What type of bond would you expect for 5dt og4+qu*ib
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecb; 4a0ysjulew enzfs 2i5 /1;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 ycyq*4wu0 n+zhkbz+:$ \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 f wo6jg m0nj;,are they?

  Would you expect the moleculelwnvd1d b8a(y u;u3 m(2j5 qra $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atomu:e-4k vxfg. rj,nx/i/2 mzlc ($ 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 leavemiu oq*o .fs- b4pdv:* the metal entf - d:vsm4p*iuob.qo*irely?

Explain why the resistivity of ,j9h0l ak q u.qcya cf10w9+6o+sc dvxmetals increases with temperature whereas the resistivity of ha ,qu 9fyods k+cx6 +00.jc1 lc9qawvsemiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifi* 94 tvgwg7 t)x/xi rs-r- os6.hngviper. Explain how the current is rectified and how current flows during each h/i- * gxoitswgn r-9gh7x pv.st46r )valf cycle.

Compare the resistance of a pn junction0jhbkii18vr-+. -jsdg 2 bbrh diode connected in forward bias to its resistance when connected in reve1-j2kv08 irr.shdj- +bigb h brse bias.

Explain how a transistor could be used aty-) j f1/onm8 .mivgjs a switch.

What is the main difference between awf6qd. /oxlfhp/:adtm3+r, n-type and p-type semiconductors?

Describe how a pnp transistor can o8wu jd1 r/g4hsperate as an amplifier.

In a transistor, the base-ej 8;afk0ozq(8aefv : dmitter junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)ea k(ja 0;dov8q8: fzf?

A transistor can amplifyqej)ah 7o//pn ckdwr* .mw;7n an electronic signal, meaning it can increase the power of an input signal. Where does eo/ndm);w*7wn r. pa/cj7qhk it get the energy to increase the power?

A silicon semiconductor k1f:ely y-yc urj,*q; is doped with phosphorus. Will these atoms be donors or acceptors? What type of semiconductor will ru:y1cqfy ;,j*yk -le this be?

  Do diodes and transistors obey Ohm’s law? Explain. {y8tdl 6zz tf4m*es|no}

  Can a diode be used to amplify a siy64+equdcyzx(*hc,w w o1uav0 zx/ 4rgnal? Explain. {yes|no}

  Estimate the binding energy of jw1 /cjs4*skpbmyu1-:vu j4ea KCl molecule by calculating the electrostatic potential energy when the1sj mjp j1u4uwe kyv:4s- /bc* $ \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 Probl)h56j(dm dm5 qwkh mu6)k9 -w1y jnqnkem 1, estimate the contribud55m(m-) 6wh1hkj9duk)mnq nyw6qkj tion 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 energ.5ung ,x c8u9 zxt3ncegww yrug)3u ;)y 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 ygdb ag( wj .6nlg*o:8per mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion fac8jbw gn: (*.agldo6 ygtor 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 thatsgx27vtdtn(a 1 l d1( xd.hf+q in the text for the states in the formation ofn xd ds7.(1agh 2vtdl 1ftx(+q 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 quantity z3r.fblmaf u5f+(krno+ds4/ e+ qc; k$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “charafyf -j03j.nt;anzi80 y a-uc wcteristic 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 charactc:9 hbc -e3o1r:afzaveristic 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 8h: 5oyrzj9ljof 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 moleculo8slf/6 0+w kiw,* uozyrpm9k e given that three successive wavelengths for rotational transitions are 23.10k6+smz ruo8wlf, oykwi/ p*9 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the stiffness constant3l o1:n/uac szsz l59wqtr.mg ,vvy ;1 $ 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 neighi uv rc493z/dkbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two near /93rzcdiv uk4est neighbor Na ions? D =    nm

  Common salt, NaCl, has a density of; tb9d7 v: 2,cl b u/mdzmox(ckco0ly4 $ 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 w*rgj 6u-zxw+rhose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why td82e;w6b(w2 oqd:qx :/ainivg(c1y m1noc h yhe sodium chloride crystal is a good inc;wq8 6 vhwdgxm :n2(y/o:n(yc2oideb qa1i 1sulator. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarde: su v- zqdv0eh)yko s((k+rd:d with light of slowly increased frequency, begins to chdd(rk0qo(szkv s: uev ):+-yonduct when the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-waz; cz8v ybx 3gytvf;3hrsqf x.s3;:: fvelength 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 germanium isbcl p0z9vdso4gc(* s(jn4 s,p 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence 49pl4,c0b* sj(n gscvpsdz (oband 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 arg7qto 9-z j+bh7 kbima+* zds*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 phk*v* q kz wzqut+zwgx1qwt;g xf.:f:q 92zn9/osphorus so that one silicon ato +f9q w:qg zxt1vwxg*9u/;* z kz .w:qqfzn2tkm 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 a.7) iv63v s3* pbt+fhah9xns- c w*+dmjzxeeif made from a material with an energy gap x.* hsiet3p*an he )wzfmvjd+7x3v+ a-s6bc9$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits lighd0 d pum5iv/je d4+-hmbvzm0;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 are given in (Fig. Bqmafgjh gy; tvg7w 6:z9s/w:6elow), is connected g6tmaf sy v:7g;w/wjq :z69ghin 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 y n)vnfrn(fol4)w g d8o:i9:yn. dt 5lseries 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 gke./+m/d 1 n6mnwpugas a function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rm (ioddrvqd57z6 * z7*bg5xyyectified. Estimate very roughly the average current in the output reyxy* d7gim6dd5oz*vr z(q5b 7sistor $ 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 significa+)xn2w rlyhi/nt current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the o )/iwn+2hlrxyutput 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 anzeb jl:j*)lqb. 45 pw full-wave rectifier (Fig. Below), wbpzb4qwjn e 5. *jl)l:here $ 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 relationsho:-6+0wwcwh:u wxy q ath )1 eo0a8lkvip 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 of z9yzu ./( nk;zw(m tpkthe $ \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 molebwv y5n83po/8nu1gr e9gr v;gcule 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 h2oft432 ltmjseparation 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 monoatomi/, ,ut8ot2v ctsk d2gkc solid with a weakly bound cubic lattice, with each atom co /t tu8c,g,2os vdkt2knnected 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 energy of 1.4 eV. //e6j juov/qwui(;h sh7sn u* When the molecule is disassociated, 1.6 eV of energy is released. ej o(isu 7w/ju/*/vunsqh6; hDraw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light with wav: /e woeqxs9-g+igq3delengths shorter than 226 nm will cause the diamond to conduct. What is the gwo+iexsq g/q3e:-9 d 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 dmg0/4hqx 4uovlp+ :rpp; u8d is not to react to visible light, could it make usup pd og +4hrvdux4;plq/8m0: e 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 semicondu8eou byuk;o7uye ,vor -)a8mly2.oy +0fq ne4 ctor, assume that the "extra" electron moves in a Bohr orbit about the arsenic 0 yboul8fy;uo n 7+.e4vq)o ae-8ourk ymy2 e,ion. 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 wavelengths shofji)k 9 c-+qyqrter than 1000 nm. For a solar cell to absorb all this, -cqyk)i 9f j+qwhat energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiationixsl+74 htr0l li0jf( that can be absorbed ih xllfs (i+r 0itl740js 1.92 mm. 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 fifv5ww rdy 95e.nv4k y*rst developed. Approximately what energy gaps would you expect to find in grw.fnykw 45*y 9 e5vvdreen (525 nm) and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator x0/6gtbs7usigl 9s equc k950is 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$