What type of bond would you expect for r-y*sfpy v 6/b,3tlbj
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mol9 kjw +m1d*dgkulgg30 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 molecul*: m,sdlq0ijw wlw)4ne $ \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 int3w6 g((vgu ij+lw kyx.o four categories. What are they?

  Would you expect the molecule )5-rpfw:d.vqb: ebzy $ \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 (sw90m q1yd ljm *74pqa$ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free toprd :-6yqvh .x roam about in a metal, why don't they leave thed-p h x:qvr6.y metal entirely?

Explain why the resistivity of metals increases wilf6 xv-wc+ii)o; w;lho:i s98h6w k jkth temperature whereas the resistivity 6w ;xcwi-l; flwj8h koi :his9+6ov)kof semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain w/m+c+in ory;how the current is rectified and how cw++ci; /nyorm urrent flows during each half cycle.

Compare the resistance of azq-zpi:zg )oq( ob. )m pn junction diode connected in forward bias to its resistance when connected in reversp:ioqmo-)bz(z q.zg )e bias.

Explain how a transistor could be used as omicf/2s+:8 4 0 l9nrwcifb gwa switch.

What is the main difference between n-t o4 l8e -jf/nu-2cavcpype and p-type semiconductors?

Describe how a pnp transistor can operate as an amplifierty7.xbt/ +u lr:iv k(r.

In a transistor, the base-emitter junction and the bas5e3b k4rx tw7be-collector junction are es7 k3bwe t4rx5bsentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaniu 9/fmlegi-l3ng it can increase the power of an input signal. Where does it get the l3u9efgl m /i-energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms bb ko6mk4g(q1x e donors or acceptors? What type of semiconductor will thibq6o1k (m 4xgks be?

  Do diodes and transistors obey Ohm’s law? Explain. {6,386-wim cl ybcnkwgyes|no}

  Can a diode be used to a-m d73 y4*eyianzk.xuj,hmk 0mplify a signal? Explain. {yes|no}

  Estimate the binding energy oi)f:+4p zj.rzy6dcen f a KCl molecule by calculating the electrostatic potential enere. 64c jiz :)dn+fpyrzgy 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 )-u4-d)8bcjafl 2 siyedoij8 energy of KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clo) cod8ijfesda-2 i)byu48 l-juds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding ener+llyk./7hqjel11ny4 (l atto gy 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, and e22q2 s2zolxvthen 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 molecu qexl2z22 ovs2le? 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 tha: s*v5ogo4foju*ulkluz8.9 ;au f 6mlt in the text for the states in the formation oulsfu8zum v.6k5g o 9j*;loof*:4al uf 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 quantity8;eg w0tl9dh8ll8 w m-qoje/n $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationp7qtk-uqseg6g ,mf k/a7 *6ioal 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 rotati::5o 9ut eezresv7n +konal 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 atoms in a0a 0 ipyk;9dtthe $ \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 givh(uf,x55,,x rxn-a agpk qyo1 en that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, andx- 5pho, ag qyfk1 rxu(n5,ax, 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (F6 w4wgiqkyc)4h, k+s6dc k*oy ig. 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 angxere ft5 p 3483c3;bf,e gabxd Cl ions in a NaCl crystal is 0.24 nm. b3pxr58g ge4, cf3fb 3;etaex What is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, ha6 y5k,) efh/+k*kk kz8swjjbas a density 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 i i(u e uac-o02t0i0pfcs $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy ba/0dv ybe shx 8+,xaqi:6dl xo;nds why the sodium chloride crystal is a good insula0 b sh;x/oaqvy+:ldxx6 ,e id8tor. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarde0kd9 *dofl 2vad with light of slowly increased frequency, begins to conduct d*dk0lv2 aof9 when the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wav quhm;w6vqfla: q x1+jn(5c(id q7p:delength 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 germs(l; d96msirbf* ( npxanium is 0.72 eV. What range of wavelengths can ars pdbsnlf9(mi(*; 6x photon 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 are :x 56kzm(cyrf ls k/f.udz3-n$ 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 se4 nba sxapeii)d+ci2mp 56 +:mmiconductor is doped with phosphorus so that one silicon atom in 5 + bpm 4i+em paxiia6:csnd)2$ 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 wpodhxnav7cx,eo uzq242 3l1( 39xgh z ill an LED radiate if made from a material with an energy gapxdx 2(p23z,u egv9o7 h4ox al31hn czq $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light oz xsacm v8(k8utxy)* )je7v4q f 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 ( ,b.3i*ifas jlz76y/ui lsbr-Fig. Below), is connected in series with a batter 7/zsu. b-is3*byjliliaf6 ,ry 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) is connected in series to j5e5( lly qxo7a $ 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 cnpz6 yd*+pqdkdus; )bog , 30turrent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rmqfw fs(k- )z-ps is to be rectified. Estimate very roughly the average current in the output rep(k)zws-f f- qsistor $ 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 voltageu z0pnr .r9;vj excee9p;nuj0.rz rvds 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 voltage is to be rectified with a full- e en/q e6+ivs/htq,i3wave rectifier (Fig. Belovt+6i, eneeqi/hs/ q3 w), 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 th(l- xm70n 4kye z/kalme 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 cki4;.;c5 djk zqp/pbs) f(kgenergy 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 energf1 ypczh/4i 2gy 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 betgv9f k8vd. d(3li)2 kmoo: qbnween 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-gvg*,mwwh9i - /ffzq solid with a weakly bound cubic lattice, with each atom connected to six neighbors, each bond having a binding g/vg- qh*fm - 9fww,zienergy 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 anuvp7o2k99mwvq tj4,(,sg d itl/2 lxs activation energy of 1.4 eV. When the mole9/4v ov,usjt9lds,(72 lxg2tkmq wipcule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is - xos uhsg2,6efound 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 condu2 g6s-se xuo,hction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV setb/orpj :b*rhg7l( e i4vb+j f6 is not to react to visible light, could it make use vj*lp i+b/(6gbro7f e b j4rh: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 dop ; 4xn8n.:y:.hjzul yoz*asjued silicon semiconductor, assume that the "extra" eley:n.j*8j;l zxusz u oan 4y:.hctron 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 wavelengths h9.af 2yo2ew 0 rnazq)shorter than 1000 nm. For a solar cell to absorb all this, what energy ga noera 2f9qw0 a.z)h2yp ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest ) )5+nwt z8qk(xtp l-lf.cnciwavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semiconductortc+ 8l5twplkcifz).n )( xn -q? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red *u *0 ts(afpceLEDs were first developed. Approxi tfa*pse(* 0ucmately 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. Belynm8 erti-/q 0ow). 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$