What would be the advantage, in Faraday’s experiments (Fig. Belo4 cci,5toaf osj14nl ) f.zyg-w), of using coils - . igz,cyo54f fn4)jtlao cs1with many turns?

What is the difference between magnetic flux and ma7v6p. uwb ),5gee mqix(bgj:s gnetic field?

Suppose you are holding a circular ring of wire an m-exarwn5.i9d suddenly thrust a magnet, south pole first, away from you toward the 9n5 e.-mrwixacenter of the circle. Is a current induced in the wire? Is a current induced when the 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 moving in the vicinity of a very long straighi wf,ck-k3qnl:byra cvl:,fsxj-yl m3+ 20)qt wire carrying a steady current as shown in (Fig. Below). Find the direction of the inf-2k3nr xf m, :lk30b-lvq:aj)slc,ywyc q+iduced current in each loop.

Suppose you are looking along a line through tt:m3 .cjdv ay;he centers of two circular (but separavdjya; .m3:ct te) wire loops, one behind the other. A battery is suddenly 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 of6 4ws9wtptu3 cm f1er) the induced current 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 travel over a distance, a “nfx ;apzn4k;6 jg/em +shielded cable” is used in which the signal wire is surrounded by an insulator aa6n/;fn pje+4 ;xzm gknd then enclosed by a cylindrical conductor carrying the return current. Why is a “shield” necessary?

What is the advantage of placing the two inmo(gs x ;8eullku0 vp :pxz-9)sulated electric wires carrying ac close together or even twisted aboutpul; xxu: 0pl9m8v-gek)o(zs each other?

Explain why, exactly, the lights-o6yuacu)(acwn,i y* may dim briefly when a refrigerator motor starts up. When an electric heater is turned on, the lights may stay dimmed as long as the heater is oni an, 6u(awy*-y)uocc. Explain the difference.

Use (Fig. Below a) and (Fig. Below b) plus the right-hank )hhv /rh 6/9e7twfsed rules to show why the counter torque in a generator opposes thhfthh k7/ 6vsr9/)ewee motion.
a
b

Will an eddy current brake (Fig. Below) wori:i 3/vkmtt6r( v1b 19t ztgkmy.due1 k on a copper or aluminum wheel, or must the wheel be ferromagnetic? Expitegtyvm9 i( 1zt/36du1km1b. kvrt: lain.

It has been proposed thetgj0o64t 9paf 5fho )at 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. 9oafft6o 04pj he) tg5The waste then is allowed to slide down an incline over permanent magnets. How will this aid in the separation of nonferrous metals (Al, Cu, Pb, brass) from nonmetallic materials?

The pivoted metal bar with slots in (Fig. Below) falls much more quickly throughbsox frn8zh+wcl2 /8o1xq:s2 a magnetic fiex 81nq c2+zhl :rwofosxsb28/ld than does a solid bar. Explain.

If an aluminum sheet is held between the poles of a large ocp mjr 49ae.7bar magnet, it requires some jop.9rc4a7 em force to pull it out of the magnetic field even though the sheet is not ferromagnetic and does not touch the pole faces. Explain.

A bar magnet falling inside a lpvpgb2g; :x9hbh 50yvertical metal tube reaches a terminal velocity even if the tube is evacuated so that there isb5hgxbh; 0v:2y 9p pgl no air resistance. Explain.

A metal bar, pivoted at one end, oscillates free:p/mk +l57p:.l xq4nb dsyttw ly in the absence of a magnetic field; but in a magnetic field, ip:n:w. s7/+p tky4xb5 dqlmtlts oscillations are quickly damped out. Explain. (This magnetic damping is used in a number of practical devices.)

An enclosed transformer )z;zetghn. hwe5 at28 has four wire leads coming from it. How could you determine the ratio of turns on the two coils without taking the transformer apart? How woulnz2at;8gt w. 5ze)eh hd you know which wires paired with which?

The use of higher-voltage lines in homes — say, 600 V or 1200 V — woulx/ps1g*dr9do :f z6 jsd reduce energy wdsopdx s*:/g1f 69r jzaste. Why are they not used?

