If you charge a pocket comb by rubbing 2 3f80zg s +r*,csirfmdufmfi4 qy80a it with a silk scarf, how can you determine if the comb is p ,q0 *f+fyra8m2si4u 0 smcrdg fzi83fositively or negatively charged?

Why does a shirt or blouse takeua*b3k yu smy;stb*d.lww 0c90+)kt (gnsoi ;n from a clothes dryer sometimes cling to your body?o ta0s; byy*km ;ugsn wd3*s+(kb. )0cl9ui wt

Explain why fog or rain droplets tend tooeszvwvr;f5b1.-6n eje evtf r7 p.3: form around ions or electrons in the aiv.efv b;w jer:6. v5pfze 317onsrt- er.

A positively charged rod is brought close to a neutral piece of pa/n/ t.0h-pzq c0 .pnhan (scuwper, which it 0 hpn. 0tnq/sz(ph.nw u -/ccaattracts. Draw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have t1efgksjhzd0nq- 8e l*0 d0k2x he ability to pick up small pieces of paper? Why is this diffi-0dkxh ej2zn 1de 8*0kglqfs0cult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” tjy63 zqkx,z10 l r6e8o2iadf k0ab)z in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metal nivmbo h3*.-nobject can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. W*bn.o3i hm n-vhy not all of them?

When an electroscope is charged, its twog q/8qy)/n xt jk5owkh42s:j j leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t separate tyhn2k/x)/ gjjws: 48qq5k oj further?

The form of Coulomb’s law is very similar to thlqn co3h)7 4vfb2mhz)0 gfld;at for Newton’s law of universal gravitation. What are the differences between thes3 vb;2f)o hlm4 7qn0zcfhgl) de two laws? Compare also gravitational mass and electric charge.

We are not normally aware ofwn3 da7 nh6 dy 0c*f+qm.;z/bkvqi0w p the gravitational or electric force between two ordinary objects. What is the reason in each cqhvdq*3/z.wn;bap 7f0 dycm0w+6nkiase? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why n::vi yl3ob3jkbx p(rf*f q4 :yot? (See Chapter 6.)

When a charged ruler attracts small pieces of pape /, ydu+fexob7r, sometimes a piece jumps quickly awa fuy/,7exb+ody after touching the ruler. Explain.

Explain why the test charges we use when measuring electric f/zq nuz0bp1oq-m/t)n ields must be small./z-q0 tu /1m)pnbzn oq

When determining an electric field, must we used*c6knw53 c r9vv1dmu a positive test charge, or would a negative one do a cn6 9rvdw*u5kc31dmvs well? Explain.

Draw the electric field lines surrounding two negati 62gy1friig 6rve electric charges a distance l apr26g 1ygri6f iart.

Assume that the two oppcu b6hino2q2e5tj2w ws2jqm: b;; w;gosite 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 2n;6wgbje ;cw qw 22s2;q:5ombutijhthe electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. Firsta qqz q/(ninbt5-a .(k 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 field (ti(.qn-bq nq/a5a zk strength (strongest first).

Why can electric fielc5 0e;o1k ljq;or.kn td lines never cross?

Show, using the three rules for field lines guwbpqx+18nb (:c2d u ziven in Section 16–8, that the electric field lines starting or ending on apw:x 8 nuq(b d1zbc2+u single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a point alpthww0 p5btbs*1 2(3-kvu fnf ong the stpw-wkfb(25 t un0*sv pbt31hf raight line that passes through them where E=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 located on an electric +qw6vr b9.v uifield line at some point, such as point P in Fig. 16–31a. Is the direction of the vel6 rwq9 iuvbv.+ocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge which is b8;pg,d/myrn 1( hdneinfinitely long. (Hint: Use symmetry.) Is the electric fi /pb y(nr8h,mdg; nd1eeld uniform in strength?

