What would be the advantage, in Faraday’s e-n5q. zarzv 4ixperiments (Fig. Below), of using coils with many tz-v i4n.z 5qarurns?

What is the difference between xn68y7 n .czdlhd)fd -magnetic flux and magnetic field?

Suppose you are holding a circularinpf 2362w5dk.c)pv )b a. *iveve mpk ring of wire and suddenly thrust a magnet, south pole first, away from you toward the center of the circle. Is a current induced in the wire? Is a current induced when theck 3i. 5v b*aen.wfkipevv6)p pd2m2) magnet is held steady within the ring? Is a current induced when you withdraw the magnet? In each case, if your answer is yes, specify the direction.

Two loops of wire are movin -:qmljw5lsa wi,*8 lukwy 8q9geh;.ng in the vicinity of a very long straight wire carrying a steady current as shown in (Fig. Below). Find the direction of the induced h; eun-gmq8k* yawl,:9l8qiwwl5js.current in each loop.

Suppose you are looking along a line through the centers of twoqr e0sb ( 1 )b,w3dx/cysg4mqala 2s/m circular (but separate) wire loops, one behind the other. A battery is suddec sbd/wa3q qm0aslmsb(y,er) x 412/gnly connected to the front loop, establishing a clockwise current.
(a) Will a current be induced in the second loop?
(b) If so, when does this current start?
(c) When does it stop?
(d) In what direction is this current?
(e) Is there a force between the two loops?
(f) If so, in what direction?

  In (Fig. Below), determine the direction of the induced current16fxhmkb+ a 2 z5fnc.g in resistor $R_A$ when
(a) coil B is moved toward coil A, ----待选择----increasedecrease 
(b) when coil B is moved away from A, ----待选择----increasedecrease 
(c) when the resistance $R_B$ is increased. ----待选择----increasedecrease 

In situations where a small signal must c 5f, l4mzvmr 49yil08h4u1 iypveoy (travel over a distance, a “shielded cable” is used in which the signal wire is surrounded by an insulator and then enclosed by a cylindrical conductor carrying the return current. Why is a “shm 8 umv( 91ylpy5z fi0irecy lo4hv44,ield” necessary?

What is the advantage of pl ;2yxx suycx:5y;m7ujacing the two insulated electric wires carrying ac close together or even twisted ;7yyum cujxx;ysx5:2about each other?

Explain why, exactly, the lights may dim briefly when a refrigerato 6bt o-i+ochw;*ez kb8r motor starts up. When an electric heater is turned on, the lights may stay 8w ;z6-oebokchbit *+dimmed as long as the heater is on. Explain the difference.

Use (Fig. Below a) and (Fig. Below b) plus the right-hand rules tq n*wp2:ek zl:n 2oyh.o show why the counter torque in a generator opposes thkhn *ze22.qpny:l : owe motion.
a
b

Will an eddy current brake (Fig. Below)3 v0bey + /i9ir;nch4mjr uf+e work on a copper or aluminum wheel, or must the wheel be ferromagnetic? Explainh39r cv0+n;m/bu +rfe 4iiyje.

It has been proposed 9-(wsn53 ndxlx8 ehvu that eddy currents be used to help sort solid waste for recycling. The waste is first ground into tiny pieces and iron removed with a dc magnet. The waste then is allowed to slide down an incline over permanent magnets. How will this aid in the separation of nonferrous metals (Al, Cs3 ud(v w9-5nxe xh8lnu, Pb, brass) from nonmetallic materials?

The pivoted metal bar with slots in (Fig. Below) na 9kiq*2:iskbvh2 z6falls much more quickly through a magnetic field than does a sol2 nhiszvb 2qi*k6:ak 9id bar. Explain.

If an aluminum sheet is held/k6dp 4sstag,4e2i vy between the poles of a large bar magnet, it requires some force to pull it out of the magnetic field even though the sheet is not ferromagnetic and does not touch the pole fac,dv4ayis/es tp26k g4es. Explain.

A bar magnet falling,5 kxtw6 5zjik inside a vertical metal tube reaches a terminal velocity even if the tube5k, z tj5iwk6x is evacuated so that there is no air resistance. Explain.

A metal bar, pivoted at one end, oscillates freely in the absence of a magnjovqt l 8qbn6x7/ 0m,letic field; but in a magnetic field, its oscillations are quickly damped out. Explain. (This magnetic damping is used in a numbot/ , 6lvx8n0mlq7bjqer of practical devices.)

