If you charge a pocket comb by rubbing it with a silk scarf, how can you determ *if 0nss juq1pmi( :r91uf-vqine if the comb i n1: (q*rspiujq suv9m-f10fis positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometime 1 qnb)-89l:3i at iagzetv9ius cling to your bod3 981bvil:aztug- tae) in9q iy?

Explain why fog or rain droplets tend to form around ion +f t4 ,1nrviypc+g3zvs or electrons in the ain c+ytgz,i1 pvrv+f 34r.

A positively charged rod is brought close to a neutral piec-k+ q+b5pcs mse of paper, which it attracts. Draw a diagrqsm- ks c5p+b+am showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that hasi,w+v+ 2s1oucp 7qky y been rubbed with a cloth have the ability to pwqis+21 cu,o yv+pk7yick up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” i ,yj;dtycf/a 5n the conductor.

Figures 16–7 and 16–8 show how a charged rod plata0lcg.7je u9 ced near an uncharged metal object can attract (or repel) electrons. Tat7.el9jcu 0g here are a great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charge-nya+:wuzh0 z1/z6f mjkv,pr d, its two leaves repel each other and remain at an angle. What balances the electric force of6krm:j,azhn w+p10yvz/-uz f repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law of u74mfg g7nd s7d*j 2krbniversal gravitation. What are the differences between these two laws? Compare also sgnd27 db7mrg*jf74k gravitational mass and electric charge.

We are not normally aware of the gravitational or elect+f. mp7m9s w lzmgv8ejnqws,,68d,nm ric force between two ordinary objects. What is88 fznmpe7 ,svw,9w6s.jmd +lm,q mng the reason in each 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 Chapterc o*z+ q3q*wk95v trre 6.)

When a charged ruler attracts small pieces +wegak6b sh27of paper, sometimes a piece jumps quickly away after touching the rh 2b7wk6esa+guler. Explain.

Explain why the test charges we use when measuring electric fields m7ept3ckh4 t ddh3)zc - pb.5wwust be small.57zpcb.3 d4dwhw -t)kpc3t he

When determining an *e c yx0p)v23dofduu/electric field, must we use a positive test charge, or would02d e d/y voup)3fxc*u a negative one do as well? Explain.

Draw the electric field lines surrounding two negative elec*qhjx+dyx( , 9mbbm-m tric charges a distanced ,- bxxmy +9qbjmm(*h l apart.

Assume that the two opposite charges in)5c oq1ponfin t-)(cqmfh, v; Fig. 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bottom, left, or right — if-pf(cqih ;vm,cn) ont)1qo 5s the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. Firsnl lx.z .9xptg/. kipu3j3zc /t draw an arrow at each point indica3kxcx. z/j.g/ 9u tl .3ipzlnpting 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 decreasing field strength (strongest first).

Why can electric field+ws(lod -0eki lines never cross?

Show, using the three rules f2p id+c1 ib(b;boa9ykg0f- cc or field lines given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetricallyycd-0c kfa2oiib;p(+ 1 bc9gb spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there aj3x s 2psxgjp7r96*vy)x q/bb point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the samegp/7j)23xxs sb x6*bqrvpy 9j? If yes, state roughly where this point will be.

Consider a small positive test chas bn +7+g)ac )w4;dodpfzn/llrge located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration oo+ na+dcf nsgw)l/p4l)b dz; 7f the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge whi 0nnkqpt /y*cro1 -/qlch is infinitely long. (Hint: Use symmetry.) Is the electric field unifo /tp -nclnky r0q*q/1orm in strength?

