What quantity is measured by a battery rat6h ni7x/ v0 xnr2463oi )hrteyy ug2bping given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connecmp txr /:doyy*d1kd/hnvq+cq9- s ,/ey/(tdwted to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, evw/ytd*yqemso dnt 1+q/y:-k( r x pd/9c ,d/hlectrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, bacqwe,a k7,a 4fttery voltage, battery energy, battery power, or battery resistw4qk ,ef,a ca7ance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it ist sdh,fz-t2 j8 not really connected to the ground, what is meant by this expressids 2tth, fzj-8on?

When you turn on a water faucet, the waterzr5r),u83uqg lt:no x usually flows immediately. You don’t have to wait for water to flow from the faucet valve to t5:runx)uqrlg 8 3,zt ohe spout. 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 length have the same dd mw snurm9z 9 y5c+,pk.l7w /l3j(ibaqak75resistance? Explain39k kn.l (j75cbwr/ap +7zw9id5laq, um y smd.

If the resistance of a small immersion heater (to heat water for t 7yrgxuuu )d-;0ev-si ea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating procri u-y)0x7; g-dusve uess? Explain.

If a rectangular solid made of carbon has shuy7 *2whfe0 m* sq-rrides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) wr*ye2-7s*hmf hqu0r 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 b3m/db)ojq 1hv jt-vuhi oz(-4 urns out?

Explain why lightbulbs almost always bu/s ffzjl9+ x8u-sd38hla lrh/ rn out just as they are turned on and not after they hafalszsd38l h+rf /l x-9/hu8j ve been on for some time.

Which draws more current, +b )7c4gi;l2+ n kq;lg lba1sjbzd/dea 100-W lightbulb or a 75-W bulb? Which has the higher rez;1a)qddb l n2bglj;s +bl i+gc4/ek7sistance?

Electric power is transferred over large distances at very high voltages. Expl p4m :rns;3wgxain how the h;4pnrgs w3mx:igh voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangey:h8wn:lf 6rp 7gtg s)rous to replace this fuse with a 25-A fugl yt6p:sfg8:n)7rh wse?

When electric lights are operated on low-frequency ac (sdoo4( qaqp3f0 a-r kp1ay, 5 Hz), they flicker noticeably. Why(a3 p041 f rkqopq-ado?

Driven by ac power, the same electrons pass back and forth through your readi, 8y 8 pio.7rwz hmjvz,q18snrng lamp over 1rjmv n8 is78pzor 8,zqyhw,.and over again. Explain why the light 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 t,)rynj:z60j 6 s gdhirhe toaster is turne0zy66h rgj s,rj:)nidd on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Expsed0z t :s gr)/si-6x+ysskg,lain.

Different lamps might have bau*nf+hyq /)ae-k8 vaftteries connected in either of the two arrangements sa / )8yeh-q*vfuk na+fhown 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 a,n sr;bie( tt*re flowing past any point iitnsr(b *; t,en the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of+se-xqc dkd12 d:gv6 f:ucwa6 6.7 A for 5.0 h. How much charge pasvk6 xwcd dg2fe+ds:- au q6:1cses through the battery?    $ \times10^{ 5}\;C$

  What is the current i* nygqfty u00lm v.v(/nvi *)vn amperes 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 current rqpn bd,y+77x9 av: 9fjw m2afvz/vi8 of 4.2 A?    $\Omega$

  What voltage will prore7 t)sitc29i+hq l6i duce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggui9):fdgf2o agj, w4a ed 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 el yz-4t v9rmh cdx(,dt(ement with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whoh+2a 11.w0ru 9dotvnuul/ b suse 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 2800 A (Fig. 18–34).e1 *atv8js p/z The z*1ja/ tv8pse 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 draws 6.50 dd/skl(l;s :h 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 *d.ri e bnay2+of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungsten wire whose resistance is x*woq3nyjd0amq ) k21 $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1uq30t nz5/nhezz u/4 yd l4(uj.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the rd)5n pv8a l uc6zhgu3.esistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diametepu8u)dhv .l6acgnz5 3r.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungste6xo 1)ussok) hn wire of the same length? Give numerical deta k6o hs1s)xo)uils.    mm

