If you charge a pocket comb by rubbing it with 3dk(zrsg6 myspb+ ,5b a silk scarf, how can you determine if the comb is positively or negatively chs r56b bd,gpmyz+3k(s arged?

Why does a shirt or blouse taken from a clothes dryer somn9x5 *l0qcyyjetimes cling to your bod *5cyl 9qjyx0ny?

Explain why fog or rain droplets tendiawg so b.3:e) to form around ions or electrons in the air:b)oe w.gs3ia.

A positively charged rod is brought closl/9+t -6xsm- ;.mj1cu e9*jfetx7c bsumar tne to a neutral piece of paper, which it attracts. Draw a diagx*l mfu1 tb+ a;er/c j mtctm-9su7j-.nx e6s9ram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler tvv, 93f .zwgsghat has been rubbed with a cloth have the ability to pick up small pieces of paper? Why is this diffzv g wg3f.,9svicult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the;9kece rq 4 o.(mfdh;s mo8s2q conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metal 0ru,4c/ wq/*tje ohe tobject can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Wh,u0ewh 4q/otjr cte*/ y not all of them?

When an electroscope is cdcwun( pi7 l-0piw7g 2harged, its two leaves repel each other and remain at an angle. What balaiild0 (c-2wu7p wngp7 nces the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similari8p)r+qv 8t ih to that for Newton’s law of universal gravitation. What are the differences between8i itv) q+8rhp these two laws? Compare also gravitational mass and electric charge.

We are not normally a.;:wgqovffblm0x h+w3j ,v+/6jb rcaware of the gravitational or electric force between two ordiqj 3:m+h,vjw0al;.xbc6fb g/+rwf ovnary 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 conservative force? Why ormi0y 5 rdbs3k)tb qdn3 w48 bkg7bm;,u why not? (See Chapter 6.)

When a charged ruler attracts small pieces of papersesms5 b*x 7gb(j/4wd uxk;l6na7lqtd 60z0 t, sometimes a piece jumps quickly away aftekld bznl0 gqxdb st jsmuxw;6 5470/7s*a6 e(tr touching the ruler. Explain.

Explain why the test charges we use o+wvtom2:htn /l(q3 xwhen measuring electric fields must be small.t2hqo / n+l xvwmt(3o:

When determining an electri jr9zp6vaq* e/c field, must we use a positive test charge, or would a negative one do as well? Exrjze9 a */6pqvplain.

Draw the electric field lines surrounding two negative electric charges a dista1/ yueecl k3,gnce lyuee/3g k c,l1 apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart.i-kwie tfzk s/ax40-1 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 field the strongest? The weakest? Expla k-ai/sft0w ez4i k-x1in.

Consider the electric field at pointsp(hzb( 8-mfjdd*4 cbi 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 placed at that point, then list the points in order of decrea8c- hmfbp dbd(izj*4(sing field strength (strongest first).

Why can electric field lin 2q-k; rt6gze(ouz z 7ykc6ou3es never cross?

Show, using the three rules for field line qfm3*mp9fs,ym. s5 d lz(te4hs given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced aro(lm,* .hqmdfs 9ym5e3tfp4zsund the charge.

Given two point chargesvg h pwik d06(.j97retxis6 jb04 z*pf 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) 0g vb(j40.pfh9 7k6ixjdpi6 e *tzrswthe same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an electric field line at some8r ,vnpl kwx(ar8m *sh9.b /uk point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along w(k8xp. nua 9h8*m/,vk brlrs this line? Discuss.

Sketch the electric field lines for a uniform line of charge which i y-f8gqdb*a 8cx5dnk2nr.yn4s infinitely long. (Hint: Use symmetry.) Is the electrickydd.2 n 8yc x5nnf4-8agb*rq field uniform in strength?

If the electric flux throlb 8hg7h 9oa8 5,4ltq9 +jtn9aluf yapugh a closed surface is zero, is the electric field necessarily zero at all points on the surface?a5lp 94a 8qtnfj bga+h97ylo 98,lhut 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 surrounru8. 8yje2f( f/ b*v7f;qu *ldagdtxfded by a spherical gaussian surface of radius r. If the sphere is replaced by a cubefl7*buju. yaefdq 28*g 8vrdt f(x;f/ of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge 6sq bz*np7x:o7 kz a1 ah2kci7of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the dn o1*ty;u cmn*hpe.( electric force of attraction between an iron nucleu.y e;n* nud*hm(pot1cs $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force/zmg2p+ z lj+x between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the forc c(kmq+cv-cju i// sj-e a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles e5qc eo- p8a)tx 7lk;w:dfn z3sxert 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 forsf(*nb:x58q.jx b:8 )m i ajsc:kcxmtce on each of them is found to have be8mxs(.: in kqxjbcftsj:cm*x 8:a)b5en tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a nho k+1i()b ri b ,:k;hcaa/psmc- :daket charge o( 1ki/rbkckp -;oc+s:i:am,a hab)dh 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 elec(ylx5(b:mo aa :q .9nplo(tpi trons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electricra30b46do tj*w -wdzrf p/pb0 force holding the electron in orbit $(r\,=\,0.53 \times10^{-10 }\,m)$ around the proton nucleus of the hydrogen atom, with the gravitational force between the same electron and proton. What is the ratio of these two forces?    $ \times10^{39 }\,C$

