If you charge a pocket comb by rubbing it with a silk scarf, how can you dete 1nhs jr)qjryf66 e(y8rmine if the comb is positively or)je sh(qyrfy6jr1n8 6 negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to*q vn-: y:z-tb)if ah-4hwwpiq(krh 6 your bodyz4t-hbrhav h:*i-6nw f kwp-:qy qi )(?

Explain why fog or rain droplets tend to form+nb,yxa 8jp8s7 4 thkk around ions or electrons in the air+j 74,xt88 khsykbap n.

A positively charged rod is brought close t0t .p.vif o5jio a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain why atti t5.0fov ip.jraction occurs.

Why does a plastic ruler that has been rubbed with a cloth tetqfk42ly .1 have the ability to pick up small pieces of paper? Why is this difficult tqe2tlfy4k. 1to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the conducpmbsh9mww ::1tor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metalew29hk7xl4qq/j8tlek ydq, qa9: *k w object can at :x9k9 2qjqehyedk4ta qq, 8/kl*lww7tract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other and remf14 + (hz:juj ct*uo9qmy5clfain at an angle. What balances the electric force of repulsion so that the leaves don’t separate further?cy z9 mtuj1u4q5j fol*+:h cf(

The form of Coulomb’s law is very similar to that for Newton’s law of universal ny7dgc;hxis n l242 e si41c8sgravitation. What are the differences between these t2sd4cngy2c1i7 ;84s e lsinxhwo laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitatio- p eghi5cr*)uv0 95pp k r63jtv9gagxv6 lrm:nal or electric force between two ordinary objects. What is k)gae 5 h36lp*g 0r- 9uvcrvg9xpmt:5p6vjri the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a con7pg2op6 :spe6u s9dcs servative force? Why or why not? (See Chapter 6.)

When a charged ruler2a5 )palrx*pww diavn sz8b4p2y 77v* attracts small pieces of paper, sometimes a piece jumps quickly away after touching the ruler. Explain.da7v2 bi2w5 7 rp a *)ln4*ypwvaxzs8p

Explain why the test charges we use when measuring electrib :;p 2 g.ebxv8v.qowgc fields must be small.v g.;bb .qvxe:2po8gw

When determining an electric field, mus*,2me rttzu 0bxye *0ft we use a positive test charge, or would a negative one do as well? Exz,0 20yx tb trf*emue*plain.

Draw the electric field lines surr5j dd;q 0.v1 ozxtdrr9s0 qv3counding two negative electric charges a distance l ap;d3odcrdr 00qt.v1 jxsq 9 v5zart.

Assume that the two opposite charges in Fig. 16–31 3q8n-a, hef8gjlz-fn r kj)h6a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which ng8aqn)-6lj8f-j z ef , khr3hside of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric fiel izcj7 u7j/wx,d at points A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positivzwiu/jx7 7,j ce 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 lc/zy g720g;4 slwffr cross?

Show, using the three rules for field lines given in Section 16–8, th51cdgi m/py7 v dl,:vsat the electric field lines starting org sy 7vdcl1/,:imd 5pv ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a dista1 .sjxb9se0 a. 64klimz/ebbw i, wv)lnce l apart, is there a point along the straight line thatezl9,l vkw 4w6b e. aimb.ss/0b) jxi1 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 on an electric field 3pf8 ozdbf 8,b,.3ismjx:oifline at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration ofi3p,m so zjb:fo,b d8x8.f i3f the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line oy3qhx- cg;9 hgb7adg p 9tvi.-f charge which is infinitely long. (Hint: Use symmetry.) Is the electric field un9hgdg vc-tx-7i9;agp h .3qbyiform in strength?

If the electric flux through a closed surface is zero, is the rpl2p1 qjii8 ve)y bj3t1z*vshz5 66n electric field necessarily zero at all points on the surface? Explain. What about the con3)jt661bz1 pp lq*ivn5rh vszy ej28iverse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by a;ug ;wfel mc.5 spherical gaussian surface of radius r. If the sphere is replaced by a cube of side r, will5c; l;m.fuw eg $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make *c13xc fn c:ndup a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the el w0tbm,mq dzvjk24g 5-ectric force of attraction between an iron nucleusg-mq vmz w ,0j5bk24td $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive elect/50 dzbw qj1mbqr7-dl rical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of theydq7c6c*ui3la:* qkex 0v -v n force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exergpr3ppv;qt k +ge;zbs3 j/.t: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 cmifr- e3ple8htxu*53: bj /y zo apart. They are moved, and the force on each of them is found to have been triple3-/:rhteyxi58zjb3o*eupf ld. How far apart are they now?    cm

