What quantity is measured by a battery rating given in amper g,zio 2s*wf3ee-hours $(A\cdot H)$ ?

When an electric cell is connected to a circu8c*fkb/eb ghr w18e 7f*q1mm w;yp/ahit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons;/ep8b1gww m cf /*k ah1bhqyrf*me78 flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery78 x+y/rdw6b1lhc x kx current, battery voltage, bat/lc 1wy x8h xr7x+kb6dtery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “groundf5;d,9 3(l ztio 3rec*azdgxi*c0b(uonk uz 6.” Since it is not really connected to the ground, wizd3kin (( b;uc3gez**d0t 9 x5, ofou6 larczhat is meant by this expression?

When you turn on a water faucet, the water usually flows ip6m5t lnmzpd(/nq g.8mmediately. You don’t have to wait for water to flow from the faucet valve to the s m/lt5mgnpq.d(8 pn6zpout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same lengt r8 x.5c7c3ytcmwq4 uf)s5fej h have the same resistance? Explain57f.w)t e5 c crc ufm8qjy4x3s.

If the resistance of a small imme+ a) ac8cefxrcs 6/ppx3b6m 2hrsion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating pr 62/xxa 8)6e+cmfsr cac3p bhpocess? Explain.

If a rectangular solid made of carbon has sides of 3lg78qh5ljmp2/5fuagpb0m s - q0w ihlengths a, 2a, and 3a, how would you connqlg5m0aj8smp lh5 i0h/3q -2w bpg7ufect 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 x/t5hn ,*,w zm; weicplightbulb burns out?

Explain why lightbulx,ytix ,5tll,4otn a )bs almost always burn out just as they are turned on and not after they have been on for som x llt ,xott),n45,iaye time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which h;h/ vxa3im ye*as the higher ;i/*m h3aevx yresistance?

Electric power is transferred over large d6rwyf p:s3v, +vbs)bwl : /hwhistances at very high voltages. Explain how the high voltage reduces power losses in the transmission lisvwlhb)+pw rf,ys6:: v3hwb / nes.

A 15-A fuse blows repeatedly. Why is it dangerouo*6dgd0 uvy-to 0 kb+es to replace this fuse with a 25-A fuse?y+k-0vb tod ed 0ou6*g

When electric lights are operated on low-freque yyzz;z )xo*+wncy ac (say, 5 Hz), they flicker *o yzy;zz x)w+noticeably. Why?

Driven by ac power, the same electrons;hh* vefq7kqdj,m-8 ae *hv/bb o) u:x pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead v )-x bo7 f*de *jhu8k,/b;ahmevq qh:of going out after the first pass of electrons.

The heating element in a toaster is mad i6j3.f frbt4fo6v2vh e of Nichrome wire. Immediately after the toaster is turned on, is the cur3.vjohbf 4f6ri62t vfrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explfc(e aq 4ii--ldz;xp-c1jr5d ain.

Different lamps might have batteries connected in either of,kgom;: rbcj) the two arrangements ,; kmg jo:cr)bshown 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 flowil1w) ,ufv le9awxw3mxs9:rz .ng past any point in the wire per sevw :xsw mu.l fxrw3l99)ez1a,cond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0n jl4xfiw /630-enikv h. How much charge passes through the battw ni-36j04i felnv x/kery?    $ \times10^{ 5}\;C$

  What is the current in amper+uttw,0(1aq9 d rfy9t.wcxd2w x fd1qes 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 1208kh9 lz vp3w i ehuk 7r96zcq:u6yqz.- V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thrououz l8) b0gkb 74 fh):*hwengg* j8k hc5qu2udgh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when xwn.1mhf ,vte7 *6jczplugged 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 htb ws;jbde0; a+c +-rfas 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 co : frnvwu5bu)3nnected 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 dc electric transmission line carrying 2800ty1q, cr0 hik9 A (Fig. 18–34). The line h90, yq 1tcihrkas $2.5\times10^{ -5}\;\Omega$ 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 2 f5fx 1.mijd7 /ogxp-i40 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 rhkh8,p;j muif38d tp1 esistor.
(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 wire whose resist:v1bmag ef t550, lijsance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 m-g u:x9d3v aq5cy0jvom in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wirefo +:saznv o l3qn-.l, bt8xt) 2.0 mm in diameter, n8-) n la3,+vs.ql fzbtotox:to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have thb2vx3szdn fio3v u).ie j972se same resistance as a tungsten wire of the same length?f2 z id)9ujn7ivbs3.3 2s ovex Give numerical details.    mm

