What type of bond woulrbb:pb:r cr/b : ha8c8d you expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecu3qhr:e i2/iz /v4dfxgle $ \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 moleculeu foxcdm /zyq./8;x .n $ \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. ifvxk: 0ln,s:9l 0ad eWhat are they?

  Would you expect the mol va (s44mr(rubecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon ato8da qd(b 0ez.gm ($ 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 etiea,smrn wuwz6 9j:n:3e2+leave the metal enjn,m6e9w a2s u+w:z:nter3ietirely?

Explain why the resistivity of metals increases 6gy; ezfhdv8 afez66 )with temperature whereas the resistivity of semiconductors may decrease with increazz)da6ff8gee y vh;66sing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain18 ag d8 8dh1q,fhm.vbw2kocbv/1na t how the current is rectified and how current flows duriot1hghaf dw ,na.b8v28kd1/18 v cqmbng each half cycle.

Compare the resistance of a pn junctio4 2 p5 p/w)jxvfmh(qygn diode connected in forward bias to its resis/m fv p5 w2x4pg()qjyhtance when connected in reverse bias.

Explain how a transistor could frff3f)qq zcv: (+dw1be used as a switch.

What is the main difference between n-type and p-type semii jvar e/l -/cfl:xex8g:k+;iconductors?

Describe how a pnp transistor ndf4sr0eq,,xc 3f4 ch can operate as an amplifier.

In a transistor, the basex05/ ccdxpg 2q-emitter junction and the base-collector junction are essentially diodes. Are 2xpccgd 50/x qthese junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can increase 1ke)lp( j jlg-the power of an input signal. Where does it get the energy to increase th-gk e1 j(ljpl)e power?

A silicon semiconductor is doc q0ygeh5k,vz h-e l9bh7pshlw..h* see6(s.ped with phosphorus. Will these atoms be donors or accep0 h-e y9.eh7k,ssg hz6ec hlps*b(ve.h w.5qltors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Expl5,+llhq)peyj5r6 dd 6pf ax1kain. {yes|no}

  Can a diode be used to amplify a signal? Explain. {yes|4/xzvvb y9++y0eqggjn3w q4b no}

  Estimate the binding energy of a KCl molecule by calci1e-gafc 5 +uculating the electrostatic poten5fic 1c gu+ea-tial 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 is 4.43 eV. From th0o cf:lmfn0 3a q3sh/ie result of Problem 1, estimate the contribution to the binding energy of the repelling elec/ah3 qm0f0 3flnc:ositron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding en u bev2 vx.m3cy3cx 9a;.pt4qhergy 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 experis s3(0mho(fyk mentally in kcal per mole, and then the binding energy in eV h f0( yoss(k3mper molecule is calculated from that result. What is the conversion factor in going from kcal per mole to eV 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 tl, ,8numjl9 xnhe text for the states in the formation of ,u9l n8ln,mj xthe $ \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 quantia81y 9cvtqfab )ika3k) pb,x6ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotatiow,f58 hvd6ariwf2g ;qc tn+ d*nal 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 rotational energ- iyu( tbm0d1uy, $ \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 separatn*ypsc0a-i r9bpd o9vpe bmm+,hp2- )ion 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 le:kqb++pemkx) jf3 c, hngth for the NaCl molecule given that three successive wavelehb+f mxcejp+kk q,3:)ngths for 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. Belbt5w se)wdd/3e b7,xvmlbb22ow) 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 “nearest neighbor” Na and Cl ions in a NaCl crystal i3mw10p5 bg awog - 8ygbbxq7.bs 0.24 nm. What is the spacing between tb myab0pwo8g3qb. w 1xg-bg 75wo nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a densc(sq jl/c((ut ity 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 foh7d)) y)l;/tlys:t l:mga z npr KCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis offpxqx:me 7)n8 energy bands why the sodium chloride crystal is a good insulator.e8fpxq7mx): n [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequeno vd5v2 1s5epi q,8b;ccato, mcy, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the ene5p;q12ie,av doctc,s 58vb morgy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-1 34f7 uyfvbi-1sdifo wavelength 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 io; (yr j/cgc p5l+dn2ctfua8/ s 0.72 eV. What range of wavelengthtfj8dcycu +;on5pl c/gr2a( / s 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 are +z)g/srla d9bjz.*ze $ 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 with phosphorus )o/l9lti v )wgso that one silicon atom iltvoi /l )w)g9n $ 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 an enef5ulisr9 y 9eki ,u5o;(pg 7wargy gap ugy(9u 59 oakfwpei rs;i,7l5$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light os 3wgeyma,6v7 f wavelength $ \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.c7q/ndrcx 5 /l Below), is connected in series with a battedcqc x//lr n57ry 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 conn8jg+sw ljktocf:bd 5;9q v.y +ected in series 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 ,ej5 z.-xpdc q84uvyra function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. E*6m xuabngrl 41p;m j-:ctu6istimate very roughly the average current in the o4um-xba1 ;gtmni6p:ju6*rc lutput 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 s9 fq,* fndq)tiignificant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate oi*t,d)9 nqfqf f 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 with a full-wave rectif*bk7+(1sl ezg /fjuk nei0ml (ier (Fig. Below), wher+ngl eszki(b*7m0/ul (1jkefe $ 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 betwdqhdt2 v)6+2:vy yhn reen the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy q fsmyq6;9tq1re9;upof 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 an atom or molecule ian*0ehse j1 b2s 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 sewuh-a8q+t2 gp), duir paration 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 qj8+ian . ro-rcmbv 7 x5qb)jj0ve1v, solid with a weakly bound cubic lattice, with each atom connected to six neighbors, each bond having a bindivqovbxn8 )rjm c ,a 0rqi-+ve57j.b 1jng 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 enet6k0/:t be dosrgy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule. 0s6t d/:ebok t

  When EM radiation is incident pe ihk1 voy;l3oj)38 non diamond, it is found that light with wavelengths shorter than 226 nm kn3eji l8)hopv31oy ;will cause the diamond to 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 ligw8j e (+ppebuzz);q+h ht. If the detector on the TV set is not to react to visible light p)+qw(;uebhp8e j zz+, could it make use of silicon as a "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 semiconductor, ab0ikih wb8: h77x kyv/ssume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into account the dielectric constantx :8kb0kh7ivwi 7/yh b $ 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 ha9v;9 jo k5kuunviua0 -s wavelengths shorter than 1000 nm. For a solar cell to absorb all this, what energy gap ought the matervu io;uk9 5v90au -nkjial have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that can be absorbdi1 j* 8c-tge* /vmnciedet gcdj8i /icm- 1vn** is 1.92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became availableeh9v m mj(80v+cgpig1 many years after red LEDs were first developvp98e0 j c( mmvg1ig+hed. Approximately what energy gaps would you expect 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 (Ff) c)j16hu6 my0rndqi su -x/cig. 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$