If you charge a pocket comb by rubfu x/;.mo272ewf lk gsbing it with a silk scarf, how can you determine if the comb is positively2x/m7.;gue fsw f2k lo or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to your 7)umu(z(pnqt1d* l cw body?((p) mzwc t7d ul*1nuq

Explain why fog or rain droplets tend tshdg vx, 0 vb50x5zn :j;jij:0)ax sgxo form around ions or electrons in the aij5jx sx si 0gn:0x0 5vb)gva,jhz:dx;r.

A positively charged rod is brought close to a(dk*-v oky3 ie74ysvp neutral piece of paper, which it attracts. D-pv3(v*od k4yyei s 7kraw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has y4edszus2p4/x7 m0 hubeen rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficult to do on a humid day?s 2h/py0mxdz7s e u44u

Contrast the net charge on a co skmmz(0qh g4rn4tl (u pp 2v-k..id7lnductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 h sg3 e;yjcw q0-,ee*ashow how a charged rod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why notwghaey e-e03 ;cqjs,* all of them?

When an electroscope is charged, its two 1gwn g/)5fuu7g a1 i4tnxbwmhxj; o5, leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t ,m on /itxuw4nf 1g5;1jgb5h7 )wgauxseparate further?

The form of Coulomb’s law is very similar to that for Newtoq i0fswu/v50mc:s q;cn’s law of universal gravitation. What are the differences between these two laws? Compa5 mu/qisw0vq 0ccs ;:fre also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force between two a1f /sh)v o-vegzx6v t8px5 b+ordinhg/ts)v1boz+e68f5- x xav pvary 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 or why not? (See wgt7 9pt ru/d/ -4yt7hfz5mo qChapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece jumps qui*dlob*hx/ k.9 6rhhe wckly away after touch l/ *bh*.ow6hkreh xd9ing the ruler. Explain.

Explain why the test charges we use when measuring ele , oezqnp5ry8,ctric fields must be smallqnyz8p e5,,or.

When determining an electric field, must we use a positive test ch,l*wi 9 ) udhxyhc9nzd1+u oz*arge, or would a negative one * ci uwyl1*o)hun z,xd+zdh 99do as well? Explain.

Draw the electric field lines surrounding two negativ6gftaed 4b a iw;4s0k4e electric charges a distance i0b;a st4d4k6ef w4ag l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Consider mr5cb:5 7f.ef j2vrnl the magnitude of the electric field 2.5 cm from the positive charge. On which side of th c5lm25r7nbrefj f.v: is charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electri.8xbut prm9+5ho/5 gs adlq*q o:n(kmc field at points A, B, and C in Fig. 16–48. First draw an arrow at each q /kpu5x9mlngotmsb8ah dq.(+5 r:*o 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 strength (strongest first).

Why can electric field lines never cro )e r,94iedf5vm8 tzr4p;gnofp1h9ncss?

Show, using the three rules for field lines given in Section 16–8, tha15 syin640zhw)zut9ofxapa7 t the electric field lines s4 zsfona )0y5 uwx1 i69ph7ztatarting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q l 0sc)(fl xan/and 2Q, a distance l apart, is there a point along the straight line that passes through theml/)lscax(n0 f 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 f;+l)g,pvjh .:b c kaq)qsbakiw( pu 25ield line at some point, suk)uw:sg a5 qpbi)+ clbk,.hv (q;2pjach as point P in Fig. 16–31a. Is the 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 whic9/thji vmtun/ -po7 6hh is infinitely long. (Hint: Use symmetry.) Is the electrictt7 nuh6jm/v-h9p /oi field uniform in strength?