  A certain copper wire has a resistanm3+c:hms. ec sce 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 (o-x xdzmsf 0dmx :ef1*:9edi6 mriginally at*eexfmmm:90-df1sd:d zxx6i $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will b .3gilrl*7dc have the same resistivity as tungsten does .cr gl *bidl37at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb haogrl6 6a51 h5sg5a frjgb;v/cs 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 12ow7s*d6b; vs ivhn m6yv8 uglvp -r3along a 26-m length of household no. 14 copper wire (used in 15-A circuits). uo;g2 8rds n*vhv7-3blpvv16 s myw6iThe wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides o8-iw-ng e qcf;f lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, ;ngwcf qe8i-- respectively (Fig. 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 res/d8i-c mptj g*+d k1vc,rfi 4listance. If one has twice the length of the other, what is the cd/8 - +tc*rd1l,iimg j4vfpk ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected x-bpir. 2l2mj to a precision 10.00-V power supply, and a curm p2. rijb2lx-rent 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 copper followed by 5.0 m of al4i)2 ha/r otkiuminum, both of diii )at /kor4h2ameter 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 resistance not ch*kf di7h :m8gtange with temperaturm8*:gih 7 tkdfe. 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 elect rn / c-5vb3m7 yanq+ke 3ukne8h:ke6iric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. Whatey-7k:uhv38 krnneci+maen/ qb 65 3k must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of-d7an;pr*:nm hud m7o a 3.0-V portable CD player that draws a maximum of 320 mA of curren mm -o 7hnndup;:*7radt?    W

  What is the maximum voltage that can be-zq/k g1 twn ruo9x.g8l; 8wwn applied 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 lial a5w 0m f:x;86 xvfyt(*sslvghtbulb connected to its proper soulsama8:0 5(stwxf*f vyxv ;l6 rce 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. Cc (w 5dwa:h9ak,t0 fhhalculate
(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 hay,kv vb2 5hej3jgw1me m80i c-s two settings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, whe9x i1 yg2x+:,jgmp bqiud-fr98lx pn1re electricity is delivered to homes at 240 V. If you use the lightbulb in the2gifxm9-,nur9jd +yq 1pbi x18g x:l p United States at 120 V (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 55 +(rh25jic enp0-W toaster use in the morning if it is in operation for a toec j+n 52hrp(ital 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-Wk au9d)6krp9a porch light on day and ni6 u)dak p9a9krght for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries codf2n 4m8;xlhh nnected in series as in Fig. 18–4b (Fig4 n hmlf2dx8h;. 18–36). The bulb draws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energ )9s*syx :0l,aarirc yy 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 Fig. 18–20, gm09xxhn /*gucan be used without b 9nxx*um0 gg/hlowing a 15-A fuse?    bulbs

  An extension cord made of two wires of d scaa u6t57*z4/w pbuiiameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much po*u4w a/z u6b5a7 pcitswer is dissipated in the cord?    W

  A power station delivers 620 kW of power:gnv7e- ttrincq761 m at 12,000 V to a factory through wires with total re:6vmrqcn7t-7 e gtin1sistance $3.0\Omega$ 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 2xcp rr io0 *8t:.csk5idljd3)40-V line is 17.5 A. At what rate must cooling water pass over the coils if the war0o.*l:jrkpix isdc) d35tc8ter temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for coffkg0v;h116c5 ;fj pr abauhetmu/s8 q9 ee or tea. Ih169rge1 v;ku5b8a0 hj spq;/uactf m f 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 an/faj..nh9m6fnv w 6c $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acros k(u8dtl)nhv3t s/s (ds 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 resistan y8mlj*/cbih* hc+t ayc))cr7 ce 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 alternating current in a 1500-W device is 5.4 A. What eqqz4mb1umwgx 4566umddy 6cz3: mx0is the rms voltag zdmxuemq6wg x 53ydmbz mq4 :661c40ue across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectk9ls suzz+98z ed 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 instantaneo ka(pu:i2ai: gkp)ws+us power dissipated by a 3.0-hp pump connected to a )iu+ kwpp( a:g:si2ka $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to avc/60*adz cs h $240-V_{rms}$ 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 cokhx a (,. bmf5w6kdkj.pper wire carries 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 x3v wf-(2zf5srjw 0h dwhen 22.0 mV is applied to its endszhwv5-w2f0fx s(d rj3. 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 Earsd 1)t 2rc ya+bl*)vsath’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 tho zcoc tbz2vw++u 4+2qxcmv9gsw*9.he 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 electric field across an axon membrq0awvgf 897)a ag *m6 nzlq5trane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated w+h7*dbbrg n; yith an electric pulse. The action potential 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 t br+*gnh7y d;bhe 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 to trant1 wutt;,h -hvfmd 6d5:67l rkyk+lh qsmit one action potential along the -l1:dfh67 65rutvtm hh, w;ylk +kdtqaxon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. 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 potential,i+m7 mg.;hawkz cla cm(/16pt $Na^+$ 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 i3l j 2ez.ve+qx8anr 1rn 1.00 ampere-hour?    C