If the electric flux through a closed surface is zero, is the electric c(s9mbh/yda mx2 * as:wgk .n-field necessarily zero at all points on the surface? Explain. mab xk9mnsc 2a.ghs*:/-d( ywWhat 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 a spherical gaussian surface oc/r/rwf((dxbrjsqg2 . ++ vvsf radius r. If the spherw s d (/bvsvrqr+j(fc/r x+.g2e is replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons m933r 3wi vmytfake up a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attr. ,yj :xrv(ljh e7rdb:action between an iron nucleus e:,vb:rl(7. yj hxr jd$(q\,=\,+26e)$ 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 pro62 2j0o3wtwe .o 7i kfpftdli8tons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude xasuu/jj4t(6k/s+ b,vk w5lk of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particl up cpsfr6)/c8c3 r,g5*z o2rasw cul1es exert a force of $ 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 m yqus1f:mr 3d3*1n5vzsna apd 5asz3.oved, and the force on each of ta3z fsa:nqu3z1yd.s5mr13*va spn d5hem is found to have been tripled. How far apart are they now?    cm

  A person scuffing her fe1hq: gda,dt: 5v jrso9et on a wool rug on a dry day accumulates a net charge of :q r, ddtj1sv9gah:5o$-42\,\mu C\,.$ 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 ko hh i91uxnkh1 -4hhz+e+zpk+ g of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holdir(tbwg6 ,6ruhb htm-1olft0 1ng the electron in 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 ap,5qky;l+q lyisje gmt;v .s3*art. The sum of their charges is ;mq .*i;teqskljly5ys g3v ,+ What charge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge / tlhvtdq;w 2;9adlc+$+75$,$+48$ 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 particl2u ,si/ gsmm q6 3rxfhljkcjn:u14;4r es of equal charge, $+11.0\,\mu C\,$ 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 z6hkr8sawi j7 /km4;ga side. Determine the magnitude and direction of thwzs 8ih ag ;mj/k76kr4e force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges,ujdjl 4v6 (.m:xwe0iyn,+r vd on opposite corners, are replaced by negative charges of the same magnitude m.,+edjdv 4y06n ujir(:vl wx(Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of si jg:mqw9ff ,ztkx), :gde l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charge :f:fz,9mx )tgjk,wq gs.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at e:g gfv.r69dfthe corners of an equilateral triangle of side 1.20 m (Fig.fe. g6vf9drg: 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 ujl+*0 fj(u qyof $560\,\mu C\,.$ 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 spw+v80 :urknbaheres have a total charge 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 transferr-b hx451fuf iuzoy/ 9-oxui/o ed from an initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 m i4/1/uoouh5fyo --fi9 xzbxu N. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude+ :xyt nzu ku.im4qx18(yr jw8do*uw 5 and direction of the electric force on an electron in a unwn(u8ux+iyt54 1y o qxzmu 8j.r:k*wdiform electric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it expb ygxpn,5 h)-veriences an electric foy ,) gph-vb5nxrce 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 on aj6jie)p.7g85 3 ey rgkwz/ fmz $-8.8\,\mu C\,$ 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 of the elecg 9l j ijpdfot0o933i-tric field 20.0 cm directly above an isolated09 ti g3o f9lijd-poj3 $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced bk6l)1kw bdkz4foh */sy an electron in an electric f/ kfwhkzs6*lk 4obd1)ield 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 direction of the electric field at aon2,--b*4tex+gg jfv /fkddy point midway between aj+d2g,vg*b deot -4 x/fk-yf n $-8.0\,\mu C\,$ 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, t4;p c gpy4vqm;he electric field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where a p0k fx wkonvj;4u*a6( jroton $(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 uniform esv je7o5opo ,gt.js f+1gp3:blectric field and accelerates to t.gv 3 +1eg7ojop ,bso:tpjf5she north at 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 midwir0v9bv sxe i/g8, eq(ay between two equal but opposite 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 electric field at the center of a flo 3p brl z 74abgdm4,sc9ie9/zn05n square 52.5 cm on a side if one corner is occ ar0elpbf54 zbl7in43dsz9g o9m/,ncupied 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 atn g;myt:nj5 ;. zuf4dqd+3en y one corner of a square 1.00 m on a side if the other three cog4.qy; d uzmd+j n3n en5:ft;yrners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of them/c ofisy66xt ;-yt o. electric field at the point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distancemoy- xt. ;/ ftoic6ys6 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 electr8 iafu8)) ayd4wflg,/gsep ,xic 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 detc*6q)dnh ge.hs x0hh(ermine the magnitude and direction of the electric field at points A )0(hdhnq*h6gs h.ce xand 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 unknown point charges;m7jwg gpc6 t lo4:sz+, $Q_1$ 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 magnitude of thmv t ;gs6o8gq7mlp6u.4y ,fkje 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 charges8 .uv 6lq,f67g4o;y pm smgktj, a distance x from the midpoint between 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 enters a uniform p99 q(;.yhys5o jfqw belectric field parallel to its direction of motion. j ;5y9q.yowp sq bh(f9If 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 cubical box 28.0 cm ona+j gju1,-:ku;e w.pwe0hro o 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 pla ur./+.kt,enslz -rclced in a uniform electric field of magnitude -ksu. ,rce ll r/z.nt+$ 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 objej7k.ka0xs))o b(myaj(y7 q fl/ rp3ypcts, $O_1$ 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 placed in a uniforzqn5*m:,cl,ol tb uc 6m 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 betwee f k j4kqipywwq/7(7)gn 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 (ass/kp(k g47)iqjyf w7wqume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outsidec-jf 9cow/ut t.w+ ag; a 3.50-cm-radius metal ball is $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.00 m carries a tota40 gx . -j:0mhiqklfk qq,8tjbl 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 xey/*e2) cllk9j+ g ac)sklsrz; q ;8iat the center of an uncharged 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,lesixc zykrajc *q) )l+;2 e;9lg8/ks and (c) 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 helih -qm1dls y83s.vrj7kx-shaped DNA molecule are held 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 atoms3hmk1 8 s.s7jrvqd-y l is 0.2e and on the indicated C and O atoms is 0.4e. Assume also that atoms 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 the elecw,cpai h21d(9jrjgmo27ld 6y zv+wv+ tric force between them is equal to the weight of either at the Earth’s +vw72ahr oji z+g pyc91dw(2jvl,dm 6 surface?    m

