What type of bond would you exp htg w70d;z4ad5t;turect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecu 2)kli qql9y8zle $ \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 moleculev-(tm:hqh y+u3 e6boi nrml-0 $ \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 categocjz1t ep0(d)h1q yyx 4ries. What are they?

  Would you expect the molecule+r/y uay6c*p7h k/uvv1h4x ys $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon a1*u6sk ew m8qi::u h8nb (bn*-a m/ +ptohopnrtom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't thmeh07nmlpe+) w,;xj6 v vt+ qiey leave the metal entirel)xv i n ;wp6,m7vq+jhm0+eetly?

Explain why the resistivity of metals increases with temperatul/qh.g- 6ccn cm1c.h kre whereas the resistivity of semiconductors may decrease with increasing temp6h .cq./gc1lc-mkh c nerature.

(Fig. Below) shows a "bridge-t.:aj 6 e ju7st,mcy9jns45chgype" full-wave rectifier. Explain how the current is rectified and g795 mj4, j:cat y.shunejc6s how current flows during each half cycle.

Compare the resistance of a pn junction diode connected in forwci .digd3/*9 vsu)6 l davkrj4ard bias to its resistance when connecal43* ui v./gdivdsr) 9dckj6ted in reverse bias.

Explain how a transistord2d.n* 8rz(gltq9qp y could be used as a switch.

What is the main difference between n-ty en2q,wr nv(0ype and p-type semiconductors?

Describe how a pnp transis (dkcsjw6.)r77r+gvra2cr pwdl v55ator can operate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junction arf8fixno1lcs u,c 4d21e essentially diodes. fs, ox 2c lunc14id81fAre these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning (3 knj8h+xo xu +my23g 2qkv hoe(luc8ewd- m0it can increase the power of an input signal. Where does it get the energy to increase the power?dw8h(hmgcq0 +xluje 83 v(2-xn em+k uy2k3o o

A silicon semiconductor is doped with phosphorxqr8uli) -9ixus. Will these atoms be donors or acceptors? What type of semico9iiql- urx8x)nductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain.v.m5 2gsrs6txuts3 0e {yes|no}

  Can a diode be used to amplify a signal? Explain. {vltp n5 ilo3 au6h*(qsu6 r,a;cl5 uq6yes|no}

  Estimate the binding energy of a KCl molecule by calfw *q.91 s (q44 jbdl xm.nf,d1uivfinculating the electrostatic potential energy q*fud1 4 .4 .v,9qfslmjbn1dw nfiix (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. From the result of Problem 1 3ikiq o+, +scent+gw1, estimate the contribution to the bindinqi 31+n,kowi t+ges+cg energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding en. k1zv p:bu a9a0kpesni ,dj(1ergy of the $ \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 per mole, and dl:yl /nxiw96 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/lx dlni w6:9y 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. ;qkc+hh 3; stwb waa98eql0h for the states in the formation of the w3q.ak;0 cah8 wq+ lh9;hbt se$ \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 quantitf 4wmk:z7gq6 czi9r ks/44i yqy $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationaako8n6ab8kps aje8a 9 ) o8c1zl 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 rotatio: a p85)hk(kdovsbec 9nal 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 /ztd g,s/4o6 *exrrkz of 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 tha * 7d tyufnvpq+9m6v3e b.plwkcvvewgj( -)91t three successive wavelengths for*-9)1 dn vewqk.pu9(wybmvvjtp 36 e 7vfgl+c rotational transitions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. alg,h2ma6e8/f c3of m Below) to estimate 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 “nearestrzz 4+(f,9*n m o6lfkfea) .g0yfmrox neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. W9emoozk46*ny) +a(lx g ffm0rzfr. f,hat is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a densi3 -w;v80- smio4d4udz vpbxqtty 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 density5i-gqrlrr* c 9 is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis; 9su8,i e0hmr61vz lkv6zyyx of energy bands why the sodium chloride crystal is a good insulator. [Hint: Consider the shells of svy9y8z zx mui;61l vkr0e6,h$ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slovs65*gh za z3vwly increased frequency, begins to conduct when the wavelength of lighshv*zav5z36 gt is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-1.en94 t2suq x yrrc1ynvnf9 9wavelength 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 andj.:b5zp6-4 z pjvfnjj conduction bands in germanium is 0.72 eV. What range of wavelenj5 zjbpj6 :fpz -4vj.ngths can a 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 arfis2pn,z.1 cle $ 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 semic;q3 +j j: :ypymwyai.ronductor is doped with phosphorus so that one silicon w3;jjaq+yr:y:. i pymatom 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_{\text{doping}}}{N_{\ce{Si}}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if made frojf u;g3d/91l4mp 2:mejiuf hem a material with an energy gapj: h 9edej4fl1 ugm3;i mp/2fu $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavele c+ 21ysw*ksyqnu o.4qngth $ \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 in (Fig. Bei qke2,m84+h vvilnvu7mef5q50+ ( vzahmpw/ low), is connected in series with vqm8 +h5ukwe +aqe57vmpv i 4l h(/zmi0,vnf2 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 4;5s us/;pnevs wiz4b to 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 ofzd(u3vc0 facn: b)kz.*g7l gz current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate verzc)iq08(/x7wor d dovyh7h7ry roughly the average current ind yzcwxiq/rhod(7ov )0h 7 8r7 the output 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 significant current only if the forward-bias voltage exyv0flqgr wf9sd06 1k yt tu(74ceeds about 0.6 V. Make a rough estimate of the average cu0 0u(t vdy9r1lwg64q tysff7krrent 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 with a full-wave rectyreee )4*nb8n ifier (Fig. Below), wr n4ne eyb*8)ehere $ 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 belt3 ,j5 ;l;xq7-u bgt)qhvel ase current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy ofbw-,d2dsf1 gg t tp4 l;9wkl)c 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 kine5up9k *sfzrc p+t, 9tetic 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 s3 j zx8.1 fskxc5m5fyweparation distance between ions is about 0.27 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 wit2cie+s1/ o mukk+z1gbh a weakly bound cubic lattice, with each atom connected to six neighbors, each bond having a binding energy of + bkg+2ou/ce1sz i1 mk$ 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 foundk 38 g -.yrlix2sd,(v lpcy+om to have an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw amy2g, k3ylcl(dop+x 8iv s .-r potential energy curve for this molecule.

  When EM radiation is incident on diamond, it i4:gow7u09k hdd3 c 23a/rr i kegav7pks found that light with wavelengths shorter than 226 nm will cause the diamond to p o2:9 e/70h 3gkdrc37w kav4gauird kconduct. 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 hx07 y*iw.ztxon the TV set is not to react to visible light, could it make use of silicon as a.h0 x7izw ytx* "window" 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 silicon semicozk :s9i 94gif4qpyhb0 nductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For 4iyqfbi0 z9k h4s 9gp: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 wavelengths shorter than 100d(v+wj6 ro(dstpg 2n:0 nm. For a solar cego rtn6d+vd2s( p:w( jll to absorb all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longesc7 /cfl4cuole7 +kfu d +hq+z-t wavelength radiation that can be absorbed ifu c+ u+ 7cfk qzod-4l7/+lehcs 1.92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs b)ctl46 4872bncxv 9 uy06apltedzdu xecame available many years after red LEDs were first developed. Approximately what energy gaps would you expe6txe vu)c8a4249b 0zdnx l6lpdy 7ut cct to 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 in (Fig. Bdp15s)3lo4y vxhsglv r6y 2f8 elow). 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$