If you charge a pocket comb by rubbing it with a silk scarf, how ./uuvb)ax qd (can you determine if the comb is poxd.q vu(a)/ub sitively or negatively charged?

Why does a shirt or blouse taken from a clothes dry)m-21dtvshq,/z6wp bny +sun nlb5y 8er sometimes cling to your body? m 2y u+bdn qst znp6n,vhy8/-)wb5s1l

Explain why fog or rain droplets tend to form around iokneu(e2ph ;srd4i:u;3 qie5b ns or electrons in the air.3(i5 bh2ukse4 q;; :ueip dern

A positively charged rod is brought close to a neutral piece of pape56io.4zmh2z*h h * x c;c3 g(hzwjgoytr, which it attracts. Draw a diagram showing the separation oj3 .hxhc5z6wh*co*hzyg gz (42ti om;f charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the abilisigkz(+5 34 zjle,tikty to pick +z 4lk,j 5kiezi(3t gsup small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge onxh+aolji7 f yq, -yz6g r:,nt5 a conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metaou 8.8y+g3 t 1h/h4b teb+uv lgn tcd351cjyfal object can attract (or repel) electrons. There are a great many u+h5 ev3yh4j1ocb8yg./3uab8g+1f tdnlttc 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 remain at.2ts l* k,oabc an angle. What bs.lc ,kobta *2alances the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is vzq7 jlr zhdp0vw)nq5vi0.n 21 ery similar to that for Newton’s law of universal gravitation. What are the differences7r2 1l0v.w5zpzqnqij dh 0) vn between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware:jck+c4 e0 xny of the gravitational or electric force between two ordinary objects. What is the reason in each case? Give an examp:+y nkj 04eccxle where we are aware of each one and why.

Is the electric force a cjuhlnk 1z 8n5.onservative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper pdfjj+p6g 0 0psgi8i(u,/uttd k.n(e, sometimes a piece jumps quickly away after tos /pdgft0n t g( (8,ep.jpi0k6 udiu+juching the ruler. Explain.

Explain why the test charges we usn4 0va8ygon1 ve when measuring electric fields must be small0g1v 48oynnav.

When determining an electric field, must we use a positive test chaxzwl 4+wd+ou-rge, or would a negatx-u++ wwdolz4 ive one do as well? Explain.

Draw the electric field lines d)pyj 0x x w/o lqzg)m*d4t;q)surrounding two negative electric charges a distance)lddtmjw)p;xg*y) 4o z/q0qx l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Consi+ * omp2hyhh5/qs3lbcder 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 weakest 2qmhb5pyo sclhh+/*3? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48nyd n+e9ksh 88. First draw an arrow at each point indicating the direction of the net forc+ nhdekys9n8 8e 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 never cr ;)m*a/3spqg 3uu uzt83 obvxloss?

Show, using the three rules for field(q, fa+7v vm1zt qg ra5(uem0k1jf8zq lines given in Section 16–8, that the electric field lines starting or ending on a singltk +g qr1mq( zae5q7(mvv 0uz8f ja1,fe point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a point alo:qa;y:g/e j2 2:f tzg2vl-go hxo2ax 1g3 hmbvng the straight line that passes through them where E=0 when their sighfooh2g:; 3-:zax 22eb ja2y qxt/ :m1vlgvgg ns 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 f3mdb askf1-t 3ield line at some point, such as point P in Fig. 16– kf1mt-abs33 d31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of ch)bi r-kwc+8 0e(eff o (r(cwaharge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in strengcwerc)fo(eikf0ab (h-8(+ rwth?

