What type of bond wos: hw13 t1dl.k*vu cujuld you expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molee qskv: z4i*xz7;;ee0o0fdi yhsn 3+ucule $ \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 moleculo3j6eudp0,e ui4ww ( de $ \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 are(ixaw(,:ufwa+uan p(/ha u 7w they?

  Would you expect the4uayohx8z mryk(,,p)vb m5+g molecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atsgke f*hz2mc m3a* n3-om ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam et tkq/3238 d8crz;fqsajli1about in a metal, why don't they leave t283kcj/qztr8s la ;tq1e3 dfihe metal entirely?

Explain why the resistivity of metals increases with tem3eji8 qg4im w5perature whereas the resistivity of semiconductors may decrease with 43j iw58 mgqieincreasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how tf1r.ly gahvi:o ib+8 7d7:7reuqih h6he current is reciiu+h7.6 1rfhbvrqd8oe lhy :gi7a7:tified and how current flows during each half cycle.

Compare the resistance of a pn junction diode connected in forwar bxwcf a-q)q/1d bias to its resistancex /f 1q-)baqcw when connected in reverse bias.

Explain how a transistor could be uz*q8 a.rbn *thz-1hn lsed as a switch.

What is the main difference between n-type and p-type semiconductorpmq3 gwc; zygn :8*e/:4bupuis?

Describe how a pnp transit b3pjue :5 daj:),zwkstor can operate as an amplifier.

In a transistor, the base-euet 2h 8wh3w-yr2und9gxpjq,0 l er* /mitter junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the app/l2wdwy 90rge q2 *nxjt3p8herh- ,uu lication shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it cas9h5 hn t8g+m7h70sgclxyklzv. 79og n increase the power of an input signal. Where does it get the energy tosm5hgvlg9 xo ng9t0 y77s z h.l+hk7c8 increase the power?

A silicon semiconductor is do)rb; rps;2zjidr2:jg5 sz sm0ped with phosphorus. Will these atoms be donors or acceptors? What type of sems )p jsgisz;j5r:z b2r;m0r2 diconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yes|vjj9*msx - vf-no}

  Can a diode be used to amplify a signal? Explain. {ye5zltxoyo2 +.j nis6p4 s|no}

  Estimate the binding energy ps1n 8i1th7 ri0rfi*f3 t6chb of a KCl molecule by calculating the electrostatic potential energy wh rth13i8rh17n0 *ftsii 6fb cpen 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 of Problem 1, estji/,j; )qpinb 33zmti imate the contribution to the binding energy of the repellzq,bii3 ;3i tmjjnp /)ing electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding9: 7 zlz9ndux yllj**a energy 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 kcalt34nxz 0ra j2htwoj, 7 per mole, and then the binding energy in eV per molecule is calculat h4zxtojrwt 0,jan 372ed from that result. What is 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 h 3vyn4suv5:pd.awyeim4)d,r ra1 m) the states in the formation o3 uda5vse,ia. mv yhpr:)y r)n4 1dw4mf 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 ik11k6lv ss9vy $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotaid -rzagc 6,7ational 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 rotawkgmg w4((+do0giz7w sg 1sq(tional 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+ kv5c75daw bo 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 lnr.ziua)n( 1qength for the NaCl molecule given that three successive wavelengths for ua)nn .qz r1(irotational 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 esttmj31 t qiqhr.59;c hpimate the 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:z y9c ;5zwgwi g*t(ea )viav. Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two ne;ai5weivwzc)*zg9av. g :t( y arest neighbor Na ions? D =    nm

  Common salt, NaCl, has a r53lo-ad8m lm 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 fo*v sir4g/rk)y z wql 6k:1h*bvr KCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chlorigoc8 zbj1xg cy);9t 1lde crystal is a good insulator. [Hint: Considerz9) t xo 1ybgcj1;8glc the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, begin.y256u mymxf is to conduct when the wavelength of light is 640 nm. Estimate the size of the energy gap 5.fy2mx ym 6ui$ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an el z4ux6h9hb0 acectron 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 valey4tobjc(a ,n 8nce and conduction bands in germanium is 0.72 eV. What range ofj(,8a n4cbtyo wavelengths can a photon have 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 are8k hif(bc 8ruc;ft8cjpt8 (.7df0xlr $ 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 t jlk-2av *jbv1hat one silicon atom i2k*v 1vbaj-j ln $ 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 fxb vpd f0+1,vwith an energy gap x,vvp +01bdf f$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light oa k b3 0bwt6,2j6csorvf 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 giv.l;tfmff3b 9k en in (Fig. Below), is connected in series wi tfk 9f3m.;lbfth 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 cg rl5n6 ( w);ypor6 r drx-u00)pwonqyonnected 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 a func:/ *md) zw + w2t:xkmk.ynonkftion 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 roughlyu.va 88; kden3i1s(ik5fz 7sro7dzq n the average current in 8ku8 nknz5sofq;r 3vi .d717 s(ei dazthe 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-biaj5m xbw r j1h7ix/59gjs voltage exceeds about 0.6 V. Make a rough estimate of the average current in the output r j 1jxghmb9j5x57wr/iesistor $ 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 wp-4oah/- k j/ h7wwvjspsj1;i)o4hntith a full-wave rectifier (Fig. Below), wheres)jho;jphto vwa / kj4/ n7-s 4hpi-1w $ 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 cu3bbh3d6;+gmd /q a s7co msltn8kvt;4 rrent $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding enerz3 fzn0fa-(m9 vtfr 0zgy 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 molecjyrg-hba *.*fcv6 -y h/t,rvhule 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(cajmm 9:x,t*z iqoh0.27 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 bound cu.s,hui3 e4qnnbic lattice, with each atom connected to six ne nn,u4h3.iesq ighbors, 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. When / iudg*pcq5s03 fedf xrdo + ,9va7sg/the molecule is disassociated, 1.6 eggs9+efdr7d,ocp qa 3x*s 5 0if //uvdV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it p cu1h0gm;ar( 1yx (2+fy clnjis found that light with wavelengths shorter than 2210fnx(;ahycgljp+2c(r1 y m u6 nm will cause the diamond to conduct. 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 se58evd -jnybx7 wl(: xtt is not to react to visible light, could it make use of t7l :x-x8e(vjn dbwy5silicon 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 rzb) 5d7.goyg "extra" electron moves in a Bohr orbit about the arsenic ion. For t5ggb r)y ozd.7his 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 shorter than 1000 nm. For a so3g q wg.4iv-zqa u+xg-lar cell to absorb all g .gqqa gx3-+4v-zwiuthis, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that wsrryt+8 c7:rcan be absorbed is 1.92 mm. What is the energy gap in this sew+8 trrc7:s yrmiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs 0f* ;uwypc sm)became available many years after red LEDs were first developed. App0w;upmy*sc ) froximately 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 shown in 8xcxrw4mkh-aa48f5e5e )b +aza.re p(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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$