What quantity is measured by a battery rating given h.8cj;plwwmge bnfk x88j 5p :t-yd0* in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away wg*)jr z7p,k (g *q u0ag3hafrfrom the negative terminal in the c* g3wk,rj7 rqzu ha*(pfg)g0aircuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battery:s tq6.4z t4equk0tib voltage, battery energy, battery power, or batter:bztu6qt 0ie. 4q4stk y resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since ia,x)4u) jj5eub:ip (rw u3gmjt is not really connected t uui5gj m,3xwr)4pbj (aje:)u o the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediatelyq mpq8hn9b(6p6hla5l . You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect598h mal6qpqhl(p6 bn a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have*n;(mo 0m *kztbndqs v6 a7js0 the same resistance? Explb;tj6( *oa*kq vsmd s0z nn7m0ain.

If the resistance of a smu kfr,wj-6wim k*wj 554uxe.ztc13qhall immersion heater (to heat water for tea or soup, Fig. 18–32) wu 15 kr-z.x3e*546tw,wj mih jkfqwucas increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, anzi o csb2g(6 qb3mp++5iuli,md 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the3l ib5+biu+gopc6(zs, mmiq2 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 lightbulbmow01* husd)iic+f l; burns out?

Explain why lightbulbs alit7qb512xkob2w 5 p rvmost always burn out just as they are turned on and not after they have bepv7 215 qbrxw2bk 5itoen on for some time.

Which draws more current, a 100-W lightbmn:n08spxv v*ulb or a 75-W bulb? Which has the higher re0xp8 sm:*n vvnsistance?

Electric power is transferred over large distances at very high vol-;(6n0xbptk4- 5hijdtxcm 4 3tg9 rt+ d rexxztages. Explain how the high voltage reduces power losses in z c(4txbxp-etnt- r6+hr kmgddti9xj 4; 5x03 the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to rea-nay.c ;lb5 fmcof3 /place this fuse with a 25-Acl5f .o bn/;3aaf-mc y fuse?

When electric lights are operated on low1g; krg qgfj,b1m/lah90pj)m cp*v3 x-frequency ac (say, 5 Hz), they flicker nv h cj 0ma)k9fpgb/mjx3g, *g1lq1 ;proticeably. Why?

Driven by ac power, the same electrons pass back and forth4)m,o gpqc, 1ngoqx*m e9bht6 through your reading lamp over and over again. Explain why the light stays lit instead of going out after 9,qm bo exh4pq* g),tgm6o1ncthe first pass of electrons.

The heating element in a toaster is made of Nic-mr ez ne e-8k/lyt8i(hrome wire. Immediately after the toaster is turned on, is thz8iey-me nkrt 8l/ e(-e current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Ekn2 vx gjg l56tt-(i7explain.

Different lamps might have batteries connected in either of the two arranguvd7 xofrccd41j9kxw kk0.6*ements shown in 0dc1x 9 7ruxdvjkf.6*c4kkwo
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 cbue7 ik5mq5e5 +3i0gvq9jht flowing past any point k55qh3ec guq90 5vibij+tm7ein the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a curren, c8 y wg/ys-0hkdc7rat of 6.7 A for 5.0 h. How much charge passes through the batt-wr,sy 0g7ka h cd8/ycery?    $ \times10^{ 5}\;C$

  What is the current e-ses 5.rq 8mnin 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 pre*th: c-8sak voduces a current of 4.2 A?    $\Omega$

  What voltage will produce 0q--8 e x9i4uazpp)2f6uzcp8a r5uyzj .25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggiz-2v 0 iw7wykql9an )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 /*8, pfkox d 2xyqf9vda 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 connected to a bulb whose resista / m.(:8; gx7;z owthw0ztpa+xl csnuznce is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transm6j fbsx:3f 3zcission line carrying 2800 A (Fig. 18–34). The line hass3b :f fxjzc63 $2.5\times10^{ -5}\;\Omega$ 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 V (cf)k0g osyzs*;b8yq .
(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 resi.7k aq1cj82 x3 fgxmccvgfp:8stor.
(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 d5txa, 6 4jnz)-sqqwj$0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copp8 8v frtjq y3f36.w13jkbk yu-gg3tb zer wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0tu583hy m5z1u5hx yog mm in diameter, to 20.0 m of copper wire 2.5 mm in diamzy3mh yxt8ug 5o155 hueter.   