  What is the average cur:c 9q jf(b0bhcrent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with tfxf ez 4p*kpjz)mnqz **z t. v:gge7)/he 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 12-V batte )pvz)mg/4pze:7 ffqg.je * xt*knz*zry 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 nei 6b n5v;i4sit is made of iron, what must its d;v4 neins5b i6iameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is)w q-0t.kqbjb defined as the reciprocal of the resistance R; that is,t)qq b-.0 jwbk $G\,=\,1/R$. 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 pjww72 +gqw j9uower. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire linq+2jwwjuw79 g e 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 heater ci; bvv(;5ep v$3.0 h/day$ (“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 da (7gvvrt r)6gz io; 6:eri+rwrapped together side by side to make a thicker wire. How does the resistance of this ne:drrre zt6av7ig( )gi;vor6+ w combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V4nf f.ucts: i(.
(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 gmp yu(wj 2r/rbx;zd:-e *4tybe thick enough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is ryej rux 4td(:m-bpg/z* y2;wto 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 given by the equatios/e 49yf2 a6xeikvn*h n $I\,=\,1.80sin210t$, 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 ofzdes7) 4a)xfb energy per second to the interia)xz)7fb ed4sor. 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 t3d/ 1x(qls9 atcc8 dfiwo 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 transforms f(3al/9cdid xq c81ted in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is u s+gmrw 4ci.kjv-pjz+ ;h*jr0sed 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 7/xna0yd dk3 oa 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehiclejxx; j5lq 0gdf.h-4z kl23)vjmcs, na makes use of storage batteries as its source of energy. Its mass is ldvsx,-q ma ;f5j4) cg .zj02 nlkjxh31560 kg 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 resistance amgdenk 2w0lq*p2 ,v; 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) 8k gz0 q)g+ w-efw1 k;om:opvfis designed to carry an 11-mA beam of protons traveling at veryfpwe;fqkg)o1km o8-0 :gw+v z 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. Tzg9oanib-3 8rr0tixsl;9 s h.he connecting cord is copper wire with a diameteozs3r9 h89 sgltrn.i 0x iba;-r 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 sbcl:sctbi2. 26j ax6 95 W when connected to 120 V. The heating element is a coil of Nichrome w 6c6b: l bs.saci2x2tjire. 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 about 12 V when theye2h(+g1:nejhy ) b aabdn) p: car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%() nbe:j2bd1hyna a )e hp:+yg. 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 ateeye8qo(x (ukk(jyxy3dtbt j8* v t2 n*mb4 4, 120 V and 40 W for household applications. Lightbulb B is ratx*2n 4tj(evy4y 8b, ek8 u km qxyetdbj(*t3(oed 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 ;7kb/ncy j gg,9;vvxmgike4 0to connect a set of appliances at 120 V, wh;xbck;g0 4ye7i,m v9g jg v/knich 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 and an outside diameter oe) in8w(ub6y5s*lkmso 6sz: nf 5.00 cm (Fig. 18–37). What is the resnwsuk y5(bo6 e:8) znl*6mi ssistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length do,ji 9sf9 9 v/og4 xle5eqkyde9* jhm:qubles, by what factor does feeedy/kx s9 o 5qj,h9 94i:gj9q*lvmthe power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20r+19 nz.yejbs*tc px1 A and 3.2 V. If its resistance yn1sr 9z*1e+bxjpc.t at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$