What type of bond wouldtexow7 0 ;cp-h you expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule s)39p b bx)xee$ \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 t2) uw/ap9sgg$ \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 categor d:*ew.d ugbkvj nbmc:f5);pi+5-u v pies. What are they?

  Would you expect the mfyro*4eih /e .olecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon cz3hphxsq3 ,6,()bjlvty r9 eatom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to r-ea052sokx5fn m jwx)oam about in a metal, why don't they leave the metal entir 5e2jf oxm)xa-0wkns5ely?

Explain why the resistivity of metals increases with temperature wher1b-p(n z*lvok1x 5hpu eas the resistivity of semiconductor*1-u vpklb(nzho x15ps may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the 8wrxzudtl 6sn k -92)vyo8t t6current is resk8 z6v-) 86wtnl9uxtd oytr 2ctified and how current flows during each half cycle.

Compare the resistance of a pn.phnwa ,3url1 junction diode connected in forward bias to its resistance when connected in reversela nrup3.w h,1 bias.

Explain how a transistor could be usj)ig.fz phcnh59i3scu0 vj4 4ed as a switch.

What is the main difference between n-type and p-type semiconducf: xi4aguv+;c4oi n, wtors?

Describe how a pnp transistor can oper29.pz+:2 rzxt: +g(tpfa:uit xwyq-s kx k/lpate as an amplifier.

In a transistor, the base-emitter junction and the base-colkoa*85s x/:qp* uiwek lector junction are essentially diodes. Are these junctions reverse-biased or forwark 8/:a*xs*uiq o5 wkepd-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, me,hr 6 rx,:he3z.gfsr gh0y:gm t+xct+aning it can increase the power of an input sig zsrx 63g+rmygt+e: 0.gtfc,xhh : h,rnal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will theby)h2k.x pu- hse atoms be donors or acceptors? What type of semiconductor will th)uhbxp k2. -hyis be?

  Do diodes and transistors obey Ohm’s law? Explat.1ze,n3f*zmi(lj6 vq 3/gfkh am6 foin. {yes|no}

  Can a diode be used to amplify a signal? Explai2 -9hjmg-.8yvknlus )sv /voan. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the elexv7 m dht5,;(:os c3pn osugq6ctrostatic potential enhxm; sg3ocv tu(dpns :,6 qo75ergy 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 Probleml 7.c/mrm1j/(st) hvd)q-bb yjn z; co 1, estimate the contribution(. dh7;scmbmlnrco)j )vq- /bz tjy/ 1 to the binding energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy 1we2te(8 aq deof 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 o9 m39,r(w .ptq*n: jfjamkry eften measured experimentally in kcal per mole, and then the binding energy in eV per molecule is calculated ef9 ,trm9wn:.jarmq(3y* pkjfrom 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 thvi eo*f6mx: ct/1cr b8e states in the formation o*r ti8 1xfbc6e: ov/cmf 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 quanti4:/xq5hdhg 6 x*tkqn uty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotatioybk 5q3 2pofozf ,y8xdz- p2h)nal 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 enep9(/8 jk j a-yb2hkpehrgy, $ \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 separac;m t.1 -0azlzxzql+7uf ;gmjtion of H atoms 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 length for trs*d) kx*4aus qz42 ;p v)co-f t(ltgwhe NaCl molecule given that three successive waveleng*x)rus; kzfwp42l4()q s -*vtgt daoc ths 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 n1cl3qu7o 2.r 14o*ddz+(d)r5qphcvx ryemo 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” Na and 5dajbv 01(g 9 xi vxtw*h*4edxCl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbt(5* 4*v 0 b w9h1xeaigvxdxjdor Na ions? D =    nm

  Common salt, NaCl, has a densit:om krequ.fu(f 9lxw-5m42n by 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 K+9bcv ps*t6xyCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodq5z qu;dx4o zr6-5 c1 uoxf1jaium chloride crystal is a good insuo 1jfxq5zr4oz;5-x u6 c1d qualator. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombardedid /9n( osa 2/f;optci with light of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the efno(p 2dis9;a/ ct /oinergy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wsrrrqqz wteoqr h( *:,(0e h**avelength photon that can cause 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 valence and copn76 +s fdx utv;.o5v:u6 dyzwbmf2 n;nduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an elecow; mdf2ndp6nb v6yzu5u:.sx + ; fv7ttron 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 ar-v p3 bd0pnkoe 7mt)p(u80g/frft2yle $ 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 xgk0j(i0a2d/:2 e- mjtyh bkz/+yedi so that one silicon atom in h/ td0 ky2ezdji(+yi:jm /ba-2e0xkg $ 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 with an e.7ppcprlr,bko69.r plb6 2fg9z d* tpnergy ga p..p9p9clfgobd b,6ptr7klpr* zr 26p $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits ligh ( tbp1 p3aeebq(dw:td).z/slj m1(c tt 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 current-voltage characteristics are give8r085/dz5 .dxtqksv8ej3.kc afozb n rtm j 44n in (Fig. Below), is connec b tnrek.sj 08aq.8v5z 4txzo 8m3/ jd5f4dkrcted 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 dioder + iel.1)xs7idq8wsj s o8fo5 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 function of current, fl ny) u9(w4cbuor $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very rougm;bqoxi46*k/eebag yj87 v /ehly the average current in evgj i7bq4xe*k6/ b8o;emy/a 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 currenyw9no-0vyvhv;ts 6 ;y t only if the forward-bias voltage exceeds about 0.6 V. Make a rough estima9 -;vy;vv 6yoy ts0wnhte 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 rezm e s*z-fe-vue b78h2ctifier (Fig. Below), whee8zve7e b-f-zh2sum* re $ 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 tu :co2ff qu o e:/bh +5fn)0m:1hl0dex9urvzkhe base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding eng56q-mafzm b4(t.- 0gekeba lergy 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 ene-yp8htr /z ra*rgy of 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 distance between ions is gck ./7ok84q,t6kf s:r pt tk zb4pzc)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 atdrcs.8x i31+lipqofj76yk j* om connected toioyxj+d6s3 .8i1*qlp jc7rkf 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 have an activation energy of 1.4 e i),7o*xh8b5 qj zt6dexzhr4tV. When the molecule is disassociated, 1.6 eV of energy is releaxx4i*hzo rtqb z,65ehj8 7) tdsed. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is founzqwb( v* g1xjtp 5h8r6d that light with wavelengths shorter than b6h8xw 15p*rvj(zqg t226 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 is not to reac5hcllk+s m*uk- .)exp t to visible light, could it make use ofpl*ls5h x)- k uce.mk+ 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 dopex c2zvpy88m y:m.mz,w d silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the groundm:cmzz myx8vy.2 p8w, 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 wa*iy m2tk/ 7s2ibb7tgcvelengths shorter than 1000 nm. For a solar cell to absorb all this, whcby2*t7gis tb k 7m/2iat energy gap ought the material have? $E_g$ =    eV

  For a certain semico tls /a/ab4;y4f:hkq q+vj,jsnductor, the longest wavelength radiation that can be absorbed is 1.92 mm. What is thl,/t;qhj j q+ :f/aabs4ky s4ve energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs bdg6o:7ib.g /9gpilw jj m6 du4ecame available many years after red LEDs were first developed. Approximately what energy gapj/ijdg669gd4 g pibmwl:uo 7.s 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 regulator is shownxni3kpi2 hqv+:7 dv3r 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$