What would be the advantage, in Faraday’s experiments (Fig. Below), of usinfqn7 c z.vpw)-g coils wfp v)q-n7zc.with many turns?

What is the difference between magnetic flux and maxubi/ z+13 1(r xzo*m jd*uxrkgnetic field?

Suppose you are holding a ciriv- f qc30u 7.rfkqv82h d/fwbcular ring of wire and suddenly thrust a magnet, south p fu7wcbf8vq i 0d/rh.-q2kvf3ole first, away from you toward the center 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 ms;(fkylxf1jqn .b r17oving in the vicinity of a very long straight wire carrying a steady current as shown in (Fig. Below). Find the dirj lqf.1y( b;71fs knrxection of the induced current in each loop.

Suppose you are looking along a line thr8p-xp75yn4f c:g)oiyg,m rcf ough the centers of two circular (but separate) wire loops, one behind the other. A battery is suddenly connected to the front loop, establishing a cgy 7ni,8cg pxf-)4 rf:5pmycolockwise 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 curru) rl8r,hl vs+ent 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 trav8sy i/r fh:zc7el over a distance, a “shielded cable” is used in which the signal wire is surrounded by an insulator and then encloser/:iys8zch 7fd by a cylindrical conductor carrying the return current. Why is a “shield” necessary?

What is the advantagfa8 mb-k (7 zmkeb/t+ee of placing the two insulated electric wires carrying ac close together or even twis7(bmeze8-ak kt + fbm/ted about each other?

Explain why, exactly, the lights may dim briefly whe*8:kr9vqd .rp wd apb(n a refrigerator motor starts up. When an electric heater is turned on, the lights may stay dimmed as long as the heatew pa*.8vd9 ( b:rqpdkrr is on. Explain the difference.

Use (Fig. Below a) and (Fig. Below b) plus the right-hand rules to show u*qr( )ru ih7twhy the counter torque in a generator opposes the mo*u r i7uthq()rtion.
a
b

Will an eddy current brake (Fig. Below) work on a coptv*5 ze*rtsw m 2aoy60per or aluminum wheel, or must the wheel be ferromagnetic? Explair s*e0 am2zoytv*w6t5 n.

It has been proposed that eddy currents be used to help sort jwy-mm lnr s)44/ 8djk j3uwa6solid waste for recycling. The waste is first ground into tiny pie/)3uj86 -mw 4yws rjd 4nmlkajces 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, Cu, Pb, brass) from nonmetallic materials?

The pivoted metal bar with slots in (Fig. Below) falls much morek2 t,b 1os)swi0 -y.ya uxu8px quickly through a magnetic field than does a solid bar. Explainuy uo-p 8yaws b0 x2xt,s1.)ik.

If an aluminum sheet is held between the poles owqr z v+7nppby0x,m6vsib* 2 *f a large bar magnet, it requires some force to pull it out of the magnetn pmr,vwbb607pv 2y i+**q zsxic field even though the sheet is not ferromagnetic and does not touch the pole faces. Explain.

A bar magnet falling inside a i3ig6 4xqcq /fd)v;ebvertical metal tube reaches a terminal velocity even if the tube is evacuated so that there is no air resistancic;ib 3g6x)q4ef/ qdve. Explain.

A metal bar, pivoted at ohn8*w0w,td8x u2uc 3qy rr0onne end, oscillates freely in the absence of a magnetic field; but in a magnetic field, its oscillations are quickly damped out. Explain. (This magnetic damping is used in a number oh uc rynud0,wo0qr3 x8w82 tn*f practical devices.)

An enclosed transformer has four wire leadj-nq+41yeut6 v y gfb6s coming from it. How could you determine the ratio of turns on the two coils without taking ty-+eb t6n1uyfg6 jqv4he transformer apart? How would you know which wires paired with which?

The use of higher-voltage lines in homes — say, 600 V or 1200 V — would reducwy)q - htm7thqb0pc 9n-3 +fqce eneqy tqbph+-n97-)ht 0wcm 3qfcrgy waste. Why are they not used?

