What type of bond would you expect fo1)8 ctqu vm3q wcdt n,p6v.lw,r
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule5 +lkjrk/bn 9n $ \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 moleculdatxnl /+h 2sk173- nnb agnq+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 divided into four categories.pt )z2ksi7cz* What are they?

  Would you expect the molecul2yo ppgc57xd( ugbvn/;uo) o,e $ \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 (n3uj dzt; ,+jk$ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, wdei .::fca swiy1r.d5hy don't they leave the metal e1fec.y:d:i adsi w5 r.ntirely?

Explain why the resistivity of metals increases with tempd 4v,)s-p vqum3w3h jaerature whereas the resistivity of semiconductors may decrease with increasing temperqu, 3 v-jma3 swd)4pvhature.

(Fig. Below) shows a "bridge-type" full-wave s5x.k ahz:n47 .:tzuxd q3 yuorectifier. Explain how the current is rectified and how current flowsusn.z: xy q7.t4 3kuho5 :xadz during each half cycle.

Compare the resistance o*h p-nj 4+yykxf a pn junction diode connected in forward bias to its resistance when connected in reversey4-n +k* xhypj bias.

Explain how a transistoknq xd 111obqcgmqk.y)v pih0n-3q ac:v53 w2r could be used as a switch.

What is the main difference between n-type ah7(1wao*ubpe xx )r4 und p-type semiconductors?

Describe how a pnp transistor can operate aeu t*/b)um yg 2q2/bzns an amplifier.

In a transistor, the base-emitter junction and the base-collectorea03bcq, bx(e(o+m+ frv*tqkz ) )nqg junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Belo3v(ae,gonemf q+(c rz)x 0*+ tq)bbqkw)?

A transistor can amplify an electr3s0t 4u2iudq8k cn+;niw; fozonic signal, meaning it can increase the power of an input signal. Where does it get8+sz;; i w3ci fqnnuktoud024 the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will tk rkue7j5em)54dax* b hese atoms be donors or aujebk)akdx 5em r4 57*cceptors? What type of semiconductor will this be?

  Do diodes and transistors bzjlj:l;jgr 32 gyp0dj8 4*vpobey Ohm’s law? Explain. {yes|no}

  Can a diode be used to mp/ls i8myj79 amplify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by*yo,chfp ;1w 8fovhefss8 u*0 calculating the electrostatic potentia **vouse0hfs8fyo 8wh1 c;,pfl energy 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 4.4- +8zrd89ud(0dviyx mbf n0wbu3d1 io3 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clovuxuy im 0 br+ofdz8(0w9d- db3di 18nuds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy on(gv31ajb1zyt2k)7 a di tvx2f 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 then+ihezyp4 ier,6/ce y6 the binding energy in eV per molecule is calculated from, e6 cypie6iryze/ h4+ 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 in the text for the states in the fpvflllb m(o9 l+x/3, oormation of thbp(/9+vl molf ll, o3xe $ \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 / 0fygms (dob01tu;: i2ign ji$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational b(24pifhm3e j 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 energy,y9(ilnh q 2kok n6 0uu-buh3z* $ \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 Hm s.x7q0:uwx ju l325fm6pbcsy u* )jb 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 molecul in.2z;zo:/4 wgmuw mxe given that three successive wavelengthz.m4 i;ugx:n/w o2mzw s for rotational transitions 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 e9y zyqt1rg d.w9.u: y8gzp a5wstimate 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 crystal iszb3 s6eb.i op* 0.24 nm. What is the sb6 3p.b *szeoipacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a ddt+x+we nvzfk-;o 1,gt eni4)ensity 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 isunohzf/1 n*:7z4 d iak $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloricc t7o)d4mmg 5de crystal is a good insulator. [Hint: Considtcomc45gm)d 7er the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased fre2ee sm+j6bl- uquency, begins to conduct when the waveljl-ebmus+6 2 eength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an elhq*u5+k bgyr2 - tyy3zectron 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 gerqc1b2m83sldx y9za9g manium is 0.72 eV. What range of wavelengths ca c82xbgasl9mq31dy z9n a 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 arel rjk/rx )cg :+h/fz*g $ 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 thox7)+ ehl chp9at one silicon atom inpohh+7 9c e)xl $ 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 material with an engaa38);g m(j7r7x 6yq hnebxxergy gap 7n86 )a gr(qabmx3;yj xe xhg7$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wave bxwkii-dwe )2cj7sm :; b3sf/length $ \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 (Figgtj)8 ud1ax/d. Below), is connected in series with a battery and a t8adu)dg /x1j$ 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:2scjri1soo4 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 cugw d;i:x77lzo3 ol3xxr:,jadrrent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very rough,qh06**ey:a8 fi5 oza wxwuqd9rw4aw ly the average curreqaw6a0 reuw*8 *xydzo 5a 4whfq:i9,wnt 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 cufultw kw w5 q)9+6bd.pge+i7 drrent only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current inb f 7t9g.d)qid+kwp 6w+ wlue5 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 q.ko t/g9c/lclv 5;7 kvn yxy+rectifier (Fig. Below), where vyql cc.;n+o /g7k x/ v5tky9l$ 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 cu5wf0h t a:jah(rrent $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy.1)v 5p smz:ftwdwv*laal4r 6 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 oqpcaymfr 9 ff. ,f3wo8y(9c3cf 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 ;bao5hws 8y iqx,2t1d distance 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 bound cubib0qu wya4 +ekye 62kw+c lattice, with each atom connected to six neighbors, each bond having a bi4yk k6w euwq2e a0b++ynding 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 enero vqvs y0 500fv,i4 zbocf,e+jgy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw 4v 0,bq 0cfjsfoez 5+0ovy,vi a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that 4o, uwo kz9tp5light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence bandowu o5 4,tpkz9 and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emebl)o x5h jmqzdd4 ,y.xcru.c20j.j 1its IR light. If the detector on the TV set is not to react to visible light, could it make use ofu,) chexjoyjb.lr.xj d 4cd zm5q1.02 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 semi8* ry gh6ap4pzwl )no+conductor, assume that the "extra" electron +p *6hwg)z8rln4o py amoves 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 rjrpra( mle w0c;o5 41has wavelengths shorter than 1000 nm. For a solar cell to absorb all this, what energy gap ought the materirj(;l ec4a m05wp1rr oal have? $E_g$ =    eV

  For a certain semiconduc8w-kdsc1 ;te ator, the longest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in thiwdatce s1-k ;8s semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were1fvxx hy b2a8)t5m-q7hm4ag n first developed. Approximately what energy gaps would you expect to find in green (525yn18gamt-) 5 xqfaxm7 hb42hv nm) and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is f.ja41+ zpeya 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$