What type of bond would you eg)z6kfbj 5y0; ;g0at60 glv nuifgggd wl;e: 4xpect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molec*sah 5q,//:jre2b0pwt ilcyc ule $ \text{CaCl}_2 $ could be formed.

  Does the $ \text{H}_2 $ molecule have a permanent dipole moment? Does $ \text{O}_2 $? Does $ \text{H}_2\text{O} $? Explain.

Although the molecule6(2 efvl qug :ihy)fw) $ \text{H}_3 $ is not stable, the ion $ \text{H}_3^+ $ is. Explain, using the Pauli exclusion principle.

The energy of a molecule can be divided into four categories. Wha-wz4f:k yby. mo ie,6nu s1mn0t are they?

  Would you expect the mozju w97r wh:+llecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon2b*lupml6rfo n1(z 5 p7pb rl- atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal,x:g.oz*xm:ml vmh +g1 why don't they leave the metal entirzm:o1xmlxm: g . h*+vgely?

Explain why the resistivity of metals increases with temperature whereas thez li *.q5 .+xhksgrjk1 resistivity of semiconductors may decrease with increasing temperat1izr 5.*ksljk hgx.q+ ure.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the c3ucqo*f0q34s mcl:le gco1m4 urrent is rectified and how current flows during each lqc4f14ecumo :lo3m0 3q*csg half cycle.

Compare the resistance of a pnr+cq i eh2g:br kw)y19 junction diode connected in forward bias to its resistance ber+1:hiy cr)k9 2qgw when connected in reverse bias.

Explain how a transistor could be used as a sfp) 0mrck rua99y2 p78hy(ts pwitch.

What is the main difference between n-tsloa -* :1tyzmgv 5zw2ype and p-type semiconductors?

Describe how a pnp transistlj,y v*bjp*9mtnn 5h3or can operate as an amplifier.

In a transistor, the base-emitter junction and the base-cob; yo1fch+ho2n( 8..l ddyaj;k a(ndmllector junction are essentially diodes. Are these juncko 1d8blmy(ny fddn(a.hoh+; 2j; a.ctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an efle8 oc;wp5*utxf4/vd c7t w;(n oo3dgg8g +zlectronic signal, meaning it can increase the power of an input signal. Where p t;ec85wfgctd on3vo(d7 xf/8u;g o w4+zg*ldoes it get the energy to increase the power?

A silicon semiconductor is doped with phosphorur (;h dyx*eea*s. Will these atoms be donors or acc(rx;h *a*yede eptors? What type of semiconductor will this be?

  Do diodes and transist .klxqv/h zrwk/z*a ,)ors obey Ohm’s law? Explain. {yes|no}

  Can a diode be used tr 7(g5crt5wmq d8tn/z o amplify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule b:u47; v nkrfl3j t .lfopwiql)5**kepy calculating the electrostatic potential en;k fp l *4urnoqewvt 3.l)*k:7pi5ljf ergy when the $ \text{K}^+ $ and $ \text{Cl}^- $ ions are at their stable separation of 0.28 nm. Assume each has a charge of magnitude $ 1.0e $. Binding energy =    eV

  The measured binding energy of KCl is 4.43 eV. Fro 5znb2k98f1em,g csn qm the result of Problem 1, estimate the contribution to the binding energy of the repelling e8g,f9k 2zmnnq s5ebc1lectron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of to i+/*gp)h+u vyrx5ar he $ \text{H}_2 $ molecule, assuming the two H nuclei are 0.074 nm apart and the two electrons spend 33% of their time midway between them. Binding energy =    eV

  Binding energies are often measured expeflsy q2w4j2b wq8b8c )rimentally in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion factor in going from kcal per mole to eV per molecule? What is 2 qwj qy8f8w4c2)lbsbthe binding energy of $ \text{KCl} (= 4.43\ \text{eV}) $ in kcal per mole?
We convert the units =    $\text{eV/molecule}$
For KCl we have =    $kcal/mol$

(a) Apply reasoning similar to that in the texc3axn982l attt for the states in the formation of th ttnl 82axa3c9e $ \text{H}_2 $ molecule to show why the molecule $ \text{He}_2 $ is not formed.
(b) Explain why the $ \text{He}_2^+ $ molecular ion could form. (Experiment shows it has a binding energy of 3.1 eV at )

