If you charge a pocket comb by rubbing it with a silk(,uat;qnz7 h 2asa tj. scarf, how can you determine if the comjzna tu s;7 aathq,(2.b is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to youd q* v0ho q1/cjhw(e;qr bod q/c wd1(qh0hq* ;jeovy?

Explain why fog or rain drop a/jcecm;b6x- lets tend to form around ions or electrons in the aircmx;a/j6 -b ce.

A positively charged rod is brought close to a neutral piece oec s* ww-3i1vd*sk-iaf paper, which it attracts. Draw a diagram showing the separation of charge and explain w- ewa ski dvsi*wc-13*hy attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the abilityjab9 atr8olk.-vv/c , to pick up small pieces of paper? Why tv9jav bk, 8.laocr/- is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free chargeme4: :om0 fw0jx6oexcs” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged m:au,-g9cgl 3bgsfj u5etal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some ofu:gb -3lajfs9c,5g ug them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each othe4/f ktao0,b usmkj0 8wsxum hl+7wb99r and remain at an angle. What balances the electric force osm9jmk b x0ahfw9wuou t/k07+l4b8 s,f repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law of unkr6snaa8 eagrl2ro6q09x4 6z iversal gravitation. What are the differences between these two laws? Compare also 4aoaxns 966rlr 8 kqga2z60ergravitational mass and electric charge.

We are not normally aware of f23 :h:q0p*fkro7z v8y rmnwx the gravitational or electric force between two ordinary objects. What is the reason in each case? Give a qvx3:zrk:0n*f2rp 78y fow hmn example where we are aware of each one and why.

Is the electric forcem*i2wl8z fpn/gnj /(e a conservative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimva ;ta 8u6ycd:qf 4a0neq9:imes a piece jumps quickly away afi6ydcfnau: t9;a 4e:80a mqqvter touching the ruler. Explain.

Explain why the test charges we use when measuring elecczapx3my( y7 )tric fields must be small.)my73azp (ycx

When determining an electric field, must we use a positive test charge,mv6j95c ko9ti or would a negative one dmv5t99k6 jioc o as well? Explain.

Draw the electric fiex// 0lo itgw(m:mb1kgld lines surrounding two negative electric charges a distan0o kg gmi l/(:x1wbm/tce l apart.

Assume that the two opposite charges in mqqbk93zp 0z6Fig. 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 thekb6z mpq3zq9 0 strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. Firstf,wn e 3)hlv(g draw an arrow at each point indi() gl we,vhnf3cating 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 lines never cross 9nai jwd8o;;eeja5 2g?

Show, using the three rules for field lines giv4 f/pac* jc tw6c +oz983pkc,n ) yzan.blaht8en in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spacedt8c*k p+ha6c)8f/o9 zbln4 c .ztnjpway3, ca around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a p i2 h k)a+(,0kiazono1ir w-vnoint along the sin0k o2 irv)+-i,a( wnohazk1traight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an electricpbjeo* fla-z ohc)09ykfo49h )* ex7 e field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discy*hoz e7cbx ao0 e9 )fh pj)l4*k9e-fouss.

Sketch the electric field lines for a uv;in.zmi :;jvv6f3 wbniform line of charge which is infinitely long. (Hint: Use symmetry.) Is tjw;bm :6vvvf3 ;i.nzi he electric field uniform in strength?

If the electric flux through a closed surface is zero, is the elng 4qj3f7vg l:ectric field necessgf:7vjgn 3lq 4arily 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 sur0ncza :y k 89pn7nkr8nface of radius r. If the nrzy8: 9 a08 pncknn7ksphere is replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up 78fk e)rh7r t1rn7f lfa charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attract88sw ynj2wi p-ion between an iron nucleu8 swjn-py2i8 ws $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical for,2nr s*3 )cwhrbl f:oyce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitudeysmnt23 ghmws7)o 51 sl/fhs1 dqqj(5 of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a,b 3dbg 8;oysk 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 8sq6zw:dkw,cf f. ;b, a-e wws;0rns6s.45 cm apart. They are moved, and the force on each of them is found ,-6s ek0rbdcz:s;6nq ,faws .ww fw; sto have been tripled. How far apart are they now?    cm

