What type of bond would you expect f-.*gj ji e-jl iy04fsl7kcu-hor
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molec)yl)w wv6wm9iule $ \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 moleculedc jq.+ o(-gbqv/h1;psf cwv a938zdk $ \text{H}_3 $ is not stable, the ion $ \text{H}_3^+ $ is. Explain, using the Pauli exclusion principle.

The energy of a molecule cdqa/ snjs;ftj4.x2 ogk *,v: fan be divided into four categories. What are they?

  Would you expect the 6)9ip rz )og wymv8m t rs9qlc,7bo.2xmolecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carb t+tyn ,4hb7fion atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a ew3 phb;*0i wfh5)s8nww e -pgmetal, why don't they leave the metp30)*wgwi5wfs8 hh;eewp nb -al entirely?

Explain why the resiso3/tu2y cqn2 wtivity of metals increases with temperature whereas the resistivity of semiconductors may decrease with increasing temperaturo qt y3/wu2c2ne.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the curren 0hlqguob(/ 6kgd bi+/t is rectified and how current flows during each hal06(/gb bigo/lq dh ku+f cycle.

Compare the resistancer nsvs 5r0ao;js)8/vor nu .ybu,,wb - of a pn junction diode connected in forward bias to its resistance when connected in re0y,/5)r-8n os vv;jbr bras w.onu,su verse bias.

Explain how a transistv11w30v2tz gozu )geqor could be used as a switch.

What is the main difference between n-type and p-type semiconductors?u8m :vw q; c+2cpqp-bp

Describe how a pnp transisb(tw*u5lgm b /c og+v8tor can operate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junction a 4mg0 v m2jskw2umfo5p(d4/cpre essentially diodes. Are these junctions revev2/4 p mf (0mgmwup 52co4jdskrse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an 0f 7vg)u +.kwrtv5xyjelectronic signal, meaning it can increase the power of an input signal. Where does it get the energy to increase the pow)t +wvf7yu0vxk5rgj. er?

A silicon semiconductor is doped yb:(z9 e; hwyz2qy o5m-zv5i dwith phosphorus. Will these atoms be donors or acceptors? What type of semiconductor will thi5dezh(- y b 5;iyy:mvozq2z w9s be?

  Do diodes and transistors gw-qwudfx,9kq .h 0 x(obey Ohm’s law? Explain. {yes|no}

  Can a diode be used to amplify a signal? Explain. v,2fwi. q9 qdye)/90h01karj ysoo eg{yes|no}

  Estimate the binding energy of a KCl moleculehwbqn.dsy/ 6 v+4sn.v by calculating the electrostatic potentivndq vhy.b+/sw64n. s al 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 b it(u4w4o)fa em1.jgthe result of Problem 1, estimate w itgab1. 44jeo )u(mfthe 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 ene wiaf-v-( i0d )ceo43a-aonpyrgy 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 experimenmxbiy1tn*s w+0:x*rrt ,ad e5tally in kcal per mole, and then the binding energy in eV per moly0w d+xsi r1a5**b en,:txmr tecule 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 states ih,azakj sm2o38:0x n tn the formation of0nzoamh,8j:tkax 3s2 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 quanti20t/etr4bc mwc1)lw idqi 7 o5ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characterist0 scm lp c/hw6:gnht,5,iqe)o ic 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 rotationalb11i.sway 86hx2vvi ls6p 6wx 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 separation of H atoms in 4myciu4jf9;vo h1p -u 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 given thatrg+00 jcta*za three successive wavelengths for rotational transitions are ag+ jr0tzc a0*23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. 5agou0x ()cym 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 neighbor” Na and Cl ions in a NaCl crystal:o6huwzs;ei.r itzj l;x4,, h is 0.24 nm. What is the spacing between two nearest neo4:es;wilzzij .,, hu ;r6xh tighbor Na ions? D =    nm

  Common salt, NaCl, has aapkn axr -cp*(*i/ lu8 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 densi4 *z0q/olxoz rg xip;3ty is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis g3rj-g i,pu94js.7 rd: ivcwoof energy bands why the sodium chloride crystal is a good insulator. [Hint: Consider the shells of.w3 spr, d9:o7g vg uij-c4jri $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with lig3l.2 yh-ni7 rdp l/sxhht of slowly increased frequency, begins to conduct when the w lih 7 ./lndhy-rsp2x3avelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength pln4qs9: so82syxev y4hoton 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 conduct9bwkrl) )a8x zion bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band into the conduction r)9 xak)bw zl8band? $\lambda \leq$    $ \ \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 q ibfia :*cq0g6m d5 2s7hcpl3$ 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 silicooig t vgj,5t88rh1 9pxn semiconductor is doped with phosphorus so that one silicon at8h jg9oi8xt5r1gp, vtom 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 wnq i0d4) y-fvmy80cgdill an LED radiate if made from a material with an energy gap 0c4 f)8dq0iygv dy-mn$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light*j fqybkvyn1+vpbk 0 :o9arej1+0u 7c 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 4yfo*fc 4r)8 hxt8yx jcharacteristics are given in (Fig. Below), is connected in series with 8xy)t44h o rcyff8xj*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 diodevx*p)*yt. 9johdqr i d3k) 2bugvw))hq*4a xz 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 funndct 7u ;s;shy-c cn23s, c)ywction of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be ri-m*sdqs6x 8 of4q2 c9rmdn 7tectified. Estimate very roughly the average cu2q dot rfmn6 s-mci97d* x84qsrrent 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 only ifad/iwsh. vi0 vtcc2 bq+* nt.6 the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of t6bc+stt 0iawn*2hd.vc ./iv qhe 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 rectifier (Fig. * 0nitfnz9b2+ wtx hu5a*r1x.uokee9Below) 0+iee o5 kr9btxnzx*aht9.2fwn u1*u, 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 relationshi zx+m 0bd1z):d1zuxzrt zm.:zp 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 oa+(yb7.klrauui wd) k n 73-eef 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 translatiokcl+ 1uxbsc5jjwi +6oxm* 0 b+nal 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 dista9ojec0ckoj1qws, 8 7ance 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, with each p7.tie 430e rg48 mkcwqui6g aatom connected to six neighbors, each bond having a binding energe g4ri k34eic 7a.g mqtup680wy 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 exza, o *z0l -6zx*qz/v-wyemh nergy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy cuqy/aoz*x z*- lx 6 ,hwe-zv0zmrve for this molecule.

  When EM radiation is incident onn(2qunx9/opdirs -s,/ n9va h diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap betwee2u d9 pri aonqsvxh,n-s/9(n /n the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. Iod9n)qzir)29 bp p47.d5.fk pgnwlfu f the detector on the TV set is not to react to visible light,dw4 ..un )qr)ofppnf b kl29ig pdz759 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 ina(fb, bvu qubkc60)u)* -,dj9/x rulmibjl a + a doped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For r6 al udcf +-uju)/9 *b bubkx,qbva( jli),0mthis 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 u (b.kpoymlz .vj;n 56than 1000 nm. For a solar cell to a. 5 6uvj bl(;m.ypozknbsorb all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation thl**e(m w3 w5e2 hexanxat can be absorbed is 1.92 mm.axe3wh *wex52(m n*l e What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs werebjkl.aq9i,;k jxb oebg3.j2se qq8.; first developed. Approximkb9b x j.2jei3;q.ks8b o aj.eglq ,;qately 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 voltag0 0ko f0mm-+igiqwhm 1e regulator 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$