If you charge a pocket comb by rubbing it with a silk scarf, how can you determi*hzagp xn4)d )ne if the comb is posh4 z)n*dgpa x)itively or negatively charged?

Why does a shirt or blo jm3f-/gdkv , ;h(lst pi0ntc0use taken from a clothes dryer sometimes cling to your bopv0 ,/ fh;nk(ji0d 3ms -cttlgdy?

Explain why fog or rain droplets tend to form around ions o tafux9x t/ zcrb+6n;v+qb+f -r electrons in the airbb+ft/xz;rf9n+tu vc+q xa 6- .

A positively charged rod is brouhm ,9bre 1e4spght close to a neutral piece of paper, which it attrac9s 14p,mrb eehts. Draw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that 8 n5sbvat 082iezg0l 7gbk+gxhas been rubbed with a cloth have the ability to pick up small pieces of pabes2a tk5ggblxn0+0zv i8 78gper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the co0c f3pt1cfix -nductor.

Figures 16–7 and 16–8 show how a charged rod uluz6eb ;tk:*24e r qz6jubkqjr9+4hplaced near an uncharged metal object can attract (or repel) eltru4l eju+qk:bh*kr; u z96z6 eq4bj2 ectrons. There 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 cha8as *3qyihpyuc r 03/zrged, its two leaves repel each other and remain at an angle. What balances the electric force of yyisp8r 0qcha z3u*/3 repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that forj +lhfts90.5fu wn*bi Newton’s law of universal gravitation. What are the differences between these two laws? Compare also 05ft+9b isj f.*nwulhgravitational mass and electric charge.

We are not normally awar4uv6ij4hqa--fq ax xn hskg1a ;)(d-6rfzf8z e of the gravitational or electric force between two ordinary objects. What isa14jf6g -u xa (a hn-sfx4;)i6dq vqzhz8rfk- the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Whytuiuk/:4uc u)q+*r)ln 4l y wk or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sui o1 6gbo)y0lometimes a piece jumps quickly0gu6b 1ly o)oi away after touching the ruler. Explain.

Explain why the test charges we use when measuring electric fieldsgg-0kip4p4xk) i /u ps must be small.ik )pp4is4p ux/g-k g0

When determining an electric field, must we use a positive test charge, or would hvtc8v.vl c23 a negative one do as well? c28v3.vtlvhc Explain.

Draw the electric field dy(.ecmd3 gu( lines surrounding two negative electric charges a distance l apa.cdm( e du3y(grt.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Consl+/ png3bni5 oider 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 bp+og/ 3nin l5the electric field the strongest? The weakest? Explain.

Consider the electric field atlw9p jt9 f.j8i7w apym0j:2me 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 placmip9p90wtjj: w a l. yf82e7jmed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never cross y t4rr8,,pmjs?

Show, using the three rules for field lin0t;(lyleef m /5gq4i ees given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced around the chai/fm ; ye5gql4(0eletrge.

Given two point chargon to:onrugsj+.* ,w 5c;v6 eges Q and 2Q, a distance l apart, is there a point along the straight line that passes through them where :c ,oo*;o nr.ju6nsv5tw +gg eE=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge locate70txz-.br i.dqak2 5ajh*w x ad 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 of the testj*7 d2r.qxi ht50.b-aaxk waz charge along this line? Discuss.

Sketch the electric field lines for a unifor-dn qmpj)d6 6 p+8+du+t;gv bqma4rhlm line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field unibq 4d6lm++nqud +ap)hd -pgtvj8;m6 rform in strength?