If the electric flux through a closed surface is zero, is the electric fp,xgg5lab/puu* od fo3 q,n:xh/r7 5tield necessarily zero at all hp gxgn/a / :u p*t5qo57lbuox,fr,3dpoints 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 a spherical gaussian surface of radiuso g8:w bheey(7 r. If the sphere is replaced by a cube by:7ege8 w(ho of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge of nemg.46 9uh hk pl*fbkq dup9cz+ k-:,$-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction r ey-3 ;yfhe5gqey+ kbth04d1between an iron nucleus ;r-0h eq b1 4kgyyy5 eheft+d3$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical rni69 c-rl-+f :hk pdf n.xi9pb pv (ir54-apdforce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of qh3w8cfdo 1tw-k q3d,m) k1mbthe force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles d- k cwhs2s/+yexert 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. The 7/ 1.pd )rz+uwnhmasxtm j+*omdpb 0.y are moved, and the force on each of them is found to have been tripled. Hou/ mhj7 0z1ps*x)b+rtd nwp. o.ammd +w far apart are they now?    cm

  A person scuffing her feet on a wool rug os h 5 .7biknoyr(aid93 .b(e35xdl kjqn a dry day accumulates a net charge o5.a 3n dk9idx(h(krjq73bi l5osybe.f $-42\,\mu C\,.$ 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 inc;v:sg58q:uyu jw ;vz 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orbit 5k) u 1ufm,8 )gynqzzh$(r\,=\,0.53 \times10^{-10 }\,m)$ 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 d8+/;glo1 anc jwlowt,7 k6 oxxistance apart. The sum of their charges is What cw8/7jg lwkx c;oao,lo1tx+ 6nharge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge yjr,35w dp0 kl$+75$,$+48$ 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 char/rz 7h3xx* -mqgod*mb/c1ckut( by3 r ge, $+11.0\,\mu C\,$ 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 placln7xbgas; b5x0 jpt-n:h 5eg:ed at each corner of a square 0.100 m on a side. Determine the magnitude and direction of the force on each hplbgb :s;tx n-g:7x n0je55acharge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of therykib,: 8 j3hl positive charges, on opposite corners, are replaced by negative charges of th3 r:hjliky,b8e same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are zi)e3 z.jnvu7 point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q,z7i zj .ven3u) 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 equilateraln6 g+t m 8xt wdn-f:zlqji b6b/9dv,7z triangle of side 1.20 m (Fig. 16–53). The chargb-dm,8:gbqxzid6 9tw n ntz + 6vj/7fles 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 evb*iro-4 azwg-.3hfcharge 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 spheres have a total char*reoha,bh /g22lt mh9oya3t.po l/c, ge 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 un*rxj,yu mlyjegs0)gp(3 j 4 2ncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How man 2x,mp0g3e j(sjyjuy*n4g)l ry electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction o-i +le-z*o c-wgktd *tf the electric force on an electron in a uniform electritg k-t+lze* -w- dioc*c field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a5l,u w 8ft(9e3nyu) rgni t9cn uniform electric field, and it experiences an electric forc(,n) 3 fitu5nce grl 9w8y9unte 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 a 0g.gswh emh 39$-8.8\,\mu C\,$ 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 fielh*4 y5arx+h7 b3its2el cm; jnd 20.0 cm directly above let;74 rsh+x 3ja iy5m *2chnban 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*ow6xgd jj73w* a/ cbjs0)fvan electron in an electric field o j* jdg37xao*)sc0fj/v wwba6 f $750\,N/C\,?$ 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 direct :bug*,m i(rycion of the electric field at a point midway between a y(ribu mg:* c,$-8.0\,\mu C\,$ 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;, qcr o a9ht2ijx)hih+;sx *d 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 spa4i8whr;7na r oty +vr:dt4uq(7xh:o/z ed- ruce 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 electric fieldjkao:+us64 vi and accelerates to the north at a rate6 aou4ski+j:v 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 b 4-+bh:cjtku7pw+sq-epbt1 mut 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 square 52.5 cm on a side if+zam gd1,aqtyk1(k *e one corner is occupiekgt y mdqz,+ 1aa*k1(ed by a $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at pe )(7o a orvc7x+.mil)4zrmjone corner of a square 1.00 m on a side if the other three corners are occupi)r pjmm.7 (ove7xlz 4aco+ir )ed 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 ts)x2g: (q00nji jg fgshe 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 Q, x,i sg)x gjgqs(: 0f0n2j 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 fieo+-heeg0u n+1sn 6ko 0pj8gpgld $\vec{E}$ 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 la9ml g5b */ceof the electric field at points A and B ig*b95acmel l/n 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 unknownez, 69m ck1uj+np-:fmoiwn 9r point charges, $Q_1$ and $Q_2$ At a point on the line joining them, one-third of the way from $Q_1$ to $Q_2$, the electric field is zero (Fig. 16–58). What is the ratio $Q_1/Q_2\,?$   