Show that the quantity-pf s,s7z./ of4gyaj i $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “chara 2c+,sjj+n sdhcteristic rotational energy,” $ \frac{\hbar^2}{2I} $ for $ \text{N}_2 $ is $ 2.48 \times 10^{-4}\ \text{eV} $. Calculate the $ \text{N}_2 $ bond length. $r = $    $ \times 10^{-10}\ \text{m}$

  (a) Calculate the characteristic rotk:1 ,oy1lab cso4/jzr. 6w ro a2q.pjrational energy, $ \frac{\hbar^2}{2I} $ for the $ \text{O}_2 $ molecule whose bond length is 0.121 nm. $\frac{\hbar^2}{2I} =$    $ \times 10^{-4}\ \text{eV}$
(b) What are the energy and wavelength of photons emitted in a $ L=2 $ to $ L=1 $ transition? $\lambda $ =    mm

  The equilibrium separation of H at hrsk8ujca ) f8r,vt,6oms in the $ \text{H}_2 $ molecule is 0.074 nm (Fig. Below). Calculate the energies and wavelengths of photons for the rotational transitions
(a) $ L=1 $ to $ L=0 $, $hf $ $=$    $ \times 10^{-2}\ \text{eV}$$\;\;\;\;$$\lambda $ =    mm
(b) $ L=2 $ to $ L=1 $, $hf $ $=$    $ \times 10^{-2}\ \text{eV}$$\;\;\;\;$$\lambda $ =    mm
(c) $ L=3 $ to $ L=2 $. $hf $ $=$    $ \times 10^{-2}\ \text{eV}$$\;\;\;\;$$\lambda $ =    mm

  Calculate the bond length for the NaCl molecule given that three successive wave/*f oqj 8q6 mrevw-uze.4oa, nlengths for rotational transitions are 23.8u v woq4 a6jqrz,-*emn/foe.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estim (yctz4uvk tyo ) ;bqjz9j3o(7ate the stiffness constant $ k $ for the $ \text{H}_2 $ molecule. (Recall that $ PE = \frac{1}{2}kx^2 $) k =    N/m
(b) Then estimate the fundamental wavelength for vibrational transitions using the classical formula (Chapter 11), but use only the mass of an H atom (because both H atoms move).$\lambda$ =    $\mu m$

  The spacing between “nearest neighbor” Na and Cl ions in a NaCl crystal is 0.24 tgy g7b1 d8y*2ca63mj,bxn rcnm. What is the spacing between two nearest neighbor Na ions? D = axc bnrc,67jdg3 m* gybt8y12   nm

  Common salt, NaCl, has ab y* 6( pmj2q)s8 /kpdov.ycok density of $ 2.165\ \text{g/cm}^3 $. The molecular weight of NaCl is 58.44. Estimate the distance between nearest neighbor Na and Cl ions. [Hint: Each ion can be considered to have one "cube" or "cell" of side $ s $ (our unknown) extending out from it.] $s$ =    nm

  Repeat Problem 13 focpseq hs 56p8rpy7*u7r KCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride q3b4oqi(i*w-os. kz zcrystal is a good insulator. [Hint: Consider the si k-zoz(qsqb3i o *w.4hells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombardedcyc; xt,dzl ), with light of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate thclt,,z y;)xd ce size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavele+j2 p4zg /flhhngth photon that can cause an electron in silicon ($ E_g = 1.14\ \text{eV} $) to jump from the valence band to the conduction band. $\lambda $ =    $\mu m$

  The energy gap between valence and conduction bands in germanium is vr wwu x*3u+l-0.72 eV. What range of wavelengths can a photon have to excite an electron from the r-w*u+vux l3w top of the valence band into the conduction band? $\lambda \leq$    $ \ \mu\text{m}$

  The energy gap $ E_g $ in germanium is 0.72 eV. When used as a photon detector, roughly how many electrons can be made to jump from the valence to the conduction band by the passage of a 760-keV photon that loses all its energy in this fashion? N =    $ \times 10^6$

We saw that there ar/s dnlqm.oweuzhri.1ex4y4 l3qd))( e $ 2N $ possible electron states in the 3s band of Na, where $ N $ is the total number of atoms. How many possible electron states are there in the
(a) 2s band,
(b) 2p band,
(c) 3p band?
(d) State a general formula for the total number of possible states in any given electron band.