  A certain copper wire has a resistan182n x04nz: zsuem elmce 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 (original wg3jf66hyue, ly atf6w u, jh3yg6e $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity ae1c(:xsv 3fux s tungsten dv :c3 (xufx1seoes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb hau(aq3kou- b 6,wyqarlf8k7- i s 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 26-m length of household txx,4 7 iu9yu fft1+cono. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carriu ff7xt +1u, tiy9c4oxes a 12-A current.    V

  A rectangular solid made of carbon has sidem nk x9.wecztu1 kn4:2s of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18 19c:w2tzkkux ne.m4n–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 twice the length of u ufp7xl +a;m 6se7a;cjji9+ cthe other, what is the ratio of the diameter of tije6a +c sp;j 7mxul9 f+ac7u;he longer 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 supply, 1oe7zzlzvmbc -wa4 26 and a current of 0.4212 A is precisely m azlz-4v e cbwz27o16measured 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 alkz6juh(9 3dvwj ym6 m0uminum, both of diameter 1.0 mm. A voltage difference of m0u6 6j39hzymdvj w (k85 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+ o, (gdpi.wfg, it is important that the value of a resistance not change with tepg.,+f i(wdgo mperature. 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 ;y kbp,hg.ft-)nd2 nueyxv2 .vno(+t of an electric oven is designed to produce 3.3 kW of heat when connected t2v p bt;y h,+nfn tkg )o.2n.uyd-(xevo a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws a xi61j; *n6dx2j fqucf maximum of 320 mA cn 1 ;jx6uqfx*d6f2 ijof current?    W

  What is the maximum voltage t sp3o()e4hd2 nxt2ns lhat can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through,wr1mtgy45eaw:8 qh ,(/vwa w m a 75-W lightbulb connected to its propewyetvwh :4m8,1 w awaqg5(/rmr source voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. Calculam/mpg. g-zk6scq o,fg5dzrv7)-p 7 y tte
(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 setting+x jk )y(ux esy(w1g 4rr(x4ips: 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, where electricity is delivered to homes meuc3;lpb( 6lat 240 V. If you use the lil ebl m;(pcu36ghtbulb in the 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 550-W toaster use/2gufa 7drmb/ in the morning if it is in operation for a total of 15 min? a7r/ m fdu2/bgAt 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 k6; rnirr22p zw *p8fug* g4dcmWh, what does it cost to leave a 25-W porch light on day and nigh2fupm6c8* rzgr rw*4pn2;ig dt for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series asaewbr-,)d(3unfxg j m8(snz* in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA wsgznrma,(b 3)nu (fd 8-wej x*hen 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 wdr(q+ne isf.5- -h zdstored 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, can hddy (2eglf ) ba2v:/ube used with g2/e aub d)vd:h2fyl(out blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 168vh/29h mrmf 7r1cu te 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 poweu1 fc8hvt29me/rm 7r hr is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory tht) dgtiu4;a)i rough wires with total resista) g)tdu tai;i4nce $3.0\Omega$ 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 connek zp6:mxqa 4u3cted to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise 4mauqx6 pk z:3by 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 (xk85 1xfd ohvcoffee or tea. If the heater can heat 120 mL of wate1h (5oxvd k8fxr 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 currl5j* rag rnslyzk4 91.ent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose zrvlq,w8b1e83 hmi: 7 m lau6wpeak value 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 d,. )yli()zpfb6 rcz kthe $120-V_{rms}$ 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 currentrtfb*wnb p6/;a dtu88 in a 1500-W device is 5.4 A. What is the rmsa6 db/tb urp*f 8n;t8w voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to vv o+luwn e3;2a $660-V_{rms}$ 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 32qe. +4kpkyyk .0-hp pump connected to y4ke2kk +p.qya $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tmni*cb8wa6kf b5 omkez- 05j5o a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a tiny curjed.e 7yxik3 e9 qp:z)rent 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 k8 sv (sv.ca2uwire carries a 750-mA current when 22.0 mV is applied v2sa8suk(c .v 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 tf 3abwwhj0 x7mxby+;sh )sm9, 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 

