If you charge a pocket comb by rubbint1*4z/efhd t am64pqher 4g lo7hq-i7g it with a silk scarf, how can you determine if the comb is positively or nezip4m47r*/oe g ht aq-4d7qf61h etl hgatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes staz++ evwuv3 11tf8kghsr uz 6rc3924a pzq+cling to your body2esv16r+ u3tpz4a tzs1u ++rvkwf hc8a9qgz3?

Explain why fog or rain droplets tend to form around ions or electrons fm tee7uc-3 1nin the aicnef t1-me73u r.

A positively charged rod is brought close to a neutral piece of a-v)rc rvqhn)x:)o ;vpaper, which it attracts. Dra)q))rn:v; vo-rhcaxv w a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth- xw tntiu: 4+p zeop9h::ogcgj6,5ff have the ability to pick up small pieces of paper? Why is this difficult to do on a humid d9j txh:ofo4g z:w6nu+5-pi,gf tcpe : ay?

Contrast the net charge on a conductor to the “free charge 5d pzp36 xnxs ,ok.4rcw0:uvos” in the conductor.

Figures 16–7 and 16–8 show how a ljbrk,8 l56pf charged rod placed near an uncharged metal object can attract (or repel) elfb6l 58rp,jlk 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 charged, i*txnhzms tg8d1: .i(rg+ily4ts two leaves repel each other and remain at an angris*dzyt.8:h+(m 4 ln1 gitgx le. What balances the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law x lb +hnl4k7+pof universal n +b74xlklph+gravitation. What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or eqe4pue;cyt6 ;z3jf )vlectric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of each one and wpq;c ze)tj uv6ef4;y3 hy.

Is the electric force a conservative force? Why or why not?uu6rq0 w+5 hkk rgr*-u (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a viw7ph,s :ks av +e:xv(5 u-e0m6goh wpiece jumps quickly away aft7- avg ewois:v:6p+ h(xvm5euh0sk,wer touching the ruler. Explain.

Explain why the test charges we use ;dy3f)ukjd h* when measuring electric fields must be small k yj;hfud)*d3.

When determining an electric field, must we use a positive tm+nu6hnu:; ;swwb h:dest charge, or would a negative one do as well? Explabmu:6hdw:n;u w nh +;sin.

Draw the electric field lines surrounding two negative electric rfymuj 2ig:5+o +u/ n+w-fkuc charges a distance l w+:+jf2oyc+ugikun rf- 5/m uapart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Considexeqlai+rxria;sp6 5+,,c x k+r the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bottom,,i+ +c;rx6iq +lap5arsx ek,x left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and 0 vzk)3poma9zw m(g7w 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 l0 )kgw3(z aop7mvzmw9 ist the points in order of decreasing field strength (strongest first).

Why can electric field l0gn9pl (nsnp7,;lvda ines never cross?

Show, using the three rules for field lines given in Sectuia5 0dz a28d m28.oovyyab d1ion 16–8, that the electri182bdo5 dv0i2a aya .m8yuo zdc field 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 to,ttth3q 4;orp:wt- l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where tt;r:t t3toh4w , q-opthis point will be.

Consider a small positive test charge located on an electric field2 o :*-qecg (rojhb3je line at some point, such as point P in Fig. 16–31a. Is thejerj(qb23oc og-* :he direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge wheb6ikz q5q 0g77z5q+uquk:f d ich is infinitely long. (Hint: Use symmetry.) Is the electric field uniform6 eq7f0zu+zi:q qq k k7d5ub5g in strength?

