What type of bond would you expect for :*x7gsnb2 i+: nkr op-+lct1oyphi0u
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moli)k2s*sgzn2q:g-g wl9plq l-ecule $ \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 moleculotr -v*hf**zphe yt 5*e $ \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 dividgd4vwu l5i 02q+gxji w )wj.j/ed into four categories. What are they?

  Would you expect the n:qhtk3 apa1x8zc x: 0molecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbgk6e/:r(mqkgbzg 124v;0 oj lekk3 cck s9 bd/on atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam abo-qkf i6jb*i1hut in a metal, why don't they leave the metal entir1bq- ki j*6fihely?

Explain why the resistivity of metals increases with temperatur*m.4rjj. ktr:fp p-pde whereas the resistivity of semiconductors may decrease .ppjrrd . pf:k-4mj*t with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain hbmt,7( p xv9rbf 0u;-eqplfc ;ow the current is rectified and how current flows during each hxq;mbp,e0c rftl;9(fbv7 u p-alf cycle.

Compare the resistance of a pn jm6w9lf3g vnlg5 nn0d+unction diode connected in forward bias to its resistan+n3w0 l 5fm6vgn l9dngce when connected in reverse bias.

Explain how a transistor could b5n8 zvkd red595r9( e* bt5ukfc4uryo99v dl se used as a switch.

What is the main difference by xibrj78t )h/etween n-type and p-type semiconductors?

Describe how a pnp transistor can operate qzx3y1o (x*hn *re4oras an amplifier.

In a transistor, the b3mn a (b9cv uz*rl3i7j:0ny+ slnmg-tase-emitter junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased o tirz*v33 g0mlns9 unnyjb(7lm- c+a:r forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an ebp9kfevov0u747m 9pi lectronic signal, meaning it can increase the power of an input signal. Where does it get the en7k9b p4vmpfve0iuo 9 7ergy to increase the power?

A silicon semiconductor is doped with phosphorus. Wil xat3 7f;(go*ddp/c4 a7k glmtl these atoms be donors or acceptors? What type of semiconducta4m; 7/pdlf( k7dc gttgao3*xor will this be?

  Do diodes and transistors obey Ohm’s law hs/x1 9wokb2q? Explain. {yes|no}

  Can a diode be used to ampbhuw5xjb/8 gr 3cp- 9oe+l6sl lify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the ,j.y .:hi,c/mazmh,z*hde eg dlftf o4-r 8j6electrostatic potential enj,6mf.jt-y/8ihm4f,ea c,:z rlho*gdz d eh .ergy 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 ;mm)ssr c7 6ha7y0tcu result of Problem 1, estimate the contribution to the b) rac7;tcmssh u0m6 y7inding energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding enenpgyej)bs 0n*aj )4u;+0kuvcrgy 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 peuqt1h 32 yf,ax3zj1z10fumh b r mole, and then the binding energy in eV per moleculb10hz ufutyhm133x2qz 1a ,j fe 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 sim 4ih:5 )zm02fox qkxbgilar to that in the text for the states in the formation of the 5q mf:bg)2 zhxxko40i$ \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 o 0a3 idob 3p/;rdrwm3$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristicmphp o;zc5*s 3 .tkn5i 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 rota/ph*i( lt4dpg9xrp)e tional 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 sv z2b47 uia tcje cxtcob369*.4h3esof 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 lengthka lqxqe4l-4)7zl7d 3 ukpf)w for the NaCl molecule given that three successive wavelengths for rotational transitions are 23.1 mm, 11.)l zlp 4kxe47f qua7d3)qlkw -6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to esqb,6x v:wxhr9nxk (*xcxrm,li:7 bk4timate 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 crysm0sms tt12 /z1by rcuzviae79r 2h -(stal is 0.24 b1ut ze0s 29 srt-2(rhci v7myzs1/manm. What is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density of wi (bo*) db6tu 4br(ckxr1s)+w2lr mf$ 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 dv:)xed(enl93u ;* :d nin c5h dcrrc/KCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy w 3fw9l1pir .qbands why the sodium chloride crystal is a good insulator. [9r1fpwi3 .w lqHint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombardkm 3+)uldbcz(a9a 2aged with light of slowly increased frequency, begins to conduct when the wavelength of light is 640 n2g 9)c+a(a d3kmzau blm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength pho3 7o.b p;bjaeyton 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 valfqa /eiry3ia* + 8bow. rn-xn8ence and conduction bands in germanium is 0.72 eV. What range of wavelengths can a pho+ i nr/ aireo8-8q3bawn.xf*yton 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 arleol0 cq i5 z:cdb/(z0e $ 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 ta66k ih):dzp9 mzq0rs8zs k ;ohat one silicon a 8kdm )6zk9 sap6o0qizhzrs ;:tom 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 LED radiate if made from a matv)a td0 7ztqx4+ffi tdr*l7,w erial with an energy gap w 4)t qir+, x*t70zalffdd7vt$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits ligh kezn6 3mgt ;j2p/k 5tugp7lo*t of 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 (Fig. B wulk.8mhtuih18f1 ;b 7h0cijelow), is connected in series with a battery 8tl80w11k h.mufhcu7ji ibh; 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 (Fu( pvz/,) ocyiig. 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 as a function of current,i75g zd )ljj.m for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very roughly the 7l4j -.kds54 rkiz wbzaverage cu.7kr-wz4kds4 zbl j5irrent 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 passe ar ilyu/ h5b 1vr3lr3k6yl8w;s significant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the output resisty y8ur ;6/31blrkra wlv5l3hior $ 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 (Ficq62o;.8 qfoshh lg ;w j7kyo7g. Below), wheq8; w7hqgj;.kysclhof7 o o62re $ 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 basq8u2dg t, r0boqduo +,e current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy ofee+m y(+iqn:n 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 translatixm e z xfq5o-*rk6h0k51: bul* rcr9wzonal 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 dqlz n-pmtin bmwt5 /; 8db 6,0c*,nspristance 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 boun+j.p -c +cv*+uzxwm bgd cubic lattice, with each atom connected to six neighbors, each bond having a bindingjzc*p+x c+vw. u+mbg- 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 ener1eyi*1* .shcqw / qxdygy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curyi q x/s1*1.deyhc* wqve for this molecule.

  When EM radiation is incident on diamond, it is found that lskz22 rp89smjight with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and th 8229mjskzr pse conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR lig0n z bndru,,v .s/e mww8s;6xrht. If the detector on the TV set is not to react to visible light, could it make use of silicon as a "window" with its energy6/ zedusb mr,s .x;wwn0,8rvn 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 that th-2c57q qg4s /e3npcz(py dt iqe "extra" eleecs ppi(2z- 4 57 n/tqqd3cgqyctron moves 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 wats5t*q a4wmvn3cl d 53velengths shorter than 1000 nm. For a solar cell to absorb all this, what energy dmc5w a 35s tvnl*tq34gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that mi2/ueoa2e ,s)gja*t can be absorbed is 1.92 mm. What is the enjao *ui,g)t 2s aeem/2ergy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red f sou42y2qzo odti +y8nwr--*LEDs were first developed. Approximately what ener2nto*wsr-fy yz8u+d4q2 io- ogy 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 v1ef :qa e4psgse5zw1(o(lz9 regulator 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$