If you charge a pocket comb by 3* g-xssj: wd rxa+yu-rubbing it with a silk scarf, how can you determine if tyujsrd3-:xwx*g+-a s he comb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer scpns/nlotup)4)iprl yy d ( ;r1 +1bl8ometimes cling to your body?lli(o 1yb8;s/n4ptn l1r) +p)cu p rdy

Explain why fog or rain:84f g 6h+m(g f* 1lg avarb-oyrg-ogc droplets tend to form around ions or electrons in the airrfg1oh gyl*-:garggo (48a cv +bf6-m.

A positively charged rod is brouiu+v 1qslrv2)debz.. ght close to a neutral piece of paper, which it attracts. Draw a diagram showing the sepa+lvisd)r2e1.q vz. bu ration of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have t z,2rnd *vwq*pgmn0 f0he ability to pq ndn0v*z0g2fr*p,mw ick up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” a6p)2w a sdopk8+ormal;d 4z.in the conductor.

Figures 16–7 and 16–8 show how a charged rod placa.ilg32,3xcr +1 pmzm:vcqnw ed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as sh :,vclx 3qpm2 3wc1gn.+mairz own. Why not all of them?

When an electroscope is charged, its two leaves repel each other and remain atska-n 3dds)b +9bf(d2q yy4xs an angle. What balances the electric force of repulsion so that the da3n-fdxks q42ybdy ss)+ b9(leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law of univ 7e q7/oc*brjiersal gravitation. What are the differences between these two laws? Compare/r eb77oj*icq also gravitational mass and electric charge.

We are not normally aware of t dv( ygwnvx2;-he gravitational or electric force between two ordinary objects. What is the reason in each case? Give an example 2(vwdnxgv -y;where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (Srcjbe8nom hj /7c27 t6ee Chapter 6.)

When a charged ruler attracts small pieces of paper, somklqm/ljv1 )j u 6,)y9d: ljzapcn2ik2etimes a piece jumps quickly away after tvya6: jj))mnd 9k1l,l2j k c2izpu/lqouching the ruler. Explain.

Explain why the test charges we use when measuring( xlmm+sq*re 8 electric fields must be small.lr(x8q +s*em m

When determining an electric field, must we use a positive test charge, or would, m u)bxj9l;sq a negative one do as well? Ej)l;m ub,q s9xxplain.

Draw the electric field lines surrounding two negative elect59:t68w, yfi l7ch 9bdr)dfj y4xb*bgpq x3 sxric charges a distanc gf3tb py dbf )7 dqic4yb*98j:9 xwx5,l6xhsre l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Considd3/w8 pby* idp.i7hj:g 0 nsgqer the 0/pd ii:j*pnhg8qsy .3bdgw7 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? Explain.

Consider the electric field at points A, B, and C +hj0k()qbkb *gj un0oin Fig. 16–48. First draw an arrow at each po+juhk*bkqj 0bgo)( 0 nint 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 strength (strongest first).

Why can electric field lihn99d s0j1lqgsk u*tx ( 7s8nsnes never cross?

Show, using the three rules for field lines givejv:y8g zn0y u8n in Section 16–8, that the electric fiel0u8g :jv8znyy d lines starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a point alonv:nprh tu+;b7ou m(8jcia h-6g the straight line that passes through them where E=0 when their signs n coj:+bhuu;im(6t8 7p -avrh are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located oqrrue x.yq p-8 :bwj2/n an electric field line at some point, such as point P in Fig. 16–31a. Is the directiuyqw 8 2rxqe/:-jpbr. on of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform lin fxk6zj/ *opsv5w/n/c+ yhjql5,)w she of charge which is infinitely long. (Hint: Use symmetry.) Is the ele,/s 6/)cjfyln/5 xjs*zhwqp+w okvh5ctric field uniform in strength?

