What quantity is measured by a battery rating given in a .fj5(b hr 3prz+vg qp-ref7hsvm2::smpere-hours $(A\cdot H)$ ?

When an electric cell - 4sh2)yqfvqgis connected to a circuit, electrons flow away from the negative terminal in the circuit. Bf gs y2q)4qh-vut within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: batt )loyf/ nzj8*nery current, battery voltagnl)8/joz* nyfe, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it osz6yerak(h-fkz;t3 2e) t4 lis not really connectez2)asf3etl(ezr4k -;yoh 6tkd to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You d7tvo4 zmb+5;z 6vyqxhon’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 wiqzo5 yx+vv;tzhm6 4b7 re to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length dpb jy)zf*)-k r;dfs8 have the same resistance? Explain y zrb8dj;sf))*d-fkp.

If the resistance of a;a bc*ufl;6ia small immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or;u ib*ala6;f c slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, howdd+rpd/zs;4- s im+pw would you connect the wires from a battery so as to obtain (a) the least resistance, (bp s pd- /mwz+ds;4dri+) 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 burhrk525wod 6+e3k goavns out?

Explain why lightbulbs almost a q7i.nyg;te (ho en62dag1rh+ lways burn out just as they are turned on and not after they have been on for some tim 6ihgn;(g. heart 127q eydon+e.

Which draws more current, a 100-W lightbu)1gm*c 2 f l)u 6dmrgz z:;fbmcjuw4z5lb or a 75-W bulb? Which has the higher resig m) u l1r4bzzd*fg;6czmw52ucmj)f: stance?

Electric power is transferred over large distances at very high volvr7 *ql ww gie:8a/2w3mbb-zuhp( ( fs7o1czotages. Explain how t q 7*c:pmews(wul37ao/ zo h(vr -bb2fz1ig8 whe high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with jkm1 ,ksa;cnxl3;r a gm722cqa 25-A fuska3mgc mc1xka s;q,r2 27ln ;je?

When electric lights +vkuq;5 5x:i+qwzqle9j dc 8oare operated on low-frequency ac (say, 5 Hz), they flicker notix+cq oeijw kz:8+u 59dvl q;q5ceably. Why?

Driven by ac power, the same electrons pass back and forth 1 m.mwn:m0c ypthrough your reading lamp over and over again. Explain why the light stays li :mw.p1n 0mcymt instead of going out after the first pass of electrons.

The heating element in a toaster is mad7rbcvqd4oc(+ e of Nichrome wire. Immediately after the toaster is7 crco( qv4b+d turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a;he3 j5rmwrg x/z-j *-p+frk k resistor? Explain.

Different lamps might have batteries conwr,s v mfmrb4h o 1 878mmx9z/ii/m2prnected in either of the two arrangements shown ix rhmbom 2 m4r/z 78819isvwp/,im mrfn
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 flowingx 9k6tbg yn)7o past any point ink79)6b t xgnyo the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a curren 6h, b:n2ncczpt of 6.7 A for 5.0 h. How much chh bpczc2:n, 6narge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current ivk mbtkz6xl5l+ *tv )/n 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 currenelc b9 nm/8cr:*w qet+t of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through ajl q5f zqp 0,vg/r3h,e03okxk $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5,za.3 lmb/)vng ljqy.)ab2r x 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 elemendy:n n 2j s6om+yj tl-:tka+w9 l/vab/u. nml;t 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 conne 7ixjgc(vjbp/veo hl3* / p;8mcted 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 truhik0nd5f+52vdjr(qj k2k:qw: b x c,ansmission line carrying 2800 A (Fig. 18–34). The lined5 50qrhd:vjkni,jc+ 2: b(fu2kw k xq 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 v3fwvqiqs 32 j5gfk36pmid6*ht9 dk, 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 4i,md +e6prm 461 8r7jywmiqfjox9muof 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 tu6l kp f8f46er dhcoj/z:uj y-)ngsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length fsg9j725lr +buhd,hh of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 16ltrx 7w6- 8hvon fpv5qi2fy(0.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper 25 v8xy f7lw-6o nqpi6rfth(v wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tu rak0m.aeyv d: zzi//1ngsten wire of the sam0akame1i/ rydz : zv./e length? Give numerical details.    mm