An enclosed transformer has four wire leads coming from up* l9l7e.f +uhgrjoio:6jz/it. How could you determine the ratio of turns on the two coils without taking z gu:7jp*irh6u lj9+e/foo.l the transformer apart? How would you know which wires paired with which?

The use of higher-voltage lines in homerob, r*wvs:dblh3 62zs — say, 600 V or 1200 V — would reduce energy waste. Why are t*zrvh blwo bsd,623r: hey not used?

A transformer designed for a 120-V ac input will often “burn out” if conngo7eiii7k 6 drmz;m70py p(r6ected to a 120-V dc source. Explain. [Hint: The resistance of the pk6 7 z7 6gipm ;rypm(oe0iir7drimary coil is usually very low.]

How would you arrange two flat circular coils so that their mutual inductat b.)nmsi1o+fhhd-iy(c 7jb- nce was bts c7nfd1ib-.+myo j(- hi) h
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery in (Fig. Below) affect the time needed for t8y,7 1jm g;agus 5ixishe LR circuit t xs 1m5,aiis;gy guj87o reach
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can the rms voltaubhm7mz6d, x- ge across
(a) an inductor, ----待选择----yesno 
(b) a capacitor, be greater than the rms voltage of the ac source? Explain. ----待选择----yesno 

Describe briefly how the frequencljin wk1)ob (e2/o)f bw86rqi99 do ogy of the source emf affects the impedance of
(a) a pure resistance,
(b) a pure capacitance,
(c) a pure inductance,
(d) an LRC circuit near resonance (R small),
(e) an LRC circuit far from resonance (R small).

Describe how to make the impedance in an LRC circuit a minihqb wl*jf a 4f hysen7t968.9cmum.

  The magnetic flux through a coil of wire containing two loopgy*c)xtxn z5fwz6(i0s changes from -50Wb to +38 Wb in 0.42 s. What is the emf induced in the coiyfgz50tnz )*ix6(w cxl?    V

  The rectangular loop shown in (Fig. Below) is pushed into the magnetic fdh ,0gqn)j r;bield which points inward. In wq);jdb0hn ,r ghat direction is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fig. Below) is beinnkj rm -e3t:6mn0wz.t eg).ang inserted into the coil. In which direction is the induc) mw6e.. 3egm0zn:n-jtknatr ed current flowing through the resistor R?  ----待选择----from right to leftfrom left to right 

  A 9.6-cm-diameter circular loop of wire is in a 1.10- b3u*7 ywy xu)g:zg*eoT magnetic field. The loop is removed from u3b 7w)gyoe* yzu*xg:the field in 0.15 s. What is the average induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wi skh.epga:k h4 0-yqqgo23c7j re is initially oriented perpendicular to a 1.5-T magnetic field. The loop isy4gk kehog7qh.-pqjs a 30:2c rotated so that its plane is parallel to the field direction in 0.20 s. What is the average induced emf in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wir /gyfu8ipbx076m; p9 h+bdhzk v jsf24e coil is initially oriented so that its plane is perpendicular to a magnetic field of 0.63 T pointing up. During the course of 0.15 s, the field is chan+7hpkm92fsjgfdip/0b 468 ub;xhvzy ged to one of 0.25 T pointing down. What is the average induced emf in the coil?    $ \times10^{ -2}\;V $

  A 15-cm-diameter circula)j3p py,3ix/w 3qyh ywf9az*ar loop of wire is placed in a 0.50-T magnetic field.
(a) When the plane of the loop is perpendicular to the field lines, what is the magnetic flux through the loop?    $ \times10^{-3 }\;Wb$
(b) The plane of the loop is rotated until it makes a 35$^{\circ}\,$ angle with the field lines. What is the angle $\theta$ in Eq. 21–1 for this situation? $\theta$ =    $^{\circ}\,$
(c) What is the magnetic flux through the loop at this angle?    $ \times10^{-3 }\;Wb$

  (a) If the resistance of the resistor in (Fig. Below) is slowly increased, whatvng/q(5)usxb4x3sta .h cn6k is5ng sxh/uxak4(nbv.6stc3 ) q the direction of the current induced in the small circular loop inside the larger loop?  ----待选择----counterclockwiseclockwise 
(b) What would it be if the small loop were placed outside the larger one, to the left?  ----待选择----counterclockwiseclockwise 

  What is the direction o7ytd 0 xk ggp3*jq8bh00 )fauzf the induced current in the circular loop due to the current shown in each part of (Fig. Below)?8g j3at007f) qk*pbdyz gxu0h
a  ----待选择----counterclockwiseclockwise0 
b  ----待选择----counterclockwiseclockwise0 
c  ----待选择----counterclockwiseclockwise0 
d  ----待选择----counterclockwiseclockwise0 

