1a/ 2-;4u sbqpualer *plications. Lightbulb B is ratp/e2lz ua-fqb1r42a e spu;r *ed at 12 V 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 con/7lwhfqjub3t .y7vduw ) x ;/fnect a set of appliances at 120 V, 73 yj. 7;x lhtwfdw)v//uuqfbwhich 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 diameter of 3.00 cm andy5 y+oiq eqp,tf 96o,i an outside diameter of 5.00 cm (Fig. 18–37). What is the res6,9 eyit i5,pfqoyoq+ istance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so thaz+rqyo 9g onx..u2p.t t its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage sourc o.r + x.92yg.tzopnuqe?

  A tungsten filament used in a flashlight bulb operat. *kzsz6 odm u*1/gzvtes at 0.20 A and 3.2 V. If its rszuok/1**d6tvm.gzz esistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$