What type of bond would you expect 8 54cg aw9jnv g(5+ldxxvh9rgfor
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule flh 9m h5)vyfy4 jgw89$ \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 g) uf1r0 3j as1ecybj3.:odhe5 xdpb( $ \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 d9 kiyw/ ou4m3c9a 1ghare they?

  Would you expect thenv-b;u q 7u(mr/iggw* yv7k 2l6io 8ey 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 ay0 e4yuku6yso(7 fy7m tom ($ 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 7i8kqtgkx w7,ryk 8sfeg4 7-dleave the metal entirq ,7ke74s8rf7wk8g kig t-xydely?

Explain why the resistivity of metals increases with temperature whereas the rh/1nbjjzt y4 1usjov9 o-w40oesistivity of semiconductors may decrease with increasing tyo 4h t/jswujv 4b1no j1-0oz9emperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Ez.cdt96oe v; qvrv25m xplain how the current is rectified and how current flows during each ham6 z docev2qv;59t .vrlf cycle.

Compare the resistance of a pn junction diode connected in f3g.o ao7 s.rirorward bias to its resistance wg 3.isr aro.7ohen connected in reverse bias.

Explain how a transistor could be r9 f0z/olnpv:h7 dxu :used as a switch.

What is the main difference between n-type and p-typehrrs:b9ao.9n0ucd41 - b k hvm semiconductors?

Describe how a pnp transwa*v tzrn)t eu)1m4hb t6ps3-istor can operate as an amplifier.

In a transistor, the base-emitter junction and the base-co31,1ylve ym nfoyix):n y)-pwllector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown e1n)yvy, )fy: 1p lx-mwiyo3n in (Fig. Below)?

A transistor can amplify an electronix5do e4/v48mtmx(h q4 e;wawi c signal, meaning it can increase the power of w qoeh4 /m58it;avx ew4mdx (4an input signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms be donors or .6 ,uob7vm qto4mhrz7 md37fx acceptors? What type f,4777zuh rotb.v 3 oqmm mdx6of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? )mbqj08m mb n.jd *tc/Explain. {yes|no}

  Can a diode be used to amplify a signal? Expl;qoxy+, a8t .s4 rfod-ho9eokain. {yes|no}

  Estimate the bindingwjg:yijwm79r1ld/s b3xw:. e-ust0n energy of a KCl molecule by calculating the electrostatic potential energy when x9 .17tjl dji g3rbw sn-:yesm:w0/uw 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 the resu sucqyf,1c/8m-b s( sogd b4u1lt of Problem 1, estimate the contribution to the binding energy of thom/-,g( fbc41y8qss1du bs u ce repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding ene e.wwh me1 6r;ju)x62.run khnrgy 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 experimen )f: lw7eeii)rtally in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion factor in going from kcal per moli)f)l7: r eeiwe 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 sycuz:i78rwfp )q. .i yimilar to that in the text for the states in the formation of uqiz fr.y87 yw).ic:p 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 quantir8 m l(k,2 .9bceehgoo),ssdpty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteri5 f:3 kfvdujvr-24nfnmdx 2i6stic 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 chaaf qjf/5ky8wc xj )nm:+nr2q:racteristic 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 separation of H atoms 4 *w ,)f6yhp;gn lpugb6nqpy2f 1tr 9pin 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 m;vgcuycn 5n5i6 ;+ vueolecule given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7.71 mn5 g6 5ny civuec;;+uvm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate tz7 qci-i2p nj v:+ndj3u23uakhe 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 “nj. wqji+j-a vg ir+*g2ur0s7q lt9t5iearest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. glgi qq2.as+ rjw-i tj+5 7trvu0ji 9*What is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a densityci/t aww1wnk9,9*hn7zo 0 vm kurw6 8m 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 whoq8 37 rahsbwvcm+6uq.yod- dy8h 0 7zose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a good fm d h79ely52 zdtg3n*insulator. [Hint:*m9e7dlfn5g2 3hyd t z Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, beginsad;,cb xcqy(.5-tov,lzvwl . to conduct when the x (l;, - cvzv5,ybw.a.codqtlwavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavezzhi-k,y;-9n9q aq0 yyg 2t hglength photon 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 eca /xr -ecukdb*291cgermanium 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 conr* kc ccue2-9bx/e1 adduction 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 areo:1qwvew/g*f98q cog $ 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 nx f 0py0yl2p drx.;b5doped with phosphorus so that one silicon adxxpnryb. l 0f0py;52tom 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 mapr9o cztydk-q 4y q)3/de from a material with an energy gap qdr43/z-9 pqct o)yyk$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light2hl 0i7m czs5nwtv*m; 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 characteristicxeb0 kx *+my, or-mrh g(4zr1i w6mpd4s are given in (Fig. Below), is conne,10 pg+ mxomzw44e(im brh6rr*x-y dkcted 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 (Fig. Below) is connected in series k19fwnlo1ohq.d2;3 tf whb ;-b naf0x 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 current, t9z 6k;u x/tse+ ru;dvkfvj+ v.pwh)2for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate veryw7zxdg:x;bd66o6/q w)nri l y roughly the average current in the output resistqxwwd7n 6g;b ix6 /ldy) orz6:or $ 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 if n* (y+s9xwl ypb3hw .athe forward-bias voltage exceeds ab*+s wa9 pylby.w 3xn(hout 0.6 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 with a full-wave +xhszq e nct1)-) sc,9d7 ajsyrectifier (Fig. Beyh)cq n+ d,x )as-7 z1tejs9cslow), 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 relm06(oz +pidx kw3vf; yationship 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 bidz2 qlk y1c+2m(2af 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 or molecule is aboutbys hz. f9ajm3lcgjw w0.y1,- $ 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 0.27 nm.khh a n,:b,4 6sm,yvilkp pi9 cp+/1mc
(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 atom cuk o/.-lj4mmr n .)dywonnected to six neighbors, each bond having a binding enely-) ./m.romdujnkw4rgy 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 acqiufuziwy 9rb 6.7d7 -tivation energy of 1.4 eV. When the molecule is disassociatu7 fz9br6iwi .du-q 7yed, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that lzljl) xe )boybj*8e;q -. kz-uight with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and thy. oqle8x;- u*l) bjkezb-)j ze conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detectorc+z f/ cbil-pp y8 y8-w4dq gq6x;boo+ on the TV set is not to react to visible light, could it make use of silicon as a4dyo6 f-bwxy8 q+ ql8 pz-cb;ig/+poc "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 thaj:ciaok0e :ht3ugf, wi):6 +w:r9xk pghde6a t the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into au g9ie,p6ifgr6 acda3)kh0w: tkxewh :oj:+:ccount 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 s4c (1e d bo)xa 1-r(huabnt/ayolar cell to absorb all this, what energy gap ought the materialy1xb) anco -/(uah1r ( a4edtb have? $E_g$ =    eV

  For a certain semiconductor, the longest wa kuhl 1u g5p bv(j3p.9gfo5-yuvelength radiation that can be absorbed is 1.92 m-.lu5 ug (pfy5hpbuvj9og13km. 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 were first ,de dxl24ik/odeveloped. Approximately what energy gaps woue /i,o 4dkdxl2ld 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 regulator is shown in (Fig. Belw 5:o 63aqzpmzgzhu qf91x2 g2am8r)gow). 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$