  If the solenoid in (Fig. 7* lpzgfxd ylo: ((ms7Below) is being pulled away from the loop shown, in what direction is the induced c( gy 7f(dxpo: lmszl7*urrent in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular tod,7bz1 lfje4c(l*ll +8kenx k a circular wire loop 12.0 cm in diameter is changed from +0.52T to -0.45 T in 180 ms, where means the field points ad,clfk7en8j+z 1b xlk(*e4l lway from an observer the observer.
(a) Calculate the induced emf.    $ \times10^{-2 }\;V$
(b) In what direction does the induced current flow?  ----待选择----counterclockwiseclockwise 

  The moving rod in (Fig. Belog(z.ufr f5g2 w 0sin* z7i)eaow) is 12.0 cm long and is pulled at a speed of 15.0cm/s If the magnetic fu.z5farwo07e*(i)f2ng z s ig ield is 0.800 T, calculate
(a) the emf developed,    $ \times10^{-2 }\;V$
(b) the electric field felt by electrons in the rod.    V/m  ----待选择----updown 

  A circular loop in the plane of thiyow ak/.4ja8 zk :luhj;s,5le paper lies in a 0.75-T magnetic field pointing into the paper. If the loop’s diame/ u 5;a,ao.jyzk 8iklsl:w4j hter changes from 20.0 cm to 6.0 cm in 0.50 s,
(a) what is the direction of the induced current,  ----待选择----counterclockwiseclockwise 
(b) what is the magnitude of the average induced emf, $|\varepsilon|$ $\approx$    $ \times10^{-2 }\;V$ (retain one decimal places)
(c) if the coil resistance is 2.5$\Omega$ what is the average induced current?    $ \times10^{-2 }\;A$

  The moving rod in (Fig. Below)iw5b3:pcnm(:hfp( ufts 13.2 cm long and generates an emf of 120 mV while moving in a 0.90-T ma(:fftw3h5cpn b pm( :ugnetic field.
(a) What is its speed?    m/s
(b) What is the electric field in the rod?    V/m  ----待选择----updown 

  Part of a single rectangular loop of w m -egx6wa6ck5ire with dimensions shown in (Fig. Below) is situated inside a region of uniform magnetic fk 66em5gc xwa-ield of 0.550 T. The total resistance of the loop is $\mathrm{0.230~Ω}$ Calculate the force required to pull the loop from the field (to the right) at a constant velocity of 3.40m/s Neglect gravity.    N

  A 500-turn solenoid, 2a *gjz 21o 7 +e5hzkkiidsk*v0i pp2s15 cm long, has a diameter of 2.5 cm. A 10-turn coil is wound tightly around the center of the solenoid. If the current in the solenoid increases uniformly from 0 to 5.0 A in 0.60 s, what will be the induced emf in the short 21v0 d *iiah7spsk 2zjog kke+i 5p*z1coil during this time?    $ \times10^{-4 }\;V$

  In (Fig. Below), the rod p.kw7*:zidc ; e3gu(xr zm4gg moves with a speed of 1.6m/s is 30.0 cm long, and has a resistance okz( e.ggx 4wgmud*pc;37 : rzif $\mathrm{2.5~Ω}$ The magnetic field is 0.35 T, and the resistance of the U-shaped conductor is $\mathrm{25.0~Ω}$ at a given instant. Calculate
(a) the induced emf, $\varepsilon$ $\approx$    V(retain two decimal places)
(b) the current in the U-shaped conductor, $I\approx$    $ \times10^{-3 }\;A$ (retain one decimal places)
(c) the external force needed to keep the rod’s velocity constant at that instant. $F\approx$    $ \times10^{- 4}\;N$ (retain one decimal places)

  A 22.0-cm-diameter coil cons y 7:wkryuro lg;,+ nr4tym)q*ists of 20 turns of circular copper wire 2.6 mm in diameter. A uniform magnetic field, perpendicular to tg)nrtlwmo;,:7r *kyu+y y qr4 he plane of the coil, changes at a rate of $8.65\times10^{-3}\mathrm{~T/s}.$ Determine
(a) the current in the loop, $|\varepsilon|$ $\approx$    A (retain two decimal places)
(b) the rate at which thermal energy is produced.    $ \times10^{-4 }\;W$

