If you charge a pocket comb by rubb +kdf0 2i(mcia4gw n;oing it with a silk scarf, how can you determine if the comb is posi2o ici d+(mf04g awn;ktively or negatively charged?

Why does a shirt or blouse t:k md-vzq*jzar3z)fc) h g*9taken from a clothes dryer sometimes cling to your body?az9v zcztf hmg)*:kj3-rqd* )

Explain why fog or rain droplets tend to form around ions or electrons in the n:( kxshed7* )lcmiu6air.h : knxdm7(e)sc *u6il

A positively charged rod is brought close to a neutral piece of p (w5)qo hmvrc9*)bb kyaper, which it attracts. Draw a diag9cb)qwb(rmy *h) 5kovram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that haxbu9rr(ml5 - wu(/- evh kd0aqs been rubbed with a cloth have the ability to pick up swr uu-(dl5(qvmkha e /rx90b-mall pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge r1v mxu2*xc y9c57ymbon a conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a ch x-vld)hby7y*arged rod placed near an uncharged metal object can attract (or repel) electrons. There are a yv7l d-x)yb h*great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charu3v8lh ana;g7-)i l fwged, its two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t separate further?hv ;iwg3-fanl8l)a7u

The form of Coulomb’s law is very similar to that for Newton’s law of univz0ixd ix/ 12yb*ktf3k se+r 0lersal b t iixlzk/ ks20fedry1x3+* 0gravitation. What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force between tw hqr)td8(.kleo ordinary objects. What is the reason in eh e(k)dqrl 8.tach case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapter pmnkkqf ,d .+6*bhu:-wu+jte 6.)

When a charged ruler attwsb1;q7 anb /9m1wdsb pn 9fw/ iq)y)bracts small pieces of paper, sometimes a piece jumps quickly away after touching the ruler. Explain.w/1bmsqw bi7b99 ;na)d bynp) f/wsq1

Explain why the test charges we use wwvgk4w5 -2 smthen measuring electric fields must be small5wsw42vtk-g m.

When determining an electric field,0wh,f lxu*xck y8.p 5r must we use a positive test charge, or would a negative one do ashwk*,plc5y xuf rx0.8 well? Explain.

Draw the electric field lines surrounding two negative electricfda qylq g4.2y,bt3(4cs wv5z r f)p 7vkt/yg- charges a distance l apa t3qtq2ygy.p rf-v dgby/ zc,f4)w4 vslk7a(5rt.

Assume that the two opposite charges in Fig. 16–31a are 12.0 8kpjot,ge l nvvbu;wq (8 hirq4;a1/1 cm apart. Consider the magnitude of the electric field 2.5 cm fromp okih8vg8qb / nr1;v41 w;late(quj, the positive charge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric fiexg/ jr7d/h; 1 yrs+qrdld at points A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasi+ds/r71qgr j;r/ xhydng field strength (strongest first).

Why can electric fiel0 oc)ixp gd0-uvh98 sjd lines never cross?

Show, using the three rules for field lines given in Sect38jokfsl zc4ln/ nflm5)ez: .ion 16–8, that the electjn4 so lz/elfnk cfml58 3:).zric field lines starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a ,j, tc /wgbtodr0/d4b97c sippoint along the straight line that passes through them where E=0 whegcdsptbjb ,0r/9/wdt4c o7i , n their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an electric field lx /;jts. ud2dline at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of thejdt 2ls; .x/du test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of 2budg/w j(ko9 charge which is infinitely long. (Hint: Use symmetry.) Is the eld o(kguw 9j2/bectric field uniform in strength?