If the electric flux through a closed surface is zero,wx7tml3.rfy- .j )pqw is the electric field necessarily zero at all points on the surface? Explain. What about the converse: If-7 jwl. .)yfwqrpt 3mx $\vec{E}\,=\,0$ 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 il zcomiunp*yus50g ,v,) kyqiep /1(86il3r r. If the sph/i,sp) (mr,gz3k5oiq6 8lyilu *c1 yneuv i0pere is replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a cv:dl6;bqzxy g .xa6s+ivta(7hnnn 3lsni:- 0harge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attractionlnry,h46vavu q/o/ r8 t st:ilsr/n(0 between an iron nucleuat nqi l8hnrr:, 6vv(u/r /o/sty l04ss $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical fkn qy g19j./yrxn-x,y:s 9 i,pgjld. dorce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude 9fpkg)n6kb:ui , ny f3of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust partp96 goa/:yhft/j9o fi*v9 dz bl -byc3icles exert 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 force 8yhvyx;8(c: p ai+iaz on each of them is found to havpaxz8 ;c h8i:vyai(y+ e been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool zne*,5nip okp80 i8lf rug on a dry day accumulates a net charge of 5*n pkii,8fo0z8epl n$-42\,\mu C\,.$ 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 in 1.0w9bcivw:dyy qi v0f5qvk 6v2 .n+q, /f kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric fbrt+9, hctfw; orce 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 f3g1ltz7a0g o yin,srm8 4mhc3ixed distance apart. The sum of their charges is What charge must each have in ordly7z 3 g, o03cmr4ht1amgi8sner to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge sj9rlt57i66 biou )um- ( ky5hzv0 hul$+75$,$+48$ 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 partizpxpm3y eev -skb-+8;cles 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 istf+o t.c oo3(g placed at each corner of a square 0.100 m on a side. Determine the magnitude and 3.+f tto oo(cgdirection of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive chargeld0*a-tqhmr : s, on opposite corne0rl-t*a dh:qm rs, are replaced by negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square,ej:o7 f1m20ya blhk f of side 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 other three charge2lkhf0m,7j be 1ofy:a s.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particlekiy 0:jvrb p8:s are placed at the corners of an equilateral triangle of side 1.20 : b08p kijvy:rm (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 2-q 5 3xwdtxiktotal 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 spheres have a total+9reoh1rf ag) y ac1z0 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 ball ty n4ry o8,)u fqpiyh fg-snchz0 ,)(*bo an identical ball 12 cm away. The force of attraction is then 17 mqpbh)4 -gyfu i ,nyy*8f hzo(0sr),cnN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and dit,qitj c*5zxxerzw x0a2q- 8, rection of the electric force on an electron in a uniform electric field of stre 2e0zaq,txz8trw*5q- xx cj ,ingth $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences an9t.m1* qzmbw r electric force o.mbr *91wqtmzf $ 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 ond nz/3b1;5rwcy h 3jvn 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 electr f7bs e9k/.a6o 0 kg-lwyo0)qoid0gduic field 20.0 cm directly above a9dkawb-/sg du fky)o7gqie 0 6lo0o. 0n isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of th r4k i:)hvzt+nrq7*njq 26-:ah gxoipe acceleration experienced by an electron in an electric field of qt)g ijr+42*kpr o:nhvqi7z :hx na-6 $750\,N/C\,?$ 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 midway58wq;t q(aex9dr*. vdc xh9ie between a (ex v;9aqht8 wrdecxd5q*i9. $-8.0\,\mu C\,$ 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 avzeqdo/51; 7fdvfcl*t s xr-1 bout two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space wherm)*p5j xblk5 ye 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 d .pxs;zqnh*-f d0 3 tgdibi1xtp,h37in a uniform electric field and accelerates to the north at axhtzsh1ipp*.dn30 ;fb x7 gidq ,-3td rate of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between two equal but opposite point charges isg ))ifpt:rxvp5k iez43 g9qz6 $745\,N/C\,,$ 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 *az*qv.nr2 nus u,vye-ka/ l5 square 52.5 cm on a side if one corner is oc*5,u kve-nys.2 r /* lnzquvaacupied 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 a339 xmtlfdlvv- 5d0 :9qabvi o square 1.00 m on a side if the other threev0 - iad5vl qvt3xmb39 dl9f:o corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and + l;u/dagxgejln /g3.p y2o i,l k*zo6magnitude of the electric field at the point P in Fig. 16–54. The charges are separated by a distance 2ag;nkl+gdzjox. 6 ,/*alg oey i3/ pl2u, and point P is a distance x from the midpoint between the two charges. Express your 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 electriwf*1yl2ob nbc3z- acng 9pz*(c field $\vec{E}$ 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 ubv6 2lmmywvbs75. h d- 6e/frcx40gsthe magnitude and direction of the electric field at points A and B in Fig. 16–57 due to the two pedylw/50-v hsmv6r7sb fg uc4b. m6x2ositive 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 pog03idtpea 1 iq3p+xg:int 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 z3 b8gb.fl8 olllz/+7zml 2jg1xd y0tpoint P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P2lg8l8g3dlllz m+ z7o 0.bbytfj/zx 1 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 uf hcpfa(t3ck-*m)059 j vmvrz; mi/qwniform electric field p qfjamf(mvk p cc0-) 5;9tz* /mr3wvhiarallel to its direction of motion. If the electron is to be brought to rest in the space of 4.0 cm,
(a) what direction is required for the electric field,  ----待选择----rightleft 
(b) what is the strength of the field?    N/C