  The magnetic field perpendicular to a single 13.2-cm-diametgw0 ugqj7 u.q*er circular loop of copper wire decreases uniformly from 0.750 T to zero. If the wire is 2.25 mm in diameter, how much charge moves past a point in the coiuwg.q uqg0j 7*l during this operation?    C

  A simple generator is used to generate a peak outkgv x.9c;uwk+ put voltage of 24.0 V. The square armature consists of windings that are 6.0 cm on a side and rotates in a field of 0.420 T at a rate of 60.0rev/s How many loops of wire should be wound on the squwg9 uc+x.kkv; are armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idling at 1100 rpm p u,c/ 9,ymtaffroduces 12.4 V. What will the ou tput be at a rotation speed of 2500 rpm, assuming no,fauty f, /c9mthing else changes?    V

Show that the rms output (2gtn 70e l39awd1dxqz Section 18–7) of an ac generator is $V_\mathrm{rms}=NAB\omega/\sqrt{2}$, where $\omega=2\pi f.$

  A simple generator has a 320-loop square coiq+)zivy-t a1h jj31o zl 21.0 cm on a side. How fast must it tura3oyj)q +tzj-v11z ih n in a 0.650-T field to produce a 120-V peak output? $f$   rev/s

  A 450-loop circular arma tnpm, h/s;0fgture coil with a diameter of 8.0 cm rotates at 120rev/s ;/ gp,0nh mfstin a uniform magnetic field of strength 0.55 T.
(a) What is the rms voltage output of the generator? $\approx$    V (Round to the nearest integer)
(b) What would you do to the rotation frequency in order to double the rms voltage output?  ----待选择----oncedoubletriple  the rotation frequency

  A generator rotates at 85 Hz in a magnetic field of 0.030 Te0 ym 0-qn;6u*qu:t (yerqeulg5rsp). It has 1000 turns and produces an rms voltage of 150 V and an rms current of 7sygrtm6 (*0 -q;nul5ueyp e qe0r:qu) 0.0 A.
(a) What is the peak current produced?    V
(b) What is the area of each turn of the coil?    $ \times10^{-2 }\;m^2$

  A motor has an armature resistance wwimplf*))zcz8zwm0 * 4i 3o tof $3.25\Omega.$ If it draws 8.20 A when running at full speed and connected to a 120-V line, how large is the back emf?    V

  The back emf in a motor is 72 V when operad67pl3s-qnr: vh t. jv51hncuting at 1800 rpm. What would be the back emf at 2500 rpm if the magnetic field i cvhrp5sjl1. hn-tdv6u :nq73s unchanged?    V

  The back emf in a motor is 95 V when the motor is operating at 1000 rpm. Howa)y9ry5mu xu 3 would you change the motor’s magnetic field if you wanted to reduce the back emf to 65 V when y9y rm3x a5uu)the motor was running at 2500 rpm? reduce the magnetic field to    % of its original value

  What will be the currentccc6gsgy 40(u .m*q0bx 1jmg z in the motor of Example 21–9 if the load causes it to run at half speed? g 4c00j6* mmg1cx ugyc(qb.sz    A

  A transformer is designed to change 120 V into 10,000 V, and there are 164 turnsu *x iwg5ni(-k in theukn- iwx*5(gi primary coil. How many turns are in the secondary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V ,e .zbfp6yno7to 120 V. What is the current in the secondz67n bep. oy,fary coil as compared to the primary coil?   

  Neon signs require 12 kV for df8.i ad:o,,nckl/5-x ojso x their operation. To operate from a 240-V line, what must be the ratio of secondary tooo-/cdx,, 8nsok.d:ila x j5 f primary turns of the transformer? What would the voltage output be if the transformer were connected backward?
$\frac{N_\mathrm{s}}{N_\mathrm{p}}$ =   
$V_s$ =    V

  A model-train transformer plugs into 120-V ac and draws 0.35 A while supplying(k5aujf;nz tq g*;qau;w ib+ 4 7.5 A kb4*a;iwg5a ut;(n;+ zuqqf jto the train.
(a) What voltage is present across the tracks?    V
(b) Is the transformer step-up or step-down? this is a  ----待选择----step-downstep-up  transformer

  The output voltage of a 95-W transformer is 12 V, and the input current id, jjp4ws:*vhrsb (n3 s 22 A. nwv 4j:dhs,p j3r(sb*
(a) Is this a step-up or a step-down transformer? this is a  ----待选择----step-downstep-up  transformer
(b) By what factor is the voltage multiplied? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ =   

