What type of bond would you expect 7+c wy6hdmhi( z576h t ,dl,m0 krisqrfor
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule bxjqe 62cjmu/r 8i30 o$ \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 moleculeov: grl:/)tmj s 4yuc2 $ \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 ar0n00g1 rm;i yane*:rsvxqf5 m e they?

  Would you expect the molzfyvs*-vf)70 )mfx lmecule $ \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 (:6uilgo 2qjocx i/jcso((0pa-o n) db4l+dg, $ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam (fls,u 8d xts.about in a metal, why don't they leave the metal entirely?.u,sslt f 8xd(

Explain why the resistivity of metaltqj:lo ,bj4/f06ses1 ,bpn rxs increases with temperature whereas the resistivity of semiconductors may decreasls xn b1f,r6op/qb4st,j ej:0e with increasing temperature.

(Fig. Below) shows a "bridge-type" fult8bpw gwm(9 nl*j bj3 (e sak3;lql61el-wave rectifier. Explain how the current is rectified and how current flows during each half cycle.;1g3wet*j(m96 8ea k l3pbs( nwjll bq

Compare the resistance of a pn junction diode connecteb 7 (tzxj ;isxqvx)b4zawsdyur0e2f 1/8nq03d in forward bias to its resistancevwf8exa1/;ysbxb0z3z)0( 4dujrn 7 sqq2 ixt when connected in reverse bias.

Explain how a transistor could be c*ga f fbi0a;(used as a switch.

What is the main difference between n-type a53+ kaqi: vhqt on:h w2n -5wy0oi:zwdnd p-type semiconductors?

Describe how a pnp tr+ipy-ehd j2;.lw0e 4klcr7 jyansistor can operate as an amplifier.

In a transistor, the base-emitter junction and the base-tdigt3:d t8)jcollector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Belt:d gd)8j i3ttow)?

A transistor can amplify an/6n aywud (fr/ electronic signal, meaning it can increase the power of an input signal. /d n( f6w/aruyWhere does it get the energy to increase the power?

A silicon semiconductor i i(igwzsjx g9e m4,c(7s doped with phosphorus. Will these atoms be donors or acce 9i(xg em gzj,sw(7i4cptors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {ye e4ff/ 4r-01ghbhm)vynvgm ,as|no}

  Can a diode be used to bu4bp ut(b4 yb80q4v)1 zcbluamplify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calc aktqr .w/o: cop7u.fm.;q dt0ulating the electrostatic potential :.u;dpkc tat 0f/mowqr.qo .7energy 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 zl-xfb7;+oi lof KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling elecixol +f ;lzb-7tron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding en e5awy qvsa(et)h 6byo1 497rfergy 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 per mole, u8 rjgik w/3d0and then the binding energy in eV per molecule is calculated from that resultkigdu/38w rj 0. 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 forr5/z7 d(h,ymrcz0r cy the states in the formation ofhcczy m5rd (7ry /z0,r 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 m0durz g4i/w)$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational energ wepr*5dx6 sk7y,” $ \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 eb( n4cc6jkh 0knergy, $ \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 o5-e(dxaf) xy uxug-.w f 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 three suu jmsjif5a tx2uy7k4p/e,+8 *pe f(jxccessive wavelengths for rotational tra 7jsj4 ef8 *pxm/+ fky5upieuaj ,2xt(nsitions 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 estima vea0w9v83c- : -nnmf4rpmfuste 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 : wqox3:6 icwtkfb97 h“nearest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor Na ions?ihkw97x3 6:fcw:o btq D =    nm

  Common salt, NaCl, has a dehcde607l1 xy ansity 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 wzgmg8x3zs/9 jf)rxti/x)i )ohose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chlr k(c6v72rsd0ewrm/ doride crystal is a good insurck/r w 6(v27d0r sdmelator. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly. x) x6,k)baa9 jadpzr increased frequency, begins to conduct when the wavelength o6)arpxjd,ak ) za 9x.bf light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an2nl-v bepek (+ 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 banqn p /9rb+lczmv(1nqdn.t e),0x1ehdds in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron +q 90rcnd,l/npbh1eq1e ) m(vxdn tz. 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 6uyewtw. tvwd)::3d f+mvfn /$ 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 thaflklp02m6 p d1t one siliconmp61 l0lpdfk2 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* k)v;01::0fwdx v pgjxifvm c an LED radiate if made from a material with an energy gapvvw )*jmxgkixdp0ffc;v0: :1 $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelengthd.h1d phkw k0o.pb/p2 * shi9n $ \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 characteristi - nhme1*mrzi4cs are given in (Fig. Below), isr h1-*mmie4 nz connected 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 ofs 7(34 w;asqsjsr/e udw:va1c (Fig. 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 +;bekpn x q*dac:r9chsj m15.as 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. Estimate very r6i3yizyu2n : ioughly the average current in the output resiz3yiu:ii6n2 y stor $ 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 onl43tqibb(et)fypswj )bd(l26 y if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the output resisto()) 3by(s 2dliq4ewttf j b6pbr $ 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 (qg)pp)qhv x+m3 (i i+c5))*bbsexd xxFig. Below), whe3)xq sq g))*+5phip(bbcxv x+ xmdei)re $ 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 relationsh2cefzi 9(uelrij;xc4g32 5iwip 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/beg3 if9s1e kx5 5l7oew0fur 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 moleculwe ;d/c4tg,k6huzk. xe 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 abo ut9a -n hwh7m((y3mjuut 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 solidh; ,/gy 4irkp (wqtm(o with a weakly bound cubic lattice, with each atom connected toht g iop/,kyw m((rq;4 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 have an acti(t3wk8 xk etr-vation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curvtt wekx83(k-re for this molecule.

  When EM radiation is incident on diamond, bzim rn8e,y:r57( m bpit is found that light with wavelengths shorter than 226 nm will cause the diamond to condy,p 8zmnbm e5(ib:7rr uct. 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 tkj14bzl q90ifhe TV set is not to react 0zfkb jq149ilto visible 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 sedp- e(j9l i8ytml1w7w7q fg o2miconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into accountqf1 9o 2 we pjmlyd-wi8g(l7t7 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 raae cdf. 9omne /mhm/xy6,ey..diation has wavelengths shorter than 1000 nm. For a solar cell to ameh,yadmo 9y/em6ef..n.xc/ bsorb all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longes-x d ss+y s .(t)awyxnjx1v3:fk. og.ld8s8d pt wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semiconductor:s xykp-)yg j8a.s3swdn(.1.8lf+sd v dxx to? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many3o .0elal7ur nv;6qze years after red LEDs were first developed. Approximately what energy gaps would you el z.eo6q;l a3ner7u 0vxpect 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 (Fig. n:zq.8lk6s hdy;nyw -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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$