If the electric flux through a closed surfab+3.9e/ssu 9 n .dewpifyrrg.ce is zero, is the electric field necessarily zero at all points on the surface? Explasf w/9 9.rip3b+ r.sue ynde.gin. 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 radius r. If th) b9wwva m p7o)axhs(7e s9phvsbaoa ) wx7 (7mw)phere is replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make ufezz9 o q1h.yy9 (vwh7p a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of 4s2.jzlxh +6mg a48 ttr7euxjthe electric force of attraction between an iron nucleus7s+jgam8xe46jh xt2zrl4t . u $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force between two prof/a k d*+4qrtbofq; , ext p,.sigie:7tons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitudezmz;q1hc9j mr5 ,)6 nqz:qb vu of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exer:y.nyqj m;eft.xc)p i y3j,x1 vq+wx -t 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 tgvh;5vi;u/w n90 vcq. They are moved, and the force on each of them isvgu;tni5vq 09;vwhc / found to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a n o*3dh:tn/cekatd x2 ;et charge of k:/3tod2 e xcna*th; d$-42\,\mu C\,.$ 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 electron0yejy0y j-9d -wv cj:gs in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric fp tn(c:qm/af s*- qq9eorce 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 their chargm- 0g*vfo(qi-dsq q6 fes is What charge must each haveqqi-mo*f -6q v(g0fsd in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge knzri2q r )tk:/ ma0k0$+75$,$+48$ 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 chargezmpls1vb ;. fe8via16 , $+11.0\,\mu C\,$ 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*/6yseyxo/f9 k(q cl4 ieyta: 0.100 m on a side. Determine th x y e4*t:lcysk/6aoq ey/f(9ie 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 charghn,e9rq9 yru1*(r6atyhn .k1l;pyz *yk)mnh es, on opposite corners, are replaced by negative chargae lkh91h)my h;* *p, tkn91 yruqr(y.y6r nnzes of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnibl)gwvi47,mu +hyg z )tude Q, 2Q, 3Q, and 4Q (Fig. 16–52) + g 4wu,vg)milyzb)h7. Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the corners of an equilat9relu79 u* q.w)crn sseral triangle of side csl9 .9uwq* re )r7uns1.20 m (Fig. 16–53). The charges are $+4.0\,\mu C\,,$$-8.0\,\mu C\,,$ and $-6.0\,\mu C\,.$ Calculate the magnitude and direction of the net force on each due to the other two.
$F_1$ =    N
$\theta_1$ =    $^{\circ}$
$F_2$ =    N
$\theta_2$ =    $^{\circ}$
$F_3$ =    N
$\theta_3$ =    $^{\circ}$

  Two point charges have a total cha0nb 9q*nu,wpqy3t5ki q(8 vhcrge 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 chargqhn 948e *ztvde 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 pl7vm5 vitvo/j)astic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the oth7v)mvijt/5o ver?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an :gtvom mnj;)(.ur yv4electron in a uniform elvtr(o u mvgj) n:y4m;.ectric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released egs 9czl 2cz ljhmp.jr)59..rmue *e5 in a uniform electric field, and it experiences an electric forcecg5zeh9s* l5ejzmm )e 2 u9p .cl..rjr 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 exerj+kwq .c5phf *7tsflwggjph(-i ( - l/ted 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 t7)bklm .te*crqbt5 w1he electric field 20.0 cm directly above an isolaq1*. k bl retb7)m5tcwted $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electyzn5n 55 7udefron in an elect yzn7f5edn5 u5ric 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 fieled6e i.ai9x8m d at a point midway betwei 9md.ixa6ee8en a $-8.0\,\mu C\,$ and a $+7.0\,\mu C\,$ charge 8.0 cm apart? Assume no other charges are nearby.    $ \times10^{7 }\,N/C$ ----待选择---- towards the negative charde opposite to the negative charge 

