If you charge a pocket comb by rubbi)s ( ga tu1:zl4k:/(wy)i7nlsugsvy dng it with a silk scarf, how can you determine if the comb is posi iu1yl:l av7k/)( ):tss g (ysw4gnduztively or negatively charged?

Why does a shirt or blouse ta j;xt50 ni6rc v3it)gsken from a clothes dryer sometimes cling to your body5 3r ;x6cv)i njg0stti?

Explain why fog or rain dropleh(r rob.vj;md,y0n h-ts tend to form around ions or electrons in the airdh .nbvr-(;0,jyh r om.

A positively charged rod is brought close to a neutral piece 7 8cfv(s dx3juof paper, which it attracts. Draw a (sdx7u fcv3 8jdiagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ability u3r8ti.( xbf udyq3)nto pick up smub tq 8rnx.d(3 yu)if3all pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to p;d8 +vjxc/ef the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an unchargx*1n 6o lzl. hqe0hq0jed metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them0noh x h*6e 0jqz1lq.l move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other glmo2(uhnz:6b6rfn + and remain at an angle. Whatzhg+ofl :66r(nb n mu2 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 of universal b: zmc1op2i(fgravitation. What are the differences between these two laws? Compare also gravitational mass and el:( ipzcomf b12ectric charge.

We are not normally aware of the gravitational or ox2h sf 4b;-wwelectric force between two ordinary objects. Wh2 -hx4 wwbf;soat is the reason in each case? Give an example where we are aware of each one and why.

Is the electric force z)t2fi (k4f90(pe/qet cyqf ma conservative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece jum9ebk3d(vc;s dht r8: gps quickly away after touching the rckrv dh:te ;938sb g(duler. Explain.

Explain why the test charge g wcztjtm*7dft (i770s we use when measuring electric fields must be smallzm7gd *wi7tt 70t(fjc.

When determining an electric field, must we use a posie8 eb)z cpm;-0b1ilxa tive test charge, or would a negative o)x;ib-0pezalb 81ecm ne do as well? Explain.

Draw the electric field lines surrounding two negatixt8np 1af6gus azp-xb90y 2s1ve electric charges a distance l aparp1 6psy g2na0a f18zxtb-u9xst.

Assume that the two opposite charges in Fig. 16–31rzh0 pyvs 4r8:a 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, boh vz4spr y:8r0ttom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–4io4wbzs+3b8 nwz l 0k gx/.9xp8. First draw an arrow at each point indicating the direction of thnxp ob3 l g4wzs.iw908k z+/xbe 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 ne6gyev.bq.j z .ver cross?

Show, using the three rules for field lines given in Section 16–8, thaia5p6 6(jqfk- oprq9et the electric field lines starting or ending on a single poin jkoa6q- 9 5pferi(q6pt charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, au;iid f;/ m +;m/xfgf7jta/wtyex 0+i distance l apart, is there a point along the straight line that passes through them where E=0 wh0f ; j/utmm;;/w yiit/++afieg fdx7xen their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge loca fqy,9dl6r,pd ted on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity andf6qr9,lp, dyd/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform l pe *+3na2bysf /gh9bpine of charge which is infinitely long. (Hint:+2 anpe s9pb3fgyh*b/ Use symmetry.) Is the electric field uniform in strength?

