What would be the advantage, in Faraday’s experiment38 t +be.m4zw 0sswqcns (Fig. Below), of using coils with many tur nq0w8ec3w.ms+4 tzbsns?

What is the difference between magnetic fq .50ntu t8ct nfl:e:mlux and magnetic field?

Suppose you are holding a circular ringly/ fvx;l8v m:ho( i;f of wire and suddenly thrust a magnet, south pole first, away from you toward the center of the circle. Is a current induced in the wire? Is a current induced when the magnet is held steady withinv/v;:lxo iy8mhf ;f(l 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 straight wir.npzpv of+fz4cv 2ng c( l7t:0e carrying a steady current as shown in (Fig. Below). Find the directcp :tc7g v.zf 0z4v(nfp+ol 2nion of the induced current in each loop.

Suppose you are lookinglt*td2 ere3xi ,- zc/l along a line through the centers of two circular (but separate) wire loops, one behind the other. A battery is suddenly connected te cxtd3ez*, li2- rt/lo the front loop, establishing a clockwise current.
(a) Will a current be induced in the second loop?
(b) If so, when does this current start?
(c) When does it stop?
(d) In what direction is this current?
(e) Is there a force between the two loops?
(f) If so, in what direction?

  In (Fig. Below), determine the direction of the induced curmxp)) k:. du)sscxhd44s u0h/ gntgw5rent 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 “shie.hro50p /h bd ;r5mxqklded cable” is used in which the signal wire is surrounded by an insulator and then enclosed by a cylindrical conductor carrying the returnk0o b5/qm. d;h5prrhx current. Why is a “shield” necessary?

What is the advantage of placing the two insulated electric wires car65f+yy y,rapcrying ac close together or even twistc+,y prfay56yed about each other?

Explain why, exactly, the lights97ppuel;w a/b may dim briefly when a refrigerator motor starts up. When an electric heater is turned on, the lights may stay dimmed as long as thp;bp/9euw l7a e heater is on. Explain the difference.

Use (Fig. Below a) anvj ik4 7n:q)egd (Fig. Below b) plus the right-hand rules to show why the counter torque in qniv:) g k47eja generator opposes the motion.
a
b

Will an eddy current brake (Fig. Below) work on a copper or aluminum whe1rm z,s .ly4*co1)pbfobc k(gc,qg-q e 7h.tb el, or mog,sq ge.lkc7f. 4 ,1(zqhyr cmp1cb tb o*-)bust the wheel be ferromagnetic? Explain.

It has been proposed that eddy currents k+*u r9 +xkry9mnv bq/be used to help sort solid waste for recycling. The waste is first ground into tiny pieces and iron removed with a dc magnet. The waste then is allowed to sx 9brn+/quk*mk +r9yv lide 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 moreajg .jnmb+,t3a jz:) j quickly through a magnetic fieldtgj,a3n+j azm . :jjb) than does a solid bar. Explain.

If an aluminum sheet is o5cq;5- gvil03 *kijifnd k0yheld between the poles of a large bar magnet, it requires some force to pull ;g0jodk53l-* kv5icn0iqf y iit 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 vertical metal tube reaches a terminap pxy9w86d (wc8/k kbsl velocity even if the tube is evacuated sob 89k6ww xy(8cs/dpk p that there is no air resistance. Explain.

A metal bar, pivoted at one end, oschp x e 4yozsi*,n140iaillates freely in the absence of a magnetic field; but in a magnetic field, its oo4 nix eis041yz*hp,ascillations 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 it. How could y p7o+hy9fl8p5,fqz +hot3rllvi 5m(o ou determine the ratio of turns on the two coils without rp5lqohml5v(f+ 7+t89o,iolpz 3y fh taking the transformer apart? How would you know which wires paired with which?

The use of higher-voltage lines in hqbg+s qzf io-/ c )qz1w 5g/nju/va3g:omes — say, 600 V or 1200 V — would reduce energy waste. Why are t 1f/ucav qqb-jw n+//)o gsqiz3g5 :zghey not used?

A transformer designed for a 120-V ac input will often “burn oud12yurxn y)59g vgi9 at” if connected to a 120-V dc source. Explainuri5vayy9 g1gn9)x2d. [Hint: The resistance of the primary coil is usually very low.]