A transformer designed for a 12xswlx8 uf9f0 cx7 scc *jjlh16zgt);,0-V ac input will often “burn out” if connected to a 120-V dc source. zcjx;s0 7lx gjxcuf w*h),89ltc 1f6sExplain. [Hint: The resistance of the primary coil is usually very low.]

How would you arrange two flat circular coilon, df8ntl .l8s so that their mutual inductance was n8df8,no l.tl
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery in (Fig. Below) affect the time needed fsz /rifdef0w-ss2p j 4wqk:.na 2z 2g(or the LR circuit to reach if:2sz sa gdw2- /pn4( k2.qf0r wjesz
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can the rms-d38h gna3sd+o1 vdyr voltage 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 frequency of the source emf affec7,-gd0qu18g s6ymfplpt:y nzts 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 minimug, qno:ap kz3e4d.xn,m.

  The magnetic flux through a coil of wire containing two loops changes from -5003w-yn5sp jjt 7fz1a pWb to +38 Wb in 0.42 s. What is t-y3 nfpap 7 0zwsj5tj1he emf induced in the coil?    V

  The rectangular loop shown in (Fig. Below) is pushed into the magnetic fhim.aii-x o4: ield which pointsmio-iah4x i:. inward. In what direction is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of thexm;jbs /os /g1 magnet in (Fig. Below) is being inserted into the coil. In which direction is the induced j;b/x/ m so1sgcurrent 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 1.10ol j4l1)cdt;ol8b bpk;2ns k*.aoq 3o(o(puc-T magnetic field. The loop is removed from the field in 0.15 s. What is the average indukp luljo; 34noq8o;oda1pt)(b s (2 cb.lc o*kced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is initially oriented perpendicular to a :lku-b9f)*dvq / aszirzc46a1.5-T magnetic field. The loop is rotated so that its plane is parallel to the field direction in 0.20 s. What is the average induceda/d skz*v9caz )4qr-6fl bu:i emf in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wire coil is initiaq(j2- pq0dh m6lqs )sblly oriented so that its plane is perpendicular ssl2bmhq06q-dj(pq ) to a magnetic field of 0.63 T pointing up. During the course of 0.15 s, the field is changed to one of 0.25 T pointing down. What is the average induced emf in the coil?    $ \times10^{ -2}\;V $

  A 15-cm-diameter circular loop of wire is placed in a 0.50-T magnetic fiqy f-.91t plpmdi rv9+8evc,aeld.
(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 resisth6g rp cz91*tnor in (Fig. Below) is slowly increased, what is the direction of the current induced in the small circular loop insi6 zp9gh*rntc1de 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 of the indu -t+tk9yiv,9yg ekhv1 lm9xr(v)zhb(ced current in the circular loop due to the current shown in each part of (Fig. Bektre zi9tvbl x9v+ h)-gk,h( yy( mv19low)?
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. Below) is being pulled away from the l:n0 k8ubea eteik )50loop shown, in what direction is thn)aket ee5l8: 00k biue induced current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to a circular wire lrs;u3e7d3l rfz v+da0oop 12.0 cm in diameter is changed from +0.52T to -0.45 T in 180 ms, where means the field points0ude 7s3 ar3;+lrfzvd away 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. Below) is 12.0 cm long and is pulled at a speed omeoy0;a 1 apo/f 15.0cm/ p01oma;aoe y/s If the magnetic field 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 the paper lies in a 0.75-T magnetic fiel,mr)5ohw dmq4uw-6u*uz vk4uo h (n,td pointing into the paper. If the loop’s diameter changes from 20.0 cm th t un)uwu-r4 ,*q, 4mkvohzdm5(u6o wo 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)is 13.2 cm long and generates an emf of 120 b vc2fc7m.rsfro*0zmn 7 zs++ mV while mv fmr7z.m0+snr2z* cb c7 fos+oving in a 0.90-T magnetic 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 wire with dimensionxo5 (y3remi5 2lrzs;us shown in (Fig. Below) is situated inside a region of uniform magnetic field of 0.550 T. The total resistance of ; i2ouer 3(y 55sxrzmlthe 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, 25 cm long-k-lz56o;ctx kv9ep +u+e jac, 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.jxk+eoc +p -ea6-clzt;uv95k 60 s, what will be the induced emf in the short coil during this time?    $ \times10^{-4 }\;V$

