If you charge a pocket)w c( .vxc+bne comb by rubbing it with a silk scarf, how can you determine if the comb is positively ore x)+wb(.nvcc negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes clipxm2 bc)bhc- .x5d)gtng to your body 2b.gmtc hdb-xpxc)) 5?

Explain why fog or rain droplets tend to form around ions or e5lqb/4i dn2rj0hc fi8 lectrons in the airqdil 4 /2c5n08j irbhf.

A positively charged rod is brought close to a neutral piece of paper, which ig3zd+t(o -mte dd*:wit attracts. Draw a diagram showing the separation of charge and explain why attra d(:+tmw z3td *-goidection occurs.

Why does a plastic ruler that has been rubbed with a cloth have tsvp 6we ad .0fyfb0 :ygi:1a6ud gogfc+(5i ;ahe ability to pick up small pieces of paper? Why is this diwy6ggdsyfv a ;if. ac 0(5ef0:i :+ob p1d6guafficult to do on a humid day?

Contrast the net charge on a conductor to the “freertzm 0-iw4wu 69iz1 cf charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metal objg j o,jpn,k1) nruwc4*ect can attract (or repel) electrons.w )r ,uc *4jjpng1k,on 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 lpskg3tq40i / en5b,eand remain at an angle. What balances the electric force of repulsion so that the leaves don’t separate furth4qt3l5ikge /n0sep ,ber?

The form of Coulomb’s law is very similar to that fo8emjj hrn w+z7j1(ur. r Newton’s law of universal gravitation. What are the differences ber(j1 jj wh7m+ n8zeur.tween these two laws? Compare also gravitational mass and electric charge.

We are not normally awarglv 0mb5 ueat82w-o7 ce of the gravitational or electric force between two ordinary objects. What is the reason in each case? Give an exampl glt0-womu2vec5b8a 7e where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapter 6.)/ejp1cu (zqxoe2 59 eg

When a charged ruler attracts small pieces of paper, sometimes a piece jurcipll1+qzt w w52 q++.w2daimps quickly away after touclpcqt2wr+ i 5awl i2q+w1z+.dhing the ruler. Explain.

Explain why the test chnc odg153 1tegarges we use when measuring electric fields must be small.5ec 1t1dggo3n

When determining an electric field, must we use a positive test charge, or w 6zm)dhe9apj1ould a jah6p md9)e1znegative one do as well? Explain.

Draw the electric field lines surrounding two negative electric ch-z io-em70fjwarges a distance l aparzoj0 -e-f7wim t.

Assume that the two opposite charges ih y:m+v(eshma0j y4uv4 p4.+p0uhb vgn 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 whehg4us4y:v 0+jp4v y a vhp.b mu(m0+eakest? Explain.

Consider the electric field at poi 6v0/9ds cikzo 6)x rluwle):ints A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strengtrdclsu 9i)o/ 6 ewv0)z:i x6klh (strongest first).

Why can electric field yxm .c1u6w 3sllines never cross?

Show, using the three rules fnzeom6-71t n,q fsp8oor field lines given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced arounet1 z67non -f,qs8mpo d the charge.

Given two point charges Q and 2Q, a. +g0ofe;syn rh6sj+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? If yes, s jefs; +h.aorn sgy0+6tate roughly where this point will be.

Consider a small positive test charge lou7m qrra,,n ,fcated on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration ofumrq,,n ,arf7 the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge whw5fdxatub,b 7q3gvgb3 :pdw kkt 9.: 4ich is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in str fg 3,:.4t5tq :gub3pbbkd kavw9w 7dxength?

If the electric flux through a closed surface is zero, is the edju8c8k3 bqh;n 3p2v+lth8lb*r he. vlectric field necessarily zervvj3pb 8kdhcl rq2uln8 .;bte +h *38ho 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 a spherical gaussian .p8z mvulo :woe i1z+;surface of radius r. If the sphere iszm:8e zo.;p liw1o+v u replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a x k)1v y-(p0;c nzq+uvx xn51ixg wlh)xi*y/ocharge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric fovn d3o1n , )hi7z9ttbcrce of attraction between an iron nucleus 91 ) t7zib3hnn,vctod$(q\,=\,+26e)$ 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 protjey 3 1o pe *go(ift5(c;at1auons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the fom-f/ xj /p s0c;vpfp)mrce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust part -tfo8w:sh aa3icles exert 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 8.4gu.l18c t y(7zlifh /a5 cm apart. They are moved, and the force on each of them is found to have been triplg z.t1c hi7/yla8uf l(ed. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accud;z0umq ) mh 0e2ipm;ymulates a net charge ofi ;2yu m;0 p)qdmmz0he $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charge of all the elecgl6is 4+a mcnd gx3 *3bbth6(ytrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric f*/i ft.jv z .+fc,npmr tf; xrr;l-fx+orce holding the electron in orbit $(r\,=\,0.53 \times10^{-10 }\,m)$ around the proton nucleus of the hydrogen atom, with the gravitational force between the same electron and proton. What is the ratio of these two forces?    $ \times10^{39 }\,C$