If the electric flux through a closed surfac.94mk 2c 1gimd radn(oe is zero, is the electric field necessarily zero at all points on the surface? Explain. What about thearki1 gd.d4nmc2 mo9( 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 sphericejt 4 hyp1q(28u2 jrfjzij)i ;al gaussian surface of radius r. If the sphere is replaced byfp1r4t(eijjhz j; 2u82i y)qj a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make 2 aw68xg2d ncmup a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric for-m 6nc p-vef9+rk 76/hf(n t uews5jdoce of attraction between an iron nucleusksn pe 9- 6c5v-u+7(fefdr 6nwo m/hjt $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical fof. *m 5ya31dz-socin lrce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of th; 99vpfisq p2xe force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a foiaun9 *g6yx d6 zp2.) fjexmw0rce of $ 3.2\times10^{ -2}\,N$ on each other. What will be the force if they are moved so they are only one-eighth as far apart?    N

  Two charged spheres are 8.45 cm apart. They are moved, annr7va396ajte) ea uw (d the force on each of them is found to have been tripled. How far apart are they a(e)n937vrwut6aa je now?    cm

  A person scuffing her feet on a wool rug on a dry day accumuvb : s7a x4w8b 4-yvk.nxt4tpplates a net charge ofbnvw p7y-4pk.484b xts ta:v x $-42\,\mu C\,.$ 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 electr/d3 3ru,aggwt /yu45kouhgj 4nrk9 +bons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the ele grq 4vpv8r731cqom m vitsng45m,z22 ctron 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 9 /r -fxvq6)ye/rkud jcharges is What c/)- kyjrfxv6reu 9qd /harge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge na-k0 f *)mtwc$+75$,$+48$ and $-85\,\mu C\,$ are placed in a line (Fig. 16–49). The center one is 0.35 m from each of the others. Calculate the net force on each charge due to the other two.

$F_{+75}$=   $NN$
$F_{+48}$=   $NN$
$F_{-85}$=   $NN$

  Three positive particles of equa4klt m+b ,,aev2d1szol 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 0.100 m;.(7u.ezrnzt w.md l v 81qhyd on a side. Determine the magnitude and direction of the force on eaqu.der1m zz8v (dl h7wn;t y..ch charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two hgmvw 6e rnf; bh .9,n/1s,nnyof the positive charges, on opposite corners, are replace. gr;n,hvy9w/bs,n mfe1nhn 6d 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 Qm.pqty:j:*vx , 2Q, 3Q, and 4 tx*.jvyq m::pQ (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 g)p+ssezou khc;7v;t+g g m9+are placed at the corners of an equilateral triangle of side 1.2c ;t +kosgp+ge;m zgvh7+9u) s0 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 charge of e+.cij8 uqtz8zmv* /piql;p3n 5ic u3$560\,\mu C\,.$ 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 nonconductinoslmj .6:up.s g spheres have a total charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially unchargof36vc )vw 6mm77sjdckl5 d v1ed plastic ball to an identical ball 12 cm mld)wd3cvv j o6kmcs5177f6v 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 of th0q9g:n3woagtfiwrjt/; i l 21 e electric force on an electron in a uniform electric field of stretgj /:w ig2ln q;twr1 oif9a30ngth $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences anm6o 42g:)yukm) 8k awj/yjvha electric forc aw:hvuj)gomkyy62m8 /aj)4k e 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.n ox*fi+ c-ff;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 direction of the electric field 20.0 cm drg)lef. rc/r6 eoxqxr196nn 8 irectly above an isol e)xx.gnrn 66 9l1roreq8fcr/ated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron ind+9 xvp*t ;d4 lrnx-tr an electril nv x*+trrp;td-x4d9 c 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 midspmgfafl8 atp2p5+m3 4+*kptway between tm 82f 3g*5ppa+aflp4msk +tpa $-8.0\,\mu C\,$ 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 p.b-9luyr 0jbroint charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a pointr o rkv86 xu0kn) m7wtnp0fa.4 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 u dxv) pfhi9gstm1s:*9niform electric field and accelerates to the norisfpg1xsm)9 *v9t d: hth 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 midwa;lp82.7n;hy.pig8 ocnbi7 .qkhg pfpy between two equal 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 the center of a square 52.5 ct7g )qumv *tqhcj65)djrr 3g-m on a side if one c-jcrqjtrhtm*35qg)u7d g ) 6v orner 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 square3mtna ov.- x k7tib. /ia4*jwe 1.00 m on a side if the other three corners are oc3vokb/a- aijiet 4 .7m.xt w*ncupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnz9 .hjl:pj qwb599wvl itude 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 midpoint between the two9j 99lhjvpqb5 w:.lw z 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-k2qkjx fd:8 nzsnm4 1tric 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 magnitude and direction of the mphu q 9,/o(wtvf8 7rg3z z2kph:ly 0helectric field at points A and B in Fig. 16– l 0m(phh83ph,7o2zqzy:gw vu/9ktr f 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 unknown point charg+ba( (j) zebbvl7 tx5wes, $Q_1$ 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 el0uchoqall;4j.mlct o,0 q)0 1hqjr9 zectric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is onjt c .qhomu) zo,l9h1llq4r0a0; cqj0 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%l0qvk;e dqn . t5o:vj. the speed of light enters a uniform electric field parallel to its direction of m..:0joqe ; vqlnktvd5 otion. If 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 cubical boxy*s y;v2dil *g31aenmg w6/vz 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 unny0 ye;5bv, auiform electric field of magnitude; vyyb5 nue0,a $ 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 obje2f*gx bzj3c p j9td)i3cts, $O_1$ 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 a uniform fy t*-m6pcvu;hield $ 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 arg9wb4y 3;jf5 u3.,cc p an 9kr;ecnxpxe 1.0 m on a side and are separated by 3.0 cm. What is the cha39pj5,9xn x c.eyuckpb3 wa;rg;f4cn rge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius 6q( ,ashl.lp jzp4 )y/juj)so 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 c2nf . 0x0 ny:t d5:zrclaoked/arries 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 sphericalbzns/ u1j6r3 b o l30b,pb1mkapfd )k- conducting shell.znbl m /j3prsu1k)0ab63,pkbfdb o-1 (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 shell?

