If you charge a pocket comb by rubbing it with a silk scarf, how can you ukbp x *,o,jm(determine if the comb is pos , m(x*kjuobp,itively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimesf)lqw-z)fz 0e qhfxlo*lcv-v;s ;m07 cling to your bod zcz); *ehs ffvm 0ql-0oxl;wql)vf -7y?

Explain why fog or rain droplets tend to form around ions or ei z5q00tqeln /rmzu7 v 17i;ymlectrons in the air7i0n;5tq7zule mz /01iq vmry.

A positively charged rod is brought close to a neutral piece of paper, which idxw j3o+26mrtg j 8n,xt attracts. Draw a diagram twx rm8jjg2xn+6,do 3 showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth hav u,lu8 (u ks8gks:3rlce the ability to pick 8l :ugsr(lku3 ,cksu8 up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the c8wvjc-ddfo vjy9q+;x,f /6w r onductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metal ob0 zh4;twgw(hrc xen/2dut1( y ject can attract (chxny4w;d(2t1rh ( t uez/w 0gor repel) electrons. 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 charged, its two leaves repel each other and remain at+og 6lqzzl2jt: tr,9s an angle. What balances the electric force of repulsion so that the leaves don’t separatj+g ts6:ql9zz2ortl ,e further?

The form of Coulomb’s law is very si zd4 (f:z8u(j (adcqip-( jewvmilar to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare also gravitddaz(j(- vjiz(ufw (q: epc 48ational mass and electric charge.

We are not normally aware of the gravitational or electric force betswuc4ux: ;8fy ween two ordinary objects. What is the reason84suucw x:;y f in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapteo 6fl, lik -in )uly24lvi+9ye(ot1r 8*aoirkr 6.)

When a charged ruler attracts small p kr s9ghb(/t tra3b/ngg(c) d1ieces of paper, sometimes a piece jumps quickly away after touching the rulerka/t1sc tb(g3 )b(rh/dg r g9n. Explain.

Explain why the test charges we use when z gzty cv)6cm12znri h)l+00mmeasuring electric fields must be small.c2yzhrn+zgz0lmmv ic61) t ) 0

When determining an electric field, must we use a positive test charge, or w5/ha 8bxa-ymig tc)c0ould a ne ac yi/-0 gm)ba5x8chtgative one do as well? Explain.

Draw the electric field lines surrou0z,h /hbru 5w6xb c(yunding two negative electric charges a distance l ap0hhw 6x r/b5,uc(byzu art.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Co0miatn; x5fnq / lj5,/c)vykqnsider 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? Explaqi/ ,qv y5/0k)5t; jmfcxnalnin.

Consider the electric fiez1d xkv 5je)78ueh v:ald at points A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the nu8a dk 75:1)hv zexevjet force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric fielb x,9 *yj-wb5m6ukuypd lines never cross?

Show, using the three rules for field lines given in Section 16–8, that the e7 il pipf3ob4jcp0mx2+0c vy/lectric fielp00c74+bj p 2y3 mipx/ivlfoc d lines starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is theyc s ,r8go0i eu+(2lgy(q.7 qwkpg+crre a point along the straight line that passes through thckiwr 2 pqg ( ryolu,g sg78(.+yqc0+eem 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 loc)u7c .. pfxtght9i,me ated 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 mufci7pght.e9xt),. the test charge along this line? Discuss.

Sketch the electric field lt4qks gio+o*4ines for a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is theqokto+ig s4 *4 electric field uniform in strength?

