What type of bond would you expect *vv7kj,qx x x(for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecul0 v1w+ ibah0dhe $ \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 h8pj44sf 0zf6.v c wmf kpa y/cd5a*t.$ \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 int2qc ljjp;yg84zhfj 9 bb0qyh(y ()1ifx kz5q1o four categories. What are they?

  Would you expect the mvmixw :.7.vm lolecule $ \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 (dp-rbvszg6n xo 2k62u/rt ( l1$ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free t.f* h2sgluui,o roam about in a metal, why don't they leave the metal entireluiuf l2s,.g*h y?

Explain why the resistivw3 k:w2p4;wh +h.knhe/zlm sda wd ,b/ity of metals increases with temperature whereas the resistivity of semiconductors may decrease pzhn/wk kwe:ds m2h+l w .d4;,/b a3hwwith increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rex:pzyxlx.lc rqr7 m 5u) a04s3cvd)x 5ctifier. Explain how the current is rectified and how current flows during each hal4ux clmz:)d.sa q x35 y)lp 7xrc0rvx5f cycle.

Compare the resistance of abl2(wq l6 inuz:dn:r 3 pn junction diode connected in forward bias to its resistance when connect26 il q r(wnznbudl::3ed in reverse bias.

Explain how a transistor could be used as a swit 2,xefp-7 evqbm/7t r wva-eg6ch.

What is the main difference between n-type agnirf,6wl e+ij.zi, he tg b60yg18j9nd p-type semiconductors?

Describe how a pnp transistor can operate as anmuo*g 236xwyv2n l3 rm amplifier.

In a transistor, the base-emitter junction and the base-collector ju5c1xft 1ma11lb . irsxg9xz u0nction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (ax5x1bg0.s 9x1tr11ci zfl umFig. Below)?

A transistor can amplify an electronic signal, meaning it can increase the powe00tmxcv(/ umctclh19 t oj p21r of a/pmtcc9 h1vt(uc 0l xjo21m0tn input signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms be donorgr3g2*bc4 c brs or acceptors? What type of semicondubb2g cgr43*cr ctor will this be?

  Do diodes and transistorr. o9xl fb5yt(s obey Ohm’s law? Explain. {yes|no}

  Can a diode be used to amplify a s) 2ji+odtdj2) nsoft-ignal? Explain. {yes|no}

  Estimate the binding ene62ezijmxpd/0 cnv 0 6prgy of a KCl molecule by calculating the electrostatic potential energy when tj0 p em/6zcp2vnd0x6i he $ \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 ofs5wki:-db k4vewwq.p 8 t)bo * Problem 1, estimate the contribution to the binding energy of the repelling elect-qwwk8 dpt: 4si.bko* 5v b)ewron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energq f4up;x/,nqfd- nt/bj46 at ky 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 kcal pex did(l2 c6*vdr 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 molecule? Wv i*6(dlddc x2hat 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 states9vn3 a(/04 rzkojgl aa in the formation of the 0/n argzal9j kv3(oa4 $ \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 .7 wccnvoh8*vbd5-sg $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristiu7k7cndcr*nal0p l18j/l 3suc 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 energyzks53 e db9y.fe 96pmz, $ \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 lkdpz z0 k772wthe $ \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 NaClsh cpk7lp kmd5-:-0 mxwk;4zo molecule given that three successive wavelengths d7skcz4l5:hx-mp 0k w;k m- opfor rotational transitions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fi/nzekl l3b+j: g. Below) 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 and Cl ions in a NaCl 2q/t x4eqf0h: sqpw t,crystal is 0.24 nm. What is the spaci/:wpstqt f4qhe q0 2,xng between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a t e:7;fsm tj6fdensity 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 densi7 q b)))fdjguz)5 kxxjty is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystub0 ; ycwgnyytv+flcu3o.9.ho3)x:lal is a good insulator. [Hint: Conl;nct . v+y c3ou)g byufly:wox9h 03.sider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, begins tidg j qz( rqp,5y9e l/f-b)(dxo conduct when the wavelength of light is 640 nm. Estimate the size of the energy gappq(9i/dj5yq ( glfbzr-, edx ) $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can gt1gzup)y 2z *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 german.trpw 4s z57pfj.c(.e;t;xdy;jf xu bium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the toft x zy.ctrjj(.pspxu .b5 7;d;f; w4ep 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 jyg-7o4sb4 t g8k3ivl$ 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 sili dk2,k1kw5b ghcon atom in w5hg k ,d1kkb2$ 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 LED radiate if made from a m v/qo,luvn l/+aterial with an energy gap u /lq+n,o lv/v$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of os:c s jqh6sv w(jqt*m*;;zw-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-vol(6wbn u6a htd9l/19pagwvbo 4tage characteristics are given in (Fig. Below), is connected in series wng6d t1pub9a/ 4la(9ow b6hwv ith 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)p c8mh2sty44j 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 as a function of current, 2yde.i6xhmy5c x(z/s for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to blr8 0i (.ydlhbe rectified. Estimate very roughly the average current in the ou r0l h.8idyb(ltput 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-bias v4b v)fkm)7e: s8 e,afw1q fduooltage exceeds about 0.6 V. Make a rough estimate of the averag e ous7m)kq,4 vdfwb8a)ef1:fe 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-wad)uqh 1+wa*da;wspwry )8/yx ve rectifier (Fig. Below), w+s)yydq*); 8h w wpwa/dx1uarhere $ 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 abz8p pzgh ef6(94( mfmn equation 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 enerff;r;/yzi nlngy: ;)smo sw85,1o qgdgy 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 abod * /hf rrmih/fjkq;zip2- 96aut $ 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 b (v*,92j sebj i,5pkihq7pue metween 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 wexzcpq4 -2zuq )akly bound cubic lattice, with each atom connected to six neighbors, each bond having a x u 2c)-qzp4qzbinding 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 ze p *i1j.h9wo1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy cuzojpw* .h1 ie9rve for this molecule.

  When EM radiation is incident on diamond, it l mji9 x6qs)i;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 conduction banj i s;6m)9qlixd for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set zw : 4pgf kr:0eqj g6o2f8(sstis not to react to visible kq2s(z:t6rg egsff j:o048w p 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 thi:vn wut2j m 45gkbp:+r. rwc8at the "extra" electron moves in a Bohr orbit about:w:8k.cv2 b4jnrtm +ipr5 gwu 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 wavelengths shortg5jg1 fdntq 23er than 1000 nm. For a solar cell to absorb all this, what energy gapt1 2g3j5fgndq ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength ra 9 eyhgk7r lt;x8jy.; 4y4amfwdiation that can be absorbed is 1.92 mm. What is w yh.xy4y;am lkjt79 ;8efr4gthe energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were fir+-sox2*wzaojz 1qw/t; n/ mjkst developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue (465 nm) LEDs? 2/jxzqk mot1so/waw +; -j*zn
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is2g8 ie1 wbzi-x:xbr8a 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$