If the electric flux th6(m 4( mktw f03as7quc v5myvhrough a closed surface is zero, is the electric field necessarily zero at all pointsst4 30u5c yvmw67vkq(am( mhf on the surface? Explain. What about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by n bz dk,9(l0qdhl6i-xh;gz3d a spherical gaussian surface of radius r. If the sphere is regd6hb hz9d; -(zix ,ln0kl3d qplaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons mat i5;;0hyl fzp.yqd3yo8j( r uke up a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attract(icl,ipvet p8 7/e*e stq*q)pion between an iron nucleus ip*/ 7v,e tqq(*p8)sie etplc$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force between two proz+( k nejf1r.wtons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of thezkcxo8.24gcz+ ox.t d force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a force of dkx4 m +jc364ct ps;nh$ 3.2\times10^{ -2}\,N$ on each other. What will be the force if they are moved so they are only one-eighth as far apart?    N

  Two charged spheres are 8.45 cm apart. They are moved, aq(6 f:2oat (pf pnf6vdnd the force on each of them is found to have been tripled. How far apart2fpqo( nvf6f(:pda t6 are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumul (d8.epm 7wh wc(not 2xz9h+v75tkri rates a net charge of . zr 7tk(2 v+7o5c(tmwdnr xwphe9ih 8$-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charge of all the electrons in 1.0 kg kzkt0sw) 5hpi rve-35 of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron 1s g* 9v 7po+mahg+ xmwh5er1din orbit $(r\,=\,0.53 \times10^{-10 }\,m)$ around the proton nucleus of the hydrogen atom, with the gravitational force between the same electron and proton. What is the ratio of these two forces?    $ \times10^{39 }\,C$

Two positive point charges are a fixed distance apm0 kosbz f:hz(q up.8h;b jb :d2nc1p7art. The sum of their charges is What charge must each have dpzh f0k2:bb(m1 :pj;n zb. ou7cs8hqin order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge x yw4ufcns-8+rd ji 52$+75$,$+48$ and $-85\,\mu C\,$ are placed in a line (Fig. 16–49). The center one is 0.35 m from each of the others. Calculate the net force on each charge due to the other two.

$F_{+75}$=   $NN$
$F_{+48}$=   $NN$
$F_{-85}$=   $NN$

  Three positive particles of equal chavpq5 cvjbbkh b2fhnc ; 0,4a;(rge, $+11.0\,\mu C\,$ are located at the corners of an equilateral triangle of side 15.0 cm (Fig. 16–50). Calculate the magnitude and direction of the net force on each particle.


the force on the lower left charge is of magnitude    N, and
will point    $^{\circ}$below the-x axis. The force on the lower right charge is of magnitude    N, and will point    $^{\circ}$below the +x axis.

  A charge of 6.00 mC is placed at each corner of a square 0.100 m on a sid/sd-4tano4 ki jdt+jjed;+s 9 e. Determine the magn;jds ja+t9d/t4sd -4i oje kn+itude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for hh .fo u8i n0xicy /hn+it7w l3(2vq;xthe case when two of the positive charges, on opposite corners, are replaced by negative charges of the same magnitude (Fig. y2n3xv(nu8fiiot/ h lwi ch 7q;+xh0. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are poi9 b/2c8 tlmbx huiq.o(nt charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. /o(u9 tq8 l2mhbxic.b 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the corners of an equl s,+p r-ifozoukqx.d/( :ve 8ilateral triangle of side 1.20 m (Ff +-8,xpoi :zesodu/kvlr. (qig. 16–53). The charges are $+4.0\,\mu C\,,$$-8.0\,\mu C\,,$ and $-6.0\,\mu C\,.$ Calculate the magnitude and direction of the net force on each due to the other two.
$F_1$ =    N
$\theta_1$ =    $^{\circ}$
$F_2$ =    N
$\theta_2$ =    $^{\circ}$
$F_3$ =    N
$\theta_3$ =    $^{\circ}$

  Two point charges have a total charge ocvq y6t- l6h;(sp 3/fvd vzdt(f $560\,\mu C\,.$ When placed 1.10 m apart, the force each exerts on the other is 22.8 N and is repulsive. What is the charge on each?
q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C $ b =   
Q-q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C$ b =   