How would you arrange two flat circular coils so that their mbh aj8:*8oz vuutual inductance was8: u hbazjvo8*
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery in (Fig. Bq,zw9z kd10 faelow) affect the time needed for the LR circqw9d f0zaz k,1uit to reach
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can the rms voltage across zxxm 9q7-f fg: g1olioc7 a96 bsq6,kd
(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 4puesi.lq / 4ffrequency of the source emf affects the impedance of
(a) a pure resistance,
(b) a pure capacitance,
(c) a pure inductance,
(d) an LRC circuit near resonance (R small),
(e) an LRC circuit far from resonance (R small).

Describe how to make the impedance in an LRC circuit a minimqd w jzn 2yhdqssnvl.:c*-xco 36 705uum.

  The magnetic flux throug9o3 /sa.w:ekfu gs z5zh a coil of wire containing two loops changes from -50Wb to +38gsoszzfa w9u. 5e3:k/ Wb in 0.42 s. What is the emf induced in the coil?    V

  The rectangular loop shown in (Fig. Below) i0 bhc(cndjwrv5maw0 pir*1i,h,( ) gqs pushed into the magnetic field which points in0h,r inq0v mchr(c id (p j*a,ww5g)b1ward. In what direction is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the d6f zhdho5k/*6)h2 uycta; q emagnet in (Fig. Below) is being inserted into the coil. In which direction is the induced current flowicyehdfahudtk6;h) /5 6z* q2ong 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 magnb4u-tf4 r)fhi etic field. The loop is removed from the field in 0.15 s. What is the average inui4rf 4 btf)-hduced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is initially oriented perpendicular62 sl/azo,k3iw v:wum to a 1.5-T malzw vm: ask,/iuo62w3gnetic field. The loop is rotated so that its plane is parallel to the field direction in 0.20 s. What is the average induced emf in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wire coil is is.vy ox -s9q2tnitially oriented so that its plane is perpendicular to a magnetic field of 0.63 T pointing up. During the course of 0.19ossy2xvqt -. 5 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 loam1ug0ss- 0z yop of wire is placed in a 0.50-T magnetic field.
(a) When the plane of the loop is perpendicular to the field lines, what is the magnetic flux through the loop?    $ \times10^{-3 }\;Wb$
(b) The plane of the loop is rotated until it makes a 35$^{\circ}\,$ angle with the field lines. What is the angle $\theta$ in Eq. 21–1 for this situation? $\theta$ =    $^{\circ}\,$
(c) What is the magnetic flux through the loop at this angle?    $ \times10^{-3 }\;Wb$

  (a) If the resistance of the r/ oly6vqeso .+3 c+ouzesistor in (Fig. Below) is slowly increased, what ic qsu/ez36olovo ++.y s the direction of the current induced in the small circular loop inside the larger loop?  ----待选择----counterclockwiseclockwise 
(b) What would it be if the small loop were placed outside the larger one, to the left?  ----待选择----counterclockwiseclockwise 

  What is the direction of the induced current in the yo3 q2iqzlk3* circular loop due to the curr*ioq32z3 lyk qent shown in each part of (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. + gwl0* rg h5wihaas2+Below) is being pulled away from the loop shown, in what direction is ther iawggshh2l0+ a5+ w* induced current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field pdqd2nx5 w drm/a01-a derpendicular to a circular wire loop 12.0 cm in diameter is changed from +0.52T to -0.45 T in 180 ms, where means the field points away from an observer the obmd na 1qa0-/5rddxw2d server.
(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 g;1x9 yve qxh4and is pulled at a speed of 15.0cm/s If the magnetic field vx41 q;hx9gey 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 p(y47bjrl k j 4uwol)i2lane of the paper lies in a 0.75-T magnetic field pointing into the paper. If the loop’s diameter changes from 20.0 cm to 6.0 cm in 0. j4)4j2yl irwu7kl(ob 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 lm eyr*ut vjrq.8lqnm ;s+15*j ong and generates an emf of 120 mV while *ejys5r; vt nqrq .u1m*l8j+m moving 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 dimensions shown in (Fig.v gumbnp.uj2f7k+i 63 Below) is situated inside a region of uniform mbnv2j. i7fkmu6p u+g3agnetic field of 0.550 T. The total resistance of the loop is $\mathrm{0.230~Ω}$ Calculate the force required to pull the loop from the field (to the right) at a constant velocity of 3.40m/s Neglect gravity.    N