If the electric flux through a closed surface is zero, is the electric field ne7duf 7j6q l+nqcessarily zero at all points on theq+ n7 q6dl7juf 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 mmowc 5/+f:bcx e )-hfgaussian surface of radius r. If the sphere is replaced by a cubxbmcf) c-e5:o wm +fh/e of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make uh912 r4kl w4qpmsww9 5.e fivlp a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron nucled1 pwp2d6 mz2tus dpzp21td 2w6 m$(q\,=\,+26e)$ 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 protlnz63su)/ iro yy:obpx( u -j3ons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of thgs9khsuv+y .l)a1-a ue force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust parti.+fte yd:x g*a6hc:rccles 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 8.45-jdr l 8cpx:f5 cm apart. They are moved, and the force on each of them is found to have beenjlxp5 -rf8 dc: tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day a b0 ze+-n1dh+cjfrb 9wccumulates a net charge off0+dhb1c w r e-+n9bjz $-42\,\mu C\,.$ 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 thj /whga,d e-6ln/zbi0e electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding thej 914bj.,g uzgobauo4hl(u s0 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 distanceq0lna, x-12 9lmgx9 t 3;r.xaul k+kkej kfn:g apart. The sum of their charges is What ch n ag0x eftmk19 +:3u,kqa-j2l.x lnkr;xl9kgarge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge qy9wl 8huup*k )8 0ejw$+75$,$+48$ 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 ofng.k1bv3mam ,rxaui o 8w 98j9tsz 4j0 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 e1rgb)6 r(6gfdko j u5a square 0.100 m on a side. Determine the magnitude anbo(jfgk r u1gd6r5e 6)d 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 chpoyd. bfov / p)1qx6o;arges, on opposite corners, are replaced by negative charges of the same magnit x y; 1d6/qfpbp).voooude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magfn exk uq8;y)/.kyc/bnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determybq.f/n/)uye 8; xckk ine 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 cornersgr bmc0q+w fm*y9dcs v. 0)q(w of an equilateral triangle of sbd.smw0g) *0 q crc(vq9my fw+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 char4comr2llkn 8 :vtqxz+sy9w- *ge 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 have a f;6 ef-s4d,yz2 j umeaugq8w-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 57x 6mj ,gzgftfrom an initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from og75 x6gftmj,zne ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direct:flq8ifgf as +mt9.i fn316siion of the electric force on an electron in a unigas 86.im1fn tsiffl:fi +q9 3form electric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform elc3r m-*l- y*8 gouobbvectric field, and it experiences an electric force -myou-lv*3bcorb 8 g*of $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is exerted ab3k4ec+phvh2p 2xk :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 thszds) -1st(o7c;:fl 0 tjkyuie electric field 20.0 cm directly abovsls;tfdkz) (:j7oc-1su 0 y tie an isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the accelera(ct5w tim 8msjczw0k 2kya316tion experienced by an electron in an electric f i 0(tma63tk wwkmsz5j c12cy8ield 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 an2gr1mk v -oj5zd direction of the electric field at a point midway betwee1g-5zj mro2v kn 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 eo;xt rtv-:xh +oaz d5)lectric field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in spac6s4p; b mfdb9ce 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 an*1ka gv8v b/ ud2ajn* oiag(b9p.u)yrd accelerates to the north at a rate of iydgbuauv2(o.bkgpr)a*18 v*/j 9a n $115\,m/s^2\,.$ 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 bu ,socuiw jbq*wb44)1x mz0:jndc6 j; tt 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 the center of i0f ss-dds snfei m5 9bk dy(hpvqw5j.9k5 21:a square 52.5 cm on a side if one cornedv09 :n1w5s y5sqhbd5 k-2dji epsi(smk 9 .ffr 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 il d yb;.f*ruo;kw8kj -ts2oa *f the other three coroky 8fj-2tab*rud; *l so.k;wners 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 th ae7-qqipmda;,: rim*e point P in Fig. 16–54-e p ia i*7q,rdam;:qm. The charges are separated by a distance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in terms of Q, x, a, and k.

  Two point charges, $Q_1\,\equiv\,25\,\mu C\,$ and $Q_2\,=\,+50\mu C\,,$ are separated by a distance of 12 cm. The electric field at the point P (see Fig. 16–55) is zero. How far from $Q_1$ is P?    cm

(a) Determine the electric field cpf.p ca8em6ts- 86518hzzveos6anu $\vec{E}$ 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 the2v)jqru b( ;tyllbgntp5,.+ w electric field at points A and B in Fig. 16–57 due to the two positivev2.wt,)lu g;rt 5n( bpqy+jbl 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 cd9v*b z8-in5f zfp y+b6w2aov harges, $Q_1$ 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 thel9p- zq; a67*lanit zpw5y2ne point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is 5np-qez ;lzti2*aa w6py7l9 non 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 se 8jweqe5, 2i kk u.mu8gh/k)vpeed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the space of 4.0 cm, kkhq58.kvuge2 ue,m/)w 8 e ij
(a) what direction is required for the electric field,  ----待选择----rightleft 
(b) what is the strength of the field?    N/C

