What would be the advantagw*biun* *c+yj e, in Faraday’s experiments (Fig. Below), of using coilswnb*cju +*iy* with many turns?

What is the difference between magnetic flux and maq+:(/ uu obf hvol5:apgnetic field?

Suppose you are holding a circular ring of wire and suddenly thrust aex m78zue*9v dx3o- pr magnet, south pole first, away from you t* dxuo9 7v83mrz-exepoward 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 moving in the viciniq. rbjlic0d( nn*8mh:ty of a very long straight wire carrying a steady current as shown in (Fig. Below). Find the direction of j r0:n*.(8lndq bmi chthe induced current in each loop.

Suppose you are looking along a line through the centers ofav 7 m-t9ug9w/8eqwja two circular (but separate) wire loops, one behind the other. A ba8/taqvmea 9uwj -w 97gttery 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 of the it8t.xe ht ) 10z0ntrkfnduced 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 muksf e 7 /v 4e+(6vc45byujrmkest travel over a distance, a “shielded cable” is used in which the signal wire is surrounded by an insulator and thuk/e fvc6 4k+seym5je 7b4v(ren enclosed by a cylindrical conductor carrying the return current. Why is a “shield” necessary?

What is the advantage of placing thidys khznhl 05f;; ,6r,* uetee two insulated electric wires carrying ac close together or even twi;ihz,5 k*u,rftdh0y;e nl6 s ested about each other?

Explain why, exactly, the lights may dim6yzwqmuj:;1 7od o y2pd(cm+a briefly when a refrigerator motor starts up. When an electric heater is turned on, the lights my (;q cd+amdu 7w:26o1jzoy pmay stay dimmed as long as the heater is on. Explain the difference.

Use (Fig. Below a) and (Fig. Below b) plus the righm6r b0 n)mtjj9oprrubxc+(/,(vin,f t-hand rules to show why the counter torque in a generator or f)mnu/ri cm06b +( ,xnjp,or(bt9jvpposes the motion.
a
b

Will an eddy current brake (Fig. Below) work on a copper oq)n m. 4o3d8o5xeowcgr aluminum wheel, or must the wheel be ferromcwed)xn3 5gooo8m. q 4agnetic? Explain.

It has been proposed that eddy currents be used to help sort solid wastqylehe i:,,,r e 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 o e,qhylr, ei,:ver 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 thfllu dm,e7r0r 0pr7o1rough a magnetic 7rlr0d0 e7r m,lp1uof field than does a solid bar. Explain.

If an aluminum sheet is held between the poles of a large bar magnet, it requirbh( wmvd5:n ulpy0xmuf8u+c;+u 7:oj es some force to pull it out of the magnetic field even though the sheet is not ferromagnetic and does not touch the polcb:pfj+7+lxh (0u uw:uyovmd n; 58um e faces. Explain.

A bar magnet falling inside a vertical metal tube reaches a terminal velocq)tfz 4-dci;x3qobf ) ity even if the tube is evacuated so that therxfb)t)zq cdq f; -4oi3e is no air resistance. Explain.

A metal bar, pivoted at one end, oscillates freely in t xcu d4jpk)c7 +ce4du+he absence of a magnetic field; but in a magn 4dc+)u7upcdex+ k4 jcetic field, its oscillations are quickly damped out. Explain. (This magnetic damping is used in a number of practical devices.)

An enclosed transformer has four wire leads coming from ghg9f.ho u-) bs.-gh hit. How could you determine the fu ggbh -h o).sg-9h.hratio of turns on the two coils without taking the 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 — woule)7 0npjtcpdul ..tb+ d reduce e .lj+tp7tdnp u)ceb0 .nergy waste. Why are they not used?

A transformer designed for a 120v 9 w6m0m-gjev-V ac input will often “burn out” if connected to a 120-V dc source. Explain. [Hinmj09m v6g -evwt: The resistance of the primary coil is usually very low.]

How would you arrange two flat circular coils socn *vc6/4x.t(p + nuoizsunrl62qvk8 that their mutual inductance was.i+6p tk8nvq(u2lnoz6c /u scnx4vr*
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery ino73 ( ht.vnzqi (Fig. Below) affect the time needed for the LR circq3.z7nh(vi ot uit to reach
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can a x4*vm oif yn./3ts/kthe rms 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 t)- biqr( xztvtalh6x tj5)) d4he frequency 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 cil,eb v-( azu*wh;7 mex8v qz;ircuit a minimum.

