What type of bond would you uxkjk1n 2uv81t1 r bn5expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molec0r*eq ;l)f sqcule $ \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 moleculez(* kzi+3i+4lk pxbs c $ \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 categolez r ,28ua+2k7etipn8f tlz6ries. What are they?

  Would you expect the mol+ hrgqh b:ba 5z5sfa:vsj 9y84ecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbozee0,jh9efj; t z 2q2jn atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't theyib*(nlk+ we: :ht6zik leave the metal entilkn+:w z(6 k*:teibih rely?

Explain why the resistivity of.0dfj, + a r11vvfqlvw metals increases with temperature whereas the resistivity of semiconductors may decrease with increasingjq flfvvr, da.v1 w0+1 temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how tr; xeqbf me 4)25iwop)he current is rectified and how current flows during each half cycl 5ew pb4 2rqi);o)xemfe.

Compare the resistance of a pn junction diode connected in forward bi +3o2uw nm2ritas to its resistance when conuo twr2m2 +i3nnected in reverse bias.

Explain how a transistor could be used as a h/+ k,ysoa(o;xwc;m v switch.

What is the main difference between n-type and p-type 3 r*poj3u/r vosemiconductors?

Describe how a pnp transistor can operate as an ampipq1/) z g2irnlifier.

In a transistor, the base-emitter junction and the my6d/ b77lhww;f 8aj /1wqpkgbase-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Be 68 bjy7pwkqhl1 g/fw7 /wmad;low)?

A transistor can amplify an electronic signal, meaning it can tmtw **b-g r.iincrease the power of an input signal. Where does it img.t**-bw trget the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms be donor+v*yxr:g:n; f o/0lem;loaw: md3v kgs or acceptors? What type of semiconductor will th:nel:xkg 0v*+/ w; d aomo;l yrfgm3:vis be?

  Do diodes and transistors ft.0jd xs;p.i obey Ohm’s law? Explain. {yes|no}

  Can a diode be used to amplify a signal? Explain. {yfmto6sawrcm/ j 0,w5 2tc;r m3a8ed7ues|no}

  Estimate the binding energy of a KCl molecule by calculating the elec ekb +86onfwtgdt(abfiif667;11ezr trostatic potential energy wfd(w1 riztn7ff +kabt 6; oe1ibe 66g8hen 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 enqiffix 79/u1w 6quwv, ergy of KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the uuqif7v fx 91 ,i/wwq6repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of th:9k2mb hidy 0ee $ \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 nkpqa+g+j 6r8sao9y ) experimentally in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What is thpkg6s9y+8+oa nqrj) a e 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 4y4xyqzg e4-;bieilda. ) kb s37fca,to that in the text for the states in the formation of ti4i3 zys;e4x7, a)4kalb.de y-fb qgche $ \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 quantityrghz pgu(2l a,;-)g db $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic-s14ppiv n ad, 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 rotational en kv m,t/8q, jj:q7n )omt5pusnergy, $ \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 thenfh)-u 4pkd6 s $ \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 that three successiv yl 8;gikcxr8 +m0mqob ah+8f,e wavelengths for rotational transity80o;fqi mrbxk, 8hcl+mag+ 8ions 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 ttwvp-gj4 *2yqmb6rohg q84b*he 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 ci*ahguje120 l rystal is 0.24 nm. What is the spacing between two nearesu*ji l2eh 01gat neighbor Na ions? D =    nm

  Common salt, NaCl, has a densit /wyt,*vnkl 5jbk 5;n 0kjsa0my 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 w)fu9yab x hgocy9*n *c 6ib6n/hose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is af0 9klv0u(qt m good insulator. [Hint: Consider the shells of t(m9 lvk0f0 uq$ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, bwmddz-qnbm* 9 cblb jp-z21 3:egins to condu:c ql d9*2 d1pbn3b-zmb-zmwjct when the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelf812;x duhfpi ength 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 ig / sxzr vz8h c;hbyhu2)sqsq 4252-+jq- qibxs 0.72 eV. What range of wavelengths can a photon have to excite an electron from the toqzz-q s5 uhqg ;vsh)sb xy jcb-h/ +xri8222q4p of the valence 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 : :3c6u*td8:u oz6rnmnu mgvm$ 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 s9 *4aod.931k;fortuss sm mb lemiconductor is doped with phosphorus so that one silicon atom brm9dmlo.1 *3us9t; oss ka4 fin $ 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 made from a material with an enel ljt t ,-zi57xg;hjbi/surfd5,zs*- rgy ga zxf,li;u5/j*g5i hjs,- rtbd sz -7tlp $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of waveeq.0:kdyh13zb so4 lx(g:k ( 5hwj kzslength $ \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 chara haj kjr1vwhc.);+n9ycteristics are given in (Fig. Below), is cn+h; v .y9khw)arc1jjonnected 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) it,7r (b(;wm/ tyz+3 kc:)df.yptplz i )yujnes 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 resistanc:ws4 n6e. nylwe 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 rectified. Estimate vk / o 7x/;c2x5gqctuqaery roughly the average curreqc7x/tck/ou ;xaq 25 gnt 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 ihdtpu :q 44dfe 7/y948lmavnbfx(: ag f the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the averdu8qheg: a vmp/f xty(b4ad7 4n:9lf4age 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 tox: qvrt4ds:yt* ql1 .fl1 y,th be rectified with a full-wave rectifier (Fig. Below), wr, : l4 x1t:1yfdvtq.l st*hqyhere $ 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 relwas*3 di;wf j(ationship 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+t +bf*1w k7tgb0xa f4g nj -jymx-k1k energy 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 isykeom7z jyt ss35/ * /(svz4as 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, t+5gze10 s8f+s,umfn .fbbh y fhe separation 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 t(. z2cked: *ed6ko(o9bwv x-r7gxu e )pivo6with a weakly bound cubic lattice, with each atom connected to six neighbors, each bond hapoe9bwct*d6.i2 z v(ov x76)ku oxe r:(e -gkdving 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 1.4t59 wv3lzfcrij zd /+pat1 /)i eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecul v cf 5t+l/ /r3wtii9pjzzda1)e.

  When EM radiation is s dm urm9+ww99;wev q l9sfc-/5spz5mincident on diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between thwsmzm9vcwpq; 9sef9r5wl-5d s 9 /+u me valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the deiap7 g3uvtw2( yb h2wa08yk3ftector on the TV set is not to react to visible light, could it make use of silicon as a "win w2awhpg(0vk3f 32yyi8ba 7t udow" 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 semnu.h; 1wt(yxk iconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, tty1wxk.uh ;n( ake 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 than 1000 nm. .m5a7yz ltz*eFor a solar cell to absorb all this, what energy gap ought the ma5l*eya.m zt7 zterial have? $E_g$ =    eV

  For a certain semiconduct r swrq(69ok2vor, the longest wavelength radiation that can be absorbed is 1.92 mmrk2qw6 vsr( 9o. 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 dez-n-i+4)tqatwcf; el cy(. sxveloped. Approximately what energy g-ttfe i an) clxy(;w+cq-4z.saps 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 iduqwwx7z)+ 1so a7has)p(sft3:v yo 0s 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$