If you charge a pocket com0rz0;s*xytpa6o rg( g *zm/ov b by rubbing it with a silk scarf, how can you determine if the comb is positively or negatively charged/o zr(xtzmgyv *s; go0* 6a0rp?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to your (9-kso)s9asig bop yl2,x b*sbog obl-9s*koaix 9y,()sbp 2ssdy?

Explain why fog or rain droplets tend to forcawryj4)w-x -m around ions or electrons in the air)-jrw w-y4x ca.

A positively charged rod is brought close to a neutral dz;zo1b 6b1 jt. -hs 346neso,rrekfkpiece of paper, which it attracts. Draw a diagram showing the separation of charge ando6j1zkdkzeo -;b1fse4 t.h3sb 6nr,r explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cl;4r4q yglu 5dloth have the ability to pick up small pieces of paper? Why is this difficuq5rg ud;4yl l4lt to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the cond7wblip5 4uuw9iea7z s- wc f w7;elh89uctor.

Figures 16–7 and 16–8 show how a charged rod placed near an y.4dv6x 5pw o-in f7ccll/na;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 notoviyx;/nlfn- lca 57 4d6 .cwp all of them?

When an electroscope is charged, its two leaves repel each other and remain at5bsvrl2(i)) z wst 1fq b)tp)v an angle. What balances the electric force of repulsio 1zpwiftb)) rlvt2b( )qssv5 )n so that the leaves don’t separate further?

The form of Coulomb’s lawvzf c+js0au:2b4v m,b is very similar to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare alsb+4z v: 0fsbvja2c um,o gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force betwkz1rr du37c.eeen two ordinary objects. What is the reasoz1k3u7r c.e drn in each case? Give an example where we are aware of each one and why.

Is the electric force a conservativv0vpq9w j)e0ge force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces or, u pa3mxtc 0 -fu:5mz-bfkp :2y8xcrf paper, sometimes a piece jumps quickly away after touching the :caxm 5z bmr ruxt:k--2083 f,c fupypruler. Explain.

Explain why the test charges we use when mex qj(s jb/1rv+- *bv2u:d dufyasuring electric fields must be smallyv + /1-dqfur(v2js*u: jbdbx.

When determining an electric field, must we use a pmq/3l:ep0;xf +h nr/s am/; 9wudfyxgositive test charge, or would a nedgmp f r: w/ xfq/3;hxa 0/n;yle9+msugative one do as well? Explain.

Draw the electric field lines surrounding 5 lxq33iy0yr 3*scfnf two negative electric charges a distance l 3frxn3 5cly*3 fisqy0apart.

Assume that the two opposite charges iw4) xc)q3 ehghn 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, bottom, left, or right — is the electric field the strongest? The weakew4c3 qh ge)h)xst? Explain.

Consider the electric field at points-s fn h q(fi3ah+*m qa4mvf3a, A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a 4asav3-i q,f+3 anqmhff*hm( 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 x. f0e8oy gi(kcross?

Show, using the three rules6d-c49qr.: rf eis7vn 6dfkrd for field lines given in Section 16–8, that the electric field lines starting or ending on a single point charge me7dcfi94d:. q6vd-rfsn6 k rrust be symmetrically spaced around the charge.

Given two point charges Q a/zpjpgk 5qc ahk,l(; 3nd 2Q, a distance l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If3h , acppgklj;/zq k(5 yes, state roughly where this point will be.

Consider a small positi 4bba h4/4 x4dq**7)cfnmjf h ycku6vpve test charge located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of theyf644c*h b47 n mbdfqc)ju/ h kxa4v*p velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge which i 7)e2xwjos kv,ube6he+fsc+5s infinitely lonxf okbuc+vh56,2 )e se7sj+weg. (Hint: Use symmetry.) Is the electric field uniform in strength?

