What type of bond would you expect for gxf;/ yp5ns) 3 4jo.z4q1ey vpczm+ ea
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molex(9/e jziqk1f y )mwo,cule $ \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 moleculm3 r8rj; qce/xe $ \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 categoriesy7dg+hr3 /d p+i7gj tv0hi/xg. What are they?

  Would you expect theynlc7f 5n(2/yn3a jrf 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 atqk 4gh ww.m kx6uxo :rrw3-t+/yh1qd3om ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electru ;)n8 e7)g2ojnft /s so/ycpeons are free to roam about in a metal, why don't they leave the metal en o/y)o7nnjf;) s/e8u2pesg cttirely?

Explain why the resistivity e;e ul3yu3)rndppsa ;:.7u auof metals increases with temperature whereas the resistivity of semiconductors may decrease with incr ;r e:pn3.pauylu) ues7;au3deasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the-.t9dpqyhusau 6el1 1 current is rectified and how current flows during each halt- als11h. p9qu uyde6f cycle.

Compare the resistance of a pn junction diode co ghjutut).*4annected in forward bias to its resistance when connected in ra)* jgt.t uhu4everse bias.

Explain how a transistozya6 ut72q8+nvxcv6z( c mx 9fr could be used as a switch.

What is the main difference between 4;n:gcnb +w3 crl 6cohn-type and p-type semiconductors?

Describe how a pnp transistor can oper:q4+h byx qp,aate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junc 5xyy7t2uf n,bih9 um;tion are essentially diodes. Are these junctions reverse-biased or f7nmyitu bu25y,h ;x9f orward-biased in the application shown in (Fig. Below)?

A transistor can amplify an fh/ow 1 w-hc;v (4iypt,tui+a electronic signal, meaning it can increase the power of an input signal. Where does it get thv4+tf, hpuawwiy;-toc( / i1he energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms be donors or 66q8b tu 2g uxvr5qjr(acceptors? What type of semiconductor will thtg2jqrr66 xu8ub(v 5q is be?

  Do diodes and transistors obey Oheeu sndc/x*+)g89e1pd w)lsym’s law? Explain. {yes|no}

  Can a diode be used to amplify a signal? Explain. qxxfrso8c2,0g 5 cy5iw yd;m0{yes|no}

  Estimate the binding energy of a KCl molecule by calculating the .fp4j,fhlpc rcl( 1q -electrostatic potential fp rc1c4lh,(fp.qj - lenergy 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 gj(j2 7o 1f ursi(yw4ql4o -uoeV. From the result of Problem 1, estimate the contribution to the w4f7(j-lyo2q o(rjugu 41 osibinding 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 spp 4 y ai5 w6a0a2 7ih(obmz2sx,dvc6the $ \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 experim kavc )v.bmt4(c /p2u ypy9;iwentally in kcal per mole, and then the bin/w imap 2pc t.v9;kcu)yvby(4 ding 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? 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 in8 :2woky-wwrf3cf7 zp8xk4fm the text for the states in the formation ofmcwpfwo 27kf8yrx- 83 w k4f:z 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 quanti- ey*jfm2bpp25y z-bw ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational energy,”9 boigzrdn(pll:u 3sszq2+ 4( $ \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 char v;g3sp4o n9swacteristic 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 of H atom)3jowzb5:h vmr vx:7l6*nl 8i:ocd dts 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 lk: -n r wnasp:w*a93sbength for the NaCl molecule given that three successive wavelengths for rotational trans*rbsw:nws3ap na9:k- itions 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 estimat 4a,rvy 5x uksbw/xi32e 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 neigh9xumn8 g7lyt1 hv+cl -bor” Na and Cl ions in a NaCl crystal is 0.24 nm. Whc78u x+nmt91v- ly glhat is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a densitbgac*v+c5c9.hqc3) qiu gt,a y 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 density f vfhswel9, ,4is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sod982c h7qawoke*q r0weium chloride crystal is a good insulator. [Hint: Co c2h7ro09eqwq * waek8nsider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, begixy lc); )y.qzuns to conduct when the wavelength of light is 640 nm. E)y;yzu l)qc x.stimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an elecvr:ha/k bs lik3lh2i gr8+4 *stron 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 pkkpr 7kks2 ,+k8k 8xnbands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band into the ,rk8p+2kk7kxpnk8s k 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 ct/xk 4 +ju9n-vlik x7$ 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 doped5dwt+pi g.,ru with phosphorus so that one silicon atom ,p rwti+ g.5udin $ 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 ma,v1w5yt mu 5izterial with an energy gap 1m5twzy, u5 vi$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits lightutg e6/fqyc-n)u1e7h of wavelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whosets*ztd8z9.ws kxz m69 current-voltage characteristics are given in (Fig. Below), is connected in series with a ba6dss9 xzt98mk* .tz zwttery 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. Beloq;0gu6bvmdmada1 vc-i9+u 6vw) 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 asg x o1h2(c2sc; pw6gwi a function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V n vd 01hl+t0wmxtbun6y:i) 5t rms is to be rectified. Estimate very roughly the average cubt xwvny0d+ml: ut5i 6t )h1n0rrent in the 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-bv(1ztaw(z/r 6l4. h dypy(s nbias voltage exceeds about 0.6 V. Make a rough estimate of the average current zts(/ y . l4h1brn(vz(pw dy6ain 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 (Fig. B 7t(s *ueh(nnpelow), where (neuthn( ps*7 $ 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 curlu l+i3 y8puev.3 fek/rent $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding eneqrj5bvf:y s./.5 lnfargy 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 translationasvpzz o((j+z )v/psl8 l 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 separation distance betweeb :xn27fykiu+ n 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 sol9hc j6hp 94fcfid with a weakly bound cubic lattice, with each atom connected to six neighbors, each4f9phc6jfhc 9 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 act4f3m+sgl /xo0 z6p ljtivation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is releax36s4/ zlm+pjgtlof0 sed. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that ligh uelw,8w0wvctjg2f,5t with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence ban8lwef 0vw2 g,5wuj ct,d and the conduction band for diamond? $E_g$ =    eV

  A TV remote control em/: xc3udm f/xru,1chqj:rf c0its IR light. If the detector on the TV set is not to react to visible lif/dr3h q,::x1r/c x0muj uccfght, 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, assuu o;6hv 8wyg 8ftg79zrme that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground statw8 8v;yr7ogtfg6z9 uh e, 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 wrqlzzqptp e6 9v l-76w/: z5lvavelengths shorter than 1000 nm. For a solar cell to absorb all thisv e66llptq -l/rz :57p9zvqwz, what energy gap ought the material have? $E_g$ =    eV

  For a certain semicond20)rt0(cr h+bxhbo cjyh kz7p +,(g jxuctor, the longest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semiconductor? g0 yptbj+r )h+0,h7xcrohbxj z k (c(2 $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were first de khejy-ra/apx5(kl1 s 2)er 6wveloped. Apprap5kyj6hw -l2e(/1rs k) exa roximately 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 (Fig. Below). vu c:6/ 2pf-enfd7dtvSuppose 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$