  A transformer has 330 primary turns and 1340 secondary turns. The inp5vgqa8 hr:2 ycut voltage is 120 V and the output current is 15.0 A. What are the outpu:car85hv qgy2 t voltage and input current? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ =    V
$\frac{I_\mathrm{s}}{I_\mathrm{p}}$ =    A

  If 30 MW of power at 45 kV (rms) arrives at a town from a.,yecp ) o+zyi generator via $\mathrm{4.0-Ω}$ transmission lines, calculate
(a) the emf at the generator end of the lines, $\varepsilon$    V
(b) the fraction of the power generated that is wasted in the lines. fraction wasted   

  65 kW is to arrive at a+mhguwel2pr;s sdtjp h /3,77 town over two $0.100-\Omega$ lines. Estimate how much power is saved if the voltage is stepped up from 120 V to 1200 V and then down again, rather than simply transmitting at 120 V. Assume the transformers are each 99% efficient.    kW

  If the current in a 180-mH coil changes steadily from 25.0 3v sfi fn(2p7bx(uezg)xb7 2gA to 10.0 A in 350 ms, what is thfze3x( 2s(nbb)g7 2vixf7ugpe magnitude of the induced emf?    V

  What is the inductance offdp ; q)g//.q2bih8ejov q7ef a coil if the coil produces an emf of 2.50 V when the current in it chp)f; q2 v7/.bq /g h8ojdqeefianges from -28.0mA to +31.0mA in 12.0 ms?    H

  What is the inductance L of a 0.60-m-long air-f v-5(p 6 1s3yoaopvn-vdv+pciilled coil 2.9 cm in diameter containing 105psvpdcoo 3-iv +(p 6nv1a-yv,000 loops?    H

  How many turns of wire would be required to make a 130-mH inductanceyhn/e43 /e ien out of a 30.0-cm-long air-filled coil with a diameter of 5.2iye4 3/ehen n/ cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800s3) oolw89kwp turns, and it is 2.5 cm in diameter and 28.2 )8poo9 3 swlkwcm long.
(a) What is its inductance?    $ \times10^{-2 }\;H$
(b) How many turns would you need to generate the same inductance if the core were iron-filled instead? Assume the magnetic permeability of iron is about 1200 times that of free space.

  A coil has $2.25-\Omega$ resistance and 440-mH inductance. If the current is 3.00 A and is increasing at a rate of 3.50A/s what is the potential difference across the coil at this moment?    V

A long thin solenoid ohoi+b17 yykvf)vh - uak3/8scf length l and cross-sectional area A contains $N_1$ closely packed turns of wire. Wrapped tightly around it is an insulated coil of $N_2$ turns, (Fig. Below). Assume all the flux from coil 1 (the solenoid) passes through coil 2, and calculate the mutual inductance.

  The wire of a tightly wound solenoid is unwound an/ f;yx.76lfrm,x abea:r bl.n d used to make another tightly wound solenoid of twice the diam:n/7ybl6 la. brf e,.fmrx;axeter. By what factor does the inductance change?   

  The magnetic field inside an air-filled solenoid 36 czl8l574bx x d+. d wcfeb6rq5bm long and 2.0 cm in diameter is 0.80 T. Approximately how much energy is st w8+5r.bbd lefbx dx645zlc7qored in this field?    J

  At a given instant the current through an inducte1)z pzgvtooj l)(p 0*or is 50.0 mA and is increasing at the rate of 115mA/s 0je z)g z*1(loppvot). What is the initial energy stored in the inductor if the inductance is known to be 60.0 mH, and how long does it take for the energy to increase by a factor of 10 from the initial value?
U =    $ \times10^{-5}\;J$
$\Delta$t=    s

  Assuming the Earth’s ma+sj2fg x 9rg9a7sx/tf3 dvkhy+bfm0,;6j vy bgnetic field averages about $0.50\times10^{-4}\mathrm{~T}$ near the surface of the Earth, estimate the total energy stored in this field in the first 10 km above the Earth’s surface.    $ \times10^{15 }\;J$

Determine $\Delta I/\Delta t$ at t = 0 (when the battery is connected) for the LR circuit of (Fig. Below) and show that if I continued to increase at this rate, it would reach its maximum value in one time constant.