Two charges, $-Q_0$ and $-3Q_0$ are a distance l apart. These two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

  A $+4.75\,\mu C\,$ and a $-3.55\,\mu C\,$ charge are placed 18.5 cm apart. Where can a third charge be placed so that it experiences no net force?    cm

  Two small nonconducting spheres have a total c,k i)-pp/cor2c tv2 tfharge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially uncharged plastic tngdc9.me: c; 8*n1dv6tke g tball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were tra .:de6gn t;c*cdkgve81 tt9m nnsferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and dijli 71davt :l9rection of the electric force on an electron in a uniform electric field of st9 1lld v:7itajrength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a unifo k5v2vv,xrmatj/ y7r6 rm electric field, and it experiences an electricj2rvvm,v a/y6k7x5tr force of $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is exerted onlqk-62(zeo.r9*o f+ijg*esh in 3 bjs o6hlc2 a $-8.8\,\mu C\,$ charge. What are the magnitude and direction of the electric field at this point?    $ \times10^{5 }\,N/C$ ----待选择----updown 

  What are the magnitude and direction wubzg8 x1 fr9p77xkl; of the electric field 20.0 cm directly above an xrz71kpw7lb;9f8xg u isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced b3cli8 kgyo aa 66k+8fjy an electron in an electric ka8a+ fck8go3y 66jl ifield of $750\,N/C\,?$ How does the direction of the acceleration depend on the direction of the field at that point?    $ \times10^{ 14}\,m/s^2$  ----待选择----opposite to the field in line with the direction of the field 

  What are the magnitude and dqnjtce /ji3f)7 9bn6i/0atzcirection of the electric field at a point midway between ai c3 ij9 6e0bn7nf/tqajz/tc) $-8.0\,\mu C\,$ and a $+7.0\,\mu C\,$ charge 8.0 cm apart? Assume no other charges are nearby.    $ \times10^{7 }\,N/C$ ----待选择---- towards the negative charde opposite to the negative charge 

Draw, approximately, the electric field lines about two poin u psz9)bfa,rrtng:;j4+s1oet charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space wh,la:0gc 2 ljfrere a proton $(m= 1.67\times10^{ -27}\,kg) $experiences an acceleration of 1 million “g’s”? $\approx$    N/C（Round it to one decimal place.）

  An electron is released from rest in a un (7)ym4ik94((p-z 4i:es2aod tof nwby cybj giform electric field and accelerates to the north 9 2 )gy(k4 be wpo-aj4ifd:ns(mi(7y c ybozt4at a rate of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between two equal but opposuk(uq.g ce*b sacm +,y8l)++txh iy)iite point charges is $745\,N/C\,,$ and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?    $ \times10^{-10 }\,C$

  Calculate the electric4xy: hh2f(hn z field at the center of a square 52.5 cm on a side if one cornzhhf4n (h2 x:yer is occupied by a $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at one corner of a square 1.00 m ona 4h*f4peuq.zk+ ka p3 a side if the ot4.e k3f4phqzapua+*k her three corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electric field at tqy/ k:bgaw+ ;the point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a +gk:q/ytab ;wdistance x from the midpoint between the two charges. Express your answer in terms of Q, x, a, and k.

  Two point charges, $Q_1\,\equiv\,25\,\mu C\,$ and $Q_2\,=\,+50\mu C\,,$ are separated by a distance of 12 cm. The electric field at the point P (see Fig. 16–55) is zero. How far from $Q_1$ is P?    cm

(a) Determine the electoa +u ;fwl0-v0mdzy r(ric field $\vec{E}$ at the origin 0 in Fig. 16–56 due to the two charges at A and B. (b) Repeat, but let the charge at B be reversed in sign.