  Can a 2.5-mm-diameter copper wire have the same resist;w8* 5 tj87zpr/a6ozanx, 6 u wkxveoue 5q:mgance as a tungsten wire of the same length? Give numerical details. qew6t5m: ve apa 5nou8,/rx*zxowzg78jk u6;   mm

  A certain copper wire has a resistance of jng4 t:: xamm eiw4t/9$10.0\Omega$ 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 temperatuvh;jp g2yxh,+r l- :gh10vpx ore of a copper wire (originally athyvo1x pr:-;gg+jh h,2vl p0 x $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same bsy5v5 .x3ao(z; awnsb eq(3v resistivity as tungsten does e5wa.5ss bx(o; a y3nbv3(vzqat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has cuc2+ff,m 3+hp230 d*pf b *;juvj -bjdxnvmxa 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 no.c2 ud(dl+ta /tot*9ej 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 c+ 2tloda/tu d* je(t9mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, anix8 il yd(z ,wd2m7cfs6kkse;2 u)(ygd 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that pi2yy)l7ue6 xcgi z,(ss k;kf8md( 2w dasses 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 sam 7c;rk6p)jq n6v4)kchv9 ahz ve resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diamcj4)9rv 66vaq 7zk)n ;hpkvhceter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is c:c* kckj;kxo:ip x1 tu-ver7u):l x9 bonnected to a precision 10.00-V power supply, and a current of k px-v:x9 xte1kbk *i rco lcuuj)7;::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(h;6zg( 1d ljs+zh qyh followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference ydhz1 (j(z;hhq +6glsof 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 vy+ 8)vp h7+a)w-1bmctosjn q dalue of a resistance not change with temperature. For exampvwb j+hdy)a-nm7q)1o8 c spt +le, 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 electcc v;as*t2xr2ak /j3nric oven is designed to produce 3.3 kW of heat when c/2c *njv st;xrack3a2onnected to 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 tpo/3mu f(/tiav 0/liphat draws a maximum of 320 mA of cuiltp 3/p(fu0 o/m/v airrent?    W

  What is the maximum voltage that 3 mhog,qsmizxwx-b /y3p03, 5) eew gscan be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistan8kg w)0di )kn a1)+zaeoiy9vfce of, and current through, a 75-W lightbulb connected to va) y 0kainego+ 1)8i)wfk9dz its 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 rated at 110 W. Calculat:-l)w/ p.yk bixc+ij ze
(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 se(1) .rky l4jttiz4uj mttings: 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 h4zwsxzcr c mcz 434m+i-p(f0romes at 240 V. If you use the lightbulb iw4cs0(pz3mcfrrz4 i +-4 mzxcn 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 in the morning if it is in opb5 zv9q-tk (umeration for a -mqu(t5zk 9bvtotal 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 lh4 j(v0y i(1s ;hjmsfoeave a 25-W porch light on day and night for a hj1mv0y;hfs4(i jso( year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V l q.lur(5( vsvbatteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA w ( v5(.llvrqsuhen 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 stored in a 12sklc7doj s5-7so x,4ps fpmsj;.3;x1j 8er kz-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbukr k)/h3k0ai dlbs, connected to 120 V as in Fig. 18–20, can be used witho0/kr 3)kdha ikut blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diametev p ivb3e8we/,r 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 vb8w /v3eiep, much power is dissipated in the cord?    W