  In (Fig. Below), the rod moves with a speed of 1.6m/s is 3)pj5 p0ey k,is0.0 cm long, and has a r pi0k,jyse p5)esistance of $\mathrm{2.5~Ω}$ 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 consists y5 lq(zym jr+93m)mxk of 20 turns of circular copper wire 2.6 mm in diameter. A uniform magnetic field, perpendicular to the plane of the coil, changes at a ratjm)m5 zyxk(+q y 3rm9le 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 pet *h0m7emv;yj*4t o +) mvaobjc v.b3erpendicular to a single 13.2-cm-diameter circular loop of copper wire decreases uniformly from 0.750 T to zero. I. va*boe 4 vvm*mjtc3o )hmbe0 +y;t7jf the wire is 2.25 mm in diameter, how much charge moves past a point in the coil during this operation?    C

  A simple generator is used to gener4ctafqis;g / (hko / af bu7(q.pt:z2t d,bc+tate a peak output 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 b+a:ifabc(dg k .fo t/hctqttqu 4, /s2p7z;(T at a rate of 60.0rev/s How many loops of wire should be wound on the square armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idling at 1100 rpm produces 12.4 V. What will the ou tgwqx/+v5shxn* tb vnj8*vc ,*put be at a rotation speed of 2500 rpm, assuming nbq* c w8jvv **vh/tx,sn+5xgnothing else changes?    V

Show that the rms outp .hpz:;r tm7jeut (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 320v(sfny)fv n. ez+2) 9jdji5 tz-loop square coil 21.0 cm on a side. How fast must it turn in a 0.650-T field to producj2f.nv) ft(5sdezzv9 i) +n yje a 120-V peak output? $f$   rev/s

  A 450-loop circular armature coil with a2bwc1pswj )0 t diameter of 8.0 cm rotates at 120rev/s in a uniform magnetic field of strengthpj 1)2twc0wsb 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 kv .m 2-l-6hhl begi5hmagnetic field of 0.030 T. It has 1000 turns and produces an rmsv. 2g-5 ehikhm-6 lhlb voltage of 150 V and an rms current of 70.0 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 armaturewrr(b*t,p blu:gg- .r resistance of $3.25\Omega.$ 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 operating at 1800 rpm. What would be thefa36io5+vjn b h0jx gh8))dw)bxuo (w back emf at 250jwoh ogj unvw06i)a8x )xb+ ( f3bh5d)0 rpm if the magnetic field is unchanged?    V

  The back emf in a motor is 95 V whenfivf ( 0hn/(m)j* fq,q0a vsxw the motor is operating at 1000 rpm. How would you change the motor’s magnetic field if you wanted to reduce the back emf to 65 V when the mo)fvvjf q,/n( qhswx*i00am( f tor was running at 2500 rpm? reduce the magnetic field to    % of its original value

  What will be the current in the motor of Example 21–9 if the load cau :0;z.acdy cixses it to run axz .cya;: cd0it half speed?    A

  A transformer is designed to change 120 V into 10,000 V, and theriliy+6w -l)dwe are 164 turns in the primary coil. How many6ydli -)liw w+ turns are in the secondary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 120 V. What is theily7irrx :be k e4);o: current in the secondary coil as compar:eyb iirk)7;4oel: xred to the primary coil?   