A transformer designed for a 120-V ac input will;5rte0 bvcbbu57, sq o often “burn out” if connected to a 120-V dc source. Explain. [Hint: The resista,q;st5bo0vr b7b u 5cence of the primary coil is usually very low.]

How would you arrange two flat circular coils so that 4ag(qfj81cw6 b o;dw4n 4pbnj their mutual inductance wasnawgw14 ( jqj d4468fobbn cp;
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the bawwv+3+q ; bry:yy 6vlhttery in (Fig. Below) affect the time needed for the LR circuit to reachyw hvy+q 3:6lb;vw r+y
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can the rms voltage acro3zb8 )rrzc/wngi 0z9nss
(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 emfs .ix r0by4a3 w:3zexx 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 minivfx tr+fn* 9akh-8/j6 e xsm(ymum.

  The magnetic flux through a coil of wire containing two loops changes f6io)cg jjui6-7l:sqg0ny i .irom -50Wb to +38 Wb in 0.42 s. What lqoi- ng7jgyii.ci) 6u0:js6is the emf induced in the coil?    V

  The rectangular loop shown in (Fig. Beow8l5hcmyi t u.;p9n sw+lm+5low) is pushed into the magnetic field which points inward. In what di5l5; im+ulhpc. s+w ytomw8n9rection is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fig. Below) is being insertedeqyq toi6.i5*(jjanp* /uv3u into the coil. In which direction is tt* iyiv3j a/o56qj(.eu qnu*phe induced current flowing through the resistor R?  ----待选择----from right to leftfrom left to right 

  A 9.6-cm-diameter circular loop of wifzlge3/y( 5 *vfh9if ure is in a 1.10-T magnetic field. The loop is removed from the field in 0.15 s. What is the averagefhf9g lvye5z(i3 u/ f* induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is initially oriented perpendi joe:d0llzh:z7+ge 8h cular to a 1.5-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 induced el:8 :hgdzeo+jzl7 0e hmf in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wire coil is initially oriented so that its plane is p,r7d3aujdvi:9 m y;7(ym;gx kg qz n8jerpendicular to a magnetic field of 0.63 T pointing up. Durug9;mam 3dyx7qd;z8 7nj v kg:j,(iy ring 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/ l jdt1q*r(t+1 duc.y r7avoe 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 resistanco 6ly.ad: yo*q88mxw ee of the resistor in (Fig. Below) is slowly increased, what is the direction of the : .ly e8*m ax6oodw8yqcurrent 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 of the izb4 -/1 . x/g34i0b.ugvctjs oqcp srgnduced current in the circular loop due to the current shown in each part of ( /j3xsupb .c ov/4g0czt1q.srb-igg 4Fig. Below)?
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 beidud:39k*2 4 hqjwrrw ( cuz0oyce; bt75;sbmfng pulled away from the loop shown, in what direction is the inmj2z;uw5c09 4 od 3by fchdr*be(uk : w7trqs;duced current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicularbetcyx mle/( )aur4kl (25p3 /; lyflx to a circular wire loop 12.0 cm in diameter is changed from +0.52T to -0.45 T in 180 ms, wheu/cbll )x4t(xy;laf3 2p(/ryml e5ke re means the field points 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 p0d :5 0wnmluslong and is pulled at a speed of 15.0cm/s If the magnsnpm 050u:w ldetic 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 0.75sbrooj x72nf x*o.9k/-T magnetic field pointing into the paper. If the loop’s diamex/2oroj 9fnkb*. os 7xter 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)is 13.2 cm long and generates an emf wj dvc-f01 scux4ye22of 120 mV while moving in a 0.0vj cys2x4 d1f2ewcu-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 dimensions shown;t)x415/g aemeoy,wgwl jft: in (Fig. Below) is situated inside a region of uniform magnetic field of 0.550 T. The total resistance ytf;wg,t e15/ w) ex :omlgja4of 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, 25 cm long, has a diameter of 2.5 cm. A 10d/ d,gw*kix ;8zij1nl-turn coil is wound tightly around the center of the solenoid. If the current in the solenoid increases uniformly f 8*, ijdk/izlwgxdn1;rom 0 to 5.0 A in 0.60 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 spee w)uk.i30q m2 mo4ehsad of 1.6m/s is 30.0 cm long, and has a rsakmihw 2m0) oeu4q3.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 of 20 turns of circular copper wire 2.hn 81/;m e0tx1+ybks2vgdnir6 mm in diameter. A uniform magnetic field, perpendicular to the plane of the co1 h 8gkdse210yirv+/b xntn;mil, 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-diamee 82)ufdpgmi ,ter circular loop of copper wire dec, 2gid)mupef8 reases 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 coil during this operation?    C