  A 3.0-g copper penny hanbg m9k r/:ws)s a positive 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 t dvwp8o .dj)t*k. /er m99ymiab6gre)hat there is an electric field surrounding the Earth. Its magnitudey8.ebvp9 o r ak)6jm 9)t*/ ddmei.rwg is 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 of what is the acceleration experiencyc(h,)o zxq-(m -xos bed by an electro h zq,)(myxo(sxbo- -cn near the surface of the 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 stationartg2 /0fns b57y wz9qvay in the air. If the downward-directed electric field of the90vza2n75 gqts by wf/ Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the e0iuug mh/x; kqbm c6r, cug(c*n+ ;a:CO group and the HN group shown in Fig. 16–62. Thegm+cc:xc;i e u *6r/ub khmqg0nu, (;a C and O have charges $\pm0.40e$, 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 c5t 0cr) j(mw/+ugq7.z vaevylircular orbit around the pr).rt ml0jw7/+5e( qzgua vcyvoton with a speed 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 kt)ws -2wcoa8attraction, rather than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charg8s)ta2w -w okces 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 speeaw+14 bvu t-whd $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 char7znr h ( :vppm7*nog+kge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 v1fbs+,,qrpw encased in insulating plastic and suspended vertically from an v,+q wpr ,fsb1ideal 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 iv eu, r-7y:*mv-czga ( qj6rtas made with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each ma e* cy v,tgaqzum: rjv7-6r(a-ke 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;:u u.wgr37qk7o * g vku7ftbr a spark if the electric field exceeds aboutu7* ok ;rfg3uvbk7w:7 u.gq rt $ 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 0.210d9gsocyk) /6b kg, and net charge $+0.340\,\mu C$, 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 the electrons in a 15-kg bar of aluminum?h6qsu5n4l*k/zp 42w estpeae e , 3-tm    $ \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 are a distance R ap/kxh:yj5 8kvgbbt d6 8*:kdsgart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, sphere C, mg8:jb d*:v yghdt5k/ 6kk8sxbakes 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 in Fig. 16–68, at what posifwq l-gw8m.5 jtion(s) x is the electric field zero? Is the field zero at any other points, not on the x 5j-mww8g lqf.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 charges, each of charge ytsc- vp4(q(0iqt*lf $8.0\,\mu C$ 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?