  A person scuffing heh j 0;ei5i9 gs(wvm)*qh yfy7sdv 28ghr feet on a wool rug on a dry day accumulates a net charge ogye*h 7w2m isqyv8isf(gj509h) dv h;f $-42\,\mu C\,.$ 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 a t gii cb6,4)ekf3ydtbu+* 18mxx(fn mll the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the elec86pe +h 3zyx4qjx jid,tron 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 chf h i642tw0iusarges is What charge must eachsfi2 wih60t4u have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge pw1jofayob+i6 ;js: 9 os1f l+$+75$,$+48$ 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 o apwazr :uu*.+f equal charge, $+11.0\,\mu C\,$ are located at the corners of an equilateral triangle of side 15.0 cm (Fig. 16–50). Calculate the magnitude and direction of the net force on each particle.


the force on the lower left charge is of magnitude    N, and
will point    $^{\circ}$below the-x axis. The force on the lower right charge is of magnitude    N, and will point    $^{\circ}$below the +x axis.

  A charge of 6.00 mC is placed at each corner of a square 0.1001z9 b:uv ,sr9gu zd:; wj2enas m on a side. Determine the ,u1 r;:ndebau9s2zzj9 vgws : 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 charges, on opposite 6+mej) me4cg ucorners, are replacem6em4j u+c)egd 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 magnitude Q,kqy,5 iwl;3 ww 2Q,w5wqyklw, i3; 3Q, 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 placed at the corners of9v3y kb1;r2zgx3e tfu an equilateral triangle of sueg2fy;vx9bt 33 1zkr ide 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 total charghk:;g1erg uv8e 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 hav zay s3e,6sut0e 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 initih p 7b 7)h:gpl/ r1ul22znirtvally uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferrenhvpllu7ib:722h )zr/r1t g pd from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electrini/coy ;yp ck8vzn254c force on an electron in a uniform electric field of str vc/zc2yi8 n5 ony4k;pength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a u 0t9ns*60;rboqskjsoniform electric field, and it experiences an electric forsjstqbn00;r9*ok s o 6ce 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 8jw acq ncu(s;8r8 47bk.4 N is exerted on a $-8.8\,\mu C\,$ charge. What are the magnitude and direction of the electric field at this point?    $ \times10^{5 }\,N/C$ ----待选择----updown 

  What are the magnitude and directoeanj)+nw cl2ir6m aj/4wr7/ ion of the electric field 20.0 cm directly above an isolatci2nle6ajr)7 4wjn m/+rawo/ed $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experi -d: ujh6,k9w5 ep g6 1mulxha-4ksy.pkp5dgxenced by an electron in an electric field o x6w5ud.p kkgdl5 egmapx1 h9 sh4 y-,j6:pku-f $750\,N/C\,?$ How does the direction of the acceleration depend on the direction of the field at that point?    $ \times10^{ 14}\,m/s^2$  ----待选择----opposite to the field in line with the direction of the field 

  What are the magnitude and direction of the electric field at a point midway betmk 6oc*jk/ .t*4tzxq oween aq6*4 *mkot k t.jczxo/ $-8.0\,\mu C\,$ 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 about two poi- 0b)ljiii q/cnt charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric p4mej t ;7qwowb.14 smqj:d8a field 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 electric field and a84mhr8dyvm u vsp :1h5ccelerates to the ndsvph:hm5 u88 myr41vorth 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 opposite point chuqkq9:hrs i. :arges 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 o4 kbp1znm7ue+f a square 52.5 cm on a side if one coup1em47n+ bkzrner 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 side if thv6w 8onm.j3( *neqmx me ot( qmwmxemnjv8 *3 o.6nher 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 the electric fieldsut6ius ,vxw7 +yguir.i00 y. at the point P in Fig. 16–54. The charges are separated by a distance 2a, and pwy u t iu6us.r.i0+,iyxv0 g7soint 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 elejr84zz:+ y pwhctric 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 mag4p;sec s38fjj*q5t rw nitude and direction of the electric field at points A and B in Fig. 16–57 due to the two positive chargesp4swres j3t 5;cqjf8* $(Q\,=\,7.0\mu C\,)$ 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 pointge3os:hbv9p 6 9 1l*n6 djzvhh 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 elec zhak0lxk ;x81tric field at 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 the linekx x08zl;hka 1 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 unifo)0w5.ixfu/ r,x -on x pe9tdplrm electric field parallel to its direction of motion. If the electron is to be brought to rest i -.rpe)ioxf5, u tx0dnxw/l9pn 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 lc(buzwg,73) )3 hh8:jr noi b)uowmbbox 28.0 cm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed i r we x4)4ej5b9esjhd5n a uniform electric field of magnitude e4 bj9je4x e5hr )w5ds$ 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, 6zwspstj6md th)+ -j)t9vj 1l$O_1$ 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 placedpfh e1y 7n: y soidkp;wo..-mp:m,fx9 in a uniform field $ E\,=\,6.50\times10^{3 }\,N/C$ with edges parallel to the field lines.
(a) What is the net flux through the cube?
(b) What is the flux through each of its six faces?