  A certain copper wire has a resistance ofh 1 ieq(kyq,7l $10.0\Omega$ 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 cedo2 /uxgkuquga ;(0+opper wire (originally at u;/ 0(+duukqgg2ae xo$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivit 81; 5kr99dmdrnmhk re0 ufq*my as tungsten doesh8m k 0nd9;*rr ukq15em9drmf at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistar *szist4dfm4 vx ; qb5d,sn7lf*ty4+nce 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 adsl+-m3)no*qium f4 i 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire)4un3m- of smliqi*+d has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides oi;4kjf ; hgsc7f lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the sik ;f 7h;4jscgolid 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 e kv6h(tsy mvo2; a9;lone has twice the length of the other, w(hk;;myte9so 2vvla 6 hat is the ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connecte-f1a7mayvj r h f38yc2d to a precision 10.00-V power supply, and a current of 0.4hvr1a3 yyj-ffa2m7 8c212 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 fo sq2c 9rcul kf5(r f18,fopur8llowed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 8cq ,ksr1fro52rl 8 f8u(puf9c 5 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 co i f6g l7 -yde3bf8/xfkr+2hfhange with temperature. For examr-iff23l+ e876/kxydh obf fgple, 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 produce 3.3 kW of he(o.xy4r9-eckz.wtk . (xeomk at when connected to a 240-V source. What must be the resista.m -4kweoxrkk.x(z . t(ye9oc nce of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that dpbpe )mswf- x +let3*xr ls, b1/aj*+wraws a maximum o+pmp rw*/as w ,bxsj3* le-b+lft)1xef 320 mA of current?    W

  What is the maximum voltage that can betqqahx hiblj 0fjiq-0wgbi)96/7;)-8ab n by applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resis b/ka,cb7nc, f vb2effo,l1k 4tance of, and current through, a 75-W lightbulb connected to its proper source voltage of 120 V. ,bkl, 2b4/ f7knfavcoec1 b,f
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 17u*gza3o,n qk10 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 settingsm(c)l2:k lru)-x; ef puz,lr q: 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 isq-: kto7zqw1i 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 bright will it be relative t -zqo:t1k7iq wo 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 c mm w*cymydg,/1o05m use in the morning if it is in operation for a total of 15 min? At a cost of m50 cw*mg/ y,yo1dcmm $9.0\,cents/kWh$, 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 poc.0 v0jg+-hu e/gkm hxrch light on day and nigg+0cguej-mv. h/ x h0kht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V battxk1 o xm3 )+;igstc- xmdt)j6deries connected in series as in Fig. 18–+1- tddx3o m ts; ci)6gxk)mjx4b (Fig. 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 ogwbjk )8f,yw lbm2y:j +t1sdw)7z 9ji f 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 Fig. 18–20, can be 4xq2v f; jptq6used without blowing a 15-A fu6vj;p fq2tq 4xse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wirl;l+ 1vuwn*rh/a;us-i jy2cn9 6zgzf e) and of length 2.7 m (9 ft) is connected to an elecw+nf/6; z; jn h9vra-ylcg lz2u u*i1stric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V + .3qmffi7omg di4 y+efx2qp 9to a factory through wires with total res7feo9dmipfm+4gfq y 3 qx+.2 iistance $3.0\Omega$ 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 connect4zfk e8gtieled,b.3 6 2g cd6ded to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if tdkgl26b4 zftg e 8de.i3d6 ce,he water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater canrqfd51p 7y+q p be used in a car to heat a cup of water for coffee or tea. If th75d pqq1pfr+y e 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 cuid3m y ko8kl90 *dam9dp6.amarrent 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, is acrospcllo 0v )4,gns 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 ofz0q5v3x )h0tl/z( ov0fif uef 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 alternatinv f-qx9rn6; d 5jfr+oq1e ddkq(scqy c2 0ob/-g current in a 1500-W device is 5.4 A. What is the rms vnkrfx 2b96 yqd-0/ sqo 5v;ef (o -dq+1cdjcrqoltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder arw+nlx ow5)3is 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** bovtd)n po8d;l p*g instantaneous power dissipated by a 3.0-hp pump connected to a d v g*8ptdno;ob) *lp*$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectedd 0;so9 1 x6yj2hciqd(morrb4j,sf8d 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 tiedq,+;sia o9c kr6rw8ny 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 clugw 47 a1k6msarries a 750-mA current when 22.0 mV is applied to its ends. I7gawu6l m 1s4kf 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 Earthz 7r;aqd pxk11’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 Ea-b q*b diwx9 l ed7.yh:nz9aj)rth’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 oeh qv6ghu9 m;q-1 2bkyf the electric 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 electr8 gfp ss ux95t *z-qmj:ky5x)vic pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s9 ms5: g8xq5u kjp*ts z)xf-yv 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 eneru 3.8fytn7putod-wp1 -z 4,ql l:igesgy is required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitanelp du3-7u18w -gftp4i. y nzq:st,ol ce; 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 potentiaea* x.*0 sxy*ysmhc7c dv;j 4ll, $Na^+$ 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 dt0 ezyg p85h1in 1.00 ampere-hour?    C

