What type of bond would you exp fjwa77: l(vjwect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mole, cta *zs9)gg ,fnussu99kr 2ccule $ \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 molecul* :b1l; vw4qwm bzastqq0., xfdvia( +h3b -yle $ \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 djbwk4tt,u,d 7 9si9 vb x;-fcyivided into four categories. What are they?

  Would you expect the m j2xk+s,yu hwn0vi:d 7olecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon a s6wa;zek 8-fgtom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why0vds38cum- 8kuwr n c- don't they leave the metaw8- 3vm-s0kc 8dcunu rl entirely?

Explain why the resistivity of metalsz*)3dpxb.rxjlj *9d n increases with temperature whereas the resistivity of semiconductors may decrease*3rx) xn d lzj*j9db.p with increasing temperature.

(Fig. Below) shows a "bridg7w yww- kfh m l5fboba);.e*9ye-type" full-wave rectifier. Explain how the current is rectified and how current flows during each half cycfwb7fe.m*-) 9; bykya5 ww olhle.

Compare the resistance of a pn junction diode connecte x7pt-dijw v-fwe: cl6a4rjl3csw10/d in forward bias to its resistance when cj-4c w1/i07lwpsjt : wd3fvr el-ac6xonnected in reverse bias.

Explain how a transistor bwhify:,.l4 v- rsh b4could be used as a switch.

What is the main difference between n-type ap:+ 6 aif 8z /byxczdvef;sa;*nd p-type semiconductors?

Describe how a pnp transistor can operate as an l5 t;n8;basymjjcww 3 sr9q )h257jehamplifier.

In a transistor, the base-emitter junction and the basc.+ 9 dsv3l h-coyo-ncw1/bnge-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased cbcy9 dc3- n noso1 v+g-w/lh.in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can inc,o z0sgyl2a -crease the power of an input signal. Where does it get the energy to increase the power? -az0lsyo,cg2

A silicon semiconductor is doped with phosphorus. Will these atoms 20a ng,qsxmzt0:g z, abe donors or accept xa,m,:qnzz 2 as0g0gtors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm46od vwv wod6h(f5;tt’s law? Explain. {yes|no}

  Can a diode be used to amplify a signal?enbkvvvmt 08//2hisw6 (c/ds Explain. {yes|no}

  Estimate the binding energy of a KCk .rvg8-q uru4fj tj)8l molecule by calculating the electrostatic potential eu.8kvg- )r 8frjq ju4tnergy 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. Frc0zfuno1j r8yvul 4;)x,ig 1yom the result of Problem 1, estimate the cont;x1,40i1v uzryul yj8gnf co) ribution 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 enela0zjt4)/mb) *v, s t-gwsqgorgy 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 ul g.0 jtu- ycj7e+ ,zkaez,1texperimentally in kcal per mole, and then the binding energy in eV per molecule is ca+yjjlt .,1zzae cg0e7 -k ,tuulculated 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 statnsjlf .94a0(sa;v odw es in the formation of ta(o0 df4an 9 swjv.ls;he $ \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 quantity4xjfss/ avc,w:l y) 0k*z7 cml $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characte +*xrgi4r(p2 too t;lfmegdw 63iu*,sristic rotational 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 chiiauy a46y87ys z*r y2aracteristic 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 separat8 ostg p *i(zrqk4 0e-do72uwkion 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 the NaCl molecule gk8 rpwr5s1bej jen i) -226ncg-gas.niven that three successive wavelenkjr-8rb52ne.ei -g c )wsg1snn2 ap j6gths 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. w-nir19 8t6ar rtug e( 2z1d3;lcxhavBelow) 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 neighbor” Na and Cl nsbf+,i0c 3hl ions in a NaCl crystal is 0.24 nm. Whatin+3lbfch s,0 is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density of it, 8bsh8 z,chgm0x *cqu0)gl ouav,*$ 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 a -:zihf8x(h $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energ/4 7-vdi ,p/iovan *v* scfin(q lqxo/u c93rmy bands why the sodium chloride crystal is a good insulator. [Hint: Cix/ dmv* rfqq*vci/ovi l3u-9oc(4/n 7asn, ponsider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with7 2 /ttaguqol4 light of slowly increased frequency, begins to conduct when the wavelength of light is 640 nmttgoul2 a7q 4/. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength pmy .dr n4n85knszx+a,hoton 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 betweer9 bf 1rbbd;q 6t dgla*kfk+)-n valence and conduction bands in germanium is 0.72 eV. What range of wavegqa k-b)t bf+kd6 br;f9 1lrd*lengths can a photon have 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 0e.8a; c,keae6xwv ou$ 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 phosphordwmj1 gzh.t2/us so that one silicon at/z2 jgm whd.t1om 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 : a 8pok:sfwl3:7fkqxl*g/* il,mvccan LED radiate if made from a material with an energy gap kp :xm/al*7fclw,f gvc: kio: qls*38$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits ligh fe n+1zhj6u..mx7 fgsi(v jt,t 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 ,q7 t4zpzu5ctare given in (Fig. Below), is connec4q ztp u5t,7czted 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 (F-ifvy 0 jw)iz4hdu4y b1*ui9u ig. 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 cms q1mi.e(zdrx-7oj8 5obny 5 urrent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 5ioh g jkbf,zw(e+ux/m554un V rms is to be rectified. Estimate very roughly the average curr, 5 wgnkx 5fimobj+/h4zuu (5eent 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 onlc05vt8bta -o fy if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the output resio5ttv0 8f- acbstor $ 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-w.s y-jzfy 3e +:axjgciu3o/l4ave rectifier (Fig. Below),3ef+3/c zg sy4j.oj lx- i:uya 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 relationship between the base m)p3k8vh167mlsm3 * i8;c v96eohi gktfw twbcurrent $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy of thl7fn h)fvb,) ye $ \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 translat51l;d9svwveth (0c0ac8fb3o zn p- rhional kinetic energy 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 about 0ek,qqwrc ; .7xeeox7/.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 wej50 ugyh1r,, lq2m nqbo6 h7jtakly bound cubic lattice, with each atom connecte7 5lytjm2g,1,jhh0b q urno6qd 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 foug(rmd2e8s 2bw1oqv.u,2 ts j c zq-q+und to have an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule. ,s 2 wvqq-u +ozd2g2b(.cu18mtqrs e j

  When EM radiation is incident on diamongli 19a(gl*xc y1o)msd, it is found that light with wavelengths shorter than 226 nm will cause the diamond to co) l(ygagsmx*1i 9o1 lcnduct. What is the energy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR lighi0hnskac otq / ih65ipt:ogf 42(o-;o t. If the detector on the TV set is not to react to visible lighto60(hg/aots o42;o:ifhi pqint -c k5, 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 semicondu f.: tjz bcvm,j4i fd8;+m,gazctor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the grzt4c: ijf;,j8 gfmzamvd +b,.ound 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 axlbduoqfp efz74j d.h53,7 -m solar cell to absorb all thl4,hp7q.fj -z537e mxudbfdois, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation thanmeqp*ei6jah;8 ij /-t can be absorbed is 1.92 mm. What is the energy gaj/in8pi j 6eheam- ;*qp in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years aftic,*q9 y* c *iihod7ober red LEDs were first developed. Approx*7*b ch9 *,oicy dqiioimately 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 regulato t g;i/5qaftp1r 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$