If you charge a pocket comb by rubbing it with a silk scarf, how can you d b4zf25x jp;vqk16 agdetermine if the comb is p4x5jfbkpv az1gd; 6q 2ositively or negatively charged?

Why does a shirt or blouse taken fhtaj4ti(;5, :rvq .vmezj 4gyrom a clothes dryer sometimes cling to your bo,a (r4i yzv;qe:.t4hgj m5tvjdy?

Explain why fog or rain droplets tend 3e-z fr7xvo (hto form around ions or electrons in the ai7- fxve(z hor3r.

A positively charged rod is broa;g;-z4ycw d wught close to a neutral piece of paper, which it attracts. Draw a diad-4y;;g wcwazgram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has beenzw; h0wy 5jtw; rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficult to do on a hum wjwz wy;0;ht5id day?

Contrast the net charge on a conductor to the “free charges” in thefzgcw0b/pxox ln g/ )40pv0 t5 conductor.

Figures 16–7 and 16–8 show how a charged rodifobe 4.uqk+* d u(y*g placed 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 shown. Why not all of +uqu*dyei(* b .4 gfkothem?

When an electroscope is charged, its two leaves rolm d0.k o45jxepel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t separate further?j4mool.k5 dx0

The form of Coulomb’s law is very simila cawah/m :05m;klw2hgr to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare also gravita/ lwhmm ka0c awh;g5:2tional mass and electric charge.

We are not normally aware of the gravitational r77k+i22y)y hlvzjei7eru6n 7 o v 3vfor electric force between two ordinary objects. What is the reason in each ckr37yfei )277i7rjyheuo6 lnv z2vv+ase? Give an example where we are aware of each one and why.

Is the electric force a conservative forcu6oj91 w :j9 y s 9-lwvmngyrs8l9x8oye? Why or why not? (See Chapter 6.)

When a charged ruler attracts smallx.c-:a .0-gb sym6vruw(x3xy 5exuly pieces of paper, sometimes a piece jumps quickly aw3u5.x-wya0 x vcg 6rlxm:(uy-xebsy.ay after touching the ruler. Explain.

Explain why the test charges we use when measurinls/dpo6)3ykl0a d/c sg electric fields must be small.ls6add s// pkloy3) 0c

When determining an electric fien2xk-vsoki)b2 zr02c ld, must we use a positive test charge, or would akbk2c2or2 zvxi ) -n0s negative one do as well? Explain.

Draw the electric field lines surrounding two negative electric charge)6sqc j fdcot6-ek(8ls a distance (tc- 8sl fej qc6o6d)kl apart.

Assume that the two opposite char -8pts,x quy-x 4/e5fakkw(rfges in Fig. 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive chargepf-ktw/ukxf,xa qy5 8-rs4(e . On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field atbgq ekgtutj 0uu66 .va73uqs.j3 , e6h points A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order ogua,bq7e.0g6 66 vqj3ue ht3ku s utj.f decreasing field strength (strongest first).

Why can electric field lines neve24ol+ abh6rbv1fm)mg r cross?

Show, using the three rules for field lines given in Sectiuuq g ,)p+,soron 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically rpgu )u+q,so, spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a point along the(6 ro b,ivzf:x;5pu cp straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this p u6c(f bx ;piv:5,oprzoint will be.

Consider a small positive test charge lop(cf2-fd+lhu ;o5 zngao;l (c cated on an electric field line at some point, such as point P in Fig. 16–31a.flpccz; f+ g;lu- ha(52odn( o 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 charge which is 5 6t0dczkmqv 9infinitely long. z9dmk6vqc0t5 (Hint: Use symmetry.) Is the electric field uniform in strength?

