What type of bond would you expect fjkb sz7tb z1q v5 *jup2cu(7(for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mole jurf-lels jo gf:mig - ym5.39,-nl9zcule $ \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 r4kh6w5*n p z2ee;nec $ \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 it4eltnv 1 ,g/into four categories. What are they?

  Would you expect the 70eh9zg.i tju+)q:e kjs) nyk molecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atxir4i4 6ev nei ..r3dhom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don's ,- vt3exjdm)w j98ist they leave the vje,9 -8djx3 s)itwsm metal entirely?

Explain why the resistivity of metals increases with temperaturv.j0akulq;jte,5 3)g)yr ag he whereas the resistivity of semiconductors matjel )g0k;.jruga vh )3aq5y,y decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how t/3u l*3qq1 ru92j mg9ze7m1epztbirjhe current is rectified and how c g12q3um/9qjjztbr emp1 il93 ue7 rz*urrent flows during each half cycle.

Compare the resistance of a pn junction diode connected in forwarhrw7 ,tvrs2qltw)bi 3pa6 :2ld bias to its resistance when connected in revers36wb:qwpitvhr),l2rtla 7 2 se bias.

Explain how a transistor could be used k,ot;:b( sg7gf* qfey as a switch.

What is the main difference between n-type and p-type semi ird) ;,uts9veconductors?

Describe how a pnp transistor can operate a,z9 dl vhw -+z1-kbehre9 bln;s an amplifier.

In a transistor, the base-ea :2 ryifd bwzlun;;;7mitter junction and the base-collector junction are essenn27u d:iwz a;l;;fybrtially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electrogb9cfsw (;ys 7nic signal, meaning it can increase the power of an inpu9wsf cy7b (sg;t signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will thesejf ..ba33;cingl(gslt * 1ywe atoms be donors or acceptors? What 3;l (tew 3y.ligc1s ja*gb.fntype of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explaik mgv4h3syk 8/yg;5h*wwfw ,n qgy.(un. {yes|no}

  Can a diode be used to amplify a signalrgn2p+xz 4 i4f? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electcfh59/m8pxg a rostatic potpmxcf8/5g9a h ential 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 t)ehfsdw3-kpq4n d5 a.he result of Problem 1, estimate the con qpnhae5 sd-w3d4) k.ftribution 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 ncub;w )g;/5h)brjx+bw - s geenergy 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 m ,k ;r8ee)mnggole, and then thee8em ,;k)nggr 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 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 p;q -pyygvn nw-h7:7g d*nl2mstates in the formation o*n-v7pnm -wg q; :gy2ply7hdnf 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 h3va) u-js32rq2rk t3fkt-p v $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational energyzct 0m7(qso u0 7h2)mh ak-gpk,” $ \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 ugw(pqaflnfas. k8*eh 413ab*o 2zs9nergy, $ \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 anc3)xuif +wl8i-kvx g xe 2n pk*2tg 14a)e1kof 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 the NaCl moleculei39b i jx:1auf given that three successive wavelengths for rotational transitions are 23.1bu9fixa13i: j mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fy:sc w/to qq,4ig. Below) 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 neighb.lef d y9;hr(a f*+dtbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor Na t9+b(*;hfryd de lf.aions? D =    nm

  Common salt, NaCl, hasds6 x il 0+)qgf )gs4dg,v1qps a 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-3jgbm , 8gutx is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of enc.wlau5t2nc: ergy bands why the sodium chloride crystal is a good insulator. 2wc .l5 autcn:[Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bom6 ,/qmrhcbkp95w6gjcf; 0liybarded with light of slowly increased frequency, begins to conduct whemb , 6gcpkcj lr960f5iwyh/q;n the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photona3/df2l at5( 0 . 8dnjpgwaojz 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 conduction bands in germanium isqcl5/n3sm4 (cz 4 zezq 0.72 eV. What range of wavelengths can a photon have te5(/l mczz4sc3qq 4zno 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 are9p4 ( xe(.w)ypdk oyve $ 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 so t sh1qlo;p -c8mj0cn 1uhat one silicon atcjuln8o1qphc 0; -m 1som 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 materiaixe ipoif-zoz3 *:t -,qf04t vl with an energy ga f0t,ovqzi- : feo4pt*3ii- xzp $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavek7 hy yh: e0rd)a/5wbw+bjh7vlength $ \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 in (Fig. Bei lo;xkm+z 5x(low), is connected in series with a battery and mox5 xi(+k ;lza $ 960-\Omega $ resistor. What battery voltage is needed to produce a 12-mA current? $V_{\text{battery}}$=    V

  Suppose that the diode of (Fig. 1 *htyf7(aapog1b 3ch 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 resistanc:t11h:g+v: py ivaxb we as a function 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 roughly the averlyn2 27g9m7 tr;n* 3 lpixmkwyage current in the output res*;ynt977iglyr mp32 lk2w mnxistor $ 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 currentk,.t( izd6xg lo70a nkzo3r:z only if the forward-bias voltage exceeds about di6:g,nz 3 zoxa.k7ot(kl 0zr0.6 V. Make a 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 rectified wi 1oe.snm*lz-xth a full-wave rectifier (Fig. Below), whem*nx.lez1o- sre $ 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 tnx lr5w +i10ynhe 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 of7a (s4rj mip8awd m7-k 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+p7va2yjl g6rw hho4kwb3) f* 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 about 0.o jjwo;( /yji427 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 sololh; addoc+5. psn --pid with a weakly bound cubic lattice, with each atom connected to six neighbors, each bond having a do d. -o-+cpl; p5nhasbinding 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 acv*2z virl j :uyxr2/;etivation energy of 1.4 eV. When the molecule is disa:vriexj*/; 2 zy2vu rlssociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, dj 0fn (eq5jjr7/-k 62foocdnit is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is thej0 kd 5n7 d6/r-ocjqf oenj(2f 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 seme.)xwd: ,yu- himr,et is not to react to visiblyhe dwi-mu. ,e: ,r)mxe 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 qf 4uv( j+uk,d3.fgq ba doped silicon semiconductor, assume that the "extra" electr(ug q,+fkv3ju4bf d q.on 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 sg q58zs 5k.uupolar cell to absorb all this, wha 58gzsukq5. upt energy gap ought the material have? $E_g$ =    eV

  For a certain semiconu56 )tvkk5aqn 6q uu,lnt*:mh ductor, the longest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semiconduct):,u q umvln6 55ukaqknt *6htor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red L4hvowd5(e.sh4 w zf(hEDs were first developed. Approximately what energy gaps would you expect to find in green (525sh5d4.hwwoefv h ((z4 nm) and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fig. Below). Suppose tha9vca) ozlq (m;t $ 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$