  After how many time co- gbn j,7lnm)enstants does the current in (Fig. Below) reach within
(a) 10%,    $\tau$
(b) 1.0%,    $\tau$
(c) 0.1% of its maximum value?    $\tau$

  Two tightly wound solenoids have the same length and circulaq ,g cqoidn m+99rm)5er cross-sectional area. But soled+ o5 nqgi)emcr,99 qmnoid 1 uses wire that is half as thick as solenoid 2.
(a) What is the ratio of their inductances? $\frac{L_1}{L_2}$ =   
(b) What is the ratio of their inductive time constants (assuming no other resistance in the circuits)? $\frac{\tau_1}{\tau_2}$ =   

  What is the reactance of ) e6gsld)kf x:a $7.20-\mu F$ capacitor at a frequency of
(a) 60.0 Hz,    $\Omega$
(b) 1.00 MHz?    $ \times10^{ -2}\;\Omega$

  At what frequency will a 22.0-mH inductor have a luwd b2a)41.zwf fc88l p35zanp-sps reactance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will x* ( wrbjim)sof -)qa:h;jrs/ a $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the rea;jlyk2 p/rc5seb- j7e ctance of a $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance o jp1a -i0gp0 fuwqf09jwrul+9f a 1.0-mH inductor as a function of frequency from 100 tuqi0fa0 r9l1j -09 p wwpjfug+o 10,000 Hz.

  Calculate the reactanc+lg;tki0fz 3c e of, and rms current in, a 160-mH radio coil connected to a 240-V (r3l0z;icft+k g ms) 10.0-kHz ac line. Ignore resistance.
$X_L$ =    $\Omega$
V =    $ \times10^{-2 }\;A$

  An inductance coil operates at 240 V and 60.0 Hz. It draws 12.8 A. 6o20 g4;g( y0li/qcderhbm rsWhat is the coil’s inductl6 s(2rgh doc0q;0 4m b/yrgeiance? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactajzop hk4,+c2 udpg e96nce of a well-insulated $0.030-\mu F$ capacitor connected to a 2.0-kV (rms) 720-Hz line?    $\Omega$
(b) What will be the peak value of the current?    A

  $\mathrm{A~30-k}\Omega$resistor is in series with a 45-mH inductor and an ac source. Calculate the impedance of the circuit if the source frequency is
(a) 50 Hz,    $ \times10^{4 }\;\Omega$
(b) $3.0\times10^4\mathrm{~Hz}.$    $ \times10^{4 }\;\Omega$

  $\mathrm{A~3.5-k}\Omega$ resistor and a $4.0-\mu F$ capacitor are connected in series to an ac source. Calculate the impedance of the circuit if the source frequency is
(a) 60 Hz,    $ \times10^{3 }\;\Omega$
(b) 60,000 Hz.    $ \times10^{3 }\;\Omega$

  For a 120-V rms 60-Hz voltage, an rms current ofs+ws- zvm.g3bt k0/24 qtrsuk 70 mA passing through the human body for 1sk+0wb zu.srtk-t vsg/m 34q2.0 s could be lethal. What must be the impedance of the body for this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance of a coil if its impedance is w qv -+8d3m0e(h5afg3x gcvwv $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, and rn/rvb -5/ 8 sb2eepozhms current in an LRC circuit connected to ao/bs5 - p8brzveh2/ne 10.0-kHz, 725-V (rms) source if $L=22.0\mathrm{~mH},R=8.70\mathrm{~k}\Omega,$ and
Z $\approx$    k$\Omega$
$\phi$ =    $^{\circ}\,$
$I_{rms}$ =    $ \times10^{ -2}\;A$

  A resistor in series with a 420-mH inductor is drivg-vmn tat6jic, 71ur;en by an ac power supply. At what frequency is the impedance dourig-17v ; nuca,6mttjble that of the impedance at 60 Hz?    Hz

  (a) What is the rms current in an RL circuitoomy ,i,,g k0d when a 60.0-Hz 120-V rms ac voltage is appli0 gmdyo,,i ko,ed, where $R=1.80\mathrm{~k}\Omega,$ and $L=350\mathrm{~mH}?$    $ \times10^{ -2}\;A$
(b) What is the phase angle between voltage and current?    $^{\circ}\,$
(c) What are the rms voltage readings across R and L?
$V_{rms \,R}$ $\approx$    V (Round to the nearest integer)
$V_{rms\,L}$ =    V

  (a) What is the rms current in an RC circui3yhc :ccfy j+e71-a tbt if $R=8.80\mathrm{k}\Omega,C=1.80\mu\mathrm{F},$ and the rms applied voltage is 120 V at 60.0 Hz?    $ \times10^{-2}\;A$
(b) What is the phase angle between voltage and current? $\phi$ =    $^{\circ}\,$
(c) What are the voltmeter readings across R and C?
$V_{rms\,R}$   V
$V_{rms\,C}$    V