  The electric field between two square metal plates is The plates are 1.0 m on) a/s7;k;ev .opu90rjcyx( 8k bfvrtr a side and are separasv pytu vx fbkj/;7r;r0ck( a9o.e) 8rted by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-ccw(+e7u :da38a pwnrx m-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 m carri8cgstnj27 1jo vmd)rlk ,7b5oes 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 of an uncharged thin sp qzntxl* 9j0o1tm w1nad (o tup-.yj:f1o47xpherical 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 ao.f:9qayj w4n z1 nmolot0*7pt dxpju11(xt-ffect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA 8- vvr*b6 +uq wizmrs)yjq f95molecule are held together by electrostatic forcesrw 8 qq*r+5 u)zvjimbv f69-sy as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atoms is 0.2e and on the indicated C and O atoms is 0.4e. Assume also that atoms on each molecule are separated 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 electronocq;f .ngzd-siq0 8k7q(xs y /s be if the electric force between them is equal to the weight of either at;oskqc.yn i-08f7qz dg s /(qx the Earth’s surface?    m

  A 3.0-g copper penny haswn++i00yn - zmy cwr0o a positive charge of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

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

  Measurements indicate that there is an electric field surrounding the 4m3eavlj9a y d6;hht) Earth. Its magnitude is about v h l3my9j e6a)t;ah4d$150\,N/C$ at the Earth’s surface and points inward toward the Earth’s center. What is the magnitude of the electric charge on the Earth? Is it positive or negative? [Hint: the electric field outside a uniformly charged sphere is the same as if all the charge were concentrated at its center.]    $ \times10^{5 }\,C$  ----待选择----positivenegative 

  (a) Given the local electric field of what is the accelerato(lnflk05q-piqy 9uc bg/csa3)l- de2 + ptx;ion experienced by 5dgl-a p0tqibeo;k( -n9yx)pf3c+q s2u/ lclan 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 mfppcy)7px7/bm q-r /0.018 mm remains stationary in the air. If the downward-directed electrip c7)/bp /myxm f-r7pqc 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 CObh+ v*s iuwnr8yh6, )k group and the HN group shown in Fig. 16–62. The C and O havei6wkyvunbs* ) 8h hr+, 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 electroh64kknvg4 ;if n revolves in a circular orbit ar 4h;6fnvgi kk4ound 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 respmgcs.o3lb v y5u954 szonsible for holding the Moon in orbit around the Earth.ov cy u5szm359glb4 s. 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 spen zvx8mya3+ y8ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargej2.yvjq g3wj/g qz2 y+ $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 insuuwjkg9dm/qmv9m *7p :lating plastic and suspended vertically from an ideal springmq 99wmk7pj/ug: m*dv $(k\,=\,126N/m)$ 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 wirgr g*t kw93otr - +3j4eeg m7iir8/tjqes with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If -9t+843 w *qrm7g3rektgritej j oi/gthe 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 electriczvv,5z7im k+c field exceeds about,ck+7z 5mzvvi $ 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 mat se.7mv g)a-sudhyt(v3fq( uvw ,6 3oss 0.210 kg, and net 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 alumink;p0nt3m nm2hg i. zqk:a0(bvum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B are a distance R apart;h n w35no4*e d-obi(kp +,ligl 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 Aopnl*debg 45h-on+(k3i li w,? (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, 1rx +pxsf4lirzp )c9 +u4 ,zddat what position(s) x is the electric field zero? Is the field zero at any other points, not on theulppzz,4r1d)4frcx9sd i ++ x x axis?

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

Four equal positive point charges, eac x20xh(6xpb kuh 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?