If the electric flux through a closed surface is zero, is the electric field b;bam yvn72wbv0 oua uw2; ykf4jo55/necessarily zero at all points on the surface? Explain. What about theb5oma 0;aufu57jy2 vwkwn 4boby;/ 2v 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 tf 5)u*f.3ckhfawxg bz:o r7l+q kto/ 6he sphere is replaced by a cube o wxk .u+l3c/ok hfa:ftz)f7b 6g*5qrof side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a fyekpes6xv0 h 4q(q33charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an4aoumqa +n:7jj s4m s: ct.ee8 iron nucleussa7a.4 ecqm+ nu: me4s o8:jtj $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive elecytiusr1tn2 *)8 tlnp1;8vxw g trical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude 8s+f v 6tak4hrof the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles ek0rz15sf,ggke k q) 5rxert 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 t 6st- 2abiefv.he force on each of them is found to have been tripled. How fart6v i-ae.sb2 f apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day. jdv:nsu0r/o accumulates a net charge onrdv./u 0sj :of $-42\,\mu C\,.$ 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 ad-y i(2u c3urill the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orbit d9za8y+(x6vcei-e c x$(r\,=\,0.53 \times10^{-10 }\,m)$ 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 sjm; 3yo/ z-elsum of their charges is What charge must eeo;3sjm /-z lyach have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge *nta9 c4 / kyoq)y6tmr$+75$,$+48$ 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 :h wll(z0o.u dof 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 8hhl. xrdo 2)/47 kixklmjgb:placed at each corner of a square 0.100 m on a side. Determine the magnit 2k7xm4 )/jx lhhk dg:iblor.8ude 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 positiveu*xzm8f8inmuxg22xzt.-(3vsuolm 8 q w1o(s charges, on opposite corners, are81 u(mql2gz ( uuxxx mnm.fi*o8t2w8 zs-o 3sv replaced by negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of sid.: nbs pw3bar4fy)u/re l there are 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 otpb/ swu.) r:bnrfay 34her three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particlegd vn z7ix 350uijqzq(j 4v.;hs are placed at the corners of an equilateral triangle of sidei45q zqvjih.nx;3j gd (0u 7zv 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 td+mq-c a:sztibf/(f2 otal 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 spht.: ywm. xh7sieres have a total charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially uncharged plastic baxqca 6bev 9.n e3i3*vbll to an identical ball 12 cm away. The force of attraction is then 17 mN. How many 3i3vee. q b96bcx*nv aelectrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and dir3*1l) +n:ktyji bqgiu ection of the electric force on an electron in a uniformb3 u:)ni1kgyt+ilj*q electric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released ino4;zbx z;31 .s+f( m;qg rpfa6lzdp aa a uniform electric field, and it experiences an electric forcexm3+ zpf;.6 ba4pd;;fzs(qz l1ra oag 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 isw tm;j29/0c93xg /lrjiqzukc exerted on a $-8.8\,\mu C\,$ charge. What are the magnitude and direction of the electric field at this point?    $ \times10^{5 }\,N/C$ ----待选择----updown 

  What are the magnitude and direction of the electric field 20.0 cm directly abkfv sgh 7tc+udsil/+9- o39 lsove asl9v+u/dig+-lt 9sf c7 3h kosn isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an1 mv2p:5st)yb xw+tlo electron in an electt)s+ b2:x5 1vomylw tpric 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 electric field at a point midway csu)7:f0cwu tzao flmro,.5qa05 s2 dbetween a0s20: cozt5),a.5 7 qrdfcoaus wfmlu $-8.0\,\mu C\,$ 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 k oprg ,+u/io8electric 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 s(q*td*av0o st pace 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 restr(u, c r9fem8o; qjrf/ in a uniform electric field and accelerates to the n;8of,furrcj (/qmer9 orth 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 tw95bzno8y rp .uo 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..vh:sx2oup/z k *vh gg,:gr -w5 cm on a side if one corner is occupied by g z:p-vv.kgo2hwrs, gx*/:u h 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 myi k -k+dr+9.u(as0 hvw7pckat one corner of a square 1.00 m on a side if the other three corners are occu+. kvkac+sup 7yrd0-wi (m9kh pied 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 poilx6d fian: 8z94 )hm.onj t2blnt 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, xln .nl 2hozx9t4mjb86d af:i), 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 fiel ppj2q8*/ oua3hmv+eg d $\vec{E}$ 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 magnitu z/i- ei gmh.s*u( 9klihe +ah(g+0iipde and direction of the electric field at points k++9hiiiaizhp h-meug( ( *e.i0/gsl A and B in 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 unknown ( 2 q1+z 4p*engwgwvkypoint 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 s 8j0datkyzq f,4+ *e s h24,(khipkswelectric field at the point P shown in Fig. 16–59. The two charges arqd(hw4key *k4i20t8, aj +,sfsspzhk e 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 right at 1.0% the speed of light enters a uniform eleqg,a)o4 qq g4tctric field parallel to its direction of motionqqga4q ), g4to. 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 ch/9 :ov lwhn/iubical box 28.0 cm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 c*qqais -hddi1d .m,n*i wm6c +m is placed in a uniform electric field of magnitude .iiimnd*cqq s+1-,w*da6dh m $ 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,b. 3tx7 bnhgs*h*b2wj4re9 t l $O_1$ 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 placeh + cy2v4ook4cd in 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 +wcy h+ r(vzaw0v,up;square metal plates is The plates are 1.0 m on a side and are separated by 3.0 cm. z+p a+wv r,u;wvh0c y(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-r (3c ) cwwhvao(s0fto5n p9*jradius 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 radi0qvv// s fa1ufa8 rs-dus 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 centegbp76gcm q/c o u;q+opda+d37h/ q8lgr 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 inner radius of the shell, (b) inside the shell, ag qa3 ppmdg7g/c6 uc+l;b+h8/dqo o7qnd (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 molec(s i3cj0 v5yzcule 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 are separated v(yic3jzcs05 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 kr31v y92ztvda :t-*j b xkjqhmm68i* if the electric force between them is equal to the weight of either at the Ea*m k21-3 ti*j xzvqvydaj8b:tkmh96 r rth’s surface?    m