If the electric flux through a closed swqn, g 42fuc:ve)jt,r8+ ntk gurface is zero, is the electric field necessarilrc2gk ,w,t:+ ne8futq nv4)jgy 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 surrounded by a81m h,0khgq(sqc ;no a spherical gaussian surface of radius r. If the sphere is replaced (g mqkacq,;0o h1n8shby a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up atm e3u4mp8cms)4t 1dr charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnituda;xalz cpg40v f4 la82e of the electric force of attraction between an iron nucleu c0 ;2afz48xavallpg 4s $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical +xtaelb d y537onb.z/force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of thela r7c;m43wyy force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a force of)d/4fv k5 :wiy wqruh; $ 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, a1fw90kc 1m7 l(rszpvg5hyu+) j0s ifi nd the force on each of them is found to have been tripled. How far ap97c ig s0fiwfp(+zu j5ly0 1vhmk r)1sart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates ;trto3 wj,-tzr7zvb/ a net charge ofzto;vr,/3br7- j tzwt $-42\,\mu C\,.$ 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(wow aqtjqz/1 u4pap,+rh* *q of all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the e 1 th( xsso4mkiv9nv;m;d7.ynlectron 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. rk+k,zm fp) h4The sum of their charges is What charge must each have in order tok k)+mfpr,z4h
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge i lyp kjsc9),/$+75$,$+48$ 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 particlekdhd xcp )51 a:rso6m1s of equal charge, $+11.0\,\mu C\,$ are located at the corners of an equilateral triangle of side 15.0 cm (Fig. 16–50). Calculate the magnitude and direction of the net force on each particle.


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

  A charge of 6.00 mC is placed at each corner of a square 0ik9p)6menqs / b,m my4.100 m on a side. Determine the magnitu)m 9pqyb6mns em4,/ kide 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 opud9*qh n*ga0ch-duj -posite corners, are replaced by negative charges of the same magnitude (Fig. 1d-ah-0n*hujqu * dg9c6–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of masdy7 -;zk 8.z(n,k pbdi urzs8d7v+bbgnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the chargp8z r id-bs 8k,uyn bs(kd.b7 ;7+vzdze 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 equilateral triangle o*y, s7rc ttdvfzw+/m +f side 1.20 m (Fig. 16–53). The chz dyrtv +m,ftcs*+w7/arges 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 vj:my/r, eo,ta 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 sam3d t ekl4wi:8d:( rzjf :dngxu9k4)w 7f: jypheres 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 initiallp+qywn/w8rx ;ap(3 fvy uncharged plastic ball to an identica ppyw+q/f vr(n3a; 8wxl ball 12 cm away. 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 direction i6sj6;peo e2osukag r;9 9fq,of the electric force on an electron in a uniform electric fiel;or, gf oq9e6;psai9ue s62 kjd of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electre:.:z: (y( zejeybve vic field, and it experiences an electric force oyvbyzj:.e(e:z e v (e:f $ 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 exer y7wfdb- yk9w*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 the electric field 20.0 cm directlqk/y 0)boe3x8h65p(sxiq ds ey above ab s3 / x6ypk)sh(oq85dq0ixe en isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the accel5:cz zdifzvg7t( 42 g9lcyh se0tii-)eration experienced by an electron in an electric f g5li7s) cg-fc ytv: zz(0ieih2 4zdt9ield 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 field at a point midway be r95(oq7e, r g+0hn9n cb(uqmtv7ch txtwe7tx hm99qrh7(o5q ( ubgc,+ rnevt0 ncen 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, thj :fh-cje6bl1 e electric field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric fieldzq18k+c xk8-.;:blrh a v/qkea.u h zv 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 uddt0hjua+j * g5/b)o lui sn()v0w8 rin a uniform electric field and accelerates to the north at a r0jd l8 *)vu+0otbnu/u) darsj5ghiw (ate 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 eqpr2/hw 8 +mnbbb :kdn)u olu:9ual 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 at thex3 fbnq4m*lb zw( /ozb0aa76 g center of a square 52.5 cm on a side if one corner is o/zb0*fmwxaqbo74a z l(6n 3b gccupied 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 k i +48.inhnr)4j:+uilw n * yfyeov*xone corner of a square 1.00 m on a side if the othinen+i .+ofx* :l8u wy)4rnyv*kj hi4er three corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitp6vonvr s308t0vtvc4f e)8u zude of the 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 mte 8)pcr0v86u f 0ns43vvz tovidpoint 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 elec*uv2gt 9z*uj r j4q+bltric 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 maig cr r)jyh::0ra5hz/gnitude and direction of the electric field at points A and B in Fig. 16–57 due to the two pogarcrh h 0zjyr:/:i)5sitive 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 chaqf y5odjrv b;,,13 8*;,jwrtf vw; vvnzxjvd( rges, $Q_1$ 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 thuot/fm2l op 22e electric field at the point P shown in Fig. 16–59. The two charges are separated by a disttm22ul/op2 f oance 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 the right at 1.0% the speed of light enters a uniforfymdmqyim2y5:5(b+ 0 wkp0rj m electric field parallel to its direction of motion. Im+b0fyqwk5y ( p 0mi:yd52r mjf 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 ccm((h, z 9bx*4eixrccubical box 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 in a uniform electric fign 4 aa3fkm1g ix .c(,w7brwt4eld of magnitude xa7gt4,cf wb 1ir(3n k.4awmg$ 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 obj 2e9+4ynz k g3+h k:fv0vvbpsfects, $O_1$ 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 mr8 u(6yb q fp0yyqvjd b6fsxut.j9:(k8cn*: 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 plm3 s* jxdy78hvates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each ps 3*jhyv8 7xmdlate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-tm i+s 7q,kal1cm-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 o*wur / fhg)ojf:lv;6carries 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 fr;q.2fy .klj 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 shef;f qryj2. k.lll, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are hel,fhu*3 (hzan ax k4bbc-2kpz3d together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atoms is 0.2akhz,b 3z x*f4hk3b-pa2cun( e 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 el6w *jk fdnmt+r7,j.ozzz- r+dectric force between them is equal to the weight of either at the Earth’s surfn7-kz rm ,wjdf rz.+*+tjdz6oace?    m