If the electric flux through a closed surface is zerkr- q(e;x)(zh ttebxg,:9k bso, is the electric field necessarily zero at all points on the surface? Explain. What about the convz:x 9, hxrb q)kes t(t(-begk;erse: 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 ecqz.r)3v fn1wr83twvl ,gj /r. If the sphere is replaced by a cube of side r, wec .wvjvf/lwz,83qr)r1 g t3 nill $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge of v ;s kbdov39+zayyb8mo-)y -p$-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between ani;d(l:hbdn,6 4+)pfmjq o5 :i1am kt u r,xxgz iron nucleus)dg:px +di;n(to zj1m5 l:ai6rkmx4 ,hf ,uq b $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force bv;s9 g/sr1kus etween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude ofb3r5t gqs;( xh0+amoypr7d 2h the 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 z02u)tep t:a is4txs; 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. Tha5 qs+9g vdx+mey are moved, and the force on each of them is found to have been triplq mx+sv+9a 5dged. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on 5 ;-pgusdmt8cv ) ak iq1h:aa)a dry day accumulates a net charge of msu;c 5p18h)t: ada)k v-iqag$-42\,\mu C\,.$ 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 tlmf.b97 7 pbyy s 8bdtni4tbj*0+lrm1he electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding n iae(t5l4vt nxx8k*/ 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 )kn pts6(dg4q7x)jf ya fixed distance apart. The sum of their charges is What charge must each have f)sypq xd k6j7(n)g t4in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge r ,5u:u p.dwny$+75$,$+48$ 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 particw v9;fw4;+g edmx0r+feokb b+ les 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 e5 bdsqxd9 :lykh5u7z;ach corner of a square 0.100 m on a side. Determine the magnitude and direction of the force olkyhs;qud9bz 5: dx57 n each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive +t/hbz8;0kvdjte, wm charges, on opposite corners, are replaced by negative charges of the same magnitudej;+,wv b0h8/ezmkd tt (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side d(sj6w)h m; c8w3deobk, :jib7pjgn9 l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charj6g)k37ode m(d swci9p ;wjbhj,b :8nge 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 cornersykn0bs8e;7d2qmglsgz z 6w. 9 of an equilateral triangle of sig6s972z .z0wymd8k blgesn; qde 1.20 m (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 chahp 9 p,aal2.-ps4iam7pf9h esrge 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 nonconductinga 5ffz5x3x 8i2qyjo2 gbj+y)sr.oj8i spheres 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 inic3/8no h+3 yu/53ejzkyqxz p qtially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transfen5+/k8ce/y3zypo q33h q u xjzrred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of t iawl, l;aj a(acu6:4whe electric force on an electron in a unifo4l:(u;la a ajwic ,w6arm electric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a u8gshf8mkg98ilv5e ;yq6 0m t lniform electric field, and it experiences an electric forcv sh8mlg8 0 te8myfqig9l;k6 5e 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 o zpn7tvg 8/ixm4u ad,:n 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 elbgeka ic+ 5vrb;g :n1/mw, 0auectric field 20.0 cm directly above an i ;m +v/51:ncg0earwbi gb,a uksolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleratiolh/*irzrihgt70v brm 8y 8-v *n experienced by an electron in an electrl80y8v*ih- gmti/r bz hrv7*ric field 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 electr0d/j6t*u fx jn /brq vhib/s56ic field at a point midway bet6*/jfb v 6u5q0j nxih/t/rsd bween 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 electric field lines about two+6jca m),utj3wa1pw o(z. jko point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where a w55pdun-)) bkb;rt w yproton $(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 r.mvxs - 9m7gwiest in a uniform electric field and accelerates to the north at a rate mixgs.-vm7 w9of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway bnb c5a7u7 jc:8cr8oj retween 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 electri5db/u2z z9q )xjk6ojz c field at the center of a square 52.5 cm on a side if one corner is occ j2kzzoj 5xd/qu)69zb upied 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 electr2 kpm b1e9js( r/fhoe)ic field at one corner of a square 1.00 m on a side if the other threr1k se9mh(o)e p/f2jb 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 the point P vz.+ os+ (gs :ivwwpsm:p m6:*yh,qzrin 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 Q, h :*p +r+ v:zo6s(pvm ,g:.zwssqmiwyx, 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 vbv41 lfk.j -fz6nu6abldw2 49 pd7o nfield $\vec{E}$ 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 off31g ovmyqv ijv, ;bcf56mg(0 the electric field at points A and B in Fig. 16–57 due to the two positive jiocf(fbv61q;vg 3g ymv0,m5charges $(Q\,=\,7.0\mu C\,)$ 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 chargmr,tn/k :c7pccjyr+ 3es, $Q_1$ 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 electric field at the point,tur bpa )nh )we:h)(i 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,))waph t :(eri h),unb 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 enlh)g1js+q+p8jdu ohbn-cp 6 5ters a uniform electric field parallel to its direction of motion. If the electron is to b5 ph8h+c1on6 ubj-+pq gl s)dje 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 bk gv46)grux4 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 radba ky;z;*v+ na2l; tjhius 18 cm is placed in a uniform electric field of magnitudent+ ;;jh;k2lazab *y v $ 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 objec yf1m +(x8hcnd g+ ,dg*,plcbuts, $O_1$ 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 fietapo8wce dhr*+n2 *t5;gi :wlld $ 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 :fgylj bz4/mj 8m(hb-xmap:+he plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on eac j(g ml/mxa+pfz-ybjhb: 4:8mh plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radiuwarnd*j o(:hvozc(kx5bzj y .x: 4;,ss 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 qyc;-+ga n8k4xk 5 yvfcarries 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 tc29/miweoq dm ds mja /0.)tah16xs9mhe 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 inner9hq9amdjmxeo/m0i d c6.s1amswt/2 ) radius of the 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 molennv ,,oli xn j;j cuoq+;;*qh2cule 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 atoms is 0.2e and on the indicated C and O atoms is 0.4e. Assume also that atoms on each molecule are2nl;xq;j+ ni*chuqj,n;o,v o 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 force between them is equal to t gv 6qo,oku+a1he weight of either at the Earthu6,o kaqog +v1’s surface?    m