  A simple generator is used to generate a peak output voltage of 24.0 V.8fu*)xmeln1edp.w /vc ed78 d 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 60.0re /.cwfd8d7 vnelp 8* xmd1)euev/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 -nyt4m2lo7 7e yv6nuv produces 12.4 V. What will the ou tput be at a rotation sp6vyy7e-o24 ulnnm7 tveed of 2500 rpm, assuming nothing else changes?    V

Show that the rms output (Section 18–7) of an ac generator is d o ht9gymae ;14gl4xe/ +m4jv$V_\mathrm{rms}=NAB\omega/\sqrt{2}$, where $\omega=2\pi f.$

  A simple generator has a 320-loop square coil 21.0 cm on a side. How fasgc6j:p i 17edar ;zpz-t must it turn in a 0.650-T field to produce a 120-V pep ec16arzpi : j;zd7-gak output? $f$   rev/s

  A 450-loop circular armature coil with a dia1yz9sm:x xzk+ meter of 8.0 cm rotates at 120rev/s in asm9x1k+z:z y x 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.y;ulb;j,c)5q hy.sa2 ni/ clx030 T. It has 1000 turns and produces an rms voltany/x,j)5is;chq;l.y lc b u2age 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 armature resistance ofpsmkp n;( -;zj $3.25\Omega.$ 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 Vade82*gs z07sru 9uxoey g, 1rdqqx+4 when operating at 1800 rpm. What would be the back emf at 2500 rpm if the magnetic field is uncys4e, sgux09oqxrr 1 qdg z*e du7+82ahanged?    V

  The back emf in a motor is 95 V when the motor is operating * 4, rl3p a+tjhb0jc vzjcj)x1at 1000 rpm. How would you change the motor’s magnetic field if you wanted to reduce the back emf to 65 V when the motor was running at 2500 rpm? reduce the magneti v)z,jcc+j 3ra hb*41j0xptjlc field to    % of its original value

  What will be the current in the motor of Example 21–9 if the 3mqtjw1u0(oz load causes it to run at h o 0uwjq(1tm3zalf speed?    A

  A transformer is designed to change 120 V into 10,000 V, and there arn;( uqa( n+ssfe 164 turns in the primary coil. How many turns are in the second;nanf(ss q(u+ary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 89 b.xnzqkf ,k120 V. What is the current in the secondary coil as compared to the prk 9 fn,bzq.8xkimary coil?   

  Neon signs require 12 kV fo+lnzq d6y*t7sr their operation. To operate from a 240-V line, what must be the ratio of secondary to primary turnsz+sl*qdn7t6 y 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 zw6u,xmhv09w*: accwinto 120-V ac and draws 0.35 A while supplying 7.5 a:6v*wumw zwc9 hc0x, A to 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 ri)ye cq.p k*q*4 d8uq12 V, and the input current is 22 A. *i.4ukpq)eq8dqr c y*
(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. Thev2(8pmkwekiu+6 p g/x input voltage is 120 V 86upw+e( /ivg2kkmp xand the output current is 15.0 A. 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 54vmzvdl9gr v2 urcjl*qc+5+(rms) arrives at a town from a 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 townot gg:(fsoo33h uwx25 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 A to 10.0 A in 350 ms*80p0k cf43us kiit 3r(avxtm, what is the magnitus*(xcf0 at8vt k4 rkm0i33puide of the induced emf?    V