  The magnetic flux through a coil of wire containing two loops changes from)4 d y6v3uhimv -50Wb to +38 Wb in 0.42 s. What is the emf induced in the coilyh vu i4dmv63)?    V

  The rectangular loop shown in (Fig. Below) is pushedd.hpgqv; *t2 t into the magnetic field which vg *d2t.h;ptqpoints inward. In what direction is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fig. Below) is being inserted into the co;k,oo0 wksz7e il. In whic7 oez,; o0skwkh direction is the 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 wire is in a 1.10-T magnetic fieleh 2y k:*6n(ktppa6gg d. The loop is re*62 g :gh(kna6ppyetkmoved from the field in 0.15 s. What is the average induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is initially oriented perpeylh9ju5a5r9iq s ):cm bri e5+ndicular 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 i:99r y)j ua rh5le5i+mc s5qibs the average induced emf in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wire coil is initially oriented so that i49h9 y0qh1 dyl)vubjkts plane is perpendicular to a magnetic field of 0.63 T poin h9yj4)9 b 1lvhudk0qyting 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*z g4h3i6 qz7s(etikv 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 k3m.b6of.mef*db* a)v7b .j m6vc uuxof the resistor in (Fig. Below) is slowly increased, what is the direction of the current induced in the small circular loop inside the lar.vmuv.kbf.xjdc3fe* 6)* 7 aumb omb6 ger 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 induced current in the circular loop duwc :r9nxx,z0de to the current shown in each part of ,rdx n0w:z9cx (Fig. 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 being pulled away from the loop shown, io7 uhw 9e p,3qij*qfjo dsr,4d2;du)gn what direction is theq,d dqgofw*e9 o27jpu;)h si u3dj,4r induced current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to a circular wire loop 12.0 cm in diwys( .0 nf4ekwameter is changed from +0.52T to -0.45 T in 180 ms, where means the field points away from an observer ysw e04nf(kw . 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 a h+5pck3enzn 4,cnk05)hdqlof 15.0cm/s If the magnetic fild4nkhneh,5q0+5c n) zpa3 kceld 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 m4rvxh;t; ktu bv+zi1. agnetic field pointing into the px1tk;u zr; 4+ vhit.bvaper. If the loop’s diameter 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 13c2amleo(x47emfx6 j3.2 cm long and generates an emf of 120 mV while moving in a 0.90-T magneti xjco6 2me4 elam37(xfc 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 wirii,(9eux 92:ip f ukthe with dimensions shown in (Fig. Below) is situated inside a region of uniform magnetic field of 0.550 T.k(it,uhip :u9ef 9 i2x 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, 25 cm long, has a diameter of 2.5 cm. A 1iu:m+yylznr pj* w5u3*4xjfe10b6v n0-turn coil is wounip6yuzm:*nju 5 +f 0nwy*v xe 3l4brj1d 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 coil during this time?    $ \times10^{-4 }\;V$

  In (Fig. Below), the rod moves with a speed of 1.6m/s ish:9j4lg iwt y. 30.0 cm long, and has a resistance of wylti4hj.g 9:$\mathrm{2.5~Ω}$ 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 consist:e4j-bdu*wn ro(t9yk s of 20 turns of circular copper wire 2.6 mm in diameter. A uniform magnetic field, perpendicular to :r*(t kn -deuy49b jowthe 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-jeik*p+(ibhx ,zg3l85+( xq ) crxjnicm-diameter circular loop of co)3rx5* xjg bxih l8i( (, np+ckj+qizepper 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 coil during this operation?    C

  A simple generator is used to generate a peak output voltage of 24.0 zb6b0 3d dyfkp-ah-9 hV. The square armature consists of windings that are 6.0abyh-fzd0pbk d3 96h - 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 square armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idling at 1100 rpm produces 12.4 V. Whaxqe3)x44lqis ;f1 mr g.*sbhm+fc c)bt will the ou tput be at a rotation speed of 2500 rpm, assuming nothing else changes+m qi )4lfcs.;*f4b3gme xc1xbsr)hq?    V

Show that the rms outpu8pd8ei eyv;gn.gn(b. s ; apr)t (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 coil 21.0 cm on a side. Hovmq:rm6 p.xct oj2tu1wa:c ;8w fast must it turn in a 0.650-T field to producr c2wpu:v;8t1xc qtomaj :6m.e a 120-V peak output? $f$   rev/s

  A 450-loop circular armature co *i9 :)yw6oxujomdi. gil with a diameter of 8.0 cm rotates at 120rev/s in a uniform magney i:d )*ui9.ogo6wjxm tic 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 T. It has 1000 tu1 mb,2/zyvb1q bmc e.:4bnlx orns and produces an rms voltage of 150 V and an rms cu.z:n qebb, mmcblx/211 y4bvorrent 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 armaturouuxi-dx/j 0r y/o 9u0e 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.om3zmy8 .8dlm What would be the back emf at 2500 rpm if the magne8dy8mo.zm ml3tic field is unchanged?    V

