If you charge a pocket comb by rubbing it with a silk scarf, how can yka2fveok+ 5 u5gab3g 0ou determine if the comb is posi5agvu 5+ 302kok bageftively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cqmf 2td q5kp-y99hww1 ling to your body9d2f ktp y1hw -5qqwm9?

Explain why fog or rain droplets tend to form around ions or electronsz 0b7;og hkrdu.+r;hh/tzh; 4 jiv5vs in the air.tdvihr.;v0;u 5hgz+s7b ;j o hhzk/4r

A positively charged rod is brought close to a neutral piece of paper,hvd (jb44j 5gyuq*e5x*s)sp f5 fvko2 ,eng 7w which it attracts. Draw a diagram showing the separation of charge and exp5edo452qf)efxb gsvn( 7*54gj vujk h, *pywslain why attraction occurs.

Why does a plastic ruler thdbdrh4m dy5* kz xs:2 1cyz+vrj 2q+:dat has been rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficult to do on a humid day: 2dr2sdvr:+cd4qyhz+dk *j 5bx my 1z?

Contrast the net charge on a conductor to the “free charges” in the conductor. md 1n7*g0)lfko;dkxnpehn) ;

Figures 16–7 and 16–8 show how a charged rod ghfqk 1iuq- fuio3w o5,rdoe(c; 2)+bplaced near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the m qf(- bu; +croe3u2 i51,)ghqkowifodetal, yet only some of them move as shown. Why not all of them?

When an electroscope i2rrsruc q(jcz59f8m1f y*ug5 z0x; rqs charged, its two leaves repel each other and remain at an angle. What balances the electric force of repulg 2xrju9yr50 s 8cqczfru1zfmq *r ;(5sion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law of universal xi9;-ld ;mx njgravitation. What are the differences between these two laws? Compare also gra xd;jnlx;mi- 9vitational mass and electric charge.

We are not normally aware of the gravitational or electric for84h tvyn g)qgq87wbyon +tb::ce between two ordinary objects. What is the reason in each case? Give an example where we are aware yt:qntogb7v )h 8 y:wgb84n+qof each one and why.

Is the electric force a conservative force? Why or why 6v fi+i s6z5d glhkt; 5zu-9dcnot? (See Chapter 6.)

When a charged ruler attracts smallmjiqjlb- 5;7x pieces of paper, sometimes a piece jumps quickly away after touching tmj7ij ;qblx5 -he ruler. Explain.

Explain why the test charges we use when measurin*n ck)guk9 hb.g electric fields must be small9)b gkcku .*hn.

When determining an electric fidxuk u p,)bf3-7hs.c 66tc.j8xisu bh eld, must we use a positive test charge, or would a negative one do as well? Expls xbu-hudb66s hjt8u.3pci7f .),ckxain.

Draw the electric field lines surrounding two negarq b2+fg.vo9+ei h8vgw; m1avtive electric charges a distancgiebvov21+ 9ha f+v8 . mgw;qre l apart.

Assume that the two oppos.6c1qcy f3jm+bisdw54r/wy je wq. -aite charges in 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 — is the electric ff ybwq-4j.s m+iqe ay/5w .wcd3 1jcr6ield the strongest? The weakest? Explain.

Consider the electric field at points A, B, anoo2 rng9hg 5(zd 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 decreasing fie no h(rggz95o2ld strength (strongest first).

Why can electric field lines neven lzxf2n j 44npgpyu(wxon5j4;,+ t2 er cross?

Show, using the three rules for field lines given inv/ ,x.okr,a ub Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced around thx/,u.kro,b ave charge.

Given two point charges Q and 2Q, a distance l apart, is there a poij*pi-lq jrt 4 1hs,)sent along the straight line that passes through them where -1j*e)s4,i prs hqtljE=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive te t- xsn-aul;aa-o6( imst charge located on an electric field line at some point, such as point P in Fig. 1 ;m--aanutsxl-(6iao6–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of chargditi)z2f(6 yme which is infinitely long. ) mydizt26i(f (Hint: Use symmetry.) Is the electric field uniform in strength?