  A 500-turn solenoid, 25 cm long, has a di;i h5)ox2p,+usbrx ff ameter of 2.5 cm. A 10-turn coil is wound tightly around the center of the solenoid. If the current in the solenoid increases uniformly from 0 to 5.0 A in 0.60 s, what will be the induced emf in the short coil dxx+5 )u,2rhsofb ;p fiuring this time?    $ \times10^{-4 }\;V$

  In (Fig. Below), the rod m9 ee9vi la1vgn b08es;oves with a speed of 1.6m/s is 30.0 cm long, and has a9g v e90l1iev;ba8 sen resistance 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 r/hh ,5 v;zx8qr)suua of 20 turns of circular copper wire 2.6 mm in diameter. A uniform msx;/hr hzq58 ,)r uvauagnetic field, perpendicular to the plane of the coil, changes at a rate of $8.65\times10^{-3}\mathrm{~T/s}.$ Determine
(a) the current in the loop, $|\varepsilon|$ $\approx$    A (retain two decimal places)
(b) the rate at which thermal energy is produced.    $ \times10^{-4 }\;W$

  The magnetic field perpendicular to a single 13.2-cm-diameter circular loox f3aosk98tz/clnh +.gea1g: p of copper wire deeochl 9.x k:ngszg/a8 3ft+1acreases 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 uso58 luu :cm95;dhp ui.u27 lzdtaaf g0ed to generate 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 d.t5zg0iu f 5l8ua m uulcd2a;:ph79oT 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 9ooszv( e 2u1fat 1100 rpm produces 12.4 V. What will the ou tput be at a rotation speed of 2500 rpm, assuming nothing else chan ozvo (9us12efges?    V

Show that the rms output (Sectioayy(u t 3*gwyb9e 27mun 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. How hu( 5-rgw+sroh 2uah ;fast must it turn in a 0.650-T field to produce a 5hwu 2a+rr;u hoh(-sg 120-V peak output? $f$   rev/s

  A 450-loop circular armature coil with .tpn .-btup6,teb* vpiby(.i ;gf,hf a diameter of 8.0 cm rotates at 120rev/s in a tbe.i,y fv -(,n u btfhbtpp6p.*.g ;iuniform 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 7h7zw0 ejzj;d in a magnetic field of 0.030 T. It has 1000 turns and producesz7wh j;ej0 z7d an rms 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 armature rescwx s (by35so2istance 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 whed7k* ghfneh-y)o 1/ qv0ronb(n operating at 1800 rpm. What would be the bac*hon-dh1)qn7gvf 0o/e k(ybr k emf at 2500 rpm if the magnetic field is unchanged?    V

  The back emf in a motor is 95 V when the l2+yegc/cq0sk2j5 fv motor is operating at 1000 rpm. How would yocslk/ 0 egy5qvjc2+2 fu 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 magnetic field to    % of its original value

  What will be the current in the motor of Example 21–9 if m9qm:o q v)v(lthe load causes it to rvqvm mq)l o9(:un at half speed?    A

  A transformer is designed to change 120 V into 10,000 V, and lg1/0yn,e aubthere are 164 turns in the primary coil1 g0yau/lnb ,e. How many turns are in the secondary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 120 Vaj o/n ru7kp qnrlsmu8( 518(s. What is the current in the secondary coil ak np8 r5nl rq/8j(s7uu1 (osmas compared to the primary coil?   

  Neon signs require 12 kV s c3xj/l+7xf:ks/ a rrfor their operation. To operate from a 240-V line, what must be the ratio of secondary to primary turns of the transformer? What would the voltage output be if th xjrs3s:/kxrflc /a+7e transformer were connected backward?
$\frac{N_\mathrm{s}}{N_\mathrm{p}}$ =   
$V_s$ =    V

  A model-train transformer plugs into 120-V ac and draws 0.35 A whiptns0 i vyf+:4 ;da6hz9 ag,gyle supplying 7.5 At;yz y96ns 0:g afd,va +hgip4 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, and the input current isc /mkytr :+pru f+o1-g 22 A. ko-c ugp t1 y+mf:/r+r
(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 pri, kdff0li.q:2o43*sdodiqxv mary turns and 1340 secondary turns. The input voltage is 120 V and the output current is df qq2:d3,0 l.vdo o4xi kfs*i15.0 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 4qmq9lx05c rd,k dgn/0,ph 7 fm5 kV (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 town ov c6- pzf/0egnpp60o dder 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 s; l;1+d bmqm g-dlq1isteadily from 25.0 A to 10.0 A in 350 ms, what is the magnitude of the induced emf?bd1mgd1 q+;- ls lm;iq    V