  What is the average current dos c.-brvtr o3cs j6/6qx*og +rawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two he858/jam8mslv 1uf lrw o tnd48adlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last5 anjodmf/8rvw188ll 4s8utm if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of amotcnj n:o000jn aar;fobq:(c 0 zf.4 110-V, 1500-W heater is 5.4 m long. If it is made of iron, what nam:4f0ozj bo oq( t0 :ncncjf0r;.a0must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is define1ius zw,3u,*+ y ncke3bo 7ngx 8e/ebkd as the reciprocal of the resistance R; that iiesgu 1z*,uy3w3,8 bbkoex/e7k n n+ cs, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Sucfeda o+/*rj* w yq;,m gn+h/jw7fo/z ppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wzf++d*, o /many ;gh*cefwjwr// o7jqire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular hous )qy3m */q1qijye4fm;zo. nsj ehold uses 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 in half and the two lengths are wrapped together sidad2t;7xz3udoz k 5m7v e by side to make a thicker wire. How does the resistance of this new combination compare to the resis5dk 7zz;3u2xam7tovd tance of the original wire?

  A 1200-W hair dryer is designed for 117 V3+i a7o16ksj.idq 7zq*tyrbn kly(j4.
(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 thicx8k8p)hld/m5u/sgnm m n febm;/td :)k enough so it does not become so hot as to start a fire. What diameter mud)em8t:/nn )sg8x ;5d p bm/umflmkh/ st 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 of length?    $ \times10^{ -3}\;m$

  Suppose a current is given .: o 2;ygn5bem y8ckbvby 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 enjn2 yah6l n+3rxwt-rgds 9+c7ergy per second to the interior. Find+ 7xs-l6j9 r3t ay+hrd 2nwcgn
(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 materiasr he8fo38vu: l. One conductor isr e3u 8:8vsfoh twice as long and twice the diameter of the second. 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 heaqgou7-vo o+b.h,8vu vt 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,7g )e 67ywjmiz-qju:rdmpy 3 240-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 vehicle makes use of stw a ug: 1vk+c3jtba, q 7cy+-gwdpwr0-orage batteries as its source of energy. Its mass is 1560 kg and it is poweredwwp 31ua++ -,acqgyc0 wd tbj:v-rkg 7 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 resistacavm-wfq +ja ib8c : +-ra,vk0nce 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 desigun1)5h1m(,s7rqrmfg9 w unqtk -w w6 rned to carry an 11-mA beam of protons traveling at very nea q6wn 15gfhtn-1m7s (kwqwr m 9ru)r,urly 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 atc:f( c:1 cejgwrc2e,s 220-V ac. The connecting cord is copper wire with a diameter oc :e: fe2grcc,j1csw( f 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 coj*n+ahu* vz60 ei o;0plt covgo.a4r0 nnected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the dia+* oaizn. * vt;ph06ealj0r0v4cgo oumeter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is o3sd e5irq/o1 sz 50kncff to about 13.8 V when the carec1 0/k3r n5q5zsodsi 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 the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb 8fitk am34 0b-14rkzo ozb9k k1nhj* dB is rated at 12 V a -f 8k3toakzmko0 1bj4rdhz*ikb1 4 9nnd 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 connect a set of applp 7 )e)/i2 tvc:)nyj pvrdv.e.hyrdh2 iances at 120 V, which drrh:v)7 t2.ypeih veydc.n p/ r 2jd)v)aw 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 diam4cjt d6v1lm2aeter of 5.00 cm (Fig. 18–37). What is the 1vmtc426ld ja resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretibm i1,8xc exn )/cnlpw1 l3b4ched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage ixn3 ,1 m84ce bcwnli)x1pb/l source?

  A tungsten filament used in a flashlight bulb operate)jy0 h /,p2 nfbcj0jlcs at 0.20 A and 3.2 V. If it jj b0,n0jpl/fych 2c)s resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$