What type of bond would you expvib 9nnv 7m*2bect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecrof5nqnh jzy p /zv4t7.v7lmb1a q, 6mz, 8ak4ule $ \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 molecule qr6 +je ons(q*$ \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. What are thi1uebv +slj8j+ 5.g v kh6r9i zlj.v-aey?

  Would you expect the molecule(wzl v .c04bca;)i-x*qicclj $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon ato8jadam5 w;fjx7pp e* 7m ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't they leaveti p7v g:ljto r3qfyczq9h591jo y448 the metal er9 yq5pt4gz:8 9ojovq f1yt 43li cj7hntirely?

Explain why the resistivity ows23rb/c 8l1)s mibx pf metals increases with temperature whereas the resi8bw/i) ls1cbmp s 23xrstivity of semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bri8hb./t/u z apwdge-type" full-wave rectifier. Explain how the current is rectified and hozaw u// p.tb8hw current flows during each half cycle.

Compare the resistance of a pn junction diode connected in for g8l-mxspxagigdc1iw*h (o9a g84 ,x,ward bias to its resistance when connected in reverse ,(i4da8h,x am8g w-gxlg xp9so i1c g*bias.

Explain how a transistor could be used as a switch.8qy -eyvlk 2a(

What is the main difference between n-type and p-type semiconductorl rc*s kuv.:w4s?

Describe how a pnp transr vik11g8c2d zboj76distor can operate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junction amk 6 z7,niag-cc3)m pkre essentially diodes. Are these junctions reverse-biased or forward-biased in the6 zcnmp,ia3c-7g k km) application shown in (Fig. Below)?

A transistor can amplify an electr(y: suw* xuf1bonic signal, meaning it can increase the power fsx(:bw*y u1u of an input signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped witzthd(0f.5ayg 9m-4 xr qibp-+lw6w bdh phosphorus. Will these atoms be donors or acg bi9 dx(ptmlby--zwfw+5a 6r4hq0d .ceptors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Exopa. l ebw8:7tplain. {yes|no}

  Can a diode be used to amplify a signal? Explain. {yes|mafa/ u(j8sa 3no}

  Estimate the binding energy of a KCl mo-s y7e8 wdubhwwr1.;z lecule by calculating the electrostatic poten8.wbyswh1;zrwd e 7- utial energy 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 i)c 34 dsn h;ggqt,qj,ts 4.43 eV. From the result of Problem 1, estimate the contribution to the binding en s q)g,j t3cg;4dht,qnergy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of thekq 1k+rj3 .gr4qrmsylr8,(zs $ \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 experimentally in kcal sjeee,s.fm z5db80 ((gy ui78huhjg2k xc p) 3per 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(y g8euh d .(,ucihsgje m0sb3)85jfzx2pe7k per molecule? What is the 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 text for the states inuov13bpc l(j,qt;, fw efb b-* the formation of theb-,f31ufb t wb p;,(jc*elvoq $ \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 quantitb -t3 hmgb.iu)y $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic 6s 12dqvjb:lx d g8 8fklrn(j0rotational 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 char9o7e g*fcp: d n:rty2sacteristic rotational 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 rv * 4w cde2yb5em41w.wnxb; aof H atoms 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 succnizy/ph i,9vj1p qr 7;essive wavelengths for rotational transviz1h9qpi;n /yr7j,p itions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to essnse w o35btgv*5t9dqo8 h .g3t-8fxe timate 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 NaCs-ik ;3yu7ch /p8 da8ct8pap gl crystal is 0.24 nm. What is the spacin/ukit ac8 8yp-83gp;d7apcs hg between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density n+52 ey/vxrox 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 for KCl whose aes- h b4txj5o2ekl;5 density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chlie -v9tk7o-qi oride crystal is a good insulator. [Hint: Consider the shell-qii-k7ov9te s of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarq3fv5 i- knag6i*6nbvded with light of slowly increased frequency, begins to conduct when the wavelength of ln5*q6vgf 63k b iia-vnight is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that cido 2dt n+t/ t n)c:p+jtdq27uan 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 germaniu7e4gw 1+ 9 jxyrfdz5abm is 0.72 eV. What range of wavelengths can 1gdz9exw74jfbr +y5 aa photon have to excite an electron from the 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 are:mbh):oqq f-g $ 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 doped 5 x:s(j vw4rcd-+dyqzwith phosphorus so that one silicon ato(jz-5+dy sdqr:vc w4 xm in $ 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 radif)j8 est e;c 28ry*triate if made from a material with an energy ga8;2)tcjfe *ye rtisr8 p $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wave zunncad,i+* 8/ drwo,length $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose cuy(1of j.)s c3vykc10kyt:f shrrent-voltage characteristics are given in (Fig. Below), is connected in series with a battery andh k1j) kyct1 (fv3os:y0 fsc.y 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 c)k5cy+ e 7zxz;6in lito 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+njigjs9u 4 gvb *6ty2 of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very r6nub-h*g)yqu8zfi r ;zc3v 7houghly the average current in the outy vzuh3q hrz8 c)b-7;6ng* ifuput resistor $ 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 sig, s 0njll;y+; xyiihy.c4iok4nificant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the ou 4kxly yy , h;.4sli+inci;jo0tput 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 re6n ovff*l s0:6nwgc(rl: v3iectified with a full-wave rectifier (Fig. Below), *flv6:(fo:3 0ewln ic nrg6 svwhere $ 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 between the base curlhok x:9smm)j j -th*nl,*sr 4rent $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy of tj 2uia a;yx-rl.8p8tv he $ \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 translati0j aoyr()7 (dn;e.kj ksy3bkvonal kinetic energy of an 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 0.27 nm. .v27utae tg(g
(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 bound cubic lattidn9pb /6w* ;igm4plmu ce, with each atom connected to six neib6i*m9dup4 nlwm ;/ gpghbors, 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 of 1.4 eV. W) feq6oy)/enbhen the molecule is disassociated, 1.6 eV of energy is released. Draw/q b) )nfoeey6 a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light witu8ba 28qrr4(c9w y9uyl2e7d:qm cj hhh wavelengths shorter than 226 nm will cause the diamond cu bu9ywh h 9d8jm7re4:2qa8c2q(rylto conduct. What is the energy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on0;ert(vgp , hso j:wyo x03nb)4n1xg w the TV set is not to react to visible light, could it make use of silicon as a "window" with its energy( egwbv y j0,px1;3n oh)nr4g:0wx ost 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 silicon semiconductor, assume that th9( l1agt xia3v,b3l.:oag*buz8 ba hb )kl5 mhe "extra" electron moves in a Bohr orbit about the arsenic ilba1 :bg ataui9 8k3 l 5blmz)va,o(* 3x.bhghon. For this 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 radiation has w f43 f,)cf)se rbnkqw:avelengths shorter than 1000 nm. For a solar cell to absorbkwf) eq,34nbf s: )crf all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that can be a:w+h8 ;p,kh (su/. qnbzzkxdhbsorbed is 1.92 m+ qhpz.sz,h;(k ku8wbnxdh /: m. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available :w;cp 2r(whzst1kbd ;many years after red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue (465 nm) LEDs? tsk ( h:;cbz;wwrdp1 2
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltagxseq5k 0i.tm5e regulator is shown 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$