  Neon signs require 12 kV for their operation. To operate from a 240-V line,6ookiy sz0tgt h( :n2*y 3+s jii+z2bo what must be the ratio of secondary to primary turns yg+o 3i:2otijnzs2+ b (s06zhk *y oitof 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;1uth.29gbx ev x s3/s3x qtrz plugs into 120-V ac and draws 0.35 A while supplying 7.5 A to the t9;ts svh/uqxx.312x t gr3bzerain.
(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 iqo p4zdnmz:5c c*7a y*-zgh*-W transformer is 12 V, and the input current is 22 A. *a cz*o5 4pqiy hg-*mc7ndzz:
(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 primgmtl15g-wpgb k2xp yf8 d zn(f/ q.5i8ary turns and 1340 secondary turns. The input voltage is 120 V and the output current is 15.0 A.x qbli-8fw8kg1y5p5/(mz gtg dfp 2n. What are the output 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 genera dt ouvb4(if4 97f-)wih i+u*3vii hjwncoh *1tor 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 amk q88vf)q3hn-wke 66ov3js k t a 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 chang ikp)vds02v(nkq-(kb es steadily from 25.0 A to 10.0 A in 350 ms, what is the magd((k )vqkbnis2pk0 v -nitude of the induced emf?    V

  What is the inductance of a coil if the coil produces an emf of 2.uy k3p2 jj al1,- a9ye0ffrom/e5j8lu 50 V when the current in it changes from -2/2oyjr 3ef l9l0jap ue ua-8,km1f5y j8.0mA to +31.0mA in 12.0 ms?    H

  What is the inductance L of a 0.60-m-long air-filnfz ,amt : uur,w*n7izw78 l*tled coil 2.9 cm in diameter containinr utu,znm f8:7n wz *7tw*l,iag 10,000 loops?    H

  How many turns of wire would be required to make a 130h+qqa2a/6nw4, hips z -mH inductance out of a 30.0-cm-long air-filled coil h+a wzhqq,4 6ia2nsp/with a diameter of 5.2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800 turns, and it is 2.5 cm in i3l v7c9)rswvdiameter and 28.2 cm long. v3vw7i)srl9 c
(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 of length l and cross-sectional are/xxvh 1sf,.bh a 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 and used to mak,f(ri9b -/up4 v. (id izdjfcte another tightly wound sofd,rvdc9t( ii- i .z/u bj(4fplenoid of twice the diameter. By what factor does the inductance change?   

  The magnetic field inside an air-filled solenoid 36 cm long and 2.03unql19z8sy t cm in diameter is 0.80 T. Approximately how much energy is tuzlnq19 3y s8stored in this field?    J

  At a given instant the current through : o uzox,y/of-an inductor is 50.0 mA and is increasing at the rate of 115mA/s. What is the initial energz,y:xof -o /ouy 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 magnetic fielsit/ c4dkoc:t6w/ fp 0d 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 constants doesv e-j*2b,x(bn3 to jg)1:zhj:efrtv d 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 circula5 ;au9y esd8uur cross-sectional area. But solenoid 1 uses wire that is half as t; 5aye9uu 8udshick 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 oq5nvvau g2s 3/f 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-m*5dez li 5zyjpv+w 1t5H inductor have a reactance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency wildx7t2w pc0+nd l a $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactance of v +/-ejwxtw 1na $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance of a 1.0-mH inductor as a function of frequenc(-k/ufwqdudji:aq( n jo(vo5, :6 gbzy from 100 ,(g -dw(6a5vdoq uuk/zofqjj:b i :(n to 10,000 Hz.

  Calculate the reactance of, aqy1 v5kks0x ;jnd rms current in, a 160-mH radio coil connected to a 240-V (rms) 10.0-kHz ac line.kv15;s jxkyq0 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. by 78 um/ *vil vv2kq)1)eumlbWhat is the coil’s inductance? *l vum7 kyiq))28/bm1e vvlb u$X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance of a wox+x:ap 5 z1unell-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 of 70 mA passing through the humantgc a7asu)1o3 body for a)1o3u gtas7c 1.0 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 iso*qn o4bp 89dph wq82l5 nts(tk()oqf its impedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, and rms current i n( ;jic, p7)9ept,nhpdm(zdxn an LRC circuit connected to atdp;n,jp dme9( 7x(cip,hz)n 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 driven by an ac pow .wpyp;;2lbdy oft ,k6er supply. At what frequency pf.b;y2dw,l tko6; pyis the impedance double that of the impedance at 60 Hz?    Hz