  The back emf in a motor is 95 V when the motor is operating at 1000 rpm. )r er1vwrsc i ,h1v03jHow would you change the motor’s magneti,rvri3whe ) 1sc1j0rv c field if you wanted to reduce the back emf to 65 V when the motor was running at 2500 rpm? reduce the magnetic field to    % of its original value

  What will be the current in the motor ofin.ubyr m*7m4 Example 21–9 if the load causes it to run at half speed? mb*4nmuy7 r. i   A

  A transformer is designed to change 120 V iwf 9o dle8k5 wh::u z-cr61ksknto 10,000 V, and there are 164 turns in the primary coil. How many turns 9 6ow5 kesrh uc-1f8w:d k:kzlare 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 the current in the second8c5ev t/qr*z hary coil as compar8c re/t 5vhqz*ed to the primary coil?   

  Neon signs require 12 kV for their operation. To g3hmau8r.t h. ihn2 ojrnj(nfht 137jx/ ;v*t operate from a 240-V line, what must be the ratio of secondary t ihot2.htv7n*x1; . / h8f3g3nntr(urmahjj jo 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 n;rx ,p)nw9 v 89mxsyvko1/r s0.35 A while supplying 7.r n1rmvxk9y 8o/)ps;w,s9 xvn5 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 12 V, andd kze8x h7ya --qn,grsjzdyc4( u /)*v the input current is 22 A. y,cz -/( -ndugydq h7*x)4vjarsz8ek
(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 /d8imm.p3jn9 uku4ea j(x. ow:boy6yturns and 1340 secondary turns. The input voltage is 120 V and the output current is 15.0 A. What are the output 43i .:jnekao w myyuj.6/moux9b 8(pdvoltage 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 avx vg/+ bd- js9fb,7/qj kwb*s 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 town over*j ./manx9kbo5br8 4 dn 1pzbx 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 steaxw( i+xhv) s.vdily from 25.0 A to 10.0 A in 350 ms, what is the magnitude o+vi)w( sh.xvxf the induced emf?    V

  What is the inductance of a coxb4 ;yxw*xmvp vy su/hf76( *eil if the coil produces an emf of 2.50 V when the current e x(fp4wb7 y;uym *x/6x sh*vvin it changes from -28.0mA to +31.0mA in 12.0 ms?    H

  What is the inductance L of a 0.60-m-long air-filled coil 2.9 cm in dihyg4--g w1f ;akog6jm ameter containing 10,000 lohgf-y6k-mj4wa ;1 gog ops?    H

  How many turns of wire would be required to make a 130-mH inductwx.r j4a1 *agfance out of a 30.0-cmwr axfj*a 41.g-long air-filled coil with a diameter of 5.2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical x4tu +e/x*drxj ln8ou(y43f xinductor has 2800 turns, and it is 2.5 cm in diameter and 28.2 cm lon ex+ ld* f(4onyx8xuu4/rjt 3xg.
(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 lypa.ww -j ;md; 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 and used n-k wqmez86s ; +u+stc-nh i/:kc pa/oto make another tightly wound solenoid of twice the diameter. By kas6hqcn+e+ k8 tw ionp:u;msc-z//-what factor does the inductance change?   

  The magnetic field inside an air-filled solenoid 36 cm long and 2.080; wy97ahxxys1py cv cm in diameter is 0.80 T. Approximately how much energy is stored in this fieyy071 ;9p 8cvhwx syxald?    J

  At a given instant the current through an inductor is 50.0 mA and6yy 6w do,0fdl is increasing at the rate of 115mA/s. What is the initial energy st,f6 wd 6yy0oldored 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 magnje o550kj ; o;lad5gcxetic 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 constants does the current in 1/eo dgos 90 el;am0xf(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 circular cross-sectional dluhz yvo+ue;94 y6z-3wv4w k area. But solenoid 1 uses wire that ise4w 6oy ;uvh4l+u9y-3wz vzd k 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 reactanca1f*1p w*ydu saz-u,f e of 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- k7f7kd)e sp6pv3w6 ihmH inductor have a reactance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will 23h1sn08vz ,yhvll (cyi5chma $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactance of wj(e1u+.1u6,bc lu:vud f,six r)cf k a $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance of a 1.0-mH inductor as a function of frequenbvo z3ej, r,k;fmw;9qcy from 10ofk, r3 em;b;zjq,9vw0 to 10,000 Hz.