If the electric flux through a closed surfanyfsl f.5s xk*6x:vp,w(zt :b ce is zero, is the electric field necessarily zero at all points on the surface? Ex 5* 6xy(sfvzl:bn, .f:ptk swxplain. 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 a spherical gaussian surface of radius r. If th6imm1w0*p1lic mb ).w qjj :q2ebd9kve sphere is replac wl9.mmj:b*1 jpciwqkei062b q) vm1d ed by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge ovb1aelw3* g ju(sc lp1s*;ci6f $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attracr.7l4 bkkjtrlm: ; (bbxmohan)nq47 tm e: d--tion between an iron nucleus nk)m:-4m bdtb;mb(. onj r7hktl:4re qa-x l7$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical fo4 kol4*d*ovt5 bjvzyz 3f ,i-brce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force au:v e-xvm6cl tiz5t4+ $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert o1rx*rd7o)r kwl8s9sgx)gs0m ma, *ra 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.g - gq1a2bdpavlm+68w45 cm apart. They are moved, and the force on each of theamgvab2pq 81w+- g6ld m is found to have been tripled. How far apart are they now?    cm

  A person scuffing her fe050 6yr4 wity8avj cguet on a wool rug on a dry day accumulates a net charge ofati 0wvyjrc60gu 5 48y $-42\,\mu C\,.$ 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 theat+ss 8 v(+, bullm1ib electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding thek8nbazk jb :v v9+pd+ y4v(h4u 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/bn,9kuxt 7z i are a fixed distance apart. The sum of their charges is What charge muz, kti/xb9 7unst each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge ,c vpjhyj5+z4s7 pey-q) 2 bua$+75$,$+48$ 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 chaz:yc+urvej:s j1l7t 5rge, $+11.0\,\mu C\,$ 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 ea5m8 2m j;b89n gir,vosahd h5nch corner of a square 0.100 m on a side. Determine the magnitude and direction of the ,rs5n;m8dhmnagvoh2ji5 b 98 force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on oppoo7 tq ii/5 bx0( i:qryg nm6k)2zns6scsite corners, are replaced by negative chargni 6b2 qi:qn 0og 7xk)czmi (/y5rst6ses of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of eu1 ov.zu+0md side l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (0u umzoe. 1+dva) 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 triamy.o ojy,9 vu;yl hq/1ngle of side 1.20 m (Fig. 16–53). The charge;jovy19o hmqyy lu/ ,.s 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 a4hb+c2 q j3.yvl)hvn w total charge 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 sphe 8e7 pihtkxv:xotkh st s388y(u9b+82v1b cuqres 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 initiwa.6bj 7mw k+)lv ywe;ally uncharged plastic ball to an identical ball 12 cm away. The force of 6)+a ;w wmjleby7v kw.attraction is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an electron inwbf7x7v-; szsc-k -y t a uniform electbt kx-vs s;-wc7z fy-7ric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in 6cplw+s u ,s0ia uniform electric field, and it experiences an electric force opus06iwc , s+lf $ 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 ex f95ml)rww )axerted 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 fiecres or.+fm , wkn;.0kld 20.0 cm directly above an, . 0snkm+;.fekrwco r isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by c:i k r(9b;gq +:fhc 08kfr4vd,om0xe a1 ngxcan electron in an electric field of ag 0oc4 ( 01mfqi9cb;vrk:e,kr:d xh8+nc gxf$750\,N/C\,?$ 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 fie o 9tvua*.w*ryld at a point midway between a oaw v9tyur* .*$-8.0\,\mu C\,$ 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 point+c ktgx1aas 2ax.eh c n*nm342 charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point i)q 3grwx(niiqg2g 0)xzd:f: t*h c 5s wude:u0n space where 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 electgoyi2f9+dww* g8*di eric field and accelerates to8+ *d*iogy9ewf2 dg wi the 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 midway between two equal but opposite point charges i8e(6lnrek*wp e n9o vmf.nv 13s $745\,N/C\,,$ 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 square 52.5 cm on a sidesm5+/cc mck*ve5h5 ca if one corner imk5cacshm *cc5 /+5 evs 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 6ab*xsgv) pl7 at one corner of a square 1.00 m on a side if the othalg )xbv*6s 7per 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 t2g cta7ms (*.c)yqv wihe point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in terms of ca.cyv(ist g7q 2*w )mQ, 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 electric fpwk*ix:-viqb i5 ofu 6g5-/a y03-ci o-jgcprield $\vec{E}$ 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 electric7u(uff0g6 a4/9.fpgtj-mht w 1q goa t field at points A and B in Fig. 16–57 due to the two positwf g 0qgjt.9mupt-( 1ff6uh ta/7a g4oive 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 chak8--vhrpfk ;t rges, $Q_1$ 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 5 14gpkbi:czxmagnitude of the electric field at the point P shown in Fig. 16–59. The two charg gpxi:4kc5zb 1es 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 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 rijrc) /c- a uajp tscjl*-6:z-ight at 1.0% the speed of light enters a uniform electric field parallel to its dirc*c6-/t:cju--ajjl p za )i srection 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 flux from a cubical bo3 4ypsog*si u3x 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 18h.9a nx :v ruvvlfh6(zhe+o(* cm is placed in a uniform electric field of magnitudex.n9haol vv z6hhr:*f( u+ve ( $ 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 obji(d6zl pna (o/ects, $O_1$ 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 uniform 3ry0 wyllih66 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 squa;p9 lz po 1l4aw4yp.rfre 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 equaarw lp9o44p.p; z yl1fl and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.gh j; j(2a,1rti3x 0nc6 p 9dv7wawxgmx n-zx050-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 5 fhpeb*.9xh0oxfk 5x 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 ofpdoub/b-9rwma* h zx 21g9;xn ,g7feo 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, and (c) beyond the shell? (d) Does the shela2nhbo7brf, zuxgep /9* ;gm 9-wd1oxl 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 0 h-cy;ler5j4gql eli )lm 5/gby 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 ggy lr4qci0;l 5le hem/-j 5)latoms 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 electric forr:gqu+7i88my y bz2yace between them is equal to the weight of either at the Earth’s surface?yg8ri7 y aubmzq8y+2 :    m

