What type of bond would you expect0od-/tzh cuwu j,7g1p for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mole:w0 z+ ipwe c:aty a+cvb;r:ulyw(e68cule $ \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 moleculefnl,yj9fdob+6l o , 48zr9vo0xwg3ug $ \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 dividedea9q2gto w 6,e into four categories. What are they?

  Would you expect the m tq5,/b*5 u.a -osdfddpewg+h olecule $ \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 (6.my: /qx q)ci4fi cf;ipy 1sm$ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, n;p euu8b 97yyup kf4,why don't they leave the meeny , pu4fk7b puyu89;tal entirely?

Explain why the resistivity of metals increases with temperature e8ikqv9(s j(r whereas the resistivity of semiconductors may decrease with increasing temperatqvskr(ie 89j (ure.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how tnsuf (sfmog 5+4;uyo5 zwq)(e he current is rectifiey55fmue o;w4on(g s )( sq+uzfd and how current flows during each half cycle.

Compare the resistance of a pn junction diode connected in forward b xl9yh(cy(hf/ ias to its resistance when connected in reverse l(hyhfxy(c9/ bias.

Explain how a transistor could be used as a swie d*,x68 * hd80ksybvjhk ipu-tch.

What is the main difference between (xiiss7p r3) u.i.xa 9hvm8vf62ig7 jcs f* krn-type and p-type semiconductors?

Describe how a pnp transistor can operate as an vuydg 4k1o4:kamplifier.

In a transistor, the base-emitter pf +n1 7tv kdb+c6:uamjunction and the base-collector junction are essen ck1+vf7 bpt6d+unma:tially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can insj/3;w cfq+o7noa6to(n- ra n*a*peocrease the power of an input signal. Where does it get the energy(e t no6;7n *q+aaroco/nspjao*3fw- to increase the power?

A silicon semiconductor is doped with phosphorus. Will thes lwii7xz, asb a7+pjq:o,9p 1ne atoms be donors or acceptors? What type of semiconductor will thiqi9wib n,a:s+p7j7x1lpz , o as be?

  Do diodes and transistors obey Oh dxb dq)(,jfip ple7sbj29leb1)+uu)m’s law? Explain. {yes|no}

  Can a diode be used to amplify a signal l6hwa.do * eueldwgll(p578,? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculq77)(an m7a 2.solgxmich* d nating the electrostatic poteqi*sl honc772x7 (gana d) mm.ntial 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 r ),cwmh de20wc3w5o(yrv; 1qweq 4iseesult of Problem 1, estimate the contrib(vhm1i ,c wwc2eo4)53qqw;s0re d w yeution 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 of t*qz yrzq f 6xj)tw4. wgao.):ohe $ \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(0eu qnvung30 per mole, and then the binding energy in 0u3 v(nq enu0geV per molecule is calculated 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 the states i *j ; c1f:mgp.em0mqymn the formation of .m*f0gjye m ; :mpm1qcthe $ \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 4f 29 /h,m ;qv .ddeu3nrwyxvr$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic t*0x j/zmy03;7iu :c unihlelrotational 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 ch5dbrj2eh 8i(flnd n8 1aracteristic 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( zzq ia8*3t tl3j3ugy 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 thqj.m33:,;+ekcxrao3ovmt0u( 8 )p otgsge hhat three successive wavelengths for rotg3hees(8ugrj ot)p hovk0 t m3m3xo +c,aq:.;ational transitions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. v) ssq6 xh1wwospep/gn2 k2:e-+;heeBelow) to estimate 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 andc kqg j ,4jq5ut)l flc --dcq:5.ldn8c Cl ions in a NaCl crystal is 0.24 nm. What is the spacing betq-t, g q qdl4n5fcc8d j.)c:lc5k ulj-ween two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a densube9y/ ieo (-3ks(+b+kfpau v ity 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 :emn wu 8y h,7;m9.c(;judm s9touvzndensity is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal 0hqdys7 ly-e -ycp1s0is a good insulator. [Hint: Considy lsd sqyyp07ch--1e0er the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency,u(d 3t 3nqyi30 qem)em begins to conduct when the wavelength of light is 640 nm. Estima 3ie( 3qm)tymue0d3nq te the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelen5e tkomj*mbu3/ py9(k gth 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 is 0.72 eV. Wh;s a yap(de fd02g9uz36 (lcrqat range of wavelengths can a photon have to excite an electron from the top of the valence band into the conduction band?gy lsp 93 0cz de(fr6;(2aduaq $\lambda \leq$    $ \ \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-iukmlh 0ds*w e57h 3g $ 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 phosphoruspv-c.ww6u45ijh- )e2caf zn b so that one silicon enhbwi-f6cc4 v pw-)zj.a2 u5atom 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_{\text{doping}}}{N_{\ce{Si}}} = $    $ \times 10^6$