  Calculate the reactance of, and rms cuj hx w5flx2c3,rrent in, a 160-mH radio coil connected to a 240-V (rms) 10.0-kcjf23 xl 5h,xwHz ac line. Ignore resistance.
$X_L$ =    $\Omega$
V =    $ \times10^{-2 }\;A$

  An inductance coil operates at 240 V and 60.0 Hz. Itejp o k+ed8he9ozc0d2 1;ecm,v25c s j draws 12.8 A. What is the coil’s 2hs2c1o5me0eokd 8jped ,vc ce;zj+9 inductance? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance of a wel*ad+ s)t*jn ot9zg0-og ctsj, l-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 passingy 4k0dvy6bny 6 through the human body for 1.0 s could be lethal. What must be the imped4y6 nk b6y0dyvance of the body for this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance of a coil if its impedance xg8 ; uukkwq*a397ml,si;siwcd5qz )is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, and rms current in an LRC circ hw4hyk f(g 3x +s6qn/hgx7c4huit connwg3 /h c hskgh(fnq64y4+ xh7xected to a 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 aog vv+hhup()9s 5d)nan ac power supply. At what frequency is the impedanc5 vn) 9(hhap)dsougv+ e double that of the impedance at 60 Hz?    Hz

  (a) What is the rms current in an RL circuit when a au3)fcn amdoc 1x*pfp1(nt, ;60.0-Hz 120-V rms ac voltage is applied, where ;cn m)a,*3dcfn(1tpf op axu 1$R=1.80\mathrm{~k}\Omega,$ 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 currenxytz1(oxkk/5 t in 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 .q/emx7rk6g y is 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 capacitxc m*,dsy,*arj 0y9leor in the tuner of an AM radio has a capacitance of 2800 pF when the radio is tuned to a station at jy *c y lrxa,d*9e0sm,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 keihs2kuoec/r;0)ukv9 svu 9 +oo 1v) 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 the plane o kz i)c.)5dhqrf the page as shown in (Figqikhd.5c) zr ). 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+ 45rin +9qtv t9sh1wiy sayy*m 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 rated at 45 W but requires only 12 V. It contaee ihmrq +r9.r8 y;y7sins a transformer that converts 9r;r riyy sq87h.ee +m120-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 plant located 118 km from a tor +q,nftw09oq (ceh(n i-uo6 own that requires 50 MW of power at 12 kV. Two tranwqtqhe+ o9r(c o- 6fo(i ,nn0usmission 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 80% efficiency are coynejnt9ntmwnxx96y+r -2/ ; 1su)trd nnected to 110-V ac. The secondary w)-;m nd9rxyx6 jue1nsyt/9nwtr 2+nt indings 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 jbq ameg.q1616jh2jjdy e;s5 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 rails rest 9p5.p cj 0ala8jkw8- vvqnuv88c kzr;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 loss in ta ir 1ti,lny3/6k8.lmgg ,uswransmission 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 rad rgeb, g08 a,+/ eql),kpg-od lqc9vmzius of 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 proh 7k2mkh. g;netected against sudden surges in current. In particular, after the power is turned on the current should rise no more than 7.nk; mkg2h7h e.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 plajr vqg6nbj +m9z02o3nced 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 og 9rv+ mjbjn 0q623nzT/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 generator who od i3kcn*x;p6se square armature windings are 6.60 cm on a side; the armature contains 155 loopd *ic6po xk3;ns and rotates in a field of 0.200 T at a rate of 120rev/s. $\varepsilon_{peak}$ =    V

  Typical large values for electric and magnetic fiu9l,los15hz vujr8)m elds attained in laboratories arlju9o8,1vrmh sz u)5le 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 primas3nf 6guh htx+a6i7;wn+l z8 ary of a transformer whose input is 220 V at 60.0 Hz if the current drawn is 5+f x; i g87z6w6ln+atshu nh3a.8 A? Assume no current in the secondary.    H

  A 130-mH coil whose resistance is; ogwp ;v( f*ghil,;hr $\mathrm{18.5~Ω}$ 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 .n8ilo1sc2f5 ae lon u6j 1df(connected to a 36-V battery. When connected to a 60-Hz 120-V (rms) source, the current drawn is 3.8 A (rms). Detenl(8o.ci 5of6edf s1 j12anulrmine the inductance and resistance of the coil.
$V_{dc}$ $\approx$    $\Omega$
L $\approx$   $ \times10^{-2 }\;H$

  A 135-mH inductor with0gp k)s cxa;6)uvbk+ ah6 ue6m $2.0-\Omega$ 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 t- r 68mjfchx7mesv go j7925y,otch3rhe voltage across the capacitor (or inducto 7m6jhhv5mxej-o9c 3 gr2ry7f8 ,otcs r) 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$