  A 3.0-g copper penny has a positih pp-b* ees2r5gv u w e-l)z-e3)sfw,wve charge of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

  A proton $(m\,=\,1.67 \times10^{-27}\,kg)$ is suspended at rest in a uniform electric field $\vec{E}$. Take into account gravity at the Earth’s surface, and determine $\vec{E}$.    $ \times10^{-7 }\,N/C$  ----待选择----updown 

  Measurements indicate that there is an electric field surrounding the Earth. y os( 8ldj64x znu9ws:Its magnitude is abou 4nzxu9yw8do jsl:6(st $150\,N/C$ 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 acc+rhm .ybs9xc+ eleration experienced by an electron near the surface of thm+c9 .sbxy r+he 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 0.01(s6 f gwoycad3i44 zu*8 mm remains stationary in the air. If the downward-directed e*f3 c4og 6wuad i4szy(lectric 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 th,sr/l37 gj zqoi i fr-2jmc9(de CO group and the HN group shown in Fig. 16–62. The C and O rig/j7rcdm39f i2( z, jso-lq 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 revolvefe mgtg*/ ze47)wjq)til./frs in a circular orbit around the4j7 t)f./)mge r*lq twief /zg proton with a speed of $ 1.1\times10^{6 }\，m/s,$. Determine the radius of the electron’s orbit. [Hint: See Chapter 5 on circular motion.]    $ \times10^{-10 }\, m$

  Suppose that electric.tp/3zo r)l hjcc 9o;duz6 5fhal attraction, rather than gravity, were responsible for holding the Moon in orbit around j ;tup.hozd5f) r/o 9chzl36cthe Earth. 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 rf-gwybe-m1r; x82;s ya y1gp$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 ftgk2lti;c//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 enkw nia -pdg6yz u*4))qtzgm1 9cased in insulating plastic and suspended vertically fromyqk6 -ga g*4u9mpzi wtd))nz1 an 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 with “leaves” that are 78-cm-long wires wyg1xu oazk2/r6km u;-ith tiny 24-g spheres at the u2 ygkx6 - ak;mruoz1/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 geni0 kbz9ev9g(eze ;l owx73an, erate a spark if the electric field exceeds about gw vzbn 9k(lez o3ie,9ax70;e$ 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 eja0c rrpj dd pb-++ *2t,yap36l 5capnet 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 ofx :dfv0fhcu5 2 aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B are a distance R apart;9tqvd eqc5wo-d7z2k-9 bk)ta 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 then moved far away.ta99eq5 kowvk--)dt cbq2dz7 What is the force on sphere A in this third case?

Given the two charges shoa-tb ir7 9mk6s)q) iwjwn in Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other points,bi)9rqmtkaw6j 7si)- 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 charsr5z98lbupf7mt z3p/ ge $8.0\,\mu C$ 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?