  A 3.0-g copper penny hasn8-4+9en3pzgc tzwta 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 indicat7d+ a 0,noddb/ppcg )pe that there is an electric field surrounding the Earth. Its magnitude is) pd 0,g7p/n+ocpdabd 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 experien6bvt(ho srw(;q j4 mt*ced by an e *t w6;sohvjqr(4tb(mlectron 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 mtcp 4y.iu xb2;m remains stationary in the air. If the downwar2iy;p c4b. uxtd-directed electric 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 CO grou*hx 6h0/kwb mqp and the HN group shown in Fig. 16–62. The Chbh k*/w0xqm 6 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,pkr7 lnn+b3/9 pc7u ov the electron revolves in a circular orbit around the protn9r un7plocbpv73k+/on 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 thenczrpu- ww h:l5o80: zcc,nqmeo 839an gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q we,hreowwczcnlme9 0z58o p83c: qn-:ure 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 spe((7 xu rvim2bz-it*tpi k wj;/ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargenfnp mz e -qmc/7ds*o)rt c2-5 $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 encapr)xec sc ki3wq+0-,hsed in insulating plastic and suspended vertically from an ideal spring 0+- c3qic pwesx,h)rk $(k\,=\,126N/m)$ 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 “leave)pbkwhfs zz 7sbrm 7*j6r:m 77s” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nfz7b7jr b7*mzws) 6 hk7smpr:early 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 spark i1shr;w g .w0jx*p-w guf the electric field exceeds about1jhg 0w; wxp*-wsgu.r $ 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 0aj 6j+ovcik60 .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 alm ,9-)hasm aqul the 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 an10 e6*( 2ryebwzocy(4a bha7i*aoq sre a distance R apart; 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, 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 tcw0nyaa s4o**a(1i eq6robe2y bh(z 7hen 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 position(s) x is khqz;rk.m jk cv429i *the electric field zero? Is the field zero at any othekqm*ik r;v9zk 4j 2ch.r 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 charges, each+ hsw7p87k kbu 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?