Two positive point charges are a fixed distapk2 4wn etj, vw3qs*)wnce apart. The sum of their charges is What charge must each have j3s)vqp* wwe ktn2w,4 in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge dam pqssc5/13$+75$,$+48$ 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 particl yff1: 4j;nmafp+k /ezi d)f4fes 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 earl2,q i7l umr1cy 5vm7ch corner of a square 0.100 m on a side. Determine the magnitu7imm cl2yl,51 r7rv qude 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 ch;0y1 gt 0dqknerp,d,p arges, on opposite corners, are replaced by negative charges of the same magnitude (Fig. ;rp,qpk0,d t0 dyn1g e16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnitude Q,f)qq2 bj f0zradz9d6- 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, )af 6qr9d-fzd q b02zjand (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 t-5/o z ww4avcjhe corners of an equilateral triangle of side 1.20 m (Fig. 16–53).j w4zv-a/wo5 c 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 da1 rq vy*twvhz //g3piazz*0tp+mqn z38q.1 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 spheres hpo kkz8/c7 7h(6/:;ct eoydy s2odvrpave 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 fr;i328 bsrgl vnvup2u*om an initially uncharged plastic ball to an identical ball 12 cm au is * ru8vblg;2n23pvway. 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 of the electric force/,h a.fow/ ojs on an electron in a uniform es wf/h./,ooajlectric 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;qpijrtf f n4y:+8 9b7v blsdqr222 ko field, and it experiences an electric force of b;d4k+vffj2n2b7yl2qo: sr 8 pri tq9$ 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 .vm3hqf4i v: 3 w1yajyexerted 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(sva -jilg/1r y4,p5bc yv4 qh direction of the electric field 20.0 cm directly above an isolatedislvv1ac (jhg, r p bq-/45y4y $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration ex 70en:mb vwj0gperienced by an electron in an electricmnw :jb70gv 0e field of $750\,N/C\,?$ How does the direction of the acceleration depend on the direction of the field at that point?    $ \times10^{ 14}\,m/s^2$  ----待选择----opposite to the field in line with the direction of the field 

  What are the magnitude and direction of the electric field at a point midway be)f3 v-67ozj;zish+gjcq 5n k otweezz )j vcinogs;o7-hk3+56j qfn a $-8.0\,\mu C\,$ and a $+7.0\,\mu C\,$ charge 8.0 cm apart? Assume no other charges are nearby.    $ \times10^{7 }\,N/C$ ----待选择---- towards the negative charde opposite to the negative charge 

Draw, approximately, the electric field lines about two point cnz,plw c9d2: iharges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric fiy7mglb(; pij9eld 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 m.rii7vkt fz*-.,lrg a uniform electric field and accelerates to the north at a rate of gzr7-f kt iv.*ml .,ir$115\,m/s^2\,.$ 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 chargesv4-rb8 fg k+ cqg-p8rt6)zqvbmww:4v 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 cen/2ru4eal7 fkz3 pibmb1tl +hb;xz3 g,ter of a square 52.5 cm on a side if one corner is occupied by xak,3;4p bh7/ rb+b2zmlf eti13 lz uga $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electricbhr- xhrk5i10 ly. es;m3,vxrvk;v 3e field at one corner of a square 1.00 m on a side if the other three corner lx e3;-hmr3kr5;.v0 ery sv vb,ihkx1s 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 field at the point P 6-51 pjia h98r wlk8m a kk8vv5u8nlhxin Fig. 16–54. The charges are separated by a distance 2a, and point P is a disn j a-88 6vk8l5khva9hu iplxm5wkr18tance 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 91)yhide8 g6i; uquf qfield $\vec{E}$ at the origin 0 in Fig. 16–56 due to the two charges at A and B. (b) Repeat, but let the charge at B be reversed in sign.