If the electric flux th /bo gv. jchjb6neve74o706ubrough a closed surface is zero, is the electric field necessarily7j.hb egu/ 6bcvj 0vbeo6n74o zero at all points on the surface? Explain. What about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrp5ryf x md 70axwi69z:ounded by a spherical gaussian surface of radius r. If the sphere is replaced by a cube of side 9:mfy 6w5 izrdpa xx07r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up ai di jqk8x4) hyn17/a+w2dkw g charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude pgiqoy 1ha 0+3of the electric force of attraction between an iron nucleupg30 oia+q 1hys $(q\,=\,+26e)$ 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 protonh; ks05 bu dlm+x0khx3/)vj igs $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the forcv,dy a0xn *o78 eiuq1k vidf90e a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a i*a)-ifbo z,e 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, zynuf f48*3 igand the force on each of them is foui*z 4nfugfy 83nd to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a d8 3+4 z p- f:v0gjypzecwwygbi+d)y b.ry day accumulates a net charge oc y+)i-d4 wj ezbpgyv .fg 0y+z8w:b3pf $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total char4c98ybemkg7l p s-d j7ge of all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orbi*bnq6(mp -(kgru b8oxt32 sms t $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 distanr v8rqgpb1zw (a0(.a xce apart. The sum of their charges is What chpxvwrg80r a( (qab1.zarge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge /s yc8f9 x0car$+75$,$+48$ 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 cha )p3li2)7(ah8stndkmttb vm8 rge, $+11.0\,\mu C\,$ 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 0q*m :4u xf2 am*rb pe6 gnb5rubm7s;9n.100 m on a side. Determine the magnitude and direction of the force on each chargu*r*gnm m:6s5 pn9xabub7 rmb4 ; efq2e.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the poq*sq8kw 6,3iq n/qiy ositive charges, on opposite corners, are riwi /*nq qokqys3q8 6,eplaced by negative charges 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 mag9ea +j af(m* 3aaw5bmqnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (3w9afm+eq5j (aab m *ab) 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 equilatzi+3*bjgmwv6 kq f(7teral triangle of side 1.20 m w kz*( tfivgm7 +63bqj(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 hda8y :9g8hcr14 qqvl (n+ tyrtotal 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 spher 6lrby*b uvh3:k-ua q9es 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 bqwzp.9o 6p4g plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons werpo 9bz6gqpw4. e transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude .3. hkz 3(b1skp+8 qcp6hb*gifp r kuuand direction of the electric force on an electron in a uniform egbf.ku rpu6h.3k18+ * p3iqhckp zs(blectric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences6g:p4y f(l jic4vcz* l an electric forcp*v g lj4fz:6c(liy4ce 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 exertje/d6 1 dddk8mc3 q he77emmm4ed 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 elec n7j l1hsi5j;6k:nunetric field 20.0 cm directly above anjn 716;nuehil jk:5sn isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of th uccgpdi (x7pd 3t)b-rqw x4)w(+2pv 3 l*mnake acceleration experienced by an electron in an electric fielpic )*ddq c34( v-gnmkpwl bp7+(x)ru a2 xw3td 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 th,64zx3klu 5sabm-nz qfbdh9f9k3r k -ba6lo1e electric field at a point midway between a ,kk - 96ubmhoa xa-3bzs39f5 r6lqf dnzlk4 1b$-8.0\,\mu C\,$ 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 fiel dz3e -c:e5bi0gm,gdmd lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric us)y7gh9z/od/7 we 6 tt8 penf.pkx)bfield strength at a point 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 electr(-tf1lpj..uc 1(h uwxoq. luric field and accelerates to the north at a rate of.1r .1ct(.ou fqu-hl l(ujwx p $115\,m/s^2\,.$ 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 opposi r4qay-i2d6ksnfh /0 kte point charges is $745\,N/C\,,$ and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?    $ \times10^{-10 }\,C$

