What type of bond would 9i *pr/gg-w5t/i baftyou expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule atudda5p: w3 p,a- wcjl*0w /g$ \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 molecul2-ahj2ig 0k2 hs z2fyce $ \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 categoriywd/0c2bx7s a /jmy:e lz,d 8wes. What are they?

  Would you expect the molecu+3+ hr7yrcfwf th,mq 3le $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon aa75lpezq(0hf/t )g notom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in abrb14t( ikc:8 ocyi:zyne-, t metal, why don't they leave the mez:ctbre 8nb,to yi -i1:ky (c4tal entirely?

Explain why the resistivity of metals increases with temperature whereas wrlh 648ek)ht the resistivity of semi64)w rtl8hke hconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how r- juneq6fv )6mcf4e2 o 4eax-the current c6 aefm)fern-o4 q-v 6uje 24xis rectified and how current flows during each half cycle.

Compare the resistance of a pn junction diode c- 5duc 2mka94 (mratjunqt) :fonnected in forward bias to its resq nr )2a um majk4cttf-:5u9d(istance when connected in reverse bias.

Explain how a transistor could be used as a swio8a3/rd 6p24u qkjtkztch.

What is the main difference between n-type and p-type semiconduct ic73* sszx*5f d8mmm-ivoa .sors?

Describe how a pnp transistor can operate as an amplip* eh0z +i4(g9gn ;kisw9aplnfier.

In a transistor, the base-emitteo lnvyxwl o62ql(;(f,r junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the applicationyl(oq v,fox (nlw6 ;l2 shown in (Fig. Below)?

A transistor can amplify an 8x+qk 8d)is:ba/t h8qjh - khxj3.dpaelectronic signal, meaning it can increase the power of an input signal.q-.st j phi:adhhq +x8/8a jk 3xbkd8) Where does it get the energy to increase the power?

A silicon semiconductor is doped wie92(nk- l(9,wly cktjoqbf 0fth phosphorus. Will these atoms be donors or acceptors? What type of semiconductor willo9jk2 (k,(b n0 wetfqfl-9c ly this be?

  Do diodes and transistcz u* l21fqgp*ors obey Ohm’s law? Explain. {yes|no}

  Can a diode be used to amplify t*)k-wkbx /rqtg d;5wa signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule bygm/6w,g ly* m,s4ifyy calculating the electrostatic po w6/is fym,g4, gmlyy*tential 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 resjv ekeey41 sq j c,qaavix23t,.j8u **ult of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at thev cj e,i.tev 2 xa4uy*qq ksjae38,*j1 equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding enlx(7. nwatf,hergy 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 experimeq,b: *kohzdy 4ntally in kcal per mole, and then the binding energy in* dzybo4q, k:h 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 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 the states in trl edbx) z30 a059sh jn9+g,jah4nrpihe formation of ti0l4e s3 5hgp b+rd,)h xanjznraj90 9he $ \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.chjxx uh9q6/mcoe 2: y $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotation .l mrid+q.24-wentznal 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 rotationa0+b n5k uw9kell 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 aecb4 n/zpku *+toms 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 lh/g8w7ex cex ,uzdl c,-lp(3vength for the NaCl molecule given that three successive wavelengths for rotational transitions are 23.1 v 3gc-p/ ,lxlud(h ,ce78ewz xmm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the stiffness6) ucnc.hza9x cyp7c5gj( +uu 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 z fyt,s8d vi9*and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbosv8f,9 it *yzdr Na ions? D =    nm

  Common salt, NaCl, has a yl t+ujdb7yvt3cn /pgxp :9+3 fmt67j density 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 iso dz.ox 9nsx-4 $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal ie w bt+/qzi;1zs a good insulator. [Hint: Consider the shells of eq /zi1wb+;zt$ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with ligak451pf)x ;nq;he hda eej,m2 ht of slowly increased frequency, begins to conduct when the wavelength of lighahpk1;;eh ne2eqmxd)4 5af , jt is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electro vas djj ifnv.c* gk2+mqjfns/-;a(b)cn: +5pn 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 cccnp 2(x:bw.a onduction 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 tw2cc( na: .xbphe 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 aref.ht57di*hv; 5iib (cl *lwkm $ 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 dopedxfj k 0xfmc f d4fl95*d:raag(z:ht3- with phosphorus so that one silicon atom in r 3*tdm(f0f4c ak:g5jflf9 x z-hxd:a$ 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 anp5ne8*d dtauq9bo,8l s sx9;m1 c;bju energy gapd9o5;u sn, 8aj9xsb epudqtl;b81*m c $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelength nol59 my(0wad qvmw h4(o1r 054:vawnpypq8e$ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, who*)efg8 :9 nlq9/a+imrcj qbypf0 dwr/se current-voltage characteristics are given in (Fig. Below), is connected in series with :0mneilp) fr/ 9a8dywqc+*gqr/fb j9a 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.9qf;o1 v1ylu,p zlio+ 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 function4)x8ht6wyt urs+ tkt. 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 rosf;l+ guho 43eughly the average current in the output resistohs4;3eg +ful or $ 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 f,vjnq6oj9m ;p4jhi9 eorward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the output resistorm joi99jn ,vj4;pe6 qh $ 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 wi , *,dxgd ftz5hcomyy bj.j40*twkp7;th a full-wave rectifier (Fig. Bel*c d.f,5jbx k*y,wyt jpmozt47g;hd 0ow), 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 for the relationsh ) jsgv+t ;ykylwtr634ip 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 thhtaf 4whf5y5(g; oar63av 4b ke $ \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 ong es8v/gpw;fcc2i-pstz0 77r 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 distanwyg7vg99l8 zoh62tctxytn 3: ce 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 withbk o2su5xy1k3t zzgc(i5 qxo g32f/w9 a weakly bound cubic lattice, with each atom connected to six neighbors, each bond havo /(2y 5oqx w1xukbg kg9tsc32fzz53iing 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 foundmk-;og2u/ l kt to have an activation energy of 1.4 eV. When the molecule is disas2k um;g-ot/ lksociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident ony ;o,s .gs3fcd 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 s;d csyog,3.fconduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set is not to rm ezr0 5eul7g73*ptqreact to visibl m7eurg ze7qt0r*3p 5le light, 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 silicon x0v )+zmziw.q1clq 8usemiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. w+0q.lzx1ciz m)v8uqFor 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 sola6*h;pmsbf )par cell to absorb all this, what enhmfb ;a p)*s6pergy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longeso,k48 hssq7akt wavelength radiation that can be absorbed is 1.92 mm. What is the e k8a s,oq74khsnergy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs bhp8 )cv/aly4e; ,mno wk*ap5m1n h(zqecame available many years after red LEDs were first developed. Approximately pw ql k1*nyme o/cm (a5hzn h4p;va,8)what energy 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 reguoj k(7)sg7fyw lator 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$