  (a) What is the rms current in a0x)su8 clnos :n RL circuit when a 60.0-Hz 120-V rms ac voltage is applieduslc)x0o sn 8:, 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 circuit if xm(zwp)i;( 5vz(b psos.-fnu $R=8.80\mathrm{k}\Omega,C=1.80\mu\mathrm{F},$ 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 to gozdzx2+wuc.9d4 t8s w-5s*qgks5 fq 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 aab3j6yow3,*s + mwoy an AM radio has a capacitance of 2800 pF when the radio is tuned to a st,* os3ww3yoj+maayb 6 ation 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 = 14.uttrxea f )3n c q*u76;;tx.ab8 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 current loops in c1mxomg/ b7,7nu 6i8( ,wi-da jy ntsothe plane of the page as shown inntub7x i samc1g(oi68 ny 7,m-jo,d w/ (Fig. 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 c j7vo .zlhxls4ahr7wjr y) it:t1b:: a 9ygm*8m on a side 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 yc,gv/2nq dfy ,v* jv5pxt n)u*-)gmcrated at 45 W but requires only 12 V. It contains a trans 2 g)-qvtudv/),,m* gn*yx j5ccf pyvnformer that converts 120-V household voltage.
(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 24 kV at a generating )x7ctgx r)/ 8yxdxz j8zt4fv+plant located 118 km from a town that requires 50 MW of power at 12 kV. Two transt78vgrx4 x)z jx8/tx) yfczd+mission lines from the plant to the town each have a resistance 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 windingsv 0hzku 5)klkjqfv,nl1cm nfa,-s25 v3nf(h( of a transformer which has an 80% efficiency are connected to nk kjq32aumnf(n,zl,h v5kf5-fvl)( h s 1c0v110-V ac. The secondary windings are connected across 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 4zpmr*ji)s yws0d -7q m* o4qweach have 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 apartj7bhjkrv(q2 1 on 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 transboi( n/h0m:rf q*:xc w.xzu ntavw4vv8 :l8;r mission lines, $R_L$ 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 of 5.srl.r f;:9b su0 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 againsw szjuz0m r:e-ycz6 w1x1a8f2t sudden surges in currem1w-c:1z 6z yjsu8 ez0r2afxwnt. 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 coilmyollw3ol; m0zz yxm4n* +v97 is placed between the pole pieces of an electromagnet. When the magnet is turned on, the flux through the coil changes, inducing an emf. At what rate (in T/s) must the fi+4*9olzvo ln m7y;ml30 xyzmweld produced by the magnet change if the emf is to be 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltage of a simple generator whose squn1/ o++hel xzxare armature windings are 6.60 cm on a side; the ar xx1+h /o+lznemature 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 magneticai0yd- 3-f(khwb c6 kr85sp cs fields attained in laboratories are aboutdhb0 akcrf ck6-i 5 p83w-sy(s $1.0\times10^4\mathrm{~V/m}$ 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 whou 4 ,zl kdxyb9byp+vsj)6j*7 ase input is 220 V at 60.0 Hz if the current d,ypsazjl +)4kb9 d7vu6xb*j yrawn is 5.8 A? Assume no current in the secondary.    H

  A 130-mH coil whose mc3u i o 7edj2x.a)1ix(i7s8wffr:ip resistance 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 when connected to a 36-V batteoq j4tj(i( r6*rikw)fry. When connected to a 60-Hz 120-V (rms) source, the current drawn is 6wq4ifr(kjr jt)(io * 3.8 A (rms). Determine the inductance and resistance of the coil.
$V_{dc}$ $\approx$    $\Omega$
L $\approx$   $ \times10^{-2 }\;H$

  A 135-mH inductor with6l dyqc2k/1ay:i n2rh $2.0-\Omega$ 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 bqh m4m 6wyu1u5e defined as the ratio of the voltage across the capacitor (or inductor) to the voltage across the resistor, at resonance. The larger the Q factor, the sharper the resonance curveuhu 1my4m 65qw 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$