  What is the inductance of a coil if the coil produces an emf of 2.50 V wdmv:d8,vewz3b 3d r pf.naw(.hen the current in it changes from -28.0mA to +31.0mA in , mvd afev nw3dbzp(.wr3d:8.12.0 ms?    H

  What is the inductance L of a 0.60-m-long air-filled coil 2.9 cm in diameter co4 ,uzocbr +o3 /(ztxqrntaining 1z,4obz+c/q t(xr u3ro0,000 loops?    H

  How many turns of wire would be required to make a 130-mH inductance out of a 30 npai8(pmwvj*+4y .or.0-cm-long air-filled coil with a diameter of 5.p jr8a*4 .piw(movyn+2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 8o.xrpeewtc 9ik 3e)c62)y fg2800 turns, and it is 2.5 cm in diameter cre6) 3.f 9) pxtoygk2ecwei8and 28.2 cm 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 of length l and cross-sl x3jn:k3 b 5k1+*h vg1iyfnhuectional 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 and used to ma 7gv;s3gu i vg+*apo.*k1kptuke another tightly wounugu* p;aig kt+ 3*o7gv1 kvs.pd solenoid of twice the diameter. By what factor does the inductance change?   

  The magnetic field inside an 7hivo;8m;.m 5:*/yvi -p kuw(rzbk f 4fnqrmpair-filled solenoid 36 cm long and 2.0 cm in diameter is 0.80 T. Approximately how much energy iw8i v *7m4z(o.v/khp:ib r ;yp ;m-qnfrf5ukms stored in this field?    J

  At a given instant the current 3dio/rz 6*qly through an inductor is 50.0 mA and is increasing at the rate of 115mA/s. 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 enz i36lq yor*d/ergy to increase by a factor of 10 from the initial value?
U =    $ \times10^{-5}\;J$
$\Delta$t=    s

  Assuming the Earth’s magnetic jv+l 9lygv0 vtxm -9y5field 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 does the current in (Fig. Below) reach u9b b+oet2o2- g27 vrnf dzsu-within
(a) 10%,    $\tau$
(b) 1.0%,    $\tau$
(c) 0.1% of its maximum value?    $\tau$

  Two tightly wound solenoid z1d,tfdug2 hyhxyc96hxfc hh, i; 5rdei0::0s have the same length and circular cross-sectional area. But solenoid 1 uses wire thaxc,d0yzd:gr dihxth y 2:5hhfe96 0,c1uih;f t 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 iola 3rka 6n)mn 0ycdm+7zz4(p0 z/npof 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 c)ua mlrhm,2fvk5w:,i, r5 xlreactance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency wil*.4 4u sd - vfwqw;ajca*y1hbil a $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactancecu8kt1f*w i-6akyuo ,) )goieht2;f c of a $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance of a 1.fk.h 0hv ncn a)zop9*;0-mH inductor as a function of frequency fr)nfz.* ;akoncp v 9hh0om 100 to 10,000 Hz.

  Calculate the reactance of, and rms current in, a 160-mH radio coi, hi7kd1)d r2b b5vvapl connected to a 240-7 pra b)vibhk, 51v2ddV (rms) 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 dr :prmd3y/bd3 raws 12.8 A. What is the coip3d b: mr3/yrdl’s inductance? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reacxp;x1mq10wh ptance 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,9m pe let4mh +xx7y-g:g /k3sn an rms current of 70 mA passing through the human body for 1.0 s could bepnytx9xm + /m k4ge7lg3h:s- e 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 i3(jr08s7vcd/pg mdpumpedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedtu js9 bur:m+;gb w56xb.tt7u ance, phase angle, and rms current in an LRC circuit connected to a 10.0-kHz, 725-V (rms) t;s:xu5.b jb+9mugt6w7 btr usource 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 x y *(l -yf(7mzlj;icgac power supply. At what frequency is the impeda- f(l xm;z*gy7ljcyi (nce double that of the impedance at 60 Hz?    Hz

