What type of bond would you expes h2.3)zrk rrmcx* (5unbx i*yct for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moleculwmasb95,q- ow e $ \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 zh8q8ljas txnfwe20:i uj+80$ \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 the1 k( vry db uk/ip())dlb2zg2ky?

  Would you expect the molecul3 c c/b(na)vkke $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbo rtzmg4ygv2.k 528v3f+ xgiwfn atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a*skvkb+ a xqhd a8 aamp a7o5sj2:9:2y metal, why don't they leave the metal 2::y7a * 9oja8ak akhdqv+ma 5spsb2xentirely?

Explain why the resistivity of z j2c5nljwe+.metals increases with temperature whereas the resistivity of semicw.n+ j2c zl5ejonductors may decrease with increasing temperature.

(Fig. Below) shows a "br9lat)4:vu vhbdx o kx0w(p16midge-type" full-wave rectifier. Explain how the current is rectified and how current flows durvhm1( d xluk6:)9x4bwaotpv 0ing each half cycle.

Compare the resistance of a pn junction diode connected in forward bia8( d; n)j t8v oh9vxl+ocmgd* ho*(dgbs to its resgt 9mgd8jobv*( ocvd8d*) ;+n ol (xhhistance when connected in reverse bias.

Explain how a transistor coul8z e ch,ky9es:d be used as a switch.

What is the main difference between n-type ax:wn*ubp, v 5 w4h, cfmrl7l+cnd p-type semiconductors?

Describe how a pnp transistor can operate as an amplifrgym7dwec37 :w) 5gkt ;w ot.zier.

In a transistor, the base-emitter junction and the base-collector junction are eb8ksb:ton ev+ 5d b3h*ssentially diodes. Are these junctions reverse-biased or forward-biased in the applicati tnb5d b8:3hes*bokv +on shown in (Fig. Below)?

A transistor can amplify an electronic 41k 5f:jpage+ ijikt(signal, meaning it can increase the power of an input signal. Where does it get the energy to increase t5f kigi:t jj 1(+ekpa4he power?

A silicon semiconductor is doped with phosphorus.,t n0/ nk4ycbo Will these atoms be donors or acceptors? What type of semicondoy0/nn4 tk,c buctor will this be?

  Do diodes and transistors obey Ohm’s lqn97olgr 0m3 3qfn)fkm1 +* npurqau5aw? Explain. {yes|no}

  Can a diode be used to amplify a s/l,46qk l pg70dw dbpiignal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the e jfjgx:n601)1f )i ei:isr i9j aif.pflectrostatic potential ex1iii i f 9:a0pfsn)f61 )f ijg.jj:renergy 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 m wf,* d3d)ed v2c koqmc3cr*fzfg2481, estimate the contribution to the binding energy of the repelling electron clouds at the equilibrdme)2fw8*m c vodc3,34ffdqc*2 gzr k ium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy qk 5x5qyztnb4x:8y9m ;epvc: 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 experime o w:u:b+hzzwu8/gm6pntally 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 the biw:z uwbz uh+opm /86g:nding 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 qdrt+ )g2)hhrsimilar to that in the text for the states in the formation of the t)drh2 gh+r) q$ \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 quanti ie7iyq5dxa n 3vab675ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “charac 8*ix*rbffc4 qlacz/1 teristic 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 rotational t6,c2n0n n r (fcbao5eenergy, $ \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 t86z gszgvsi (v/ yvz*/t74n hkhe $ \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 5k;gf:b imqvp t: j 0w;.xp25qenz 5vwgiven that three successive wavelengths for rotational transitions are 23fqvgwp55pw2 mb z:je i0qx;n vt:; k5..1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Ffrqj1 jm-fk;sds (0cx2 0knn1ig. 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 “nearest neighbor”*q0)dfdmf lp v75jose /mslk z98+e- y Na and Cl ions in a NaCl crystal is 0.24 nm. What ise 7sd/m0yz l+d8 jo 9p)5qmfefsk-* vl the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a dec fxsob):r3(b nsity 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 wdn91 gzao,tt;wxl x4;qb//pn hose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of enw 3-n92egapbe ergy bands why the sodium chloride crystal is a good insulator. [Hint: Consider the shel p2enewg39- abls of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, begin.nv+ lw,uobm u:lk1iaxat) euj,mni v72 s,02s to conduct when the wavelength of light is 640 nm. Estim+ ulos ,k2waa7ju.l1uit )e:, m0nmi,bn2vvx ate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an el l3raj*g 9v-s93 dxypiv)hecc:k*u3a ectron 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 conductiorm *lp3;jmcpb/ -18a g5rekuu n bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band into the conduction band? jearg* 3p8 5um; uc-lrbm1/pk$\lambda \leq$    $ \ \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 arel81mo.by c5e,kqi km l*in l828ivr6f $ 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 thtl/ fzk.8 r sv/4pxx1rat one silicon atom i/f t 1ls.p zrx/v4rx8kn $ 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 material w:iyxsn(u,gw ( ith an energy gap iswg(uy( ,x: n$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelxigd-zd*ki (rp3- t 4fength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose j m:ki (mcc-(icurrent-voltage characteristics are given in (Fig. Below)mi:c -k cj(m(i, is connected 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 diodexa0mp5y6jxd g3 z e5*o of (Fig. Below) is connected 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 a funrq8a ph5s-r5 dction of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate * y7ebym-x vq.zf:rx/ very roughly the average current in the output resist*x7ev fzx/ r: y.-qbymor $ 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 excekze 2n rioudc1(w4 9-neds about 0.6 Vzerndu1nw 2ok9 i(4 -c. Make a rough 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 with a full-wavefo8kg cdzk nbr(8o, 3bx 571tk rectifier (Fig. Bedo1rocbf t,8bk3z kx gk(5n87low), where $ 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 fo1r+n(5f /kdajs.lc agr the relationship between 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 of tj-r/p9m+dpnj3 6rgc 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 mj9f,dwc wg/qi+ly 1, lolecule 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 aboutolxc+ hs ba:+, 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 suv 4 k8ujq )kdutqq;yg4,o6u7olid with a weakly bound cubic lattice, with each atom connected to six neighbors, each bond havin 6y;)q ju kt7d,gu48koq4uuqvg 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,g, y/cl x8cyjq *sxw+ to have an activation energy of 1.4 eV. When the molecule is disassociatew xs8+/*cqxyc ,,y gjld, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that lightg3; g ghx*x1ntslnk-e9jv+ u0p(f8vu with wavelengths shor3hs0u*x + n9(g l unj-kvx1ep t8gv;fgter 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. If the detector on the TV set iq,pg06 e0+yj.ixszuss not to react to visible light, could it m0s supizg06q ,j +y.xeake 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 semiconductoia-7 4c52l fct xe1 dsvq9*ssjr, assume 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 consa sq1-4 stilje7d2 5 vxcs9*fctant $ 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 nm. em,y c5 1det2,a 2lrycFor a solar cell to absorb all this, what energy gap ought the materia ym, cr,t52adyl1e 2cel have? $E_g$ =    eV

  For a certain semiconductor, the long ;yh+y2 2tvuwyest wavelength radiation that can be absorbed is 1.92 mm. What is theyuyw; +2v2hyt energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after reqh8+ 3d+m6vut6d kisv )hd *vyd LEDs were first developed. Approximately what energyt ki6hm36*+ q 8yhvvdd+v)ds u 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 regulta 9nnf 5ae l74jcus81brrht2i; d7c7 ator 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$