If you charge a pocket comb by qysk* ,bh)f;mje yb-.rubbing it with a silk scarf, how can you determine if the comb is positively or negatively charged*k s ey-qb,;h.mj)y fb?

Why does a shirt or blouse taken from a clothes drytx ,f3occ6 /ztqkq;z)z* h tmzta,:d0er sometimes cling to your bodx/)0*d tcta3 z qzzm6qh:tcktfoz,;,y?

Explain why fog or rain droplets tend to form around ions or el64b5ut o- kjdzectrons in the air.dbot k- 5zju46

A positively charged rod is brought close to a neb281gu 4e2mbf43.*i2zipwtqc65 af isi ok cy utral piece of paper, which it attracts. ze*ci fpi mbus gi21845422w6o. ba qi3tfyk cDraw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler thalv9.vmt dw7,jnp+:p kt has been rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficult to do on a pn7m kv,j 9t+wp.v d:lhumid day?

Contrast the net charge dl)+u/zw g 7xson a conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rbsbk3 u,j.ie r snm8/8od placed near an uncharged metal object can attract (or repel) electrons. There are ik um88br3.,s ns/jeb 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 eacdip+lli t. vlw.1;ti: h other and remain at an angle. What balances the electric force of repulsion so that tlp;:.d1l+ii.lv itw the leaves don’t separate further?

The form of Coulomb’s law is c/7 lzt8ogj b /okn7r8very similar to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass and 8ojz/nk7tgrb 87o/c l electric charge.

We are not normally aware of thr )kq4b e7zq.he gravitational or electric force between two ordinary objects. What is the reason in each case? Give an exampeqqkh)z7. 4 brle where we are aware of each one and why.

Is the electric force a conservative force? Why or pd4bovyft maa8u8nep45*eds m /j9b c7d8 z:(why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a cl0zp-neh(j 6piece jumps quickly away after touching the rulez0p(nec l6h -jr. Explain.

Explain why the test char3 zk4bcw4;hdk.e 2yyw ges we use when measuring electric fields must be small.e. 3d4czw;h 4yky2 bwk

When determining an blm ixop2 z-nx8q2 ,p.electric field, must we use a positive test charge, or would a negative one do as well? Explain.28lnp,p-ixx qo2z b.m

Draw the electric field lines surrounding two negahacy(5psd:+h; j emi)tive electric charges a distance l apar dps+y;h: m)j(cheai5 t.

Assume that the two opposite cham/j 5o 2lz 0uz9f9k 2bpmww7qirges in Fig. 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, b0q5j9l/ok 9ubipzz w72 w m2mfottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16++ph)c4kuk8cgqf yy9x r4 0jp–48. First draw an arrow at each point indicating the direction of the net force that a positive te4f0y)p4 rh qyck gp8++uckx9 jst 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 cross?l s/;z31umswl:a 4cou

Show, using the three rules for field lines give7kxkw,38x e vxh k5+b)bza (fcn in Section 16–8, that the electric field lines startb,x37z kah+ x)k58ecvw( kbf xing 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 there a poixx ktp . ja53)o4a+5cslpctsd6 58ukrnt along the strai5 ps) ra 68t 55 duc3ao4lsj+pxktxck.ght line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located o+cdfb1aw 6y * .tdctse6i l-x.n an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of t i.t+6tdcydsalcb*6-.f e1 xwhe velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line -ik(8q hbiw5mj21auxof charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform iw(k2b-i 8uiqax5 1hm jn strength?

