What type of bond would you expect3e5.yj ui3p9f6e rriyjet/w 3 for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecmv4lid7x c f:/ule $ \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 moleculrta+7,j7stz hwfiwe34s.w x.e $ \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.u;ao- p(s6 g9vn k5+zrdt*e el What are they?

  Would you expect the molecuq*o6/ ro/ 0oawcy )+eqgwxr,q 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 7lb,hzwv; 7ojo t4cs6hp b-a9($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metalz0o*q :j-ah18h3bmhzsf( gfz , why don't they leave th f h(zhhjafzq o01g b*zsm38-:e metal entirely?

Explain why the resistivity of.,c9,iznu:v , qblmgb metals increases with temperature whereas the resistivity of semiconductors may decrease with increasing teml:g b., m,qizv 9b,cnuperature.

(Fig. Below) shows a "bridge-typ7-/qbegd- zw(hxdp *g7fhb* a e" full-wave rectifier. Explain how the current is rectified and how current flows during eachg*g7b e dapxwdh /-f h*b(q-z7 half cycle.

Compare the resistance of a pn junction diode connected in fo;v(igop wx6- frward bias to its resistance w xpv6gw(i;f-ohen connected in reverse bias.

Explain how a transistor could be used as a switbow-j3 xxpwi b *031qdch.

What is the main difference between nsifoa85z p rn8v :k8al4ybij4l*d-/e -type and p-type semiconductors?

Describe how a pnp transistor can operate as an amplifier rz xpzte,7/1t.

In a transistor, the base-emitter junctionxkqko 6.7 n8iq and the base-collector junction are essentially diodes. Are tho6 n.ixkqq78kese junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electqcfio8c.k*3 iku h u:*ronic signal, meaning it can increase the power of an input signal. Where does it get the ehquio 3 *kc 8c*.fi:uknergy to increase the power?

A silicon semiconductor 3zi/w0t ywh vn0mft2lp2f )y+ek/7 bgis doped with phosphorus. Will these atoms be donors or accepyw )y2kp0mh+t fbe 07i /fntzg2l/3wvtors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? :mxxem 8lg8jgo;8i :qExplain. {yes|no}

  Can a diode be used to amplify a signal? Explain. {yes|3 djlai.0uy0l no}

  Estimate the binding energy of a KCl moleculewb:k ja/wjv9:+qa7e f.g7hw da,gs i7 by calculating the electrostatic potential eneh7da ,/ : b.eag7wvja+sw7fg i wj9k:qrgy 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. Fro)u w27ikhfo +tm the result of Problem 1, estimate the contribution to the binding energy of the repelling ele 7f hwt)+2oukictron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of t7lya6y f, drtqi3,km-he $ \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 exdhrwhnaxs3+ m0o0mg(7z4 /aub0yz* uperimentally in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion/z 0umu r0y7 am(bohs+x *w0 ag3nz4dh 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 the text for v37z4f+jkoq h5zp .bz the states in the formation of thzq5f 7 v+kp43jozhzb. e $ \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 quantit x,a 1))/wfcl ddr2e3n8cagyfy $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic vp f50,+mqs, fm. rukrrotational 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 e,yib3d 4b x(ianergy, $ \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 l/v/;9p1vl qtnkehw1in 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 t0y t )vqiyg0a; ife:9qhree successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7 iy:ity;v0)agqe9 q0f.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the stiffness co.t/cid qhl6v+ uq1-gq i qltv1(er)9bnstant $ 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 neight( 2h4wa7tzkpbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two neares tk4ph wat(72zt neighbor Na ions? D =    nm

  Common salt, NaCl, has a densb +7qwj kacls5y63 n;nity 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 whoseh7.i nswzwjrxyz;. ;+ wi6m.t density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium ch9/kr gzq2jbmiwx /;f:loride crystal is a good insulator. [Hint: C; wkqg:jm r 9f2bzi//xonsider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with 9a9e1ux;c) /(y -cxdut dxlq xlight of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the energy gap y)tcd9 (;-uxlq xaxdx/c1e u 9$ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in s1 nl f *0c2lxnek;i(mlilicon ($ 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 kw*vyvxmpv i8 4dlet:-ay32 , bands in germanium is 0.72 eV. What range of w 8dvptmy l2 e3y,*:-4kaiw xvvavelengths 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 arx.f.q-to4n5gqgnhll : r ol77e $ 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 wi8rg,j. sm mhd46i6cnsth phosphorus so that one silicon atomcjir ,6 ms84s6h d.mng 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 radiate if made from a material with an ai1ug bpb0d(/energy gap u0gbd1 /ipa( b$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light n p52kr dngmx1ff -y0)of wavelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose c-60if t6l4h ks:zzmzlk-cxj 3 urrent-voltage characteristics are given in (Fig. Below), is connected in -zk hi xzc04-6tz ls6fk l:3jmseries 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 diode of (Fiqfz :hv no(: vh33fgzb-y /e7gg. 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 ltra13 i6.edjsh:an / kl;4uq function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120tq6c,,edvkb wq2jtu.i +tq. 6 V rms is to be rectified. Estimate very roughly the average current in the outpuquvijd twbqq.e,k.6t +2ct6 , t 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 exc+vj1 rqta.1vweeds about 0.6 V. Make a rough e q1 .vvwa+jt1rstimate 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- ,c;/0:2omwcr* rbdi rs2yickwave rectifier (Fig. Below), where c*2ym b k: 0rw,d/isr2;cicor$ 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 relationshipmiq1h b 8su0t8 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 the nva, 1*i ewe-k7,eyy 7q d/qawbpqw.,$ \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 atom8zesptiyn9( , 71eaen 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 ab9ypg9vtm1x2 d out 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 lattice, with each atom 34.upw3rbel km ps8w6connected to six neighbors, each bond having48epbw w.m6r3k puls3 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 to0 y39q6u u9p *bk(f6i7ip sdy .sstksj have an activation energy of 1.4 eV. When the molecule is disassociatedji ys ypkuqts(d03*pb 6s96 sk .ifu97, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on c0 :o8k+jacau0 tyf6 y.bl9shdiamond, it is found that light with wavelengths shorter thankccu 9:sbl at .+a80j 6hyoy0f 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. Ijfpx cru 4 k4q1/(qv5lf the detector on the TV set is not to react to visible light, could it make use of silicon as a "window" withu( vq1xq cl5krpjf/ 44 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 so); lmedt ,.ky2 ;mzzvemiconductor, assume that the "extra"o .);y;km,e2zmdvz t l electron moves in a Bohr orbit about the arsenic ion. 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 wavelengths shorter than 1000 nm. For a solarn8e66m; jbvnp cru l9+ cell to absorb all t6rcjblm+ p8 e9; v6nnuhis, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength rb1/ jwc) l.*dr4e mot:bfm4 nqadiation that can be absorbed is 1. 4c:b* eq.mtwn/1djm )bfro4l92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LED3av6 5nsz 9i2irv-v lcs were first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in bv 2-cli9iszavn 6r53vlue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fig. Below).tnx)aml -o(zz47aw u- k01q(tefix(n 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$