If the electric flux through a closec+572n 57uixp xrezxp s xo3(kd surface is zero, is the electric field necexk sexn5oc(up7+i73p2 xxrz5ssarily 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 a spherical gaussian surface of rt fz38yek 1v2cj-5 zxsadius r. If the sphere is replaced by a cube of sid efc8 kz1j52 t-xvs3yze r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up 8m fm9jl (53emg2l+,tseb n ob,j*hh,rw 1qtla charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude ofn nyoa d-l;vcs:2-+qw the electric force of attraction between an iron nucleus a sq-vcn d:-+ny;w2lo $(q\,=\,+26e)$ 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 prototm0v0nlmqp31 d*t -c a6vk 5rsns $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of w6tvytgy 6 q3s u5.5 sc(nmag1the 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-1swumx8r/ol 6 f,0q hdjbc -w 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, and th(yd 3jd)c2p sde force on each of them is found 2s 3 pcyd(d)jdto have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day*j2v cb8nw-sh accumulates a net charge of w8 b*jshv-2 cn$-42\,\mu C\,.$ 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 th/0pi6a zrf0 pje electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric focj j6jkm( 72bk3:p ylrrce 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 chargpx g y 3mcyzarq9/.q7dx +upk(3q ;2tbes are a fixed distance apart. The sum of their charges is What charge /327kmdbt ;(c ppzxqaxg +3.yu rqyq 9must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge h ty)x:o)ff.f- txhg.$+75$,$+48$ 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 eqt5ul:txx::ao + u-xvhual 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 on a side. Deteai:,mu,-oq3wza sdvdwk35jl b o: -7irmine the magnitude and directiowa-iiq d:b u3ka,7,dvwz :oj -ms5l3 on of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on opposite c8 upg.xf .fb/li- t7- rmmj4luorners, are replaced by negative charges of the sam fx8u t7lm- ig4jr-bu.fm/.lpe magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnitude q 7:i les+mpnm;ke0)g Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the :en l;s0kmgqi e7m+)p 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 pla*.8 cbkp7;xqg 1a5kdzds w6e xced at the corners of an equilateral triangle of side 1.20 m (Fig. 16–53). The charges are xz;8x7 kkwp1.*qs6e cd5adbg$+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 s;10 d;so:h2qg gdvu- js,r hntotal 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 sphere4vp 8t3bud/dvs 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 xv379lauqdl h.v-t; dan initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is lvd.9ax q-7ltdu3hv;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 on an electron in/qt- vvk9ejoz3le( )w a uniform electric field of -etj (z k9vel)w/qv3o strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in w.z)2f krokq7a uniform electric field, and it experiences an electric force ofr).kw7o kz2fq $ 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 exerudn :pqn e8h(zln3ig)gs2(q9ted 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 2:s(7hkf( gfaauh*c3c0.0 cm directly above an fc7a3(gsauhk(h:* cf isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron in an elef2a j 5px8 7zqzrkt7(mctric field of7kzqtj7(fx pa82m rz5 $750\,N/C\,?$ 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 uunjxxgi7*3cjr 3 n+xbi0g+ b sed- -9between bx7*nesdn cj3u3bx 0- r+9-gxji giu+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, ap1o f,upy.-q-8h oakthe electric field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point i bxbub60/c/ppvh (hv5n 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 froj.-+w 2nefhaa ky 9v)dcq9 gg8* y(tcwm rest in a uniform electric field and accelerates to the north a8*dca(e .q9vgk9hctwf+ ynj a2) -g ywt a rate of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between two equal but opposite poi wk0 pqv3,pj1mnt 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 fierf pqatbro*f 2m;-4 b;ld at the center of a square 52.5 cm on a side if one corn-4oftr;bm; p*rfqb2a er 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 9 l9(ys yjb)rla31fl4jivc 8ylu:v z;on a side if the other three ljazv3 l ui;rjyl fl48:c9b )1y(9vyscorners 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 inhc z bc3(hws v(.g+x e:dm3df. Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x from gv ec +dw(cbd.3hs3.:x( zfhmthe 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 f(1u xobo5ir 0p 2mvtc0a ,ckb,ield $\vec{E}$ 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 hp6 9 ps6/9* 43u;kzo yeaphl gw1ikjtdirection of the electric field at points A and B in Fig. 16–57 due to the two positg4z 6*;sapp /jh iuytok3w69k 9elh1pive 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 til a+ye+15o ql al91 )9whovvcharges, $Q_1$ 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 a0kdq5 ywof. 8the electric field at the point P shown in Fig. 16–59. The two charges areyd8qfo5 a. 0kw 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 lightnjl si37 os*c)xk3 ;gd enters a uniform elect losdj*; g3kis) 3n7xcric field parallel to its direction of motion. 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 mb 20ukhnmh:0a 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 uniform electric fiem b*abd+ c,zb3ld of magnitude ,+bmzd acb3 *b$ 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 objso2o+kros )q6 ects, $O_1$ 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 placed8r ) o4;a;ot+owc*b *sehy6svjrb7 bt 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 t540qa6oy5qb, tezqkqsaf0 -z1(iy z rwo square metal plates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each platy kotzq4sqz( 5 q-biay 50r0efz1qa 6,e (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-c:r6 q vl+)totradius 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 carries a tozy lp1nb;/jc) tal 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 conducting fp8 0a4zj3n ev, ltcu,:cplj ;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 t8p, t:l3vj n; e4czcaju p0fl,he 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 held together by electz u u)f2x5e uj26jo2obrostatic forces as shown in Fig. 16 2j5uzobuu2)j fexo2 6–44. 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 +l9g/u 1oba knthe electric force between them is equal to t9nbol1ug +/ kahe weight of either at the Earth’s surface?    m