If the electric flux th-bdt1uu qcsie0+*5 hqrough a closed surface is zero, is the electric field necessarily zero at all points on the surface? Explain. What about th*bt 0s5c hq1+u-dqiue e converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surjfa n(ne-s4s3 rounded by a spherical gaussian surface of radius r. If the sphere iaej3-f(4sn n ss replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make n yzh+7;q2lcdup a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitudjthzczf.-.. j1j 4ffhe of the electric force of attraction between an iron nucleuj4ff.jh. zc t- jzh1f.s $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical foro0 -/-rnwg chrce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the foo7/b(h5zr46paz(f yv tha b( nrce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a fs ;v *z0 v/gczzt4ykl f9.hm+dorce 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 at,xy a1f4cla .g2vcf4re moved, and the force on each of them is foundctx g.4a 4yf,1flv c2a 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 fd cu 6dp6igev,c6nb s28m/m.a net charge of c /d6esgu .f8m6vpcbdm 6 ,in2$-42\,\mu C\,.$ 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 almiz4b+dlk9 0fc+;x 0iobsln,l the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in or2-ldyi(s vbaj6eqt6 9cw(rl7r2f. r ybit $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 aq4e8 0fl my:ksre a fixed distance apart. The sum of their charges is What charge 8mlkqyesf 04: must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge n0,h ,n7dcvyb$+75$,$+48$ 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 equawyevsu u b i*svo,45/1l 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 isd o s.3bxp9+k- urq;jyq:l-xp placed at each corner of a square 0.100 m on a side. Determine the magnitude and direcrb+p: p .q9oky3q ;d-- suljxxtion of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the pos;vjd2gr9l c5 ditive charges, on opposite corners, are replaced by ne5dgl;cv j9d2rgative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of si sj u 779gkt7ejak7x.cde l there are point charges of magnitude Q, 2Q, 3Q,cj77gx eu77ak9tjks. and 4Q (Fig. 16–52). 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 pla*3k3j 0o zqnzoced at the corners of an equilateral triangle of s0o33 k* oqznzjide 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 0 aj*y*xcs7t che /hk+total 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 sphmo4ff- g,.v nreres 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 ball to an iden j5hsmz8/zxrm4jjy + :tical ball 12 cm awmj zjsxr5z/j :h4+y8may. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and d4-yd9e6zbcn -bqdbo4 irection of the electric force on an electron in a uniform electri 9q6oncbd44bzd b--yec field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a ud.6xr: )r8 loqmhrj.k*+gv i jniform electric field, and it experiences an electric f mhi)g*koqr xvr+j :8 .6ld.rjorce of $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is exerted on 60 h.m8in by/nql vb5fa $-8.8\,\mu C\,$ 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 v:)qnsi0zf8vvzg8 m): j7ov cm.b, ku20.0 cm directly abovv :f)k8vzonmuc 7jvb :ig,8s.zmv0) q e an isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitudechw8c;dne l 0) of the acceleration experienced by an electron in an electric field of dn c;0w8 l)ehc$750\,N/C\,?$ 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 fi( m0:n)w5lmub yvvhw u 0ou04peld at a point midway between a mym:00wupn)5owu 4lh u 0v(vb $-8.0\,\mu C\,$ 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 e i7by)+q0yl zzlectric 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 space where a pro4cfmyon ., dg hj:a;,tton $(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.s(m:assux 4k2 4iylk rest in a uniform electric field and accelerates to t44k:2y .xsl( kamiusshe 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 midway between tworjj47 m)j-r wu 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 ate irof+5bez7s ws 5- :, oi.elw2;unxb the center of a square 52.5 cm on a side if one corner is occupied -oz fnl:siber5 wsx ;ewo, i+5ub.27eby 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 fia hf +(vfl0z0eq3cx6a eld at one corner of a square 1.00 m on a side if the other three corners are occ0h3f6lafaexcq z(+ v0upied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction andw2q;i njim(7 y;6hycj ur7.zq magnitude of the electric field at the point P in Fig. 16–uq6wn;7c2j qri hyjzi7m ;y(. 54. The charges are separated by a distance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in terms of Q, x, 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 fiee qz6m; a cqiyt(0w :xxp:-gw1ld $\vec{E}$ 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 theh.jm klq9no5 ) magnitude and direction of the electric field at points A and B in Fig. 16–57 due to thlohj)kq 5 nm9.e 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 unknuixbn v i/,;;qqcpm+j6 isq15own point charges, $Q_1$ and $Q_2$ At a point on the line joining them, one-third of the way from $Q_1$ to $Q_2$, the electric field is zero (Fig. 16–58). What is the ratio $Q_1/Q_2\,?$   