  A power station delivers 620 kjco qn+a7k5mz4wbj;: e)8sazw x (m0rW of power at 12,000 V to a factory through wires wit crj8oma 0mb)7z+ 5wn q jxw4:s;a(kzeh total resistance $3.0\Omega$ 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 electre5 + )+i.ezo.t2hqou+6 qzfobmbz rv -omagnet connected 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 by no more than 7.50uizqo+.zh. -ebmoqf6 bt+ o+52rz) ev $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of h*o,q/, bnhx f*hd(baiq4 ,ww water for coffee or tea. ,,dhqq bw 4*ai(/bwfhh n,xo *If 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 cijr4b b;zzn . /o)o4(ldo s;sk. yg6glurrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak valu )ll*3u3qook-nz8 .nfsr sc0je 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 thfr. e;aq78ujr 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 alterni egc4d- bij,1 rkq4 -r7qm/rnating current in a 1500-W device is 5.4 A. What is the rmsi4 47bcgm/q-nr 1 irqrkde,j- voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to .zn85/ q zq):svwl aoba $660-V_{rms}$ 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 dissi8 27a-w,;t5l fx ykkir 0qyntupated by a 3.0-hp pump connected to a ya8t5 txny 0q kru-2l;f k,wi7$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connec0zcl- v:8 ewbgted 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 tiny yi6h 1u:puz 3yfmkno; 91i*jkcurrent 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 when 2+;arwfrpn; m( 2.0 mV is applrfr+;w(p;ma nied 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 the Earto;10 * l 2p:sxzzfswish’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 f ) k 6(0tgs;oszc8tqv 2dm-akEarth’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 ; 9jcfqmrm +cy:n-1dtfield 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. T)v ,0c a wep5rboq2h-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 twe0tvb5 c-a,)qh 2or phe 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 rd kz2 z+ qwy8n(,50hqnxkcy *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 capacitance; see Section 17–9]. What minimum average po8qy0q 2h*n krdwyxnz+ zc,(k5 wer is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action pot44svcevt qh(i,6z 6q g+rl,y rential, $Na^+$ 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 -25rv71w .jzy.qark kc-lj8i1tgfq o1.00 ampere-hour?    C

  What is the average current dra-mc63h .a uxd6 (46otuu iccwjwn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car(e;hsnu jmdq.8 p7e j; with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V batte s;jqemdp ;(u8j.h en7ry 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 iye7 qz(:mfi y2x9-oqd58ysf cq/sdc0m, jow 1s 5.4 m long. If it is made of iron, whqy 09c8d5woq :z7ef- m2qsim1f co/(dxj ysy, at must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resisatl,ky9 o5qk 1tance R; 9ky l1a5tqko,that 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 aboabzyc qm8uk.f 21 o85dut 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. o ykdqfb15a 2zmc8.8uAssume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heo2 3 up)(v8pd+qrnd nhater $3.0 h/day$ (“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 len- l) sv +u4*icvmcm0jhgths are wrapped together side by side to ma+*mil0c v cs- 4v)jmuhke a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer iszbev1 vbv3+svw b(4;n 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 rg j69zctr* oucjs.8 19l fzkew:l )1ythick 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 curfg9 ol1czkzr* r 81:j9)te.j6cwsyu lrent 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 equat ox; w4./vhvsrhy;)lkion $I\,=\,1.80sin210t$, 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% efficienc8x olf 0qf). j3vvjn9qane) pgkj4j96m(- mpny delivers 950 W of energy per second to the intepfj0698)jvqvg3nq4oe( jjp mxnalm- 9kn f ).rior. 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 condu q*2pg:ttf s4m/v7k5 1bi hhasctors made of the same material. One conductor is twice as long and twice the diameter of the second. What2vf1*ki 5b7ashqhpm4 : /gstt 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 of3s xekdtq6su 4o +xl ra552kq/ volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V source. d9 )0juz1kfyf
(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 mak)x/f8/mp im2n.:wq e *qkr xvoes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powfm/)ix* . pxe:8vr/qwon kq2mered 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 ol (ulkkmfz0 .r.ix+b) f $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is designed to carry an 11-mA;o,y)j0 uoj 1fnykk 0w beam of protons traveling at very nearly th0 0k ywjjofk;)ny,uo 1e 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 drf.4*n pkb vfw(aws 12 A at 220-V ac. The connecting cord is copper wire with bk(np* v.f4 wfa diameter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. Thb86z/- nsvr gbe heating element is a coil of Nichrome wire. When uncoiled, the sb b r/8-z6gvnwire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, thl3 l.7mn/rpf7dcx ac, e system voltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the ca/npf7,crm 7 xl3ld.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. Lightbuj)nocf; (ltw:0y i+nslb B is ratedw +ln) cnio;y:s(ftj0 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 0.25 4cugn)s1o0 tfrtb1 ;k 7x7nbs9 cm is used to connect a set of appliances at 120 V, which draw 2250 W of power x nks4t)1o7n7rbsfc1u;t 0bg 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 inv 95zgk) t;s8 c3g9:iog+hekuv (vvvtside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistanck vth9 gg:89vto3z5e)v ;+sk(gvicv ue of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so ts ke7awv i.k;*dhw j00hat its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage sourew7hd;jvsw 0.akk i* 0ce?

  A tungsten filament used in a flashlight bulb operates at 0.20 A jggy sm3s (6b7and 3.2 V. If its resigs3ybgm(7 s6j stance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$