  A 3.0-g copper penny hasq ;m5y-k, b/sravab 4r a positive charge of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

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

  Measurements indicate that there is an electric field surrounding the Earr0qqv 3xubsg9 ihqj9aq3*m52+e 1 ml eth. Its magn gxim9 la2h*qe+q 5v9jqse1q r 33mbu0itude 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 electric field of (kd)vd zbnwf 7ys5); dc 7z-cy what is the acceleration experienced by an electron near the surface d) d7zv)5d sz ;cy-b7c(ykwnf 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 the air.oknq)2:t/0miwp fu11i xz ,c c If the downward-directed electricc02tu:w /,ko 1)z1pnx ciq fim 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 gxjbg0b)bjyix q.t95h gx 0 xp87zcw5)roup shown in Fig. 16–62. The Cy.x)t g 0xj5icg bb9 bpxxhw70 58qj)z and O have 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 orb/36jn(gi h7ij o teh1vit around thej itgo1hhje(3n6i 7v/ 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 responm-wy ks8 cave-m-s.vgp7m - -lsible 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 maintain the present k -8 m.-gpec-v7mvmsl--wsy aorbit? 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 speq1,3:fx5 dahf7qc) r b+vfoaa ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charg*u(z7 9fmns m-n pul8ae $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 ia+ j v,xpr0x7giog k4 6xt*:vxnsulating plastic and suspended vertically from an ideal springjxtogk xpr0x,: g4avi*v67+ x $(k\,=\,126N/m)$ 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 wirff wx5f1lao o l6t.;j 29rgr(res with tiny 24-g spheres at a9 j1rl5 .ffogrxow(2;rft6l the ends. When charged, nearly all the charge resides 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 ifpjpi+( :*tljm the electric field exceeds aboutlm+j ji: p(*pt $ 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 ner: rvfpw1g/q.t 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 electronoy r.7-omee lp)yl 1u4s in a 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 conduc/ztu5jr 0skcs ofj2gyu;o8,a6(mn ) cting spheres 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 zujsn(,agyz/ u)8cj2fc torko5m0 ;6 sero 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, at what posit hr5w n/atew1,vgkooq8 +q yuua.9g)6ion(s) x is the electric field zero? Is the field zero at any other points, not on the x arqv 5k)u,w egq aao+uyn9w/ o1 68t.ghxis?

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 v6 it /wi6p fdy/d8mrz64: mncof 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?