  Use Coulomb’s law to determine the magnitude and direction of the electli1d f)yvf;ekwq -j3 .ric field at dl wf3- eyvijf. q1);kpoints A and B in Fig. 16–57 due to the two positive charges $(Q\,=\,7.0\mu C\,)$ shown. Are your results consistent with Fig. 16–31b?
$E_A$ =    $ \times10^{6 }\,N/C$
$\theta_A$ =    $^{\circ}\,$
$E_B$ =    $ \times10^{7 }\,N/C$
$\theta_B$ =    $^{\circ}\,$
(16-51)
(16-31b)

  You are given two unknor tbi v2p.46qewn point charges, $Q_1$ and $Q_2$ At a point on the line joining them, one-third of the way from $Q_1$ to $Q_2$, the electric field is zero (Fig. 16–58). What is the ratio $Q_1/Q_2\,?$   

Determine the direction and ma6 n3wm2k ydn c6c ) b.tj4mp**w0ikydlgnitude of the electric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint betwc60l.idnbny*4cw d j6m2)k* tkpw3y meen them. Express your answers in terms of Q, x, a, and k.

  An electron (mass $m\,=\,9.11 \times10^{ -31}\,kg$) is accelerated in the uniform field $\overrightarrow{\mathbf{E}}\left(E=1.45 \times 10^{4} \mathrm{~N} / \mathrm{C}\right)$ between two parallel charged plates. The separation of the plates is 1.10 cm. The electron is accelerated from rest near the negative plate and passes through a tiny hole in the positive plate, Fig. 16–60.
(a) With what speed does it leave the hole?    $ \times10^{ 6}\,m/s$
(b) Show that the gravitational force can be ignored.

  An electron moving to the right at 1.0% the speed of light enstjb :kae .1:bj5vh: -ikm+ufters a uniform electric field parallel to its direction of motion. If eb.+ i-f m5kjs:t v:b1ju:hka the electron is to be brought to rest in the space of 4.0 cm,
(a) what direction is required for the electric field,  ----待选择----rightleft 
(b) what is the strength of the field?    N/C

  The total electric flux from a h6*(z f: hjk7hyj:uap cubical box 28.0 cm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a unio- clt*g,qv iwl*ix iam*x 55 p77icn6form electric field of magnitudet q 7*iic5g wcp*-xnl a5*ivx,lio67 m $ 5.8\times10^{2 }\,N/C$ What is the electric flux through the circle when its face is
(a) perpendicular to the field lines,    $N\cdot m^2/C$
(b) at 45° to the field lines,    $N\cdot m^2/C$
(c) parallel to the field lines?   

  In Fig. 16–61, two object 4ya4 44c hncizqqoo34e90qk ;dl8pc ps, $O_1$ and $O_2$ have charges $+1.0\mu C$ and $-2.0\mu C$ respectively, and a third object, $O_3$ is electrically neutral.
(a) What is the electric flux through the surface $A_1$ that encloses all three objects?    $ \times10^{5}\,$$N\cdot m^2/C$
(b) What is the electric flux through the surface $A_2$ that encloses the third object only?   

A cube of side l is p+bx)5 z 7otwrlvj5c9i (dggjm u8m) z0laced in a uniform field $ E\,=\,6.50\times10^{3 }\,N/C$ with edges parallel to the field lines.
(a) What is the net flux through the cube?
(b) What is the flux through each of its six faces?

  The electric field betwesyspp/ v*k g v;:n,9zv e9nu3ben two square metal plates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effzn,b/pu s :*k ng y9sv;v3v9epects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball iwbokx;frz1u*iv z .r6fuw2 ;3s $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere e u-x/yykqqryu ) o3;/of radius 3.00 m carries a total charge of $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of an unchargeg( w1t/ 0smgtlzw:(cod thin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c)m ( :ogws /(ctg0lwt1z beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are helgci: ssbn+a 3.:g s9:hc qoxq/d together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atoms is 0.2e and on the indicated C and O atoms is 0.4e. Assume also that at g xos:s .ig 3as/b9hq+cqcn::oms on each molecule are separated by $ 1.0\times10^{ -10}\,m$. Estimate the net force between
(a) a thymine and an adenine;    $ \times10^{-10 }\,N$
(b) a cytosine and a guanine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other).    $ \times10^{-10 }\,N$
(c) Estimate the total force for a DNA molecule containing $10^5$ pairs of such molecules.    $ \times10^{-5 }\,N$

