What type of bond would ;5ni v it,(yslyou expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mole8qhx8p . -.v5kehunn gcule $ \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 ,b/.fp/nmqrsq dz4q5 $ \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 dd:j opiy7d zs8yl-y)p k.,e;u ivided into four categories. What are they?

  Would you expect the molecu4ptwn 8g p2th)vkm b9;i7ppk;le $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atom q.95ect*b nog($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free tod;swae ,uc; jfl 4pv3lib+d9) roam about in a metal, why don't they leave the metal entirelf)c4ibl v3e jd,w9+la; sd u;py?

Explain why the resistivity of metals increases withtlh-c i kuql,3w aodja/8, -x2 temperature whereas the resisachj,u oqdlka - 28/ltw-,ix 3tivity of semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the cul6705uek3k ree6rpy lrrent is re057lr6u p6rkl ye3keectified and how current flows during each half cycle.

Compare the resistance of a tq6ve,ji;c :a pn junction diode connected in forward bias to its resistance when connected in reverse b;qv aei, jt6:cias.

Explain how a transistor could be use3v z (bptpq mln*0g:+vd as a switch.

What is the main differ+c(b4fmc7 pmdll20 al ence between n-type and p-type semiconductors?

Describe how a pnp transistor can operate as an ampr*reqj1 vs)wu(3u v 3nlifier.

In a transistor, the base-emittsdgi 5f/+av q .y,z;od+c- bkser junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-bia-q a,zkvbio syc+ ;/f+ 5gds.dsed in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can incre:n:p esvjer- 4ase the power of an input signal: jsvn-4:r pee. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atomye/*us.x7 fz fs be donors or acceptors? What type of semiconductor will thi7x *u.ef/z yfss be?

  Do diodes and transistors obey Ohy,s hzlc9.;0gvq q4l-:zm6jlikga,jm’s law? Explain. {yes|no}

  Can a diode be used to ampl92etl e:sv8,l1,b sihmzhg 7g ify a signal? Explain. {yes|no}

  Estimate the binding energy of e 3s che-83gkfa KCl molecule by calculating the electrostatic potce-k3f h8g e3sential 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 the result of Problnmi 9b:,e ;q81zput ijem 1, estimate the contbmz,8i 1j9ti;uqe :np ribution to the binding energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding en6su ec :6jkibdn: yi e2/o.w4v2mhdx3hxg,w7 ergy 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 perx+rwiuh6e w-kim 7a--b18io v mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversa -woiru+ix6meihw-1-7v b 8 kion 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 t)z9cmsu 7- y0 r9fu0ysh dbd2chat in the text for the states in the formation ofd-cusurm07 sc9)0z yhf2 9ydb the $ \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 quantijta2 cp5 f(qy+ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rot q:ankqou-/k .ational 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 characteristwj/ l:1:: z+nuz1: kzvzw zrctic 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 of H atoms in jz)azcw7rqru0r0i, 3x r6k 1qthe $ \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 m/b2)wzic ax7kolecule given that three successive wavelengths for rotatib/k2z 7cxw)i aonal transitions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) tc s 8hdpsd e8-rv2c9- m5sn gy2q4c6rco 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 is 0.m co,q -1 c.3xvbsam4b24 nm. What x -3mb4vc.,s cqmao 1bis the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a nepo07 89q exfdensity 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 density is km:( s58f r1kru,i fuf$ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride umqk(q2;-st(2 cps h fcrystal is a good insulator. [Hint: Consider the s;hs2upk2 fqc(-stq m(hells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequenc,rpzbr e t8+f 00z qz0v4;budby, begins to conduct when the w 40t,0rfvb8 rebz;bzq+pz 0u davelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in silicon0dhwve v6s w4vb-0c, k;fos(lh+ f4sk ($ 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 bands1g:s5xletkfe4 *:azpw07 ypr in germanium is 0.72 eV. What range of wavelengths can a photon have to excite a:*yepk0 4z f ewt7al:5sgp1rxn 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 are2 eg:xw .6cmrxpf:,ts $ 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 so that one:lj fc,/x ps:++azviz silicon :v/xz:,jaic+lp s+ fz atom 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 from a materea)2 ,4fapletial with an energy gap ) tfp,eea2 a4l$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelength fuhnhv/ )jfbluc*k50-; y;rr$ \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.c9 8q75n7jesu+65d1vxgzfb q wi a4mg Below), is connected in series with a batteryg u g5 wf vq75d1q6 e9zacx+ns4imbj78 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 i0 h):nis 0t+hwhmmw7 an 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 og;p+cdb +ubd(uc kdr u.:(+m as a function 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 roughly the u kk 1wyp;n3* hda6io30d0 twhaverage current in the outtd 0 ak pi3ykwoh wdn*h31u;06put 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 forwardaicmafu0:e v9 y;a 7x2tzs a8v: ;m;9mjdon)z-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the outp;icz90: )79 f2 ;yesmvn:oam um8ja;zxatdavut 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 rectif.x alfj vop n qidzl:rwm-5 6aey )ngx;7)+7b(ied with a full-wave rectifier (Fig. Below), wzn:pdy;ag)- (e+.l m)b5v jwx 7i7nqao l rxf6here $ 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 burlc k 3:f.+;(dnm cde;qpl9 base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding. se s;t)fhbl- energy 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 an atom or molecule is aboutb4n6t in /fn:z.)/8.z rltc leyf9js t $ 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 aboulpbhyt m4w6.u o, g0.kt 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 with a weakly bound cubic latp * p jv(g 1gmid: je+h+:vwno;hk89jttice, with each atom connected to six ::1 kdi pv joemp*g h+vhj8g(wt +9jn;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 ofcr w +z/ fzl1,wg - l;pd3kqu2mv8qtf3 1.4 eV. When the molecule is disassociw1 p3 umwzz-grkfl/ ,vd f;32q+lq8c tated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on dik u7cfp+)gwj7:apvze*yi, s,amond, it is found that light with wavelengthsu w,j7pi: fcszg)7p,*+ kavye shorter than 226 nm 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 light. Ifhea zqx6l0 zd0k 9/5oz4 fdrh0 the detector on the TV set is not to react to visible light, could it make use of silicon as a/h0oz 509lkd46r0xzhzef qa d "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 afy37 ( cxtu8wv/q5kdk doped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into account t7dv 3kqy5fuk (wc 8t/xhe 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 1000 ngm fqsn /07p9km. For a solar cell to absorb all this, /kg79np0 mqf swhat energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation j l+ 8)oocdb8kdn/s6uv.gkh 8p mhf5)that can be absorbed is 1.92 mm. What is theh k5ohgd n)m6)ks88dc.o/+ 8lpvfu jb energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years af5 wck2i, ne4,f:ovsa k )c)kziter red LEDs were first developed. Approximately what energy gaps would you expect to ficz , skw5v):)a,i2 kc4niokefnd 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 shomz2i 2 j0vr2lywn 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$