Determine the directionn m;yrxw hj4.w(10x jc and magnitude of the electric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on1h .cwyw;xjrjm04(xn 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 rightp qzymg60(ugffk7 r1-2z kg(d r(k ma8 at 1.0% the speed of light enters a uniform electric field parallel to its direction of motia kdpzmfq6fyr2 (80g7u- g( (z1mkkgron. 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 is b2 ;wiwu:paa *;ulw2b-khd1x$1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a uniform electric field of;1b2 whx/g/8 u ynuvcy magnitude1g;c2 yu /vun/w8bhx y $ 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 ob471d 3 ftguv(+efo ogxjects, $O_1$ 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 uni :e6fn9uw+4pua ahm0ws z 5*eehs*.kd form 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 z+ex. rfw)od xwn8; -asquare metal plates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate;d) f rzao-w8 xn.+wxe (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.x 4y e0avx s+pha2t+z550-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 radius 3.00 m4gu9t4ctt 81u 6f x3lmpx gck5 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 ofwwe3 n .nzfg2)yj)9n 0b5tzay 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, (bnby2z 3 af0gzwj5 .)e )9ntynw) 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 DNAv8 ikj +t:vq h um/w8gq5y;w/f molecule are held together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge+gk;u/w5/ ihwyqq8vvf8 :tjm (due to electron sharing) indicated on H and N atoms is 0.2e and on the indicated C and O atoms is 0.4e. Assume also that atoms on each molecule are separated by $ 1.0\times10^{ -10}\,m$. Estimate the net force between
(a) a thymine and an adenine;    $ \times10^{-10 }\,N$
(b) a cytosine and a guanine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other).    $ \times10^{-10 }\,N$
(c) Estimate the total force for a DNA molecule containing $10^5$ pairs of such molecules.    $ \times10^{-5 }\,N$

  How close must two electrons be if the electric force betweea 1fa-qt:b ,cxkllai /u .kh:au318 oin them is equal to the weight of either at the latlu8kk11 iqa3.oac:: ufix-hab, / Earth’s surface?    m

  A 3.0-g copper penny has a positive chart ) i9;ssjp5wlge 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 surrg3c2;ty.lq:x(r ; hcv7qg8zcyl2jx qounding the Earth. Its magnqx zy:8q7yxc;;rg t gjc2cv(lh3q l 2.itude 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 what2li njkgu59. fym4l::a9j udl is the acceleration experienced by 49l lm95fuli g:.y2 ad:jnkujan electron 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 stationary in the air. If the doh*r9 nctc dzv;l7m.2d wnward-directed electddrt; .z hncc2m*97v lric 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 CO group and the HN grouobm/ddr+s -+ 9 9-ovcxud8 itup shown in Fig. 16–62. The C and O have chargesc u+-9oddd u/ +ro -8ims9txvb $\pm0.40e$, 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 f:cd xv6q4t9c -lc7hg-frvf 4 hydrogen atom, the electron revolves in a circular orbit at-fc6x v4rdv9qffcl-h 4 :c7ground the 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 electrical attraction, ratcyt:wz: (d6 ow6c zh0x8dk1b ther than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Eak0 : wc 6tdhc:xbd8 o6zzwt1y(rth 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 (er,u56o i;tool 6iik4 zuff8n5m+cr1 tf/o t$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargep-n239gpl go m $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 plas z6 enlz,n)p,wtu8/kgtic and suspended vertically from an ulzk )/, n,8etn6zw gpideal 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-lo5w* o sgxtaw -um0;j*rcaf:y 7ng wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each mak7swj ua:; ft**0cy -ow5arxgm e 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 exceexz+siexe0ri,v, ; * adds aboutse,;e*+v, zi0dxria x $ 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 cpzavwz6ws*kg7 / sz id8i8f .5harge $+0.340\,\mu C$, 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 aohembcv9 mk2y r99(1*cdw *ge luminum?    $ \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 ap0+3q,k8 5nau2 ww: bji kzfanrart; 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 mk 5r32 kb0,nfw+ iqzua8j: nawoved 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) x is the el+e*0ckc31cuye ea4tc ectric field zero? Is the field zero at any other points, not on the x axuaece 1 e *tc04+kcyc3is?

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 chax. da+ hkd*ybqsq6zxzwx +x 30stt70 6rges, 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?