If you charge a pocket comb by+lld2wuw a9f4 6p4joy rubbing it with a silk scarf, how can you determine if the comb is positively oa42fp 4 l w9od+yluj6wr negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to mv1ya ,xj 25uoyour bodyxau 2jy v1mo,5?

Explain why fog or rain droplets tend to form atcld:x)6it; (o hdb8 tround ions or electrons in the air.bot68dx) i: ; dh(tclt

A positively charged rod is brought close to a n5e viy tw833jceutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and exj5 w c3i8vtey3plain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the abiwiw.kn2gy) 5 vlity to pick up small pieces of paper? Why is t)wvk2yg.w n5ihis difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the conductor.0m uak8njw7p ce md0m-y-(u f7

Figures 16–7 and 16–8 show how a ch-.8 ,xju 7 )hpru.hp-)grj pu kwm:gvxe))rp harged rod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as pg h.p u mjhp-:w r8uxu)gp k)j7)hvr r)-e.,xshown. Why not all of them?

When an electroscope is charged, its two leaves repel each other and r9z-o )8w3loeib k + 6o2(d6jtsvnr ocgemain at an angle. What balances the electric force of repulsion so that the leaves do) vlonj2bzkgo- +c es 36 t(6o8idwr9on’t separate further?

The form of Coulomb’s law is very similar to that for Newton’ /jm y3waz29yop.,aups law of universal gravitation. What are the differences between uw po3/y2pjyma 9.z,athese two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gryesp:gnoq06 c25 *zsigr1c a9avitational or electric force between two ordinaqnec0osc2*a1z5 sg pi 69r:ygry objects. What is the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a conser() 9j z( jc ikeqk3ixd8f3ql:9 pf)uoevative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts fq u;budg l0:evpl zvn-u clic50(6m *hx;9y.small pieces of paper, sometimes a piece jumps quickly away after touching the ruler.y0cf hp-:e * li.qvl l ; udn96(vxmcz0uug;b5 Explain.

Explain why the test charges we use when measuring electric firsmx/(vb6 zr,ji (8o/gsxw :nelds must be small.6jo :r rzw8/xg,m/bi(nx s(v s

When determining an electric field, must we use a positive test charge, orr e) x)hs5jkdgrm-8f / would a negative one do as well? Exp j5gx)/8s kd-fmh)rerlain.

Draw the electric field lines surroufzw:6 )l1nh2j poh:2i, cqwqanding two negative electric charges a distance l aparw: 1o lq6h) phnz2j2,qia: wfct.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cmry-5y0 p b2hsfix.v5di e6+jfjdf;( r apart. Consider the magnitude of the elisj j y.+2v5r5(xb;rf fpy6fd eh-0diectric field 2.5 cm from 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 field at points A, B, and C in Figyny* b7jy, lr6gefxl g5)8 zf8. 16–48. First draw an arrow at each point indicating the direz65 l8j7gg*ryf nyel, b)8 yxfction 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 liup d0r72dzu5e nes never cross?

Show, using the three rules for field lines given in Section 16–8, that the elecw.9cu xqf+m.doy j 66ktric field lines starting orm.6 q9cdu+ojx 6yk.wf ending on a single point charge must be symmetrically spaced around the charge.

Given two point char73 g3 doh4tatf yv;ht0ges Q and 2Q, a distance l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If 4f7 h3t0t h;vy ota3gdyes, state roughly where this point will be.

Consider a small positive test charge located on an electric field line axx4zdrw :yp,1gi92n6zkkk0 xb mh: i; t some point, such ik61r;:wbx2dpxzh m0gz x9 yni4,k:kas point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field li8m1 pn d.y( )turv(eqy t0(echnes for a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field unifecq0(r nd(yhm8 tuy e(p).t v1orm in strength?