Two positive point charges are a fixed distance apart. The sum of tj;p b3s6x5h mjheir charges is Whatj m6x sp;53jbh charge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge . gp*wcto:7c w$+75$,$+48$ 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 particaj 90a-f / ihjb3pv)lqles of equal charge, $+11.0\,\mu C\,$ are located at the corners of an equilateral triangle of side 15.0 cm (Fig. 16–50). Calculate the magnitude and direction of the net force on each particle.


the force on the lower left charge is of magnitude    N, and
will point    $^{\circ}$below the-x axis. The force on the lower right charge is of magnitude    N, and will point    $^{\circ}$below the +x axis.

  A charge of 6.00 mC is placed at each corner of a square 0.100 m on a side. Daib,dgj *+y 8l;9qruv nw+8o xetermine the qyjwunro l v,8+a*bd 8i;9xg+ magnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive clpxe:c ( 0-qtcww4hj5harges, on opposite corners, are replaced by negative charges of the same magnitude (F 04cqh-twc: xp( jwle5ig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there ard cgmx:9kt:)n5u5xrte point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the ot:d:u5ktn9)gc xtm5 rxher 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 equilaterals u olqyu;5te,hz4a4- b, o( f55;gmgd(xbihp triangle of side 1.20 m (F u;e 4 glty;bhpqf-5z(5ooa,uh(sxbgmd i4, 5ig. 16–53). The charges are $+4.0\,\mu C\,,$$-8.0\,\mu C\,,$ and $-6.0\,\mu C\,.$ Calculate the magnitude and direction of the net force on each due to the other two.
$F_1$ =    N
$\theta_1$ =    $^{\circ}$
$F_2$ =    N
$\theta_2$ =    $^{\circ}$
$F_3$ =    N
$\theta_3$ =    $^{\circ}$

  Two point charges have a total charge o a*rg.mqc0o)(k5fjx s f $560\,\mu C\,.$ 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 chargf /nn1l 5+ qsu7lcecmz31cyk( e 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 plasti/1 wv-*v8oz p e, c5 wj/3dntzxcudi-qc ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred frw itc8xzvz-p cvd5wq ndu 3/,oe1-/j*om one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on anmjt8 na 2zsls*+fnc73 electron in a uniform electric fijzmtla 3 8n+2nfs*s7 celd of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform elqd w7hgpge/sazs8p 4,u )1w)cectric field, and it experiences an electric forceag 4)sg/8 7whcqp1uewp ),dzs 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 xx+k4fibb; 5k8.4 N 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 e -la idqhks. isb u-0e.70dr8and direction of the electric field 20.0 cm directly above an ih00 -s ub8salq.7- .ridked eisolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron in an3e k 2 fojn2lkxym7w4 a(tjz), electric fijo)7(w,z2a eyklk2fx4mt3j neld 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 dcwd; f.c hi)bi4 2tif2irection of the electric field at a point midway betweenfb2f itw)4cdi;i2h. c 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 f fcsf1line61h7i;i4lield lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point i1x-krvc rl ;x.o b-s-hn 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 r)k/0s n6 z*iev)vog r psbgne4x mv73z,bf8(zest in a uniform electric field and accelerates tofb z30)4*mi(6v 7bo spzre8n)/vkez gnxg,vs 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 mmb:hvo 69i y+ridway between two equal but opposite point charges is $745\,N/C\,,$ and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?    $ \times10^{-10 }\,C$

  Calculate the electric field at the center of a square 52.5 fvle):lsu6q:qq w9. gaupime *2xi*,a;il* m cm on a side if one corner gx . * l* :w,iiqma6iae 2qs*le;upq:f)lv9um is 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 at one corner of a square 1.00 m on a side if the omy3du /ii ue1.n4l 3.hcbaw5+ dfbri.ther three corners are occupied byr bi15dhd l3w/n ci..3 4yi.mfuu a+be $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the elhz9qfy9+1h htectric field at the 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 ht 91 9zqy+fhhyour 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 electric fi y;hbbt1;f/ kjkb7,aield $\vec{E}$ 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 magnit *9q3,*0zld z3yn zgi rbj,ruoude and direction of the electric field at points A and B in Fig.* zz9grli3zjr,3 dyqb ,0u* no 16–57 due to the two positive charges $(Q\,=\,7.0\mu C\,)$ shown. Are your results consistent with Fig. 16–31b?
$E_A$ =    $ \times10^{6 }\,N/C$
$\theta_A$ =    $^{\circ}\,$
$E_B$ =    $ \times10^{7 }\,N/C$
$\theta_B$ =    $^{\circ}\,$
(16-51)
(16-31b)

