What type of bond would you expect for 7 c+eonn4rr6/o ca9pb
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molv c ul8xfvg 2,3p0g3we 2ka0lbecule $ \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 zbnjc4- v ck61$ \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 theb)zsa (ep9im ts jm.2j,1,rcny?

  Would you expect the molec)o+8yh q/xh:b)e 5thm:t xh kmule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon at,emtvg y p/9;kom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why ho.-o qcve( r;don't they leave the .voe(c q-o;r hmetal entirely?

Explain why the resistivity of metj.w mx rph/k,h8no5hxh-z 6c4als increases with temperature whereas the resistivity of semiconductors may decrease with incr, 5 8h wjxh-h 6ocprx4mn/z.kheasing temperature.

(Fig. Below) shows a "h k2lf94gu)b ghb bu(:fmx87 gbridge-type" full-wave rectifier. Explain how the current is rectified and how current flows durl()g4mxbu7fb :2h kh9fbug g8ing each half cycle.

Compare the resistance of a pn junction diode connected in fu*twi:w)- ;lx8 e yvkjorward bias to its resistance whetw-lv*wjx:);k8 eu yi n connected in reverse bias.

Explain how a transistor could be used a tjtg(id :d7f0s a switch.

What is the main difference between n-type and p-type s)a4h gz kny2a*1vox 6f qxg)m)emiconductors?

Describe how a pnp transistor can operate as an ampl- e munake /q0cf)my,5*(uzu zifier.

In a transistor, the base-emitter junction abs ,0 zgi3v7 yafw18nwnd the base-collector junction are essentially diob 0ws f1wi,7vna 8zg3ydes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify frjl h7k rhkuzl823 i5+em1 ;dan electronic signal, meaning it can increase the power of an input signal. Where does d 81m32lfi5 +elhhrk; zkju7rit get the energy to increase the power?

A silicon semiconductor is )/)6w wsy(b9+* ufbndjpt ufidoped with phosphorus. Will these atoms be donors or acceptors? What type of semiconductor will thibnts9 yb+/)jf6 wufpiu dw *)(s be?

  Do diodes and transistors obey Ohm’s law? Explac , jy9b+sl1awin. {yes|no}

  Can a diode be used to amplify a signal? Explain. {yes|nofc(d bdss1f/y) cy96i }

  Estimate the binding energy of a KCl molecule by calculating the yp e ab1xmnq8dp;0+.c electrostatic potential1d;xemp 0ya.pc 8 +qnb energy 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 of KCl is 4.43 eV. From the result of Probel 7ac4 gtdzf*,aa; o;lem 1, estimate the contributoe; aga7cd, ;ta*f4z lion to the binding energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy ofmg8cdk 4 idq7y g x-7338lcrna 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 pesnln. uvy **w3r mole, and then the binding energy in eV per molecule is calculated from that result. What is the conn nv3l.ywu s**version 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 tn9ole*-ofr b 4 8nnay;ext for the states in the formation of theafr*o;4 bn-ey 8n n9ol $ \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 quantity4/sw6-b .ymkthcf li)gp ht4 4 $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristi;hl *+*qrt -8z 8 *ivew ezlrdeo,rulr(a 5f)tc 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 el , qda;bfv5n0oaf n21nergy, $ \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 separat 38ag9lx xzsf(ion of H atoms 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 given that td3pi)edf ad64pp5 p t,js8l 9qhree successive wavelengths for rotationadp54i ,)ap 8ptjq3s dpf69de ll 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 8s2r6yd gm9 aastiffness 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 NaCa*+brupx5 /i dl crystal is 0.24 nm. What is the *puax+b/ 5d rispacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, h: (ggy6hbg r8)emhn*x as 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 o-fzt4 w5lrxnt/,jg h9 +qz)w whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of5s8rc g6g ropgd8, 4 3ejt+dccaqn3o; energy bands why the sodium chloride crystal is a good insulat5;ojdgcstpg3drn o+4gca3q r8 68,ce or. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with ledb 7dtq7a+:pight of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of thb:t +7pdq7edae energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelengw6pxh y8d +svsk 9r97nth 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 betweene8(hyp4)m,rrjg5b j t valence and conduction bands in germanium is 0.72 eV. What range of wavelengths can a pho8be5h,rr )jtj 4p(y gmton 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 are:0gv6wchl y;o,gw3 fk $ 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 one silico s3-1))o iilsurl ya,ayil)lr31 s asu-a)oi,n 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 made from a material wbvh1(l6bzoln*9 qb:20 xvrbc ith an energy gap bq(blx c*z0l:o6921rb vbvhn $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light o2-x cjh; 297; -gwbc5us3oszzv biirnf 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 (2c :* va3j*nvynp+c(qpg w tx:Fig. Below), is connected in series with a battery an v2gq*y: w t3xnjc ncp+a(:v*pd 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 ilu leq u4a;36to 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 function of current, rus8gpzt5o5: xyixl4 0 lhj4e;e2w+lfor $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very roughlnf 34,viz7 sfn*6nhl/5 -w ew jczid5ny the average current in the outpu 5vc,nnn5ndww 6es3*zfzi-7i/ f l jh4t 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-0u5my phv:zomlcm /i n0)-rb 4bias voltage exceeds about 00-p m h0m/znlu c)4iobr y5v:m.6 V. Make a rough estimate 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 voltage is to be rectified with a full-wave rectifier k5yg6u 4jopy2(Fig. Below), whgjyo 4kyu652 pere $ 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 betwf )c,ed.c(zrv een 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 thz6yql 4k bgm+jkkm; 9msq q;52e $ \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 translationz;p2lj)q:; 5 gq 3 hzjse4; zb rff2nx-y2xrdyal kinetic energy of an 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 -kwf,s)tv(k lseparation 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 bound cubic lattice, with each atom cisgc 7a uwl ,6;*s:dtmonnected to six neighbor:,u76 s mt*sg lda;ciws, 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 atr/7 nubz9nu)n activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule. bu9z)nr7un /t

  When EM radiation is incident on diamond, it is found that light wslmgu0 i 6,h(4mh0zfcith wavelengths shorter than 226 nmzml 0cfih, u6hg4(s 0m 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 deteez1shfqo rh8 aa.q0yo--3r y:ctor on the TV set is not to react to visible light, could it make use of silicon as a "window" with its eneryo1.0:8 hoz saqahrr3 e-fq-y gy 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 qyldz c-i,:+b pb)sx;silicon semiconductor, assume that the "extra" electron mo:z)p;qixly -+dc s, bbves in a Bohr orbit about 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 wave hb:wl ow(uhs 0e;+ld2b-3 o2uu 9olnzlengths shorter than 1000 nm. For a solar cell to absorb all this, what energy gap ought the material have?ehdb2-o (l ;luu3u9l: ow0ozn wbs+2h $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that caod.( lrn6;s e0+tsohnn be absorbed is 1.92 mm. What s6lne;hnd 0. ros(+ot is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became availablezocgtorpa( * iq1 3n(0 many years after red LEDs were first developed. Approximately what energy gaps would you expect to find og a31*ro(c( p0qtzi nin 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. Below). qrlvogbtl 4*js*+/6,i euq9 m 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$