  What is the inductance of a coil if the coil produces+bl 0shk77xo6-xjkom/vqh1 h yyp--h an emf of 2.50 V when the current in it changes from -28.0mhk- x61okxyh/o- 7hv0qlm +spj 7b -yhA 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 diameter 0ms*5a4q7onpjb 8(lracupf1 connqrcsa8ja 4 m5lo7u10(p b*pftaining 10,000 loops?    H

  How many turns of wire would b2x j:l4vzep y6h- 42xrgy6yxx e required to make a 130-mH inductance out of a 30.0-cm-long air-filled coil with a diamet eyx6-xygvlp xj24rxzhy 4 :26er of 5.2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800 turns, and it du 50u ,oeapd6is 2.5 cm in diameter and eddou6a,5 pu0 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-sectional area A zdsuw 0bj 7( d-na0idqmaz5i,n20q3 pp:3 uot 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 uj 8a)9v r/bjkp: ahx+dsed to make another tightly wound solenoid of twice the dh:b8v/r9kjadjp ax+) iameter. By what factor does the inductance change?   

  The magnetic field inside an air-fik)izu1 qqz--m gp e;ua bn.b/:lled solenoid 36 cm long and 2.0 cm in diameter is 0.80 T. Approximately how muchq-buk zeu n)a;qpi:b -mg1z/ . energy is stored in this field?    J

  At a given instant the current through an inductor is 50.0 mA and is q cj)lq+vtw/pl q94g8increasing 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 energy t9q8c/4ljq )vw tg +lpqo increase by a factor of 10 from the initial value?
U =    $ \times10^{-5}\;J$
$\Delta$t=    s

  Assuming the Earth’s magnetic field averages about l vw+)zx2cp,6(aer ty$0.50\times10^{-4}\mathrm{~T}$ 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 w 7-v kfah09vht) vzy)2u1hvzrithin
(a) 10%,    $\tau$
(b) 1.0%,    $\tau$
(c) 0.1% of its maximum value?    $\tau$

  Two tightly wound solenoids have the same length y;dvvr255rk band circular cross-sectional area. But solenoid 1 uses wire that i5 ryb 2rv;vdk5s 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 reactanc6wwd4 5frz30q, :oncsfqx +hle 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 wib,3 t syp1 -m:9r9h+ispsotbill a 22.0-mH inductor have a reactance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will a+tb)) viwbltl66t5psz ft *k2 $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactance of a q 97c-8 9scrhgjs*sh5z 2jzet $1.0-\mu F$ 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 frequencyded h)vhld h6 u3s4b** from 100 ddl*4h bs3hd 6*uvh e)to 10,000 Hz.

  Calculate the reactance of, and rms current in, a 160-mH radio coil connectey ) 5-njmlwu6bd to a 240-V (rms)ylw5-6jn u mb) 10.0-kHz ac line. Ignore resistance.
$X_L$ =    $\Omega$
V =    $ \times10^{-2 }\;A$

  An inductance coil operates at 240 V and 60.0 Hz. It draws 12.8 A. What is n85 0 ok;qv7t3y +xzc dcxar,dthe coil’s itxa ;+vcy, qo83c 5zx0 d7kdnrnductance? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance of a well-insulato6pb,wde-r1 xf- lts)ed $0.030-\mu F$ 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-Htnubdrbsrl/ ;92y 3 y5z voltage, an rms current of 70 mA passing through the human body for 1.0 s could be lethal. What must be the impedance of the body for this to oc;d/2 bb3rtyn r 9yusl5cur?    $ \times10^{3 }\;\Omega$

  What is the resistance of a coil if its impedance riq/-s -nn .+.frqsfi is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedancfwwa5oi ( 7 5;/tnjsjye, phase angle, and rms current in an LRC circuit connected to a 10.0-kHz, 7255 aj5w(y/;otiw f7ns j-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 6vz,a 3zziby1 by an ac power supply. At what frequency is the impedance double that of the impedance at 60 H 3ibyzz16a,zvz?    Hz

