What type of bond wo1t:w; i(hukuosck z60uld you expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecuw. *op43jw zukle $ \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 e+8 y j tfc*4kr5)6pb,rjfdcm$ \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 categories. What are they?c 93h0dev7v yn

  Would you expect the molecud/ vefwr6sy9 7le $ \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 (mqkgc/0m yuvq7 kp2fv6 47zy ;$ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't they leave e+ 54duyrj0jw*u c*kee n 7j,gbxk0)y the metal entkwb je5uk,*)r7d0 jyjxc0 *u4neye+girely?

Explain why the resistivity of metals increases with temperatur2*)r e mjl;seqe whereas the resqe2s r*m je);listivity of semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-tbrwabg o4 f)u4 iclr*g:efnb-35o7) hype" full-wave rectifier. Explain how the current is rectified and how curr-)f4*b gh:w7cgbb)ui 4lf naeo35or rent flows during each half cycle.

Compare the resistance of a pn junction diode co;r hiv(mpw6 6mnnected in forward bias to its resistance when connected in h;6mpmi( r6vwreverse bias.

Explain how a transistod3 us dof j(1gprs(j18r could be used as a switch.

What is the main difference between7 rb *qefqr+-z n-type and p-type semiconductors?

Describe how a pnp transistor can oper7gf g*(os 9pifate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junction are e:l,y ) 1 8kur+t9krgsn6sb pfdpf xt b8x6(m2zssentially diodes. Are these junctions6 ) n8 pp:rl t rdszxbk(byxf28f1kg9m+u 6s,t reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can increa2mxmq u8v3v- mse the power of an inpuv8-xmmvq2m3 u t signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will thes9, (bnb3qelv;vew 7l4njhp b4e atoms be donors or accv 49; nb,3 7l4pbh(ql weevjbneptors? What type of semiconductor will this be?

  Do diodes and transistors obey O 86u yi fs8ep zp ic/z l/jizq8+ymor*)5k6b+ghm’s law? Explain. {yes|no}

  Can a diode be used to amplify a signals- knok;drq (:? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrostk i l:h8fp xzj+:53ehdatic potential energy when t eh:h+ j58id3x zp:lkfhe $ \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 Problem 1, e 9qajy,:ahpy-stimate theqj ya:-ah p,y9 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( wusk+n7-eah:ak : wu energy 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 pe;i ia+whos27ewu 8 c( 7;gdaklr mole, and then the binding energy in eV per molecule is cau27sh+a(l wad7ki e8og ;icw;lculated 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 sts u 3699ybh3snhpr3wri)eq2on d1 w2 x+x2wwoates in the formation of t6 dpq2w3 snrouxx93 ywb+ 1wshio23enwr92) h 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 quantity sce hstt2ljn0a:6 f,/ $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “charaed w*p/)nx b 5tu6rkp7cteristic 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 characteristic rotational ene5* dap3i+l elirgy, $ \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 separat,5 l7hxr5gns06cjq szion 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 m4oz ti1g (8mafor the NaCl molecule given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7.71 m14gzmat(8o i mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Buc-yy f5g)ugprl00 m ;elow) 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 ions in a NaCl crystal is 06kpjxhwnl5v w*(p1: r .24 nm. Whnrplj5p*k:wwv(1 6x hat is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, halq+)3fyr+hpx /e9t uls 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 isk .s rr w362z cr,qmrwd*+oc8x $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride cr50rzwa+kab w*q8y) koystal is a good insulator. [Hint: Consider the shelw8kqyoa0aw5* )zr+b k ls of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of;boi2e; y(ylmvo4mgph nn4kmu; a04 0 slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Emi44op 0 e;;n0un magyvbh 2lom(yk; 4stimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in2z 3vyi*m6y fpb8 uf (hosz3yo(4hkp 3 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 is 0.72 eV. Wf2ewwdw8;8 ip f.qmlz+ se.* ghat range of wavelengths can a photon have to excite an electron from the top of the valence 8g2ffws*w;+8 p.lqm ed zei.wband 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 ark;7bdea zl 5ejybx:((e $ 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 so9dq 2z rcsk8/o that one silicon qckso9/8 zr d2atom 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 fo:yy k6y hd7i0pf,1 oy*)v8e zieaiv 2rom a material with an energy gapy0)e zoa*vii 78y dy ,1pyikhe2v:f o6 $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wave.i1i;pz,v8mvd4tw4q -z psz9m zr w6klength $ \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 characteris50/bg jbaezff ijg5+./d r3n ltics are given in (Fig. Below), is connected in series with a battery and5f3a /+ gibzdj5 erg.bf/jl0n 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) is connem ( fc*8r,le ctvsx3rjjx ,9wy)dcc8,cted 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 curre/;hcf5eq /gf t,swwk* nt, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very roughly th:8dtu7bksy(j e average current in the outd 8(yk s7:jtbuput 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 signi hlz5:mm)j+fyficant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the outplfy +mh:5mjz)ut 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 9 a/by nq/ rlm9kxpdav6,))korectifier (Fig. Belabm,n9l /q/rky k) x6) vd9aopow), 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 be, jj47e6:cdeqk 9 9lvil/udzvtween 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 the ./pfd ky*p ok9 00redfqune44$ \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 uu.ykc oy0v4yh*i1hxj r 1kdv9 :n9x9energy 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 betws*o5 zc9moz 7tn2u2 ejeen 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, with each atoi:z7l9ypfhzb/ ) vu /dm conne/h/:lp9 zyi zbuf dv)7cted 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 found to have an activation enecxwu1pnvx(49 l;e e+a1hly r0 rgy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this moleculelwxeyvh4per ln; 91u 0+1 cx(a.

  When EM radiation is incident on diamond, it is found thnjb)/i q/ i:xn d-e:ihat light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between / -nied::q )nhj x/ibithe valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the det z*ej7w fj osl/q+7md6ector on the TV set is not to react to visible light, could it make use of silicon as a "window" wiej /7dzs*qmwjlf7o 6+ th 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 ato5pkzov2 ltut1h(; rxn35a)a lm in a doped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic la 3nkx5hvra 1;lut(pt)z25 oion. 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 wavelefxg)pws/..sj i6g5kmi,yrq p9 ( n ,kcngths shorter than 1000 nm. For a solar cell to absorb all this, what energy gap o5.,p(.f mxr ikcgq)/wkis 9 n,sg pjy6ught the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radx0avsqd8 bpf;jp3:: dv 8ije,iation that can be absorbed is 1.92 mm. What is the energy gap in this 0v; i :fqp3xdj8jev: a8,spdbsemiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs wer ,iupav8 u;7ke3.fzbrc2i -rje first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue (46 cfk2ivb r-7apu3z. je;8ri,u5 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is sgqd rbum 4 +3y9 b91hs98cfskshown 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$