What type of bond would you expect for e.ade 7 r0)i3,ug)xcr us8t fp
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molew/byzv qql d9kf20hq 0mt/5 ,tcule $ \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 r rdc60fot)yb4-brxo k. 1*t c$ \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 inm;vbt)x3ae 1 dav664 rvca m)lto four categories. What are they?

  Would you expect the molec94 rzyem;(fu8j wbqv7a; tqv0;p1 hcoule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon7u 9k+9 fqgmptdwl5 v7 atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, whyy1-p0a 5nm pct9a )lxh don't they leave the tapan p0my5c9 hx) -1lmetal entirely?

Explain why the resistivity fz.eg)k2p6 u4k5la ayof metals increases with temperature whereas the resistivity of semiconductorz kf u.24e5 6ag)lpakys may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-xx3oe9 s8gkrblc0 :e -wave rectifier. Explain how the current is rectified and how current flows during eas 3c 9-xgr0kx8b loee:ch half cycle.

Compare the resistance of a pn junction di sm8t pyiy;fm:*w/xdj oy 8m ab.sf,4/ode connected in forward bias to its resistance when connected in reverse ts8ms,/myjbp.8 yoydm; :x fi/*4wfabias.

Explain how a transistor could be used as a swifq,ruu /y :ze5tch.

What is the main difference beau2 myok(8 k;c3 v kxbl.ov:)-zc: ubvtween n-type and p-type semiconductors?

Describe how a pnp transistor can operate as an amplifier.4alhb qt/-k4n

In a transistor, the base-r1gwj19q z ,atf .fj)i*( njwcemitter junction and the base-collector junction are essentiallijnjf c19 t1aqw w.zf(rg*j,)y diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can inc-+mpw ze0boo3rease the power of an input signal. Where doe-w oo+m p3b0ezs it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms be donj,c svdewm3,aofs7qg. + r,x 4ors or acceptq7w d3s.s cj4, ra,+,ovmgfexors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yu.r;cn4 9/1lfnpi8szw2s zfnes|no}

  Can a diode be used to hdf j gy(l: 7t6m(lsl)amplify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrost5tobn keb)-8 catic potential energy when tb b)ck 8n5to-ehe $ \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*d y9x/a 7ifvb result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the equilibrix7 vy/bda9if *um distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding r f3 ;f1 drclft)s4l,menergy 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 y* pe/)f/ b *nqjh3o2nbl7ktrmole, and then the binding energy in eV per molecule is calculated from that result. Wha j) p*yh3r/ *n7/lbqbt 2neofkt 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 the text for *d z9mofia- ca(*l*rk the states in the formation oica* zk lfrda-o*9*(mf 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 quanti37n.js1ws) blz6j bcjty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotat4 l)f2vvhtnw ji,cab.hs, t40ional 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 ro 6;v.atlc .-j5 ttn izzcur/*itational 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 atodjd w.g*02ax l xmf-f7ms 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 lengtcat olyjhdmy(/xl+-2);8 )mrpj e o4vh for the NaCl molecule given that three successive wavelengths for rotational transljr )+8ocyma-2;4( dhlv/mxtjoyep) itions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) *et zxd0h4dz3dl(9y4 m lo6iu 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 neimj:84(-./s4hmacydvgz xa fs fnk .7ighbor” Na and Cl ions in a NaCl crystal is 0.24 nsxyaf 7c/.:h asf- md84ni .jv4(mzkgm. What is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a degqby. 46* z7vbovh *yznsity 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 f*28nbkontq3 b+de- q is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystam ncjhf7jq a*6b 6qv+3l is a good insulator. [Hint: Consider the shells of ja7nqvh6f qb mc+*63j $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased id4w/rq- ohb;m ey6j 4frequency, begins to conduct when the wavelength of light is 640 nm. Estimateo hieq b rw/j6y4md;4- the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in sila) 2z :lgh5 jgg+x* p3eqhq9koicon ($ 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 iqgkfz 80b(: jxi9 7osvs 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? fs9 (ozvk8 :ibx70jgq$\lambda \leq$    $ \ \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 aras1jem)2)q(3gx sc xo e $ 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 s)m-(b)pzj7 fiqit +wy3a 5 smao that one silicon sa-bam+iz5 jytpfm7 i) )3qw(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_{doping}}{N_{Si}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if made from a material with an s tec iik13. 7;hvf0aruiy-zcb i,/;a energy gap ,r0-vzyic ibf1;h ea;i/7c.i ut3ks a $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelct1:k6gr9auujy . 5t3mzc7 se ength $ \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 in2xw)+3dw s 8ucog0ly,::al opcqm;za (Fig. Below), is con oay;c 0w2:qmwd:38a ll gc,xsp)ozu+nected 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 diode of (Fig. Below) is couua s7s-1dmr ;ldh568 m1pyqt nnected 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 a q-x75bzxjtan0b (/+njq2p em;m lzu6s a function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectims4:g9 ugcwlt h)b1em z1b*/i fied. Estimate very roughly the average cur1 4mmgubwhs:tze)g ib19 c*l/rent 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 on0jl192 yodvqphgu /b5ly if the forward-bias voltage exceeds about 0.6 V. Make a rough estquvhp 1j2y5 9o0gb l/dimate 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-wave rectifie rdo/q/ccov m:y x68x,r (Fig. Below),oo,yr/q cx:v/d8 mx6 c 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 rc48zwlcd:po:lv cg.) q8r3z (rj;eq an equation for 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 thezau; k+s d+7jf $ \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 ox5 yq2gm 3gm8if an atom 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 dist)6qwd kupat t275lk5d ance 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 weakly bound cubic lattice, with each atom co)l/ew m*8vf cs0pauy: nnected to six neighbors,wec0ymup av ):*f8 sl/ 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 activ5 5/f5bwhahmuation energy of 1.4 eV. When the mo5/hub5fm wa h5lecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond,v5vbcvo 2ja 40 it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. 0avo c jbv54v2What 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 is not to7-0o *g, ij1enfoc edv react to visible light,efjcg 0io*oev,7n1 -d 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 sil:h1v ue g.ma;hti1/n es4gms5 icon semiconductor, assume that the "extra" electron moves in a Bohr orbit abou.1tvmsag;es 1n4hg :5e/mhiut 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 104)wxdy6p gw;t zs5o.b00 nm. For a solar cell to absorb all this, what energy gap ought t)6z wx wogtb;5ds4y.p he material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation tham(4ia jia1 a b1s8.:x/n bi g;pwcxik-t can be absorbed is 1.92 inpxw8g :-ijb/bk ac.4 sa ;i1xi a1(mmm. 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 LEDs wer(g cn,h */8i t2he2tkvhg)hz5 xsj7aqe first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue 28nasthh/2(z e5h t7),qjhk* gvgic x(465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shd.szmttw-e9;vn0 c0*.x d gui own 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$