  A 3500-pF capacitor is connected n qg-g u4rmf5d .ifhvct39p*( to a $55.0-\mu H$ coil of resistance $3.00\Omega.$ What is the resonant frequency of this circuit?    $ \times10^{5 }\;Hz$

  The variable capacitor in the tuner of an AM radio has a capac 5saocg+-sbevj 6 ;x2k0u i.xvitance of 2800 pF when the radio is tu26s +e0vks- bo.xu5cvj a;xigned to a station at 580 kHz.
(a) What must be the capacitance for a station at 1600 kHz? $C_{1600\mathrm{~kHz}}$ $\approx$    pF(Round to the nearest integer)
(b) What is the inductance (assumed constant)?    $ \times10^{ -5}\;H$

  An LRC circuit has L =o5iz0z emwb7 . 14.8 mH and $R=4.40\Omega$.
(a) What value must C have to produce resonance at 3600 Hz?    $ \times10^{ -7}\;F$
(b) What will be the maximum current at resonance if the peak external voltage is 150 V?    A

  Suppose you are looking at two currei9btdco. ssh(t( u2o ,-ip m5jnt loops in the plane of the page as shown in (Fiotm( di sj ,pbu9(s5-i2hct. og. Below). When switch S is thrown in the left-hand coil,
(a) what is the direction of the induced current in the other loop?  ----待选择----counterclockwiseclockwise 
(b) What is the situation after a “long” time?
(c) What is the direction of the induced current in the right-hand loop if that loop is quickly pulled horizontally to the right?  ----待选择----counterclockwiseclockwise 

  A square loop 24.0 cm on a tpq -7 ngytsu+y3p hy/g;;l,wside has a resistance of $5.20\Omega.$It is initially in a 0.665-T magnetic field, with its plane perpendicular to $\vec{\mathbf{B}},$ but is removed from the field in 40.0 ms. Calculate the electric energy dissipated in this process.    $ \times10^{-3 }\;J$

  A high-intensity desk lamp is ratem*f-0ga gx ,h:af )blsd at 45 W but requires only 12 V. It contains a transformer that converts 120-V household volts)xgalf0hfm*,:g a-bage.
(a) Is the transformer step-up or step-down? this is a  ----待选择----step-downstep-up  transformer
(b) What is the current in the secondary coil when the lamp is on?    A
(c) What is the current in the primary coil?    A
(d) What is the resistance of the bulb when on?    $\Omega$

  Power is generated at + w3-l ( g,h*)w,gqrdkpljuic 24 kV at a generating plant located 118 km from a town that requires 50 MW of power at 12 kV. Two transmission lines from the plant to the town each have a resistalwp+*g ij3u-(hc,qrdlg)k,wnce of $0.10\mathrm{~}\Omega/\mathrm{km~}.$ What should the output voltage of the transformer at the generating plant be for an overall transmission efficiency of 98.5%, assuming a perfect transformer? V $\approx$    kV

  The primary windings of a transformer which has an 80% efficiency are connected4j)q qa -z8du .f;bw,nxrolxi3y;k j. to 110-V ac. The secondary windings are connected acrx.jq84nkrw fu)aobiy; ,z;j3 q d.l-x oss a $2.4-\Omega$ 75-W lightbulb.
(a) Calculate the current through the primary windings of the transformer. $P_S$ $\approx$   A
(b) Calculate the ratio of the number of primary windings of the transformer to the number of secondary windings of the transformer. $\frac{N_\mathrm{p}}{N_\mathrm{s}}$   

  A pair of power transmission lines each hav)bi) cd4ty-pce a $0.80-\Omega$ resistance and carry 740 A over 9.0 km. If the rms input voltage is 42 kV, calculate
(a) the voltage at the other end, $\approx$    kV
(b) the power input, $\approx$    $ \times10^{7 }\;W$
(c) power loss in the lines, $\approx$   $ \times10^{5 }\;$W
(d) the power output. $P_{out}$ $\approx$    $ \times10^{7 }\;W$

  Two resistanceless rails rest 32 cm apart o 2. evhifd+q iia*y)f*n a 6.0$^{\circ}\,$ ramp. They are joined at the bottom by a $0.60-\Omega$ resistor, and at the top by a copper bar of mass 0.040 kg (ignore its resistance) is laid across the rails. The whole apparatus is immersed in a vertical 0.55-T field. What is the terminal (steady) velocity of the bar as it slides frictionlessly down the rails? v =    m/s

Show that the power loss in transmission lines,k0p-tv vf4 ;jd j(2rn :eu6ere $R_L$ is given by $P_{\mathrm{L}}=\left(P_{\mathrm{T}}\right)^{2}R_{\mathrm{L}}/V^{2},$ where $P_T$ is the power transmitted to the user, V is the delivered voltage, and $R_L$ is the resistance of the power lines.