  Use Coulomb’s law to determine the magnitude and direction of t(dh2hw5zyf)8gp b,je he electric field at points A and B in Fig.e 5, b yp)8gfh(jh2zdw 16–57 due to the two positive charges $(Q\,=\,7.0\mu C\,)$ shown. Are your results consistent with Fig. 16–31b?
$E_A$ =    $ \times10^{6 }\,N/C$
$\theta_A$ =    $^{\circ}\,$
$E_B$ =    $ \times10^{7 }\,N/C$
$\theta_B$ =    $^{\circ}\,$
(16-51)
(16-31b)

  You are given two un.5 j8u voyer3a9m) dhbknown 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 magnitude of the electric field at kn9 riygo z78)the point P shown in Fig. 16–59. The two chi 7 gn)yok8z9rarges 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 the right at 1.0% the speed of light enters-nr wthw3w/c 86 my9uy a uniform electric field parallel to its direction of motion. If the electron cymwnyw3h r6/u -8tw9is 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 fl8:bkisl*wu 09wdm m6 bux from a cubical 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 uniforff31 unbbe)fp1f,jt qmw+*5h m electric field of magnitude +twupjfmb 5f,nffq1)1 3be*h $ 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,(dt -upt.5mnz $O_1$ 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 placede(;8y ga z1hrp 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 Th-k + s,,umrnsqm5jrt83g x svg/0np 9he plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effectsssq-5m x 8hrvns u0jgtkg,3p9+/mnr,.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius meyvk6o1vhd.n cpcffj:6v c k(d,4x*-ital 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 rv2 f4 rn xso:q88;* /gvuthlyyadius 3.00 m carries a total charge of $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of an uncharged thin spherical y/c3tkpy:(a gconducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect the yyk( tc3:pg /ashell?

  The two strands of the helix-shaped DNA molecule are held tog+vqaoi b 1irp02/e k/q5u9c omether by electrostatic forces as shown in Fiv5k/1 + qbi9eicmoa0q p2or/ug. 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 electrons be if t2 e:b nqbj lgg-e;+bn2he electric force between them is equal to thbnjnbb;e +e l 2:-g2qge weight of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive chargel2rhyuo: u8y9xbnqi7 iod /:9 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 fielde,7 -dn- 6n;.cfpkz(pogq2gyy e+jwkm. bug * surrounding the Earth. Its magnitude is abouyqf eg ;z62bepu gyd(k+g.- ,cpnnkjw*m-.o7 t $150\,N/C$ 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 acceleration experienceyl *7a:oa*d6+g ;aeayvv fsi9r u t+0ed by an a69tafred v ua07:ysyl;+*ie v+o*gaelectron 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 rad2rm ;.xhkrf1nius 0.018 mm remains stationary in the air. If the downward-direct hr;2mfx.n1r ked electric 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 group shown in Fig.ru ,kenm;3 ;px 16–62. The C and O have chargeuex ;rpkm,;3n s $\pm0.40e$, 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 electron re*f;gbx/,lfi tj o) vz1v( ywo)volves in a circular orbit around the proton with a speyxobvj)v/*otz ,(wl;f1)gf i ed 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, rathk)f-zj6c+:boe+;s swaa 3 tvxer than gravity, were responsible for holding the Moon in orbit around the j x:btc+ a);+w vas3zkesf-o6Earth. 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 spey9*(zqs-3d(ya b ga xnqa;z flp3.;zsed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chart8mtxwz2at2-qu 2,rpge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 3xqo) ;.it 2f ya)apaj n5vq2ein insulating plastic and suspended vertically from an idea vqpnf2.q x3a5e2y))t o ij;aal 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 76z7l*wrw b ba18-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires l6b*w awb7r z1each 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 excee 9c+gfmlj y m+g:;ng/eds about mlgm/ +9;e+ : fgjcnyg$ 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 bs 8x m1fx3j8x0.210 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-rzz 2nb d(gr4,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 sphe1ywzo z6eb(7;k5k qscj55 jvxres A and B are a distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An 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 wi j6k (z cq5kwzsy7ov51 be5;xjth 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. 16dcaeztf21i+7)eg, qz –68, at what position(s) x is the electric field zero? Is ea1z iq cd,2fe7z)tg+the field 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 pointwfmk;h6vikf1sd(z3 +) g+we l charges, each of charge $8.0\,\mu C$ are at the corners of a square of side 9.2 cm. What charge should be placed at the center of the square so that all charges are at equilibrium? Is this a stable or unstable equilibrium (Section 9–4) in the plane?