What type of bond would you expectm9lsxlrn841:4 h xju* in aq y-t5mai8 for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecuz1+k- q(tf(e g+xk0u t lugyw/le $ \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 molecule yuqi7;q;b *nmu juh33$ \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 divideds*jd/x8 0k jbnd rvh7* into four categories. What are they?

  Would you expect the m32;l6*jtz mi rwppu r:5.iel wolecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbj3y.kk l7 p 8 bt9eqo(j+rjwr;on atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't they lea,7s nrn9t w6 /jy+thwa*kodb: ve the meo+n,dbanrwjyst:6 * w k7/h 9ttal entirely?

Explain why the resistivity of metals increases with temperature whereas thh:m 1 7fr*lfkre resistivity of kr1 lf*r7f:mhsemiconductors may decrease with increasing temperature.

(Fig. Below) shows a "brid5 )q(nveq yxi2ge-type" full-wave rectifier. Explain how the current i n)5(v xieqy2qs rectified and how current flows during each half cycle.

Compare the resistance of a pn junction diode connecte8x:dw-yvht;)d b*pkyc i13rv d in forward bias to its resistance wk :)ct1-8byvr;3*v did phwxyhen connected in reverse bias.

Explain how a transistor could/t4 ;w*kh u0 1jq0o chsr)fazu be used as a switch.

What is the main differ; 6-wp*0 ec-9akjcb wly r;kt;z,ijmience between n-type and p-type semiconductors?

Describe how a pnp transistor can operate as an aea0c.fvxwx8* t1fg t w3. jx*qmplifier.

In a transistor, the base-emitter junctiolof3 rp 0dt64ayp6msgn2 up6sbt.y(7 n and the base-collector junction are essentiaod ts2bu4(pl7 pr0tyf.ng 63p a y66smlly diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal,)v5 jl 6+sjfx78* )skvblvmtd meaning it can increase the power of an input signal. Where does it get the energy to increas)76 vs8* j5ls )kmfvtx vld+jbe the power?

A silicon semiconductor is doped with phosphorus. Will these -op z ye9p):cnr:)mtsatoms be donors or acceptors? What type of semiconductor wi :op:pcz s e9)ty)rn-mll this be?

  Do diodes and transistors obey Ohm’s law? Explain. :xfue0o i1.,vmv6xa ;lc :v-c:pxh9p gx. ovp {yes|no}

  Can a diode be used to amplify a signal? Explain. gh (( r: r9:k;v bnn9elvyzro3 {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the ejksl64xq k/* glectrostatic potential energjksk*4 6q glx/y 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 18/n*iz e7bex+awnsh.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the equilibri*ea znw8n/i1+bhsx e 7um distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of the u)gz ts e13u7 rj.f(dl$ \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 experimentall.ofhufzuiz/ k, j73u 6y in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What is the con jikf7.z /3uhuz6,uofversion 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 tt8*sl y 2f f(g)japk5whe text for the states in the formation of the f8wyp5f* j2als )tk (g$ \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 ms4qss/i/ zk dep33 90-4xke )bygpvu$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationam/);;a ecnj*nrzkm0 i l 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 fj-9p hh3x lml4j3ei,onal 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 atomo,,;dkrw v;h prm 3: dag)8oves 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 successiv zzm0d r 7hm-/o89kazie wavelengths for rotational transitionsimm/ok0zh8r z-d7 z 9a 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 as4/ +onvobajc6b..g te 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 “jdu) m64mxam*hq90ac nearest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest n* qucd4 aa 0m6)xmj9hmeighbor Na ions? D =    nm

  Common salt, NaCl, has a dza*hdj 4 2kxu4lu3r j3ensity 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 is r 9f,e;u2ilju tt:y8 c$ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis . /pxb6.u. (jr g9,khpa-aju lyhpq;aof energy bands why the sodium chloride crystal is a good insulator. [Hint: Consider the s;hak9 a bpq.ujxp,-g. (6./jpulayr hhells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increz 9;sw nws91fpased frequency, begins to conduct when the wavelength of light is s ps9 ;w1wnz9f640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can ca m.nq kp hkmqy9s(tb* sj2))6ause 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 germanium is 0.72 eV 5km/y6. ac1d;nq fxou. What range of wavelengths can a photon have to excite an electron from the top of ao6 ymc;xq1unk/ .d 5fthe 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 arex9kk015ji v 2 r8o+nlxq o;kbe $ 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 semiconnac1 gf e8rxsj-u+x 0,ductor is doped with phosphorus so that one silicon atom sju+ 81f-,n0 grxcex ain $ 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 materoo0du;ur6b8 bz2)p yn 2nnqr9ial with an energy ganbr no9) 8pb 0z22nyr;uqd6 oup $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of waved3 y+kv udu)k0nl0c /slength $ \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 xpqz4 u6ss6 m 2p*2lfncharacteristics are given in (Fig. Below)6s s6p uq2 lfx4mnpz2*, is 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 of (Fig.l4gdz (te;m20ah 3tnv 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 o2w 7hskf+5v 6 5geli+os. qleff current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be,lxx-kedoy;4i3k ja 4 rectified. Estimate very roughly the average current in the outpu,e 4d- ykjlx4ixk ;oa3t 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 passejmn7(s rgtptw3ckl 7xz(x o5rw); /d3s significant current only if the forward-bias voltage exceeds abon ( trr)dzxsj(mwo/l5p3xc;gwt7 73 kut 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-wave rectih99.gf0 )5 m5bza n uzhgxp-dxfier (Fig. Below), where dh) a5nghb-zf09 9.pm zxgxu5$ 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 relations m.01l qkfajoo9kkt y c3sd1.*hip 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( iril(r r:q8k,t-zh2m y pkz/ 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 of an atom or mcq gmg86 1bgw .i0gjv2olecule 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 abqzvo0 fnz36s3 out 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 wmeb+mg0 )9ouyelu *d9eakly bound cubic lattice, with each atom connected to six neighbors, m oy*dm u)9ueg0e9lb+ 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 4(ux huthi55kfound to have an activation energy of 1.4 eV. When the molecule is disassociated, 1( xiu5huht5k4.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident ov.z.1 rxv fz rda nzmn3e, 3a-fyj381fn diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap betweeyv3n3,zz3arf1mzd8xa .f1vr e. - fjn n the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detectoxscw/yww85v, 8k6 g7t/joa7 p0zoew nr on the TV set is not to react to visible light, could it make use of silicon as a "wi6tkp ac 7s7w0 /en/y5 88ww zojogxwv,ndow" 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 an lvwu2c 8mgw,of63n8 tom in a doped silicon semiconductor, assume that the "extra" electron moves in a Boc28u6nfw m3,vwnl 8g ohr 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 shorter than s* p +mr12,ncn so,ik-/yaefy1000 nm. For a solar cell to absorb all th kyon*,ipca+1e -s,2sr /nyfm is, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconh;vjc;7vig9z30 nll .r *c fukductor, the longest wavelength radiation that can be absorbed is 1.92 mm. W;hnku3.jvli v*cr7fcz 0l ;9 ghat is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs becamcghyg1( cl: zxn, hqc;uk x98:e available many years after red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in bhuh(x;x yg, c:zgc l81kc9n: qlue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fig. Below). Suppow gt98.d:ebzt s10 vbqmh( 5qrse 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$