  Suppose that a silicon semiconductor is dopedivs6a :ku ;m) g0v6* he5sogez with phosphorus so that one silicon atom in og svags vzeu m66h*0i5k )e:;$ 10^6 $ is replaced by a phosphorus atom. Assuming that the "extra" electron in every phosphorus atom is donated to the conduction band, by what factor is the density of conduction electrons increased? The density of silicon is $ 2330\ \text{kg/m}^3 $, and the density of conduction electrons in pure silicon is about $ 10^{16}\ \text{m}^{-3} $ at room temperature. $\frac{N_{doping}}{N_{Si}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if made from a material with at.dz6zs5i y -tn energy gap 6tzi- zy5 sd.t$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wave+ rzpk*hf eueab*2mcw0d -/ o.length $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose current-voltage characteristics are given i-(b/ct xn (wpx pdq h8b5ct0e3n (Fig. Below), is connected q np c t8-(xt3xwch5pb0 ebd(/in series with a battery and a $ 960-\Omega $ resistor. What battery voltage is needed to produce a 12-mA current? $V_{\text{battery}}$=    V

  Suppose that the diode of (Fig. Below) is connected in series txf 0ey/gmel ;.p8n// m ol :4fxj,uigfo a $ 100-\Omega $ resistor and a 2.0-V battery. What current flows in the circuit? [Hint: Draw a line on (Fig. Below) representing the current in the resistor as a function of the voltage across the diode. The intersection of this line with the characteristic curve will give the answer.]    mA

Sketch the resistance as a function o4dr5ovjdqy ly,c 9:5t nr3fj(f current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. hn.xd1r y*-pw Estimate very roughly the average current in the output resisnyd-.p1rwx* htor $ R $ ($ 25\ \text{k}\Omega $) for
(a) a half-wave rectifier(Fig. Below a), $I_{av}$ =    mA
(b) a full-wave rectifier (Fig. Below b) without capacitor.$I_{av}$ =    mA

a

b

  A silicon diode passes significant current only if the forward-bias vo3ns.i 3b*ei 1t 1g:gr /gddqzyltage exceeds about 0.6 V. Make a rouq trzs/nd1.3gb g3gei* i d:y1gh estimate of the average current in the output resistor $ R $ of
(a) a half-wave rectifier (Fig. Below a),$I _{av}$ =    mA
(b) a full-wave rectifier (Fig. Below b) without a capacitor. Assume that $ R = 150\ \Omega $ in each case and that the ac voltage is 12.0 V rms in each case. $I _{av}$ =    mA
a
b

  A 120-V rms 60-Hz voltage is to be rectified izuk3 1hps8uub1*q- 1sk,a ey with a full-wave rectifier (Fig. Below), whyhu, u11ua k e8-q1b*sspi3zkere $ R = 21\ \text{k}\Omega $ and $ C = 25\ \mu\text{F} $.
(a) Make a rough estimate of the average current. $I_{av}$ =    mA(smooth)
(b) What happens if $ C = 0.10\ \mu\text{F} $?$I_{av}$ =    mA (rippled)

From !num!2%, write an equation for the relationship bez z;vq agpp7obp.9o; ggqolvh/+n0 .6tween the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding enc a2awg5 cnlr 4-35zl zvl,,isergy of the $ \text{H}_2 $ molecule by calculating the difference in kinetic energy of the electrons between when they are in separate atoms and when they are in the molecule, using the uncertainty principle. Take $ \Delta x $ for the electrons in the separated atoms to be the radius of the first Bohr orbit, 0.053 nm, and for the molecule take $ \Delta x $ to be the separation of the nuclei, 0.074 nm. [Hint: Let $ p \approx \Delta p \approx \hbar/\Delta x $]    eV