  A 3.0-g copper penny has a positive chargp -hi;yxp*yniq(xtgt 10/e( pe 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 indicate3hvh p7 3)x (g7qh*jew2bssyk that there is an electric field surrounding the Earth. Its map2hs3g*s x77yj )qkh3bh we(vgnitude 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 fl kq 614o2b( g0n xpw)t9lockwhat is the acceleration experienced by an electron neafo 6o1kbcg4 ntq9lx2(kwl )0 pr 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 remainsxsf 4aloq3h )r9/b:mg stationary in the air. If the downward-direca4 mlg/ fr)9:s3bxhqo ted 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 group and to/x5.oibbln rvne7-v7aj 5 - ghe HN group shown in Fig. 16–62. Thbbai/5vj5 o7vln x-n e.7 ro-ge 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 hydr mr-0,bez.m;o9 24d lgydiggoogen atom, the electron revolves in a circular orbit around the proton with a dmz og,l 4;e2b-ggod yr9m 0.ispeed 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 than gravity, were respy v 2m( dwf)k fva/zlx5/l28pfonsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what sho/ylzdmf( avx25 / pvlk8ff )w2uld 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 spe4z41h+r 6kd 5 ch2*mocpi6gudi;uc yked $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 cha6zzbz:8 lh2x xhhc u,5rge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 insulattkks.xq ub9ov0bk9, ;ing plastic and suspended vertically from an ideax09kk; bqtsuvbo 9,.kl 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 tin1evnj8tql.p; 0x4 azj y 24-g spheres a41z x t8eql .ajj0v;pnt the ends. When charged, 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 spark if th y64:dn ksl22buz 89m mew:lnze electric field exceeds about kwm69 d bl:u42m2yzesn8znl:$ 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 f-xkj62 l3oszcharge $+0.340\,\mu C$, 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 electrb v7p je/,h6lijeplsz; w/ /-wons 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 distanc qd 9jh3(8tdy, kwy3lo1wav0te 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? (tw3 ,81yvlqa9 d0khj3tdyo(wc) 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 position(s) x i,jl 24wpj3 ayvxw oz6*s the electric field zero? Is the field zero at any other points, not on the x axis?o3 ajj62w,wp4 *yxlvz

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,x9mzcjn*9 j7e 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?