  You are given two unknown point ch kqo1; b-oso4vaa52y w-l a0ezd6kv,sarges, $Q_1$ 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 thef5j7j( ry7s-t dcx:v i electric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is t5cv:-7dsj 7 xjyfi(r 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% tsq/f7ezs e,f+l ( ,lfthe speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the space of 4.0 cm+q,lf 7/z,fefs set(l ,
(a) what direction is required for the electric field,  ----待选择----rightleft 
(b) what is the strength of the field?    N/C

  The total electric flux from a cubical box 28d 8vnfilxvv aj 5 .9)np5-:zmj.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 pl 84 ggp r: r 8u4jklnwzd013mzpt/gi:laced in a uniform electric field of magnitude mlkni gr j:p0z pgw g/3zd48r4utl8 1:$ 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, dbbvhp,2 hx3.l j*aw351d cy o$O_1$ 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 fefn(ktoz21+m(gul6 r9h .ioin a uniform 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 The plateskm5o y8al4 a p4gj,-km are 1.0 m on a sideglyao5j8 am,k4- m4kp and 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-cm-radius metal 5ex0fkze-wfu *rc98d 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 raditjar xh0/cy vj gf2r;2b;5pc/us 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 aits:r;heq/3d n uncharged thin spherical conducting shell. (See Fi;3qsd :/ erhtig. 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 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) -6pzwnza4rx together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (da nr-6xz4z) pwue 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 eip 0-7jlz s/ kwxvzndq:fn6:2mm.i h 4lectrons be if the electric force between them is equal to the weight of either at the Earth’s surfacelxis4-dhizwkn7n:f0 6 z .vjm/2p:mq?    m

  A 3.0-g copper penny has a positive charge of hk*h-,1+fth6e :ghhbn1dgm-0n gw d v $38\mu C$. 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 therqer:v.ax+38 bnr5fbte is an electric field surrounding the Earth. Its b+ae: q8f3rnr xt. 5bvmagnitude is about $150\,N/C$ at the Earth’s surface and points inward toward the Earth’s center. What is the magnitude of the electric charge on the Earth? Is it positive or negative? [Hint: the electric field outside a uniformly charged sphere is the same as if all the charge were concentrated at its center.]    $ \times10^{5 }\,C$  ----待选择----positivenegative 

  (a) Given the local electric field of what is thvje(g iq4 tvjx v9hu29cpg601 e acceleration experienced by an electron near the su v (g4juh20v69j xepqi1vt 9cgrface 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 radi-olcvf .a (mup; 03(vobdp-gt us 0.018 mm remains stationary in the air. If the downward-directed a.g3vvto-(0( ub d;m-opp clfelectric 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 Cs oj/px ;qijt2 5+8vylO group and the HN group shown in Fig. 16–62. The C and Oy5t2x/o+8 ips;jlv q j 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 +w00:jaf62jmtj og oie * ee5kthe hydrogen atom, the electron revolves in a circular orbit around the proton with a spek 05je e +0jo:maj6fgtio2w *eed 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 attuxa4 zwehu6dnw2u+r6o7cz36 raction, rather than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were pa4w6h wc3zn 6x276u odue ru+zlaced 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 speknt)n8 fwj3:: 4 aniiyed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 char,a wsrs v y.-8gy.u h6m+(nm4 sht:nzwge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vertio /3 nb.z z+2tezoeitsl yh t5w5;)5pwc-cgr5cally from an ideal sprinn crt+bs iglwt5z-; 5y.5 e5z)3 2eozhtw co/pg $(k\,=\,126N/m)$ 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 wit*bm-x,b/v 9z b mugjn8h “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends/mmbnzg, 9xju bvb8-* . 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 the electric field exceeds abonda7,,h p ko,wx9g*i tut ,okhw,9t pan *xig7,d$ 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 c.0 h,p t( cm;bruhbaw6harge $+0.340\,\mu C$, 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 a ve1/6q2bhqagrr 8)fjll 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 are a vv s qcit8pp e-6:dp/6distance 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 cp/vveq dip-c6t6s8p:ontact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig ez/c-txhk2ixs rfnhd. 8 m6*50n) cee. 16–68, at what position(s) x is the electric field zero? Is the field zero atfxczhxn5 )dr068 thk .2 n esem/*cie- 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 poi o;vv65l8f. bbw,ylyant charges, 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?