What type of bond would you2 w3-:q )jrai6e ons9fdrqt f; expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mol+r ;0w+4yxs hnt-- lhu+ zogjqecule $ \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;9 *wod6 prpcw0. ycas $ \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 cavai0fw c fv:rz8*h4(ptegories. What are they?

  Would you expect the mof+: kls5m +x2m7x12q d p(f g+qoihjqjlecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon aty1tq*9(9kf ww2gjs f lom ($ 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 leab9eqh nk) x+lek;sc 2 );p)p-btv-f: lpcwnc4ve the metal )p+t4vcnlppk: qebfb)- xe9;ch2c; - wsl) kn entirely?

Explain why the resistivity of metals increasesu5tev*23s8 / rudrgki with temperature whereas the resistivity of uu/r358*i skg tdvre2 semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridg3+tapecg(5 uj39 t hmke-type" full-wave rectifier. Explain how the current is rectified and how current flows during each half cycle3j (g+9p cthak5 tu3me.

Compare the resistance:c9jvlfk8.ym ie hp/-; ejp(u of a pn junction diode connected in forward bias to its resistance when connected in pc:j/fejy9e; 8plm h(vu .i-kreverse bias.

Explain how a transistor could be ushn6y1eh dy+ k +4cc8xsed as a switch.

What is the main difference between n-type and p-type semiconductp +y19q1p8pisnmfg6q -s vx,x;gq+ snors?

Describe how a pnp transistordn4cs .nng2 g, can operate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junctio onimsa 4y6,a(n are essentially diodes. Are these junctions re6a s(im4oya, nverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can incss9 bjmn (2xv/x97 jucu neb98rease the power of an input signal. Where does it get the energy to increase the po/x9uvebjjb(nncx8799s m2suwer?

A silicon semiconductor is doped with phosphorus. Will dl 7.m 0 keas)3tgx-cbthese atoms be donors or acceptorsklxt )as- m07.d gecb3? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain.r1pg:t.q waag u8j1u 3 {yes|no}

  Can a diode be used to amplify a signal? Expm)dcr ax *xez8. ed5o +jlihtu7 7-fpml(m09tlain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrostatic 04neqs:wmi w, potential ene q:wi40nsm w,ergy 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 v5bp4u hz*6x-6bt ofbof KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clb6b6vo5u-z 4txf*hpb ouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energ h//(g5 icuv/o6 hmbqh8apznv.4on x (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 experimenm7zv4i xoa o1-tally in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What 7v4 xizo1 m-aois 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 inqaydc3oqx c1.cv +vbq +2;v3j the formation oc2x; vv1+cac j3+ q3qqydbv o.f 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 quantit e o/g xw-ld09g k io6a5/ays6blum/sbql* o,/y $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational eneroauv 0pt w5u3;ye: 8zsrybbg8.t0c e4gy,” $ \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 chamcp*f p ;v10v0jl v6olz33pfwracteristic 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 2k o:j,7 fyqt e(g huck;-5bhao)i mr 9;wly(ratoms 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 molecule givwxdo,nz:zrvdvz3 53/ r k /:gven that three successive wavelengx3k/v rdzdrzg:z: 5ov,w v3n/ths for rotational transitions are 23.1 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 constant g:9ea6vj6 aj ;o7pkak *d v0tc$ 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 ionsfyaph(h 9d-1v:sr:xl in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor Naah1ly x-s9r:dvh: fp( ions? D =    nm

  Common salt, NaCl, has a densit s iyt9/e5ehj/y 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 wh+az6//9d/2jhak .iz.-l scmcem2qpgr 6b kdzose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chlqg9t(hz.lp ) doride crystal is a good insulator. [Hint.dt zqh(9)glp: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light zv32s)p82qen (b6 ,hdxd q dbaof slowly increased frequency, begins to conduct when the wavelength of light is 64(,6e82d qdb)2dv3px sn hq zba0 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon 8 i- n,t;4vvgvt;aipif c:d)uthat 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 vadc i n2t8j g5s( gwhu1uo9j3jnb .1+uylence and conduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the va83utg2db1o. ynuu w+cjjgshnji (51 9lence band 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 are unufm *(;w;ev/n-tg p4nvxr8 $ 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 semiconducto6b o kgb7ie53ar is doped with phosphorus so that one silicongo eib3b5 67ka 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_{doping}}{N_{Si}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if m1r19 w 5da:c02wik 9 oin5rbwtcg vg7uade from a material with an energy gap giwbodwga9 21rc5 r10nui5 t9vk w7:c $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelengw;t04no(cd k qqu0o,ath $ \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 (Fi 7o 9l u4tfnw)ux7,ywhg. Below), i) owt49ln,huxf 7wu7y s connected 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 co wc4t g)h8hbo+nnected 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 e rq rk(g xq 3gd yo1b5alq( u+0e//fq,5fo3fta function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is bt8 rlhah +9:styd e8z*4)tlh8 vgm*p to be rectified. Estimate very roughly the average current in the output resv a8 t+*dhbh:8 g4ts)t*r lyhlpe9m8zistor $ 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 pass53- fy7gwr vpc0l (vojes significant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimatefryv(5po l3 vc0 jw-7g 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 voltapd)vvm*fi npq6v y5/1ge is to be rectified with a full-wave rectifier (Fig. Bel)dqp m61v/vi v5pfn *yow), 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 bajq tj)cq :2sc6tv2ym1se current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy drf)b*ln :hc: k,uv .mof 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 ab xbgp(a;g 2safp3:-p qout $ 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 separk9 0cb0mj 0pzeml (.rgation 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 monoatomic solid with a weakly j24 dttt no6b i)/qs-tbound cubic lattice, with each atom connected to six neigds/6njt t) t4b-io2tqhbors, 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. x) mxzme.87qe4 eV. When the molecule is disassociated, 1.6 eV of energy is relea7xmeqm .z) 8xesed. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamons8x+8 1za yz7elst6n md, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and 7ynl 6zmz+tss1a e8x8the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set is pveu4nv4+ k4mq9f7cg mxm. .t not to react to visible lcum+qg4f.947ev . mm4vx k tnpight, 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 donorz:)/r, vdnzvc atom in a doped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take intv:z drc,/)zvno 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 than 1000 nm. For u z/+pd++hg)6jcuysu d2(v)ag . bgb aa solar cell to absorb all this, what energy gap ought the material ha(p+d)d gzuagvub+c hu/. b2)g aj+s6 yve? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiat 5ra) mu zhd+.)2cpnamion that can be absorbed is 2 )5dcauhzpm +.na)mr1.92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became availaw8u;ovjk -i pck(cj um(1za;0ble many years after red LEDs were first developed. Approximately 0(mwic; az8c -uj(1pkkvuj; owhat 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 shown in (Fig. Belownwevqf+ xkz4+2001e j )4ofg1blxul w). 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$