  At what wavelength will an Lq j-m npm+dz* c;nipxi9*3rz+ED radiate if made from a material with an energy ga imzjnpiqcn*xr;z +93*m +dp- p $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelengtzl; xama3ga; j9p al;,h $ \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 mmn5w*x td z; gi14.:hkxeu;rcteristics are given in (Fig. Below), is connec;xg1h;5r mdu4i t.:mwn xkez* ted 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 az2xrsevo6) *oyod4/. Below) is 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 resistance asw,yj:ys ish9i yk7:xsf3 1il 2 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. Estim.wq8(g zus/:xw am2dn ate very roughly the average current in the output resistor(mu.wz /sd2gawn 8qx: $ 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 sign5m,.qj 3fs8w4k/uyb 5 ltac1dgs:b g vvtn95nificant current only if the forward-bias voltage exceedabtn,nv. s uf:3qlg 9 ygwsm54vc b1d 85k/5tjs about 0.6 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 voltrney;djg1k/frfw k cqj -33.2age is to be rectified with a full-wave rectifier (Fig. Befgrc k1-/j rjd.n;wfeqyk3 32low), 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 rel03td2 ex9hzir-.fhbhj upio v5 ,1h u5ationship 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 e +jvut31wz2 bhi rwjb;1991k abb8pqanergy 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 is about )g7/ a 9 pcwu8tq/pbr9n.pp jo$ 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 0.2/i6lwy*kmefs* iovdz. 3p x.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 boundvp- u: p5uy7tcfv 5e,1 +y*ne; xxtzxj cubic lattice, with each atom cov +jytxf eepz;:ny5- ,vt 1ucp57*xxunnected to six neighbors, 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 y x :yvp2 icgr7k6m5/phave an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy igy:c7ipv5py m kx26/rs released. Draw a potential energy curve for this molecule.

  When EM radiation is incident ondei 4l(2ax wg(egns (x8)dg 4v diamond, 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 the conductiog4)8ewdxnv 4(gxdse( 2ga(il n band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set iziwx o:4py jy/yfrut.p0/ baq0k1q29 vdh 2-w s not to react to visible light, could it make use of silicon as a "window" withikuhoy trjw40-xqy1w p/2. b9:/zq2d0 fvpya 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 semi 1vcke,:;hb2ucow h64dlt r j8conductor, assume that the "extra" electron moves in a Bohr orbit about the arse:d; j,tcv46 ech2boh rulw81k nic 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 waveledmd 6yog7;zd mtr/(o)ngths shorter than 1000 nm. For a solar cell to absorb all this, what energy gap ought /7ogmydz (;tr6d md)othe material have? $E_g$ =    eV

  For a certain semiconductor, the longestq.k 4a6; omtk+k7tgy g wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this sy.m toga7k+6t qk ;kg4emiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years xn. xlm)v8/e1sn ;lol after red LEDs were first developed. Approximatex l/).ev1onx lm n8sl;ly 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 uagqz msom:*cpdw nkj;x;-()qw+y,, is 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$