  (a) What is the rms current in an RL circuit when a 60.0+ /wf 3nui w7z+ttqik 5(.myrp-Hz 120-V rms ac voltage is applied, wherek yz 7fp5it.u+3i/t(wwqr+m n $R=1.80\mathrm{~k}\Omega,$ 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 circuk35o 1 k5lici8dm 0ovgn:qxc23 tii9nit if $R=8.80\mathrm{k}\Omega,C=1.80\mu\mathrm{F},$ and the rms applied voltage is 120 V at 60.0 Hz?    $ \times10^{-2}\;A$
(b) What is the phase angle between voltage and current? $\phi$ =    $^{\circ}\,$
(c) What are the voltmeter readings across R and C?
$V_{rms\,R}$   V
$V_{rms\,C}$    V

  A 3500-pF capacitor is connected t/c/w,hc*c mz ro 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 AM16d(ig y twe0r radio has a capacitance of 2800 pF when the radio is tuned to(610rt y idgew 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 =diq qbi+lp y) 3,gym)io0:l/ w 14.8 mH and $R=4.40\Omega$.
(a) What value must C have to produce resonance at 3600 Hz?    $ \times10^{ -7}\;F$
(b) What will be the maximum current at resonance if the peak external voltage is 150 V?    A

  Suppose you are looking at two current loops in the plane of the page as shown kk6x: rqkfg68in (Fig. Below). When s rk:x8kgqk66fwitch 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 sw-v+zf1mt iemd bt.h,0wfymh n4 j*:+ ide 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 lanmmdz.(ipx v7f9 r oj7b,s7j:mp is rated at 45 W but requires only 12 V. It contains a transformer srivx9z7mo7.dfb :j (7,pmjn 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 g8g k:yjke fv/9enerating plant located 118 km from a town that requires y9:8egkfj k/v50 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 80% effb8bkrv;lf7 *m v:v*mniciency are connected to 110-V ac. The secondary windings are connected across b;8r *lvkb*7:nv mmfva $2.4-\Omega$ 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 ek / 2-htjjam.b(iyj(1+ bziqxach 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 apart on a j:)iqcoku-. d6.0$^{\circ}\,$ 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 transmi,ak e;4 jeyi4vfa *mq7d,jmh:ga *l2ission 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 rek8j* fs)j) ww *nego7adius 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 protected against sudden sfyfw 9 -nl ;zpdu71).nizj c,zurges in current. In particular, after the pow;zy,ldffzc.nnj1 wz -p7i9) uer 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-diaqf ,udwzg* j2ude+b k8do/p+5 meter coil 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 +duf+ 5p2dgue8 ,/ jokqzdb*w (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 simp311lzapsuqss al1z)6tyvi+- le generator whose square armature windings lva sqy s3iu-+p1)1 ta6zlzs1 are 6.60 cm on a side; the armature 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 magnetic fields attained in labo7y9eug k6q8b8lqe dcg;ni/w( ratories are aboucb;i(/7g8 n6wekq el gu98 qdyt $1.0\times10^4\mathrm{~V/m}$ 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 tra r/xkg 8v:;jzunsformer whose input is 220 V at 60.0 Hz if the current drawn is 5.8 A? Assume no current in thjuk;vz8 / grx:e secondary.    H

  A 130-mH coil whose resis3zt*j2y5ajrc; s6ne +cggg6pl: z6vbtance 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 battery. ln 6.;rm9- (l:g+ brshgkgjc vWhen connected to a 60-Hz 120-V (rms) sourcemh+;ljr-svc(rnl. : 9gbk 6gg, 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 wit7y)(m /mf wa3 tj,fj; f2lralgn6nl4r h $2.0-\Omega$ 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 resont:c1s*y42-hjhy 1q4eakxt q(c m s.b d ngn4k;ance circuit can be defined as the ratio of the voltage across the cm*4 d .t: tseck q(bxsj hn-1yk4qn142;gcyahapacitor (or inductor) to the voltage across the resistor, at resonance. The larger the Q factor, the sharper the resonance curve will be and the sharper the tuning.
(a) Show that the Q factor is given by the equation $Q=(1/R)\sqrt{L/C}.$
(b) At a resonant frequency $f_0=1.0\mathrm{~MHz},$ what must be the values of L and R to produce a Q factor of 550? Assume that $C=0.010\mu\mathrm{F}.$ L $\approx$    $ \times10^{-6 }\;H$(retain one decimal places) Q =    $ \times10^{-2 }\;\Omega$