  The average translational kinetic energy of ob5c/p zln5ni q*8ow mbg.,n3an atom or molecule is about $ KE = \frac{3}{2}kT $ (Eq. 13-8), where $ k = 1.38 \times 10^{-23}\ \text{J/K} $ is Boltzmann's constant. At what temperature $ T $ will $ KE $ be on the order of the bond energy (and hence the bond likely to be broken by thermal motion) for
(a) a covalent bond of binding energy 4.5 eV (say $ \text{H}_2 $), $T =$    $ \times 10^4\ \text{K}$
(b) a "weak" hydrogen bond of binding energy 0.15 eV? $T = $    $ \times 10^3\ \text{K}$

  In the ionic salt KF, the separation distance between ions is about 0.n :)h-gaqvuia :mxrb:/q /n7a27 nm.
(a) Estimate the electrostatic potential energy between the ions assuming them to be point charges (magnitude $ 1e $). PE =    eV
(b) It is known that F releases 4.07 eV of energy when it "grabs" an electron, and 4.34 eV is required to ionize K. Find the binding energy of KF relative to free K and F atoms, neglecting the energy of repulsion. Binding energy =   eV

  Consider a monoatomic solid with a weakly bounx3v6zo zs x5xd q3xr.,d cubic lattice, with each atom connected to six xxqx .3dszvz3 ox56r, neighbors, each bond having a binding energy of $ 3.9 \times 10^{-3}\ \text{eV} $. When this solid melts, its latent heat of fusion goes directly into breaking the bonds between the atoms. Estimate the latent heat of fusion for this solid, in $ \text{J/kg} $. [Hint: Show that in a simple cubic lattice (Fig. Below), there are three times as many bonds as there are atoms, when the number of atoms is large.]$L_{\text{fusion}} =$    $\times 10^4\ \text{J/kg}$

  For $ \text{O}_2 $ with a bond length of 0.121 nm, what is the moment of inertia about the center of mass? I =    $\times 10^{-46}\ \text{kg·m}^2$

A diatomic molecule is found to have an activation energy opdn45j / -b qaz18q+ams+xotp f 1.4 eV. When the molecule is disassociataz++8 qds b1mja x4/ oqp5-pnted, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamou0k:6:j*f)zbvm.xox 3 z tur(n*iylknd, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and the conducrk3l*xkfm: v .jn x(6b0y*t:z)iuu z otion band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set is not m43q; wsyp:z,+ afpjgto react to visible light, could it make use of silicon as a "windo:4szwpf ym ja3,p+q g;w" with its energy gap $ E_g = 1.14\ \text{eV} $? $\lambda $ =    $\mu m$
What is the shortest-wavelength light that can strike silicon without causing electrons to jump from the valence band to the conduction band?

  For an arsenic donor atom in a doped siliknrb71pl t;yf1;sw+bws fr*fj3h/o 4at03xocon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this1b;173 yorh0s+kfa*wr onbjsl; p tx3f / fw4t electron in the ground state, take into account the dielectric constant $ K = 12 $ of the Si lattice (which represents the weakening of the Coulomb force due to all the other atoms or ions in the lattice), and estimate
(a) the binding energy, E =    eV
(b) the orbit radius for this extra electron. r =    nm

  Most of the Sun's raz. c e;m lin5uz8mmk/m0i 2gz+diation has wavelengths shorter than 1000 nm. For a solar cell to absorb all thiezz2 n05;i m /kmmlz+.mug8ics, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that can be abyjg j5i bw)9-up:yzw5sorbed is 1.92 mm. What is the energy gap in this semicowjy) 5:wzgi9bp y -ju5nductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available6 uboeawz7l* q .5*zgk many years after red LEDs were first developed. Approximately what energy gaps would you expect .5g* kzqelb auozw6*7to find in green (525 nm) and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown vsy4:hb:(8yyawklo-wx-: u o)yxqk* in (Fig. Below). Suppose that $ R = 1.80\ \text{k}\Omega $ and that the diode breaks down at a reverse voltage of 130 V. (The current increases rapidly at this point, as shown on the far left of Fig. 29-28 at a voltage of $ -12\ \text{V} $ on that diagram.) The diode is rated at a maximum current of 120 mA.
(a) If $ R_{\text{load}} = 15.0\ \text{k}\Omega $, over what range of supply voltages will the circuit maintain the output voltage at 130 V?   $\ \text{V} \leq V \leq $    $\ \text{V}$
(b) If the supply voltage is 200 V, over what range of load resistance will the voltage be regulated?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$