  The total electric flux from a cubical box 28.0 cm on a side ibtjk 2dfu u82;q ig;p4s $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm ici; s 6,zxo7c;iek5rxaaq3:y g(l7aes placed in a uniform electric field of magnitudekagxo7i7 e lriq53;:c azce6 s, (xya; $ 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 objectsav486 ug b5aoht)kjp( , $O_1$ 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 sjx:3 l, jiuruzw /,(oplaced 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 Thf**d+umjuk2*9xmx lyl f6 z:g e 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)? Neg:6zd * +lum9*uylmxg j fx2*fklect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.596mw5hc(vfi ,dss e-p0-cm-radius metal ball is $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.01m4 z2 w0ea 3zeqavq b-zo:ib*)6 dfhi0 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 spheridb8gswtmrl91u a* .ydhod+78 ubqgs +8+9khwcal 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 affect the field due to Q aloneur9.q d81k9ow b*+ghu+78s sg w+mdtba dy8lh? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held hhwxns+2um89ykys 3. together by electrostatiyys8m hxkh n u+w2.s39c 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 0.4e. Assume also that atoms on each molecule are separated by $ 1.0\times10^{ -10}\,m$. Estimate the net force between
(a) a thymine and an adenine;    $ \times10^{-10 }\,N$
(b) a cytosine and a guanine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other).    $ \times10^{-10 }\,N$
(c) Estimate the total force for a DNA molecule containing $10^5$ pairs of such molecules.    $ \times10^{-5 }\,N$

  How close must two electrons be if the electric force between them is equal tu.1owasi a b 0wgi-i4x.t*fm6 o the weight uf ta 1ox*mb gw6iiw.0 -a4s.iof either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive charge of jvj p (ws65fh)$38\mu C$. 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 o b gii4(*k i*l/+fo-oogayy1Earth. Its magnitudgofl/1 ik *bi+o*oyg-( oi 4aye 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 eltx.wl -5 )q*q*(w4as cheejxdectric field of what is the acceleration experienced by an electron near the surface of the Eartha*x*t.se- lw wxqe d)j(4h c5q?    $ \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 ilr30s a()re dzn the air. If the downwarl) edrsraz0(3d-directed 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 betwg ja 9pz.cs0mq-:xkev b;-9jdeen the CO group and the HN group shown in Fig. 16–62. The C and O hkcg-9ze;sb qdj-0vp.x 9 mja: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, the electron revolves in a circular or*gempgjpk;m(c e d7iu b (,mb7g)le21bit ibk (p,*ml (ecg) 7gepdg1jmb7e;2muaround 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 for ho lh7;ew+ aa1qqlding the Moon in orbit around the Earleq+;haq 1wa 7th. 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 speedts 4f;pz9+m q* ,pwzhf $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charge1-y9mbnbtiem ;z8zpzjc+g88qcp 2 w7 $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vertic,m(icod )b9z2 y,pz jially frpmc ji2 ,)(yzzod,i 9bom 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 ws qv mejwas:zzv 0c/2 3hl+00s0pudu1ires with tiny 24-g spheres at the ends. When charged, nearly all the charge resip0 e3+ /0v02 muqswaczzjd v10slu:hsdes 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 th tnp,ngii2z3u;e9x8 ye electric field exceeds aboutg293;pui y8i,x e zntn $ 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, andpvry tr jqg+9a, d)7b4 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 w g7)+smxp sq) yf8:xba 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 c-*lz dst-td+mr vy1l;onducting spheres A and B are a distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on dsllm1*t-zvdt ry;+- sphere A? (b) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. ngzz1vt +t 9u616–68, at what position(s) x is the electric field zero? Is the field zero at any other points,z6+tuz n1vg 9t 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 charges, each9wn kbs4(:rpc xop 6:r 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?