  A 3.0-g copper penny has a posima soe- 9,d .as 6-w75axpjsgptive 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 E .0lyngmt 1msf9d:x;rarth. Its magnitude ism0tl9msg n:y; fxr1. d 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 what is l:n..bv i9.*pi a(qy ft)cxmvthe acceleration experienced by an:l.an(f y.9ct)ix miv .qb*pv 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 t* n myxd8xi unz4lf+a1,+vye3he air. If the downward-directed electric field of the Ea 8el+mx+aix*4f,dzyu y13 nnv rth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group and the HN gr;v cqluj6 )r(doup shown in Fig. 16–62. The C and O hjvl )q 6udr(c;ave 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, theu+,(pcv2 nkr6 js8mczf) cc,d electron revolves in a circular orbit around the proton with a 2,kdfu c8nrc p+ cj6z)vcm(s, 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, ratheovic159;vh8icse ) vir than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maii ;v 8hios)1v5ecci v9ntain 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 speevv90 ;xm9qod+khd;,c q *fmc qd $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargmpj8mty qiy /bcfx2:. b.alh,1edz78z ch /s5e $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 itjcw7.2mp h /suspended vertically frj p/tw.7m2hci om 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 ,h+k jf-yri 176gh3ovfct - l lb5ugt1tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If th t1rh fctivjo1- gb7f3uy -k+glh,65le 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 ex i14n5ov o1b0xb9q yc+bayt 7cceeds about b1tb9b1oo +q0yx 5vacncy 7i4$ 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 dego1 ici:s)mbs 94g)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 alumi/(uh -az-iqpsnum?    $ \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; each cbex,zj;t s ;vh w;+h liy;my*0arries 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 hh bl* 0;xmi, wtzey;;j;y v+ssphere 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–i3fg(76q. dvdrb pf9(*p 9ezoo lc9yz 68, at what position(s) x is the electric field zero? Is the field zero at any other points, not on ticrb d(9y6.p( o3l zqdpo 9f7gzvef*9he 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, each of cha,e6 cl6xa x81iw,fle xrge $8.0\,\mu C$ 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?