  How close must two electrons be if the3lul 52g h;nhsqa3c-v electric force between them is equal to the weight of either at the Earth2-avuq 3; l 5nshlhc3g’s surface?    m

  A 3.0-g copper penny has a pose9( m5o,,/jeummlvu mh :l.t zitive charge of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

  A proton $(m\,=\,1.67 \times10^{-27}\,kg)$ is suspended at rest in a uniform electric field $\vec{E}$. Take into account gravity at the Earth’s surface, and determine $\vec{E}$.    $ \times10^{-7 }\,N/C$  ----待选择----updown 

  Measurements indicate thak muj35dn) du)t there is an electric field surrounding the Earth. Its magnitude id n5du)jk )um3s about $150\,N/C$ at the Earth’s surface and points inward toward the Earth’s center. What is the magnitude of the electric charge on the Earth? Is it positive or negative? [Hint: the electric field outside a uniformly charged sphere is the same as if all the charge were concentrated at its center.]    $ \times10^{5 }\,C$  ----待选择----positivenegative 

  (a) Given the local electric field j/ybyi+qgrw 1 )c /bg8of what is the acceleration experienced by an electron near the surface of ti/bj y1)bgyg+cq8 w/r he Earth?    $ \times10^{13 }\,m/s^2$, ----待选择----updown 
(b) What about a proton?    $ \times10^{10 }\,m/s^2$, ----待选择----updown 
(c) Calculate the ratio of each acceleration to $g\,=\,9.8\,m/s^2$ For the electron: $\approx$    $ \times10^{12 }$ For the proton: $\approx$    $ \times10^{9 }$

  A water droplet of radius 0.018 mm remains stationary in the umfnt7*+z.* yo3:bbg hmpl8f air. If the downward-directed electrihmlbny7ufo3* m8t zg*. fbp: +c field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the C6m;k1aftz /sryna.g u w0+p3n*wiy3h O group and the HN group shown in Fig. 16–62. The C and O have 6fa0i wg ukn1aymr.wy *hp+s; nz3t/3charges $\pm0.40e$, and the H and N have charges $\pm0.20e$, where $e\,=\, 1.6\times10^{-19}\,C$. [Hint: Do not include the “internal” forces between C and O, or between H and N.]    $ \times10^{ -10}\,NN$

  In a simple model of the hydrogen atom, the electron revolves in a circuluzcx2nfduu-w9 p( v)jee *j.lg) n2 5har orbit around the proton with a spn2g(.-2 cve*)wx5dlf u u9hjzeu )n jpeed of $ 1.1\times10^{6 }\，m/s,$. Determine the radius of the electron’s orbit. [Hint: See Chapter 5 on circular motion.]    $ \times10^{-10 }\, m$

  Suppose that electrical 7b1 g xmhb hws-),xm1/awb lz5q+0jhqs 0bme5attraction, rather than gravity, were responsible for holding the e 5b a,bj/bs+7bw hm ghh -wmxq5mq1)zxl 0s10Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present orbit? Use these data: mass of $Earth\,=\, 5.98\times10^{24}\,kg$, mass of $Moon\,=\, 7.35\times10^{22}\,kg$, radius of $orbit\,=\, 3.84\times10^{8}\,m$. Treat the Earth and Moon as point particles.    $ \times10^{13 }\,C$