Draw, approximately, the electric field lineslu,z)yl3 ck z1 about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a mrq;i * .pqx7ppoint in 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 rest in a uniform electric field and acceldiuwz+ p,wd(+.kdz3+t ;yi xderates to the north dddwi x(z. u; w+t+3,ipdzy+k 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 two equal but opposixt +s ))rrw+vjte 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 squa7c5b zvjiv*r8)f-d b (95 -g2h;gsjyughxpec re 52.5 cm on a side if one cornez*2h dy -eg f (rxv7i vg;5 gcbh-pb98uj5sj)cr 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 s6 t /6v4cqeezkwl;-h)q(mu*xng i2w r ide if the other three corners are occupied /c-wvghneex6)mz u42l 6r qw;k q *(itby $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and mag b9k 08;)z.q2jf lm .a mfp,dau6z7nbtnk3cdwnitude of the electric field at the point P in Fig. 16–54. The charges are separated )m l nnk ;wd8qbzf6,azdmfc79ba3p.k2 tu0 j. 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, 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 elect8)30bjb w 3gytsb1d 0dr wax.kric 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 the magnitude and direction of the elec* )98aj (xn8z;wio xjtokwwe.tric field at poijt8(*ojoaizw) ;w 9n.8ek wxxnts 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 point char( l84h uj9arw2b*bznqpfz9u/ges, $Q_1$ 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.vtoq(0je m6)xya 8 ht the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of)hxa(.8 0yto temj6 qv 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:n 5:b/pudl w m6gdh(h% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest n h:gl 6 dumhdbp:/5w(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 a7ul2 hfqvrpynm *e -54 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 ;ypvth.; h e2;xly:o/d onn3cplaced in a uniform electric field of magnitude /;; n.clhptn x ohyo:e;v2dy3 $ 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 objey *lm6(vc: jfqk1 rs.:mow qlfb1:o2pcts, $O_1$ 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 in3g/ge4o2 x lhz5qg .kc 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 metassm3zume m 9s5+79pxi+d 3 ijml plates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is m+z5xmei9mduj is+sp33 79 smthe charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside km 5f6 (rrxka6a 3.50-cm-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 rajwx;nv e+1p1ni7 l rp,dius 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 3ubj f,stzeg;bze s 89 ;(5abycenter 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, and (c) beyond the shell? (d) Does the shell affect b;b, ue 3jgf8sy ezat(b9z;5sthe field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held together by electrojvy*i+dlwr ,,5 9uqqaoa1pk 7static 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 als,v,wadq*kipr9 oj ql7y5a+1u o 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 electrons be if the electric force between them is equ( xhqh4 u:7pu-3bufld al to the weight of either at the Earth’s surface(7fhh:pld 3u u4 -uxbq?    m

  A 3.0-g copper penny has a positive charge /xma/9rh 6daxs* j3m5 z*5 my:. gou *vrjebqjof $38\mu C$. 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 thr3 y8u0z6 msiaat there is an electric field surrounding the Earth. Its magsym8603uz rainitude 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 q(np. n 23: g7input2wn kkkr9gba35celectric field of what is the acceleration experienced by an electron near the surface of the Eartpg7a93 .( kun n rg25n2bcq:p3 intkkwh?    $ \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 station :*h tzq,qdla7llxi .mh 6t04a40jiriary in the air. If the downward-directed electric fiairj*, 0lt70 :hhxiitq ad4 q6lm.zl4eld of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force betwee(85ja-udcg m cpv6ej : :2utqen the CO group and the HN group shown in Fig. 16–62. The :qe5ju p dcm2au:tcje8 (6 v-gC 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 atow8vdyu1 od5d + 0fc8qagu* s6 p3or1gzm, the electron revolves in a circular orbit around the g+p*8 faur301dq vyczdd1w6us8og o5proton 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 electrical attraction, rather ty c0uz8qu c 48ij0m/x ecz(yl6han gravity, were responsible for holding the Moon in orbit around the Earth. I8z/c0 miyy 4u(06cqxjz8 ue clf 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 sped0 0c ytf,p3jked $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 cha6q 4tguy lb-kerny5 00rge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vd)tga7t 3 q2m0e oc+mc4nvm3i ertically from an ideal spring 4a qto + mc32d3m7gvm0)eintc$(k\,=\,126N/m)$ 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 -hg8*vmp wv47;szjex m,yqw:78-cm-long wires with tiny 24-g spheres at the ends. When char,wv;gsqmy *hvzm 7j :xw 8-e4pged, 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 elect y mw:,:drpta+b2*xtbric field exceeds about bb+ tpdx*wta2y:m,r:$ 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 chazws 0ow30/z;j5jbk2s i xzb. orge $+0.340\,\mu C$, 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 alumi4ef5 ip0ldu+j num?    $ \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 sphereap (r:y+uwc sef ;tg)mzs2i,)s 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 id+2riguse s)p yzf ,amc:( ;tw)entical 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. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what position(s) pqnw ncbhvm*5mmzp;.i657n 1 x is the electric field zero? Is the field zero at any other points, not onwh5 ;q*ipnpz51m7m.bv mn cn6 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 jz-z3pi vh8rc7, dk+9w)) fln8xy slx 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?