  The two strands of the helix-shapeh0 zag--n5 ocxoh6m0h d DNA molecule are held 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 0.2e and on the indicated C and O atoms is 0.4e. Assume also that atoms on each molecule are sep0ga560hznh coh-mx-oarated 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 electro /mxorx :apre/z;gc:brk0l :. ns be if the electric force between them is equal to the weight of ei; : rm0x /kprcxe/ .rbzalo::gther at the Earth’s surface?    m

  A 3.0-g copper penny has a positive chaj0,rxs-* zsrl rge 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 electrin nx3 c;bpe.y8c field surrounding the Earth. Its magnitude is apxby3n .8en;c bout $150\,N/C$ 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 u/ uddo fd7d5qo:oy3: what is the acceleration experienced by an u:ddood o:dqfy57/3uelectron 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 radiu *d um(9pzxof*s 0.018 mm remains stationary in the air. If the downward-directed electric fie oz* m9f*d(upxld 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 akx0v p cbxw;y *+pv70- y*3smgxn. hlbnd the HN group shown in Fig. 16–62. The C and O have charv* yh0k7x.s 0gbmwv;y*xl 3+n-xcb p pges $\pm0.40e$, 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 ato:z 3p1/wtoy8kld op*pm, the electron revolves in a circular orbit around the proton wi/ 3t: dw*poyzpplo8k1th 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 attractiou-bwd+gu: d3l3sfii8 n, rather than gravity, were responsible for holding the Moon in orbit arl83wis 3-budu i+dfg :ound the Earth. 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 speed o :353m -f9b kros9ft,x ezq7z8zey:obbs jr 0$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chawf.:kl-/fy;iws l hy/i9p ):g l pezr;rge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vertically q.l:wfoc x,t/from qf/wt cx.:o,lan 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 lqm ;h ;u)(2y hohjfo-made with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the y2uohmj(- o;fqh;lh) spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break down and generate a spark if the electri/n+dkagb2k-zu drxeq:+8zd .kn q(( qc field exceeds aboutn /erq-8a+bng qd2d xu(qkdk(z:k+.z $ 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 mask2/xr3up l uh*legi5 ppy5)x-s 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 ba8)t-pmp+w4dz9 m azt f1 g7vxar of aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B are a distance R apart; ea,qon6zmsz( -,eif 6p jch carries the saqez 6p 6mizjsofn(, ,-me 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 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, 0bu72hzh7vmp g1 qu5zat what position(s) x is the electric field zero? Is the field zero at an v0ub 5qh2z1hu 7m7zgpy other points, not on the x axis?

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

Four equal positive point chau62 dvoxtbgqa4 v4pw/a (.h,j rges, 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?