What type of bond would ,i c eu oj 219wh:rs5pnb:u:uayou expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molejoyk:ar3u t03 cule $ \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 nqgv s:1yugm:2iz8t78w8xino vh ) 6q$ \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 d2.-xi f6n1b 1ejfea hinto four categories. What are they?

  Would you expect the mo.g(2 wi yiyel+lecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atom mpx7yi86me n 7($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't2+5c gqxpq qu7 they leave the metal entuq5+ 7qxcg q2pirely?

Explain why the resistivity of metals increases wbi+he, tmz;a))l poc 6ith temperature whereas the resistivity of semiconductors may decrease we6za);opbhl icmt)+, ith increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain l vj1dkd lgytk((oa1 mxb-)38t dahi58u(2kqhow the current is rectified and how current flows durintlh d(qgt1l j b(-vu 8 8yxd k)a32o5m(a1ikkdg each half cycle.

Compare the resistance of a pn junction diode connected ik-5oi, 4xs 4jc oigae9n forward bias to its resistance whe4s x4jo i,kgc5ei-ao9 n connected in reverse bias.

Explain how a transistor could be used as a switch.u :+yxam8n1u5 xjkqv2

What is the main difference between n-type and p-type semicon98jw 8x8ibpk vymfu) 3ductors?

Describe how a pnp transistor can operate as c +f,;+qlghh5y)lnc can amplifier.

In a transistor, the base-emitter junction and the base-collector junc* 3 ;,diez;f d.bkgrrg uh/4owtion are essentially diodes. Are these junctions reverse-biased or forwa ; bd3;kfh* drizrg/.owu4 g,erd-biased in the application shown in (Fig. Below)?

A transistor can amplify an electrona -7co*nz ,r z4ksu2rt b(kmcum :9pk*ic signal, meaning it can increase the power of an input signal. Wherepoc4 snakur,kz 2u(-7 kz*bm *:mc tr9 does it get the energy to increase the power?

A silicon semiconductor is doped with phosphor2m6 4(nkhle omus. Will these atoms be donors or aclk e62mmonh4( ceptors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. :k eka yn+czv2hu-t /sy(9hv) {yes|no}

  Can a diode be used tyaeu1 oc zp)px ad1u:wiv kn0a:6z4/( o amplify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculatin dq)icvwb ,qq1 5sf;7:, zn8ovm7p mdyg the electrostatic potential dv1),dvbpn i 5m78:q f7mzow sq;ycq,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 ene+t5j:mzyt8l.; , g m sif0vjmurgy of KCl is 4.43 eV. From the result of Problem 1, estimate th ;ju,ym8:0fttsvmj5m li .+zge contribution 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 ofb;ku9t7 mr oit+tz+vqo4x1g s-lwq02 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 oftenjpr6p.6 + qjubfxr- ny3wgm75 measured experimentally in kcal per mole, and then the binding energy in eV per molecule is calculated from that jbufnwy.qm pr-6 67rpg+3j 5x 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 the for(1u1(e da5s rt;yoss4/zdzo wmation of the sw1/u(s(o y 5ztedzd;rsa1 o4$ \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 ,luj79k; va( hy7s sc twkq4)r$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationt y) e (1hy(n:wfd(wuval 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 characz0 o5y y//5qg q) chbbdf tkd6,:v9qnhteristic 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 separad .53c mtmaft9a9ma2q tion 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 moleculu-v2fxysf 11fbo8wnz d5 79,k*vitrxe given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and fto9b,85 xx fi vny d1k*vz 7s1ruwf2-7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to est3bb:3b0txt l y 5ud5y 8:jxxykimate 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 “n*kxtp 9u6j.6cs 3 wh0;qdqoz tearest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearht69s.*xo 6pdwqq zutkc0; 3jest neighbor Na ions? D =    nm

  Common salt, NaCl, has a densssw/mf ( vtc,-ity 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 de a-xy+ bakf-ge9 btffy./89m 8rxv-hhnsity is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bandsuk enaz0(juuu3)oq/) why the sodium chloride crystal is a good insulator. [Hint: Consider tu uuak(3oju/e)q)zn0 he shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frey4:h c6lttleeyq2 9 -jquency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the ener l :he jcltey-69t2q4ygy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in swbu.;tj)xb 44 whmdgtu d/ak 5nty88.ilicon ($ 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 is 0.72 eV. Whaq72 jx9smq cddttg .,5t range of wavelengths can a photon have to excite anqct. 5,j d2 tmd7g9xqs 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 areuv16g3g4 v)l -ugvkd ftw5hq ( $ 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*f))k6z uhwh u semiconductor is doped with phosphorus so that one silicon a6))hz*w hk fuutom 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_{\text{doping}}}{N_{\ce{Si}}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if made from a material with an energyrnqtpzy i35wk 51 :5xh gap yhr i5t:kw155 z3pnqx $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelengtjb+h d *m2+zvoh $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose current-volta1esywctn7t6l2d+.s vuby* r66f . tjjge characteristics are given in (Fig. Below), is connected s61l.nystjwdv y6bt7 cf6+. jr et* 2uin 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) iyt6+1ihc31p j,fbt- ylddi bao )q17cs 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 mfo/brn;s89/lhk ,woe 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 roughjt p i1,:gbhn v;/o :p 0hfq.kkfs)a9fly the average current ikns/g;:fo.kb1j ),vhf th :p9a0qf ipn 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 signifi +: +c 6w 4m:g7he/przjbo9jfkn4r(h9tq wrfpcant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average (h o gf wr zc+9wn:m:7tk4e hjf4 b69q+jpr/rpcurrent 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 qox713bs2qk2tb. g av rectifier (Fig. Belo72oq32.1b bvka qg tsxw), 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 rel/atvb owwkw.krh8 3s.oq.+; r ationship 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 energykj s7lsgyd(54 9 mnj6*ki vx+i 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 energy of an atom wttv(5 /jtody0az -i7 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 separatj 19rkq, 3a7 x-eykpmcion distance 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,+*s7ur +*grxn n2zotss 97mkc with each atom connected to six neighbors, each bond having a binding en tcsrg77u*s+* roz2 sn9 kxn+mergy 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 havim4nw 5(um;w1sm+t 5kjg sf1qe an activation energy of 1.4 eV. When the molecule is jq+w5iu1s5;mk1 g4n m(tmfwsdisassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is 5:-r7ai mgf3o w2 oowkfound that light with wavelength:ra o 2-5g 3kmwo7fwios shorter than 226 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 .6u2jlk 1a-m a ls/whmnot to react to visible light, could it make u mslk2h-/1wla 6u.j amse 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 semiconductor, assume+oaou e3g)nmpbv z,(0 that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the groun+vu bpzgo(a,o0 n)em3d 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 xty /ys28w2 ej+m.jxm gex6.u than 1000 nm. For a solar cell to absorb all thisjj .xtmmyw2x 8+ s2ue g/.6yxe, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the lp:x+f:2sju llongest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semiconductor? lj2: sflupx+: $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years a tec l (l8bt-o3prlf,ug t2+/ffter red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 nm) an+/ t lb3,f(tcrge8ltpu-o2fld in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fixoi 0 +.: amdz8.zmhgfg. 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$