  An electron with speesomqz) ( s23er. u knyy.v(p*od $v_0\,=\, 21.5\times10^{6}\,m/s$ is traveling parallel to an electric field of magnitude $E\,=\, 11.4\times10^{3}\,N/C$.
(a) How far will the electron travel before it stops?    m
(b) How much time will elapse before it returns to its starting point?    $ \times10^{-8 }\,s$

  A positive point charges94jgx wu: n:y,-o5 )xggcjb2o ax/bs $Q_1\,=\, 2.5\times10^{-5}\,C$. is fixed at the origin of coordinates, and a negative charge $Q_2\,=\, -5.0\times10^{-6}\,C$. is fixed to the x axis at $x\,=\,+2.0m$ Find the location of the place(s) along the x axis where the electric field due to these two charges is zero.    m from $Q_1$,   m from $Q_2$

A small lead sphere is encased in insulating plastic and suspended l jmb+b5no8.hsc .vy- vertically from an idea.y8omb -nl+vcs. h5jbl spring $(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope ., 2kacm l:gvois made with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly alao mk lc.vg,2:l the charge resides on the spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break down and generate a spark if the electric field e4f,t6w qx)0 yucxikuk0lkp; *xceeds about k * kt x)qk0,fw6y4 u;uxcpil0$ 3\times10^{6 }\,N/C$. How much charge could be packed onto a green pea (diameter 0.75 cm) before the pea spontaneously discharges? [Hint: Eqs. 16–4 work outside a sphere if r is measured from its center.]    $ \times10^{-9 }\,C$

  Two point charges, $Q_1\,=\,-6.7\mu C$ and $Q_2\,=\,1.8\mu C$ are located between two oppositely charged parallel plates, as shown in Fig. 16–65. The two charges are separated by a distance of $x\,=\,0.34\,m$ Assume that the electric field produced by the charged plates is uniform and equal to $E\,=\,73,000\,N/C$ Calculate the net electrostatic force on $Q_1$ and give its direction.    N  ----待选择----right left 

  A point charge $(m\,=\,1.0\,g)$ at the end of an insulating string of length 55 cm is observed to be in equilibrium in a uniform horizontal electric field of $12,000\,N/C$ when the pendulum’s position is as shown in Fig. 16–66, with the charge 12 cm above the lowest (vertical) position. If the field points to the right in Fig. 16–66, determine the magnitude and sign of the point charge.
   $ \times10^{-7 }\,C$
 ----待选择----positivenegative 

  A point charge of mass 0.210 kg, and net chasbicp gus0 .10rge $+0.340\,\mu C$, hangs at rest at the end of an insulating string above a large sheet of charge. The horizontal sheet of uniform charge creates a uniform vertical electric field in the vicinity of the point charge. The tension in the string is measured to be 5.67 N. Calculate the magnitude and direction of the electric field due to the sheet of charge (Fig. 16–67).    $ \times10^{7 }\,N/C$  ----待选择----updown 

  What is the total charge of all the8vkrrs4fn 5w/b s jt*5 electrons in a 15-kg bar of aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B ar,kd q gtyj+ )tuimzg*:gdywr- .pv* 7 y7)rzj1e a distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b)7gp*u-d7jyt1zg:gy +rt wk rmiv yzj qd.,)*) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown ine xk0)0h3f*-jq yqaoy Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero ef*y)hx0-qyqa jko 30at any other points, not on the x axis?

Two point charges, $+Q$ and $-Q$ of mass m, are placed on the ends of a massless rod of length L, which is fixed to a table by a pin through its center. If the apparatus is then subjected to a uniform electric field E parallel to the table and perpendicular to the rod, find the net torque on the system of rod plus charges.

Four equal positive point im u6bdf(b xy9om2y7il8j g:/charges, each of charge $8.0\,\mu C$ are at the corners of a square of side 9.2 cm. What charge should be placed at the center of the square so that all charges are at equilibrium? Is this a stable or unstable equilibrium (Section 9–4) in the plane?