What type of bond wom4)l gcpbw1 or+rb/d,uld you expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molf/y d8mox ec5o+l8rm kcf4r8/ecule $ \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 ;n4;pmdohh) 5 be2mr 1h:fptry ad.md2zb8 .d$ \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 x03bapvrd a6t w -vh (o4d06z -ev;edq0bf xr9are they?

  Would you expect the molec r8zojj md9-vrmpz;q5 9n+9ajule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atom bk(sm)- t6ked ;1vs bcgm; *zr($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are fr+d, idioo 3d z+e4ybpya* qxrk 5(m/y2ee to roam about in a metal, why don't they leave the (/p* 3deryq5 42+yox+obzy dd m,aikimetal entirely?

Explain why the resistivity of metals increases with temperature whereasp 3d -ud8bqfm .d,0iyx the resistivity of semiconductors may decreaq mdu f8pd.xd0b3,i-yse with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the curro,r7aryo3s0 a+ hols*ipz5,oent is rectified and ho7olo53asyis op hr*or,z +0a, w current flows during each half cycle.

Compare the resistance of a pn junction diode connecteo6wepyw-/p t6c h8o s,d in forward bias to its resistancepp/ wt68 s ow6h,oe-cy when connected in reverse bias.

Explain how a transistor cs igpxjq:czsru-e jrfu 6v875s 29 ,+could be used as a switch.

What is the main difference betweenz p/:na;9eyam * hp;fo n-type and p-type semiconductors?

Describe how a pnp transistor can operate ahzq b -w1h7xj,s an amplifier.

In a transistor, the base-emitter junction and the base-collector jun5(th0 - vvmk*3 ercvwaction are essentially diodes. Are these junctions reverse-0th*r-v53 mva wc( kevbiased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electr.y , r;n tz:/eb0jrermonic signal, meaning it can increase the power of j/r.ryz; r0te me,:bnan input signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will thevuxc+ ;j*0l,w5gqk+yx . dgwkse atoms be donors or acceptorsd x*kuvg,yq+0jx5c; l g+wkw .? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yem;fz fu6 -.xlds|no}

  Can a diode be used to amplify a signal? p98o o76wzovdv j,.wf2 pyu) pExplain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating ok/ /)zus )y0.qagtbk the electrostatic potential energy t.u/0/)qz sa kogb y)kwhen 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 result ;acud6;1sh+l jk tsite;b+.y lia ,8hof Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the equilibrium distatj+6lud bas h18i k+ye;;.,hstc li a;nce $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energsd kz jlf,o42e 1c z)ve*(xac,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 expxn;gj +3l r7a5x k:rw2qt/4 y8oxaheb 8a :fcnerimentally 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 mole to eV per mole+/ca r:ofqerax 5k3 4gwa:n2lbjtnh8y x 87x;cule? 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 8:qs:eg-r 0twk5.)i(u* er nmhnltl r that in the text for the states in the formation r)mrk0(inegs lr-t.*wtn: :hl5 qeu8 of 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 on 1b-tr l pz+d(jx84nyyz9o($ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rocrgiri:aiw6r( b3k 97 tational 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 characteristiccqi n/5q7tpc 2 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 l54dk 5x h+id(l5xecoin 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 gi6xa xqf ah 1.cg5vglj0h8*s rw cj3-w1ven that three successive wavec18 3 l .wsw*rjxh1ac5-f q6aggvhj0x lengths 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 )1sfs-rlp6c8 cf a: bwthe 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 neigc8t)3n;*z(ox+ yavm ubkzoy0hbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing beyoa)0 ;xc3(*ub v y8+mzkntzotween two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a de/lo 5-c/0lt(jvjnmjus15 njk nsity 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 density2 ph,* wuqwz8r is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy 7bisba/vc c6 +bands why the sodium chloride crystal is a good insulator. [Hib6c s /v+7abcint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequencncu04.kk j2n g8r 4ilky, begins to conduct when the wavelength of light is 640 nm.lkkni.j 248r4ng 0ukc Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electronnyi;34oi2)v- o h b ofwllhd51 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 germzw.3vr b/6,9 iwgk-wruw+ dlcanium is 0.72 eV. What range of wavelengths can a photon hawz,cd wbuir963 k- .v/lw grw+ve to excite an electron from the top 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 arejp t a70e ou7nwx 4lr2yz5)p9z $ 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 phosphorusu; e ps94 mz,5) mdu+oy+nfuix so that one silicon atom inf4+ u i m5,e+);n9xdyozsmuup $ 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 fmhaw1tl de;xoswoe081aez8 : 9 ae+d-rom a material with an energy ga90: +d le;8weos1e eaw o-m8dz 1ahxtap $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits lighpter nbf31s1ems 6 *2lwi39etgc g.-gt 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.v-dw1(.ht) trynhz i d6 ea:0x Below), is connected in series with a batterey- xhta w(nh)t0dv 1.d6i:zry 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 to a v-w*mwg 0+mn ejpkr50$ 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 ad z1cep30jr z,pl 7lf* 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 very roughly the averagb 9-7 wbrhyi4wil 4k*n2k*bl ue current in the output res7kr49i b 4*hl*bnil2k wuyb-wistor $ 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 forwoa.vqycdm-p/4 90okc wa 1wn5ard-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current -n pao.9v0 m4a/5y qw1kco wdcin 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 boo4u)b jv3 m08kt6 xhbe rectified with a full-wave rectifier (Fig. Below), where4 jxbhkbmo6u3tv 8)0o $ 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 equatzhlac4 s e( 1ddybo+6 zyugm4v- 1k1d9ion for the relationship 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 the cugmn l, a/ i0 b/ r43+m7p.x2gozdvds$ \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 )j rs0ya;b hl)o7.p czan atom or molecule 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 sepa3ero 44/ kxn*+n szzdg vk-ps1ixt07sration 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 monoatomiurx,vueqa,-qqf;)5qv ,f 1 xtc solid with a weakly bound cubic lattice, with each atom connected to six neighu f1v-ru , )e,vfxq,;qaqt5 qxbors, 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 ,arlawjojel4)1 d+5d eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curvej1a 4awrel ,l5odj) +d for this molecule.

  When EM radiation is incident on diamond, it is found that light with 5co(gw1p8 fsz xzk5+c7cjwh;wavelengths shorter than 226 nm will cause the diamond to c78p1h+gzcc5wfzo sj5;(c x wkonduct. What is the 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 is not tox)y,*flvt 6km u xh)d*00dc og2lvv1h react to visi 6ddk0 v*cft1o*0v l x,h)l)x2yughmv ble light, 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 donor atom in a doped silicon semiconductor, assume that the "ext)3kyfdzs;banxtw3 v;9( f .yhra" electron moves in a Bohr orbit about abf9vf nz(ht;.sxw3d; )kyy3 the arsenic 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 :xl00h- utfbe wavelengths shorter than 1000 nm. For a solar cell to absorb all this ebh-: ux0lft0, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, tjxiv6irdmhtv:59 9x *he longest wavelength radiation that can be absorbed is 1.92 mm. Wh69xxr :th5j im*vvd9i at is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many yearsx(f3 zepvpn+;wx r d(7*9 b3hx,c itel after red LEDs were first developed. Approximately what energy gaplpw+;xc(3(73 h* beexvf np dizxr t9,s 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 inyh)2tsg v9(k qh)6g(j0ien hq (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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$