What type of bond would you expect for nf;;1qj)s;fi bv)xz l
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecvu f.co+k80lvs8-pkz)v yy;e oq w 8*iule $ \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 moleculdvn m,q8 mm((hc0ya *we $ \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 dividede . jki6dfn2m,s 8*l bwrikf++ into four categories. What are they?

  Would you expect the moleculey1 n2cizz34 l47 rzeyl $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atodb4o2hh f* prbyut6 o (y+e)y2m ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electronbthpufe9 +el/ 3f*w :us are free to roam about in a metal, why don't they leave the metal enti :utpuw3 efef+ bl9*h/rely?

Explain why the resistivity of *f 9c0 xxjo/vfmetals increases with temperature whereas the resistivity of semiconductors may decoxf90 *x/vcjf rease with increasing temperature.

(Fig. Below) shows a "bridge-t di8p*odph4 p2 w( ujla94l-rwype" full-wave rectifier. Explain how the current is rectified and how current flows during each half cycle. l (hioddlp8wp*a9w 2-44 rupj

Compare the resistance of a g e4ky92;( cm*1fiy/;b qm jq hmjwj3bpn junction diode connected in forward bias to its resistance when connected i4f 9b3;m ;y(jg2k /jjiy*cmmqqebwh 1n reverse bias.

Explain how a transistor could be used as a swit:)( a5xgqsrei*md4 qm ch.

What is the main difference between n-ty,qw1 rmusz48i(2ntse pe and p-type semiconductors?

Describe how a pnp transistor can operatp -75p- dwrymmozf0w 1e as an amplifier.

In a transistor, the base-emitter junction and the base-collector u7c(m/s56f z u41 bq u/qhbbzzjunction are essentially diodes. Are these junctions reverse-biased or forward-biased in the applib hbzz qc/7z1uqs 5u /u4bf6(mcation shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can incms0i*ok ii7 b9rease the power of an input signal. 7*oii9k 0i msbWhere does it get the energy to increase the power?

A silicon semiconductor is doped with idm8t p a9o7e;ig7jgu eagkz-d)gi .4e1v;h*phosphorus. Will these atoms be donors or acceptors? What*viht- k;z4oe9m 8 .pddieg 7e ga j;au7ig1g) type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explv(2 ilwzq bm1p5zo*l*5;hoeiain. {yes|no}

  Can a diode be used to amplify a signat bf,odi jx98i:;2 cgll? Explain. {yes|no}

  Estimate the binding energy of a KCl molsfza. +l)e 2wvecule by calculating the electrostatic potential enerfel)s +v.a 2zwgy 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 o.f pm5)jswpdeh/45r energy of KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the b5mj efwprdsp45)h/ o.inding energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding ener cw(.zwy 4+7 g)gclwxwgy 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 per mole, and vzuyaijrmfofgo0-,16 q5 d /7 then the binding energy in eV per molecule is calculated from that result. What isjfvqouf7o 0/-gr1a5i m,y6 zd 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 for9+ln7czmk8)m. in a1y log/p ymation of g1/clm a +ny k mp9no8.7zly)ithe $ \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 quantitymayepp7( h5q cw:9 tw( $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational ener b0wu1a 6o;;5apreiyz gy,” $ \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 charac wt,se z4c+ffw,:fx2pteristic 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 in ta:/ fm)q-anjthe $ \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 t n ;xejm7*woc3he NaCl molecule given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, cw;xen3 jo7*mand 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the stiffm/;1 o) tdnlgdness 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 neig h y8e0ykqeo4lv ng.6s8b+d6mhbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between tw bk.486nd 0qyho8e mey6+gvslo nearest neighbor Na ions? D =    nm

  Common salt, NaCl, hn hw ,w2o;kz4was 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 dens6w r)an 4nz0h+qc 8nxo9.jtleity is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis offm )2i5ol5wof energy bands why the sodium chloride crystal is a good insulator. [Hint: Consider thewi5)fo5 lf 2om shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded wit-xg(sr4*pg.u 37yxndrml7 fuh light of slowly increased frequency, begins to conduct when the wavelength ormu7-p g*nx(d fxrgl 7yu4 3s.f light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in silicola1nl34 fxobl-8ds bp qu d-*7n ($ 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 cot2:x)hi n5uv4jhg*l gnduction 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 band? 2g4uhi5ngjvh)xtl*:$\lambda \leq$    $ \ \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 hhlm(lr /4)l8yqfw-xqk4l+ m$ 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 so that oyy fy.mlw 27o5 bu+j d;.bfqa2ne siliconydbf7wuq j;mfo+y .y2l.5ab 2 atom 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 LEDik,xfrtt; ct -zu4r03 radiate if made from a material with an energy gap ,4tzr3 0ft irxk; tuc-$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of8tup nqpp2,y 2wgvkvv:f7b 46 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-vof5 vd s2.i8uqyltage characteristics are given in (Fig. Below), is connected in series with a battery and a i 8yf2v.dq 5us$ 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 ed wg4ric50*g) 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 resistanceh ;(1gama lqy3 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 n:62s o)+req+o kzpjm4 p9f inl*1hcyrectified. Estimate very roughly the average current in * pico )941: yrhjzsneplf+k+m62noqthe 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 if the forward-biasfc)u x02 yzf7 ae)n2mz voltage exceeds about 0.6 V. Make a rough estimate of the average 20eayum27fx) z) cznf 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-wavt4se o51jae e) 9ezt)he rectifier (Fig. Below),ae91h t54)jze)t eseo 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 between the base c ef, 8hlf z.ii1+y8lkrurrent $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy61vclxl 3qeq- 7mkx4s /cd(kt 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 py,rqjqu*4h +wc) v8o 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 between ions is about 0.27emju)bpqmbl0) 9: 8 db 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 solidl-y+q nydf mh*f.m+2i with a weakly bound cubic lattice, with each atom connected to six neighbor.liyy-m +df+ 2h *nfqms, 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 uxvey:u0 f ghn5d14x m8n2l)r1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a pot u:ndl0uf14x vn)y5m r e28hxgential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light with w lm1 eby*76iwbavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap betweeb7mb* w1 e6ilyn the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light vhvlzy ;3dri gk6tts+ s:);)e. If the detector on the TV set is not to react to visible light, could it make use of silicon as a "window" with its energy gasz l):6tt+vvr3 kiy )dge ;s;hp $ 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 s x rtwp,x24 xxcfy0+b918r1pbehzy x 9ilicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground s+xyy,e8xbt rzhrx1941f2 w 09cbx xpp tate, 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 wat:f1bxyj(h cm8ue)b /velengths shorter than 1000 nm. For a solar cell to absorb all f8btec u(x/:jy)1bhm this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semicon dofq4:+4qbwkgjr)qw8mcb8:y 0vem 0 ductor, the longest wavelength radiation that can be absorbed bd:08wqygvb cq 4keqm4f j 8:r 0m)wo+is 1.92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs becai.+ke npq ;p-bb -c5dume available many years after red LEDs were first developed. Approxiqi5bnudp +.;-ek b-cpmately 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 voltage regulator is :o+7uegq5jav2g7vmu 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$