  A person scuffing her feet ob zymk7o2-0 wmao c*m7n a wool rug on a dry day accumulates a net charge of o7b*0-mcm kma72owz y$-42\,\mu C\,.$ 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 electrons in 1.0 kg okz, *y.:a2s0plqd y mtf $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in o z)4;k4mmj*u9bumi pkannx 8ze b/0r9rbit $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 t 3hg(u5sqqu u hul;74their charges is What charge must each have in orq(uu4 ;hlutgs35 qu 7hder to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 2*zmrsqsu.x4;is q( u$+75$,$+48$ 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 equal chargeje5h vx8pz ;8p, $+11.0\,\mu C\,$ 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 plqh, 1ag z5:thfaced at each corner of a square 0.100 m on a side. Detera t:hzgfq5,1hmine the magnitude 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.u+anw i9 rhkil4gx52d3pn f2l6 p 1knarges, on opposite corners, are replaced by negativ32karn. k dgli45pw+ ul9i2f pn6hxn1e 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 maf b*u ofx-k*m0gnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) t*o *u- ffmkb0xhe 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 particlf3u ue- 0.grll: 0bp i :5lm8ah5eiqts cn:6laes are placed at the corners of an equilateral triangle of side 1.20 m (Fig. 16–5lnie.- e l55balg::fit6urq3 :lh0c0 8a upsm3). 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 chay)jb-n 2aq;2sl97mbdtv:lx 8 bw u7rg rge 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 have8wv f /z7v+zkz 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 uncharged plastic ball tw0ou;vw0kj;q*k o8 h(t ewu:zo an identical ball 12 cm away. The force uow(zk0wv0jqke; t*w hu;8o :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 on an ele sj.8:z8sin ynctron in a uniform electric field of streni znyj8 .:s8sngth $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and ithpf6k jr(nmeodi t,4u4 :r3w9 experiences an electricm r4r9w(d u4 ef6tkj,: hpoi3n force 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 on z6+m0co lzb:m4 e+xr5 cz1-tdcm yy6m 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 directly*q:h)me o.3dzp ugf:r above ag*pfr) uh:oqde:m.z3 n isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the o x(deb u+8q lu 2a,pq)3phtw:acceleration experienced by an electron in an electric fieuhp3):e+(olq b dpwau28xtq,ld 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 mi*a8 rgd3z,nbk4g:sj(zl z0jm dway between a ajznz4 b*,s0gkm: j83 lrd z(g$-8.0\,\mu C\,$ 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)k7sl( 5w/kj,,c v xm 7vwrztf point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where a przyy)tu h6e2afg,x7n*oton $(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 42m i)) kkhcn8 )ps 99/grfxywcc/klzfield and accelerates to the nortykfrspzxn)k/l8c) 9c h49 m/kwcgi )2h 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 midway be 9t;t 9zyu/djwsn pz ws1pzs04- q,4matween 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 cm on a side if on) 9ahelfoif38 e corner is occup)f o a8ih93fleied 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 if the o)ukxz75ob sme9rki-6ther three corners a 5rxs69kk7mu)bo z-e ire occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction1ym hb p2dlr)2;zeqlho;p w. 4rh :f+f and magnitude 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 froll h+ p2 q;hy4wmz :f;ob.drph)r21fem 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 ele*a+ rjm3idev:v2a/p fctric 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 detes n:5i)lqj-0 ipj -enyrmine the magnitude and direction of the electric field at points A and B in Fig. 16–57 due to thys-nj p0i)jle :qn-i5e 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 po6 mimli a y.8*w7iz(mbx wz7;yint 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 the zbf7ue/6/vrg point P shown in Fig. 16–59. The two c/ eu6fzr7/gvb harges 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 t5 a0a-c8jy zcxr6e vit-1p d8:a4c dsvo the right at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rescc:4x zv50- j -av8dtiay e61pc8 drsat 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 l vk f gdc/g:r+ra:y2+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 is3 q )lh np3o:lnb3kt;s placed in a uniform electric field of magnitude3)3 ;t ns:nlk3hblpoq $ 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 obje3+ 9cyy( z p5t,o*ketfnfnu,d xn4r*jcts, $O_1$ 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 placm(/:u (mcb9.pzyr;m za et*iced 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 im)9b3wm+v.ikz ,kqfcfs4gee o0a (r 5s The plates are 1.0 m on a side and are separated by 39eig(., m+s0k3w4ce q5vfafzrb)m ko.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3./k,ce4/bw* i(o.pvvrqy o2g)t q y jc+50-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 radizq 6tva ziyy,9/a)gl m)u 1v*uus 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 9x92bh7 ppjip at the center of an uncharged thin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the 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 shelpp2979xhij pbl?

  The two strands of the helix-shaped DNA molecule are held together,xq.j7wcl vv 3 by electrostatic forces as shown in Fig. 1v.,cv x lw7qj36–44. 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.m h 5q3axvf1jkh25 ic force between them is equal to the weight of either at the Earax5j1v3h qc2ifhk5 m.th’s surface?    m

  A 3.0-g copper penny has a posq20bqs p,y+ jkitive 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 fie8h3;s.;v lw 9rw3bapzqpa,svve; 5 olld surrounding the Earth. Its magnitude is abo;h3ap ;9 ;rpswv3,vsvz aqbo8l le.5w ut $150\,N/C$ 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 wha z8x/rp(/neo i/h-mipt is the acceleration experienced by an electron near the surface of the Ehoe (-p//xi nz/mip 8rarth?    $ \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 stationaxm nc28y8 aiq*ry in the air. If the downward-directed electric field of the 2na 8*xim qc8yEarth 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 a xu .gt0(tr*(id2ufui nd the HN group shown in Fig. 16–62. The C and O have charges gux*tf.i( du2(rt 0ui $\pm0.40e$, 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 hydroe+,w ro3)paqc4 x p 9mzyr)s/ds ru2:ggen atom, the electron revolves in a circular orbit around the proton with a speedq)purs )xye a /2r3d:c m9ps+grz,ow4 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 gravitw oa775+ch8ftt 3kzm ox8u+ra y, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what shoulrwto z37+7fak+85c8xo uhmat d 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 zehw1* sh2j6zq+ zi*h$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charge /qqg62q n4 ipw$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 fr jfbzs6/zn) +com an idj+z ns/6zbc) feal spring $(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope is made with “leaves” that are 78-cm-long wires with ti;vpwzvd .2 u:;gg,doxk:+lf any 24-g spheres at the endsu wf p.d;2l,dg+o:;agkv:vz x . 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 if the electric gc4*7 kk5sxp-vxm:lx field exceeds aboutmxc5sxp7 x4g-k* :k lv $ 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 maib6y/des /co .s*2 af,gz9heess 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 b,x 1a:n5m svgwjjl yvr3,o9q 4ar 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 a-r-, pkb a::+klzeo6x(ihtrg re 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 sphepik+ ( gt :-la-xrrh,:e 6zbkore 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 position(s) x is the electri9iizn( 1o pfwefhr*,7c field zero? Is the field zero at any other poinrz *7f9 ow, n(ieh1ipfts, 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 *nsvs0 z,scc7mn; 1n5 izo1wjcharges, 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?