  Calculate the electric field at the center of a square 52.5:a9s1mpbyl-8dv/t.x- ahc 8pr 82o p xuft. lh cm on a side if one corner is occupied 8 xtplyb c-la98o :p- .htduf/v2psahx 8m1 r.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 onw8y9q/ 7gyz zmne-4qv.2 gieccdj .)dn9jc+ z a side if the ot.-qey9zzc d g8/4 gjczvm92)cen.d iwj+ 7nqyher three corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of thdd .zdo11+sj de electric field at the point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x from the midpoint between the two+sd1zj d d1o.d 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 fc rkn6xo hjdpai1;: )9dm vvn; .sa.n:ield $\vec{E}$ 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 th g-fmgh)v2be ss.8 oa7e magnitude and direction of the electric field at points A and B in Fig. 16–57 due to the two posithebg).g -s oam78s2v five 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 unknavk bsu+: s(jn/4e;qc n:2ezrq d4:b down 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 direction and magnitumkj*g*d4jh (c de of the electric field at the point P shown in Fig. 16–59. The two mk*d4 h(cg*j jcharges are 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 the0 c. /f/7glvc8caf zim right at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electr70/v8mazc .i gcc/flfon 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 r tcmvp65l e4/b2or/n2 /b kxxcm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is place:4cvry-f: z zsd in a uniform electric field of magnitudez: cfrsv -yz4: $ 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 ob i6z3 ntrc40ep1d x3xhjects, $O_1$ 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 alg-p 5vm2ac7 g 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 metalme xc04qi /q-p plates is The plates are 1.0 m on a side and are separated by 3.0 cm. Whacpq /mi-x0 e4qt is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-ra8v5)eojq m11 qgf*la* uljdd eo-8y+ fdius 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 m carries a total char (p2 ,zbr:xdsz-/xr mtge of $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of an uncharged thin spherical conductbe9rgk5j x cu *::4s:c(kymhring 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) insidsburcmc::4 5 ( yjg h9*ekx:rke the shell, and (c) beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held tog03-a x0g2ebsjx j*typ ether 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 0.4etj32xj s- 0g*xb0aype. 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 sfd )xi-s24u delectric force between them is equal to the weight of either at the Earth’s- xi42)ssdfdu surface?    m

  A 3.0-g copper penny has a pt - x,1rild(awositive 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 thdvdxf-rob qt(/6q,w8fvt 0j 2 at there is an electric field surrounding the Earth. Its magni/orxfd,6twdv2b q-jt ( f v8q0tude 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 electqoh/vq-,:y 09tp x ivzric field of what is the acceleration experienced by an electron0yqiov /th:x pqv9 z,- 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 stationns ,m)z: mexc6ary in the air. If the downward-directed electric ):6nzc smxe,m 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 rbt(n8d9,v sdx80pa 6x1tpz bCO group and the HN group shown in Fig. 16–62. The C and O have charges 6s9 ddnzp8,8xrp bb 0 ttx1v(a$\pm0.40e$, 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;(3ra6co0k.y kae j jion revolves in a circular orbik 3 6arj(;.ye cjoai0kt around 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, rather than gravity, were responsible fodtmmyv/ ;3aa8 r holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what shomt8aa3y/ dvm; uld 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 pe m q36 cz,0a1cjgtcp7q:h-i $v_0\,=\, 21.5\times10^{6}\,m/s$ 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, ..1swibgeu;9 ssk arge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vt+pri7d(7wkh -9j 0d zo kg0vrjk m25uertically fromddrig9k0jtw5r-v u2+zk(ok j7 0p m h7 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 with tmdo ; h. m9-8.qa3rmmsoy es(giny 24-g spheres at the ends. When charged, n9 e mqsmos.(r h 8dg-3mo.;myaearly all the charge resides on the spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break down and generate a spark if the electric field exce0wif 4uqlqj 2: il07ogeds about qi7ilo0 2f:wlq ugj40 $ 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 charxd/28m slf hnf) 6-fkvge $+0.340\,\mu C$, 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 cha:t)aab9w 9akz q7 j:onrge of all the electrons in a 15-kg bar of aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and hz bq h o,(j5856o apddvk8)78 unpyqbB 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 tq) jbop57 8,h(adbz8pkv8 o5u yqdh6nhen 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. 1tyga1vav *c7a:nji+cdiw* ; 06–68, at what position(s) x is the electric field zero? Is the field *i0t*ig;ya: vca7wd+1cna vj zero at any other points, not on the x axis?

Two point charges, $+Q$ and $-Q$ of mass m, are placed on the ends of a massless rod of length L, which is fixed to a table by a pin through its center. If the apparatus is then subjected to a uniform electric field E parallel to the table and perpendicular to the rod, find the net torque on the system of rod plus charges.

Four equal positive point chargz*/j -w:d w*c c (;lsbkjdyw7ees, 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?