If the electric flux througpg7w(1 erpf l4c-dy;th a closed surface is zero, is the electric field necessarilwlc4 (g7fey; pd-p1r ty zero at all points 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 jqnd-x+a c 3quy: r5 p3s81eyca spherical gaussian surface of radius r. If the sphere is replace n5 c d8axjq3+:yrqy1uce3s-p d by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge of)3uld.3im)vyiacn ,x p28l*lsd q7z z $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraf; (sx o la oc6j-/hiqi b,xbtoy0:,j)ction between an iron nucleus ,j, jboa/6 bqs lx(-cy:hiof0txi;o )$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical forcfh+( p::c)+ytnwxeef :) adqge between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude ofw; )vor+i,n l hs ac+64 qs7dgu.7g )idshirp1 the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles e;ujhop tx/6s1m3 ukx3q,bv -a xert 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 moved, and the fm*+ ncq,nuu:corce on each of them is found to have been tripled.c qc:n+mun*u, How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day4o ,4uqd skejvn :;91 p6jbcwrwg87xa accumulates a net charge ofc46j wagdbpj9oxr8s:4 ekv1 ,7 qnw ;u $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charg-3sh rysa(be/9 8s qq7ijcn3l e of all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding +wc .he(o cy8ufx4y9) tawyd kbr;. 2ythe 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 a 4 fkut1 0fdkqemd.*;0o vlh*lre a fixed distance apart. The sum of their charges is What charge mut hv0flek.lod40; u*kfm d1*q st each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge pe7 9h4 gv j0ja7zirtfd;mv3;$+75$,$+48$ 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 n jn: 4mrtow z2xyyi643h t0a0charge, $+11.0\,\mu C\,$ 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 k 6y7qoq zx)i(sdt 6,ra side. Determine the magnitude and directz7,o t)q6yd x sr(i6qkion of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positiv0-1 wchzqlgq*e charges, on opposite corners, are replaced by negative charges of the same magnitude qzc0q1w -glh* (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side g9m 9pfb:y)h vl there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–5fv)9:py g mb9h2). 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 equilateral triangq6qm x9 w5cm0 0;oqm cecm(du0le of side 1.20 mw;e6 xdcommm9 0mc u 5q0qc0q( (Fig. 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 cwjq,mn5;b s;22zbxljhl0 8jk 9 r:auh harge of $560\,\mu C\,.$ 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 sphee 4)ufwijo k/3res 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 transferred from an initially uncharged plastic ball tu i * 982/(qux+gf jbsrnmbg2yo an identical ball 12 cm away. The force of attraction is then 17 mN. gqu2iny2sjb8 x(gm+ * r /b9fuHow many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the oah c; o85gv1f epk*j*electric force on an electron in a uniform electric fiel1jef8h*pa ;*5kcvo ogd of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in v1ke4a6xyy .2z l7l 9wa4bsbga uniform electric field, and it experiences an electric 2b7ae1wkyaglv49x6s byz l.4force 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 4 gob0. / jlm8cyp3nded5 llg;is exerted on 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 of the electric field 20.0 cm directly abo.yx g0n wjuu3)e y-w:kve uu -0) wy3.w:gnkx yjean isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by a(bzaurzujyt+ o nz (0-8zq))yn electron in an electric field oy yrz)z)-8o+uaj z(qt(0 bnuzf $750\,N/C\,?$ 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 uykp 6nf s2-u6electric field at a point midway betwyp fu2us6n-6k een a $-8.0\,\mu C\,$ 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 el5 zf0ro*d6mmg ectric 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 ;yxkdk(01hdd 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 uniform electric field 59z*fg 48qhhwto5o joand accelerates to the noroh5* 4fgoo5 jzh9q8wtth 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 midway between two equal but opposite04 wddd10pdw yh8v4 rtxkwc(( 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 squarqbnoodu/f+( truy-:9uj : 8scc.m+rc e 52.5 cm on a side if one corner is occupied cyu cf (-8nrb: j+.sur+/ :oqtmoucd9by 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 odvo5xae zo.) jn-(eh-p6f e7tn a side if the other three5eo x7p)-fzoeaj d6h-v .nt e( 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 tqn4hv0i3, rjuhe point P in Fig. 16–54. The charges are separated by a distance 2a,3v 4jnh 0iu,rq and point P is a distance 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 electr;sd 37y5 0zpyp4l:hptobtm : kic 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 elec an-yf:4)u+/cj7zlz6g (f xb i2puvrftric field at points A and B in Fig. 16–57 due to the two posigupu4a(vc7l) xnzyfrjb f:f z/-i +62tive 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 cnni5,uzu8 iev 80gei9harges, $Q_1$ 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 the ekk,axx. zh(1efr 2v22sj ,ewclectric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Poizx(w2ek j sef1hx,2ackvr. 