Determine the direction and magnitude of the electric field at the +wp b:w4ps(jagl2fgc/ 14qa5r 8ucudp na35kpoint P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint betweenf unb g 5jcca541a23apdr w:q4lp+(u gs/ k8pw 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 atj ao xdq5iears-p:) ovxy:os8)ri )v3-lu y* 0 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron 0)avvyqoo * :s-r)ioiu)8x -exp ly :5rs3ad jis 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 bc:qqk .i 9t1bkox 28.0 cm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a uniform electric j/ i oo6caqq j4()gm;7*q3n:k djvvdwfield of magnitude q7ok wj;ci qd*:jd o q6( 4jang)3/vmv$ 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 objects, x6yjjc9js 1+n q8m3yz $O_1$ 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 uniffyrk6,ggby /3i k3q(p k8.szform 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 squaret t-lb 6wa*/3 zufvzsw-t-pl, metal plates is The plates are 1.0 m on a side apfw 6-vw,tt- tsl- b3zlazu*/nd are separated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cmmn,ml /xoysl/l(n .v ,2c z-yc-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 total chv +dh+f 18qzuoi4(nn carge 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 uncharged thi+ .ly8u)) y:cq rievlqn spherical conducting shell. (See Fig. 16–33.) What is the e:yll.qu )qrve+yc8 i )lectric 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 shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shap(8p6 sbs4i ww j8qru7qed DNA molecule are held together by electrostatic forces as shown in Fig. 16–44. Assume that the net avesi8(p4w6 q8r wqsu7jbrage 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 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 electronsmbchym8 j. sgz; l0/-q be if the electric force between them is equal to the weight of either at the Earth’s -0m /qlz8s b.yg;mjhcsurface?    m

  A 3.0-g copper penny has a positive char .6 -;z2gpcb c+lfmy) 1cw(gdb)1hvahvi nw+z ge 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 an eler5;7zekoj zh)fo tl17 ctric field surrounding the Earth. Its magzol1ko ef7 j)r5 ;7zhtnitude 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 4e zx d62k+h p drrkk:i :f-5luz/s)si what is the acceleration experienced by an electron near the surface of the Earte-kf6 z+uiiphk5)/drdk:4l s2z: xrsh?    $ \times10^{13 }\,m/s^2$, ----待选择----updown 
(b) What about a proton?    $ \times10^{10 }\,m/s^2$, ----待选择----updown 
(c) Calculate the ratio of each acceleration to $g\,=\,9.8\,m/s^2$ For the electron: $\approx$    $ \times10^{12 }$ For the proton: $\approx$    $ \times10^{9 }$

  A water droplet of radius 0.018 mm remains stationary in the air. If tmzk y;5i+iq9g)*/pcl dicq g+he downward-directed electric field of tq/ i9 *+5;z clg igdqm)pc+ykihe Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force betwee(ll. 41yk fiixn the CO group and the HN group shown in Fig. 16–62. x.1li(k4if ly The 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 revo1uey ns u,mek.sn,n6:ia . s9flves in a circular orbit around the proton with a speed of si.e1yn.f,,6n sma u9se nuk :$ 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 electricalh2dy1drk;x ih9-j l q/eym c)lte(:o- attraction, rather than gravity, were responsible for holding the Moon in orbit around the Earth / 1meted;y od2(9ihlqcjy l):-kr-xh. 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 6d ptr6 d-5+orjnxvkq1 8z18tysg o5n$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charc4 .e/p3k c2glsag/jqg ihu*/ge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 egxtej1qw h 8 wg6s.wf3f-uhj w6);e-incased in insulating plastic and suspended vertically from gx 6twj1 iq- w ujsfh-6.;wge)8fweh3an ideal 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 wn()utt wnwu( ho8v 0kzl)d.h/ith “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 wiru n /hlu)zn)thwk w(8t0(dvo.es 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 aqc ua h)rclw a*mj2.*6dw 3ls4od2)3 o*p vbtcnd generate a spark if the electric field exceeds about*l )acl3o*uch ra2t4d3mp) 6d2qw.scv*objw $ 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/ vw;fujuerc3wpmp6: f8 39t x 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,wu 3n/ee9ttr 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 conductinxo09x k cdt0 umdklz-i/4/ wc vyw-3+y omh+m6g spheres A and B are 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 s /mxk-m04yd wlwvux/ -o tdh+i3m0+y kcoz9c6phere 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. 16–68qtzp197onxmxczm iy t -960e4, at what position(s) x is the electric field zero? Is the1xn0 xpoeztzyi 4 tc-96qm97 m field zero at 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 charges, each of/z 8av p/chwpi 4/0ykf 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?