What type of bond would y+b/c zhr3 t,cqy: 1hphou expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecules uhhjf/(/no 5ub1-dp $ \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 moleculu-zclm9 *5k tde $ \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 u 5+as(gmfc0d 9r2fvpcategories. What are they?

  Would you expect the moleculex ;2+ hqk gu7oovz0*fc $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbonqcwp2sqjc6 b-((ga 5,-uy yo i atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons: a 5qea4r 3vxds,.odi are free to roam about in a metal, why don't they leave td53o4dva.qxa:i er s,he metal entirely?

Explain why the resistivity of metals increases with temperature wyiyh 8c9q-ze6 hereas the resistivity of 896eihyz -c qysemiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wa-z/(zs6 x9hqtarm 3-vnq6muave rectifier. Explain how the current is rectified and how current flows during e t3 6aav-sn hrq/69q(mz- xumzach half cycle.

Compare the resistance of a pn junction digk3xk 5 i8(iyxode connected in forward bias to its resistance i8 (kxigxk3y5 when connected in reverse bias.

Explain how a transistor could be usedpxhyxcj+ ktjrph 90/-:s6jfs 7nb 3b2 as a switch.

What is the main difference between n-type and p-type semiconduc9itmz0(k a2rr7bf, erkcxrvk-i0,l6tors?

Describe how a pnp transistor can operate as an amplifie jt:: 5sg:j7dlvcd.dym.3 srpr.

In a transistor, the base-emwg zqp:d/c- q0itter junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown i pdqg/-c qw:z0n (Fig. Below)?

A transistor can amplify an electronic signal, meaning it ca;h1x1 sbdgqo6p7nu m7n increase the power of an input signal. Where does it get the energy to increase the 76;x su obn7mqgd11hp power?

A silicon semiconduct*rxo(;orbsd: q-ees4 or is doped with phosphorus. Will these atoms be donors or acceptors? What :bqr s e(*-xeo;4osdrtype of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Exp)e2d c;md7 if nhps6y,1y-h zjlain. {yes|no}

  Can a diode be used to amplify ayuh6ouoy7 h f3k2 bkdqg1 6):z signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrostatic ni :):dbnxlobfm -4fr+v9e/h potenrexnom::l9fbfn +-v4hib /d) 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 enesd3 u5*7: cmoc8gfuge rgy of KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at g emc53f8us7oc*u: gdthe equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energyop8l5 vhkk, agu1g5i9 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 mo.:rygohy 4 0wrle, 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 binyh4:wr rgy 0.oding 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 th:* na1ka-4zkn *ischba f4/e f,s9gxqat in the text for the states in the formation oh *,4z: n4bq*kff/n1xkac s-a9gae si f 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 quantity y: sk,az 6td/ob/pl p4$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationa:axxs u,4z8acho )j t5 0(oarxl 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 chabu.8*bflyxz 1racteristic 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 thece .ue(9lrs 5 vly,kh2 $ \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 three successive waves0-9w t:ktwfgkt 3 fuy;* m)njlety-;9 0nfk fjuwtsw:gmt3k* )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. Below) to estimate the stifo86j mwao, .sf,2 ufybfness 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 Clic(h kjcy8sa ,/w,ej mk1y /i9 ions in a NaCl crystal is 0.24 neayj ,9 c s,kwi1(/ jik/hy8cmm. What is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density of y dlbwu2 31n.v$ 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 isq;n7v/lku z mxmv47)f *4 excv $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloabnko0el*3w4*vm+ied4 6 od iride crystal is a good insulator0i63*kdo*oevbli4ned a m 4+w. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequencyw sfbc,)wlvm f4:v0i 5y69 mmq, begins to conduct when the wavey fw)wqf9,s 4m:ivcb6 lv 0m5mlength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cfsh37g pko( *mause 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 valeb/1aatlb 25m0uyje: snce and conduction bands in germanium is 0.72 eV. What range of wavelengths can a photon hamujab/2:sa l51 by0te ve 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 1dg)vd8ubkqr,7+zdar/rw 0 q$ 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+e9taa6 jza5at +o; ow so that one silicon ato aa;to+t+eoaz95j6wam 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 m1u97q,bli zoz ade from a material with an energy ga7zlb1q uz,o9ip $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wt f .dg5/mdx46l- qh1ae;fzc navelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose curr ofaf7-u6r+ inent-voltage characteristics are given in (Fig. Below), is connected in series wi 6uo7n -fif+rath 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 (fbl8 m8e4 c2fuFig. 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 functxea4njj *cw ki ro*v d.)98 u; pmjcig1gmq3.-ion 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 r0al* ak9s rak5oughly the average cursk0 *59alaakrrent in 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 fva gur-g6k )9the forward-bias voltage exceeds about 0.6 V. Make ag-kf 6vu9g a)r 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 rectif*v 6gx* b3decmied with a full-wave rectifier (Fig. Below), whereebv*mgd*xc 3 6 $ 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 .u5 ixv-a 7 mful*7;gn4cmjkr5k ow v5the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy+u-gvvhw y ( lo8jd1pzgnf6ro + n+48p 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 isq65 x(w1; v6cn(xnvz0hng d+ g qppuu* 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, thec2jj *4 h 9wvtgrjc2*m :vg+kt separation 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 with a weaqltqxz bf( 0x22 0p(w ,bhv8+r5h intekly bound cubic lattice, with each atom contbw i x5tphn xr ze2(qf2,0v0l+8(bh qnected to six 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 h82dv do)ncsrvx3s ( x(ave an activation energy of 1.4 eV. When the molecule is 2r dd8n cxvvs3o() (xsdisassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incjq2f :5ll(au cident on diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and the conduction c:lql j5au2f(band for diamond? $E_g$ =    eV

  A TV remote control emits IR li.46 w4p rmxacp1au (ed9d.frj ght. If the detector on the TV set is not to react to visible light, could it make use of silicon as a "window" with its enrc6 aw.x4(1ue f9 mdar.jpp4dergy 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 stp39sn f7l3fa doped silicon semiconductor, assume that the "extra" electron 3lst37fsp 9fn 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 shb- 2b*mqnkp8lh5wnfes;ubh: 04y k v8orter than 1000 nm. For a solar cell to absorb all q 0svf2-kb:lmue k8h n45h *pbbwyn;8this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semicond7hoh4p9o 2w9uvi .lqhuctor, the longest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in thishvh92wo qh4iu po.79 l semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years afterh8l cv/o( 2xzf red LEDs were first developed. Approximately what energy gaps would you ex f(vzcho2 /x8lpect 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 voltagep d*z.xv du 3/h)d*vxa regulator 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$