  The total electric flux from a cubical box 28.0 cm on a side i:8a0lw. hun4er xoe, bs $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a uniform electric fi m3yiq/pea8 o -dx0op+eld of magnitude ypmx8/+peidq3oa0o- $ 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, kyyx5-8ttv9xv- t mc /$O_1$ 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 fiekn0qj i-m8nu;r 4u 4peld $ 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 plates are 1.0 m on*go, ;wvij9 py a side and are separated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edgey gw9* p,ij;vo effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball is pki;2-1mm-ojj l6 7zts8yjo k:a +xgf$ 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 charge of xjqw;rxhab 5:hcj4s.-4t z ,t$-3.5\mu C$ 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 unuq+x8otpj *a,., v*q qdsa 8 bhsbi(4icharged thin spherical conducting she8 q4s b i+( hiasd*xt*joupq ,b.v8,aqll. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule az rv ixmg;u)1w20tdy+ re 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 th rw2u1yi+)vd;0zm tgx at atoms on each molecule are separated by $ 1.0\times10^{ -10}\,m$. Estimate the net force between
(a) a thymine and an adenine;    $ \times10^{-10 }\,N$
(b) a cytosine and a guanine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other).    $ \times10^{-10 }\,N$
(c) Estimate the total force for a DNA molecule containing $10^5$ pairs of such molecules.    $ \times10^{-5 }\,N$

  How close must two electrons be if the electric force betweenrnrljr k.h 30cx 4d6y. them is equal to tr.yrn 0dhrx.k l63j4c he weight of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive cham0svbql*j t5vk 1aa- *rge 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 su1ye,0d0 ox nxk xvdf*1rrounding the Earth. Its1vxdxye,d0 x fo10*nk magnitude 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 electricy) e1-6t0;p;x-zrgs bw g lvyg field of what is the acceleration experienced by an elzb;-1rg; gvgy -ytx ep)s w60lectron near the surface of the Earth?    $ \times10^{13 }\,m/s^2$, ----待选择----updown 
(b) What about a proton?    $ \times10^{10 }\,m/s^2$, ----待选择----updown 
(c) Calculate the ratio of each acceleration to $g\,=\,9.8\,m/s^2$ For the electron: $\approx$    $ \times10^{12 }$ For the proton: $\approx$    $ \times10^{9 }$

  A water droplet of radius 0.018 mm remains stationa*aie+hhi2 h/ury in the air. If the downward-directed electric field of the Eauahh+e*2 i hi/rth 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 the HN group shown in Fig. e8. z5ap1ns m p78 c+n 9jatiaev1ap3x16–62. The C and O hav a 9 8m5na.ce1szp8xpaintp+ 17vjae3e 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 electr .pm c2)chiuk;on revolves in a circular orbit around the proton with a spe;.k c2 )ipchumed 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 thanln+4c ):cdc+u:u ti8h maqqg8 gravity, were responsible for holding the Moon in orbit aroun+ )u:hncdm88:qt qc4aci gu l+d the 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)i3 c.svoq; nz $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charge ;2eet8rj)ybyg ( +ukg $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 verticaltaxd z72rji:3ly from an idea: 2rzixj7d3a tl 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 wire : /k7 jwgpq+m2ueo9ews with tiny 24-g spheres at the ends. When chareu/ mj7 w:w +oeg2k9qpged, 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 spago ve8v h-obecj0b7 31rk if the electric field exceeds about ecvgvbo oj1h3e-80 7b $ 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 ne gu5 k jxx ,39an6.ul)hqfgz8dt 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 aluminmw:azx rdx(0 5xdy: 5sum?    $ \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 c 1oo,g5ma+/tqj/ izqA 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 sphere A? (c) Sphere C next makes contact with aq5/it, g c/zoomqj+1sphere 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 positl/p p4cf6kt n2ion(s) x is the electric field zero? Is the field zero at any otherkp6 c/pt lf2n4 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 chargi ,qm)bus*9vbgib )u7es, 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?