2,nt P is on the perpendicular bisector of the line joining the charges, 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 sp/ zf5fup,g;h eeed of light enters a uniform electric field parallel to its direp zfegufh/5 ,;ction of motion. If 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 flugri* e:e u(h jk+ag)fv*:ypi:x from a 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 6ujd1g) wcef)s/sep -lxwh .w :3yt1j dir:k618 cm is placed in a uniform electric field of magnitude13)1sx. kdpcese d:6tjwjf:u6 w / -hl)ry iwg $ 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 objedet.yw.a u 91x36oc- dk; uftects, $O_1$ 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 uu3p4 b c ,fbzh:c,x b8wze8zrm( ,apa2niform 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 between two square metal plates is T:dw3xq kdlvp h6a p-z6o/6sd8he plates are 1.0 m on a side and are separated by 3.0 cm. What is the char8svq 3al/- :dwd6xz 6dkp6 hpoge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a j k2g9t .pe tt/nq:lb4iv;o t2 cqam9.3.50-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 o2-xfai)8mbn1kdg gxcwi4ct vgb1ji 2a7h;/7 f 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 unchsvn5 -vmi(s r l g(xxp,dk5*b/arged 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 tg(p(ms* -5,sx/ r xvvlndbik5he shell, (b) inside the shell, 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 helix-shaped DNA molecule are held together by elef2 cf925mcdy nctrostatic forces as shown in Fig. 16–44. Assume that the net average charge d9 c2y5cmnf2f(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 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 electric5mwqod md23g) force between them is equal to the wemdgow mq25d3 )ight of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positi i)4m3 chzz(cqnzwq7+ ve 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 that there is ktck2bzhg3eb zu;+.. an electric field surrounding the Earth. Its magniu h3;z.+bc2btzg .ekk tude 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 o0 lfw ,as6v)cbf what is the acceleration experienced by an electrovc b)0wfls,6an 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)y* alb7*.8; tcfcejiedt8 r.jru* ka stationary in the air. If the downward-directed electric fielc i fbeerdj;cyur jl7)a*t8*. t.ka8*d 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 CO group and the HN gyz, 7yg +rufj34oya9.y:v nszroup shown in Fig. 16–62. The C and O have ch,74unv3 s y fr:9jgz.yaoy+yzarges $\pm0.40e$, 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, n c,l)*wzr:zmthe electron revolves in a circular orbit ar*rc lzn)zm,: wound the proton 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 attraction, rather t518 /k makkda6uo(pgy han gravity, were responsible for holding the Moon in orbit around the Eartha/oy6kpu(kd 1a8m gk 5. 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 speed i3. a4btpp:ud8) saijetp5 p6$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charge u j2n4-wfpl s ozom)u,-;rlo($Q_1\,=\, 2.5\times10^{-5}\,C$. 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 0+ trgq5hp (ccvertically from an id5h(0 pgt cc+rqeal 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 is made with “leaves” that are 78-cm-long wires with tiny lv2 (:xnku eu:m ,yo6y24-g spheres at the ends. When 6 kelu2(,o:vyu:yxnmcharged, nearly all 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 sp.g4s lxnf y4y8ark if the electric field exceeds abouty 4.84gn fyxsl $ 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 massv4u yt +;c1xpg 0.210 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 thehk3 2vkmr, jl) 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 are a distance R apart; eanp xvzsj+ 3s+e: ,m9sdch carries the same chev+z3j xd:pns,s+ m9 sarge Q. (a) What is the force sphere B exerts on sphere A? (b) 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 in9hi)cj;.dywgvgj; 1 k Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at 9 i.)djy hg;1cjgvkw;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 7mexc qe .27jtcharges, 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?