  A coil with 150 turns, a radius of6 ux.mw,vgo)g gv;,sa tkb41 y 5.0 cm, and a resistance of $\mathrm{12~Ω}$ surrounds a solenoid with $230\mathrm{~turns/cm}$ and a radius of 4.5 cm; see (Fig. Below). The current in the solenoid changes at a constant rate from 0 to 2.0 A in 0.10 s. Calculate the magnitude and direction of the induced current in the coil.
I =    $ \times10^{-2 }\;A$
 ----待选择----left to rightright to left 

  A certain electronic device needs to be protected against suddeg,3siud/l;tt par/h+a ga d35 n surges in current 3gt3ga 5 sau+,p;d l/hdria/t. In particular, after the power is turned on the current should rise no more than 7.5 mA in the first $120\mu s$ The device has resistance $\mathrm{150~Ω}$ and is designed to operate at 55 mA. How would you protect this device? L $\approx$    in series(retain two decimal places)

  A 25-turn 12.5-cm-diameter coil is placed between the pole pieces of an electrohp w.z8/ -ymuzxv5 m*jmagnet.pmyjhmwu /vzz-*5 8. x When the magnet is turned on, the flux through the coil changes, inducing an emf. At what rate (in T/s) must the field produced by the magnet change if the emf is to be 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltage of a- gtsddv )8bq; simple generator whose square armature windings are 6.60 cm on a side; the )s8 ;t- bdqvdgarmature contains 155 loops and rotates in a field of 0.200 T at a rate of 120rev/s. $\varepsilon_{peak}$ =    V

  Typical large values for electric and d+q 7;(a sk sjxg1 a)tnvf37brmagnetic fields attained in laboratories aref skgxq)t n1abv7 ;+3jd (sa7r about $1.0\times10^4\mathrm{~V/m}$ and 2.0 T.
(a) Determine the energy density for each field and compare.
$u_E$ $\approx$    $ \times10^{-4 }\;J/m^3$
$u_B$ $\approx$    $ \times10^{6 }\;J/m^3$
$\frac{u_B}{u_E}$ =   $ \times10^{9 }\;$
(b) What magnitude electric field would be needed to produce the same energy density as the 2.0-T magnetic field?    $ \times10^{8 }\;V/m$

  What is the inductance L of the primary of a transformer ,n;8eax (ske xwhose input is 220 V at 60.0 Hz if the current drawn is 5.8 A? Assume no current in the secondk e(axse8;n, xary.    H

  A 130-mH coil whose resistanc9:tx/lrgk 8tcc.kxc4;ug i9 ne is $\mathrm{18.5~Ω}$ is connected to a capacitor C and a 1360-Hz source voltage. If the current and voltage are to be in phase, what value must C have?    $ \times10^{-7 }\;F$

  An inductance coil draws 2.5-A dc w-54+uxsw ;qu zyureb6hen connected to a 36-V battery. When connected to a 60-Hz 120-V (rms) source, the current drawn is 3.8 A (rms). Determine the inductance and resist+u64 wxb ru;sqe-yu 5zance of the coil.
$V_{dc}$ $\approx$    $\Omega$
L $\approx$   $ \times10^{-2 }\;H$

  A 135-mH inductor wihd;.ce- qhlc q9(jv k4th $2.0-\Omega$ resistance is connected in series to a $20-\mu\mathrm{F}$ capacitor and a 60-Hz, 45-V source. Calculate
(a) the rms current, $I_{rms}$ =    A
(b) the phase angle. $\phi$ =    $^{\circ}\,$

  The Q factor of a resonance circuit can be defined asdokn avj4*qo k3pt02n5 r 9g+c the ratio of the voltage across thn +ackktqv95d opn42g oj* r30e capacitor (or inductor) to the voltage across the resistor, at resonance. The larger the Q factor, the sharper the resonance curve will be and the sharper the tuning.
(a) Show that the Q factor is given by the equation $Q=(1/R)\sqrt{L/C}.$
(b) At a resonant frequency $f_0=1.0\mathrm{~MHz},$ what must be the values of L and R to produce a Q factor of 550? Assume that $C=0.010\mu\mathrm{F}.$ L $\approx$    $ \times10^{-6 }\;H$(retain one decimal places) Q =    $ \times10^{-2 }\;\Omega$