  (a) What is the rms current in ana dqw-c;/lt2 n RL circuit when a 60.0-Hz 120-V rms ac voltage is applied, wq; /-ndlt2acwhere $R=1.80\mathrm{~k}\Omega,$ 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:sq - 4ad.n1 x5+47 tlof/ulvhwakdu q an RC circuit 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 v qeq4qw 9wmkno76: ;vb 5kff*connected 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 capacitance ofpgu79-x31c(j ux+h7psv*ak m gfr ;qv 2800 pF whpghx-7v x urq;mc*v7 gp+j1f9s k3(uaen the radio is tuned 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 = 14.8 mH and n d-jj/(b*-9qdwa*uyq .dmkvns:yq;$R=4.40\Omega$.
(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 curr qrb)+6 a5hfzrent loops in the plane of the page as shown in (Fig. Below)r+)fqazh65 r b. 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 side hasq/ns1l p(iac 78lhq/,u0e3j ysaxl4n 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 rated at 45 W but requires only 12 V. It 3m5s6 *cay +dt9 xgiaucontains a trdi gs5ua 9x6+3ma*tyc ansformer 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 generatingnymke 2-u*lz) k ec*v;3/ngl n sbf4,a plant located 118 km from a town that reqa; evufbn -csl)k,n 3k gm /n4l**zey2uires 50 MW of power at 12 kV. Two transmission 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 windings of a transformer which has an 8qthr fxa 0k, wl3c27/m0% efficiency are connected to 110-V ac. The /03qt7 xchwrl 2,akf msecondary 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 transmis05xy ukg4sz wi gm;-/usion lines each 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 raiond 8zln,:5svls rest 32 cm apart 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 leq s1ks(fzgv j+79)o noss in transmission 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 5.0 cm, and a resistance oay 04ou4o xp1 nxtee8; e;mahg,vm/h+f $\mathrm{12~Ω}$ 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 prod7wy8r+f gk i: 0(zqlftected against sudden surges in current. In particular, afq:ligw0+d 8y7fzrk( fter 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 sif-b) b5vcgu8x(v*zvh i+4 ymzm4:6 rj9zdabetween the pole pieces of an electromagnet. When the magnet is turned on, the flux through the coil changes, induc5yi8s( x*+ j6z9) cd h4 zvb-rbzmfma4: uvgiving 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 simple ml.w 5 .xec+myy5n 0nigenerator whose square armature windings are 6.60 cm on a side; the armature contains 155 loops and ro.we ycxl. 5ym 5inmn+0tates in a field of 0.200 T at a rate of 120rev/s. $\varepsilon_{peak}$ =    V

  Typical large values for electric and magnetic fields ad kus( i,v+4b9zu+i++s 1a hcof* txwsttained in laboratories are( b9+xvf sth uci+os1d+saiu*, 4wz +k 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 pri 6faq0ner9a sxi56x s (o)vsiom4zk.8mary of a transformer whose input is 220 V at 60.0 Hz if the current drawn is 5.qoze )0fi ksn9oa.rxm8s4aiv5s( 66x 8 A? Assume no current in the secondary.    H

  A 130-mH coil whose resistance isp;dys:k rx1eqb uh*7; $\mathrm{18.5~Ω}$ 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 2.2r exmqd34 pksr:1 og+5-A dc when connected to a 36-V battery. When connected to a 60-Hz 120-V (rms) sopm r1r3x 4+o2kgqds:e urce, the current drawn is 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 witotj5p, lrx/e 0h $2.0-\Omega$ 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 as the ratio of th yz11frwb5tt uq6a*5f-(f3l x3zjv h p74lqrje voltage across the capacitor (or induc 6x (j *uvpw1frfq4 t qh-3zr fl7bza1yj5tl35tor) 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$