  At a point high in the Earth’s at p pr4 akz)y3xf g-:s)xza j;bmr9m0c4mosphere, $He^{2+}$ 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-dse3nqa)tq7 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 actg*+,mto) a5 cqjh uim2ion potential is detected at a point 3.40 cm down themach) o*u jqit5 2,+mg 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 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 transmit one action potentixlzs4 q81yc /bk 7*azyal along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the ena y4*z/c7qk 8lzsb x1yergy 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, pd(s d 76xsc9;hre e9b$Na^+$ 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 1.00 ampere-nl6m/ 18b li *clnwa5rhour?    C

  What is the average current drawn by a 1.0-hp 120-V motor? ;yy)vhxpjz k. y(d z9s- xd.:h$(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with theq* fnez zyz571+pz+un 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 b qnz57fuze y*+zpnz1 +attery 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 is ma vsu2: 3 bda+ran+wn*wzqoyn0v(* pc(de of iron, what must (*dqcu wo*0rasna3 p:(nn+yz v+2 wvbits diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciph1. )hoacw*q arocal of the resistance R; thatq1ah*. cawo h) 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 10sdk9 7jn1mg 2vr p+ nm7qaz4f34ed 0iw 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. Assqv dm+13 pj704dswrf4k nz 92 gan7iemume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a u0f9qb6mlx(/jl*j3 uybm ki ) 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 in ttio 4d,xfa pvb5zx3wzy2 e8 x)67o-zx 9fh4j half and the two lengths are wrapped together side by side to makz bxeax v4zfojx 2tw6h,85 ip-y dtf9xz4o 7)3e a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer isi8d9c iv+w8pv designed 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 txfl:h,cv/ *z6ix 5loz hick enough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W o5zfz*co/h 6l,iv: xlxf heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current isxib p9avijsd d.n68;: given 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 at 65%vao4j*q-uc) d a k-af)p:uoy, efficiency delivers 950 W of energy per second to the interior. Find pq4yu)c ov:kjo -d a)faa*-u,
(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 diqrr cahcb:u*r oy83+h+w- w,ffferent conductors made of the same material. One conductor is twice as long and twice the diameter of the second.o *w,c wfh3 cya:+ rrq8+-brhu 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 :cm w;nh. u(aw2q 7avqvolume $62\,m^3$ 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 s26bo+ + 2fhjvxnah*wvfm-)kfgxa9 na9 ./ ixh ource.
(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 makesub: 8 i6huk-vm use of storage batteries as its source of energ ubm6:8u-hikvy. Its mass is 1560 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 resistan-olrm pe(k3; uce 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 Ferb p-o2;0e rd:anijk(amilab (Illinois) is designed to carry an 11-mA beam odr okabp0-eijn;: a( 2f protons traveling 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 cord is copperk 2km,vl nh4ox.;uz (h5o,pkj wire with a diameter of 1.6l4 2;vj 5,hnk(hzpxkoum o.,k28 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 whs p ,r,. voulq3gq*p9tts2gk,en connected to 120 V. The heating element is a coil k.,sgt,s pq g39oq tplv*,u2rof 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 vammk/h(xq/; *8yvcni lnm1 r3zries from about 12 V when the car is off to about 13.8 V when the car is on and t8*m 1vmr k(lm;/xzch 3i/ynn qhe charging system is 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 za0ruik : ( +x.qrf8x2viwn4dynz:2 ofor household applications. Lightbulb B is rated at 12 V and 40 W for automotive appli4k2diizzr(28o urnxn .w+qx vy:a:0 fcations.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set o4w d39x8vmq1cth ve(k f appliances at 120 V, which draqcvw8hv9 md3 t(1e4k xw 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 outsid a6d3es fv00msu:hv5l6 rh3vqe diameter of 5.00 cm (Fig.sq h63d:vmf3 0 sevha5v6lr0u 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so t6d b8369l*z xknjzk quhat its length doubles, by what factor does the power dissipated in the wi6bjd nkzx *9lq63kzu 8re change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a8qla . jn0,iia:v/tcwd e8 s *jhvh6t) flashlight bulb operates at 0.20 A and 3.2 V. If its resisttw8.htlnvd ise,j a)a qhvc *06i:j/8ance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$