Chapter 12 : Wave paticle Duality

Chapter 12: Wave paticle Duality

I) Put or 1) Einstien managed to interpret the experimental results of the photoectric effect which led him to Nobel prieze.

2) Planck proposed that radiation was made up of packets of energy (quantum) or photon whose energy E = hl

3) Classical physics through the wave theory failed to explain the photoelectric effect, and the black body radiation phemomenon.

4) The optical microscope proves de Broglie's relation for particles duality.

5) The speed of (e m) radiations varies according to their energy.

6) A wave describes a collective behavior of photons.

7) Quantum mechanics is based on assumptions which agree with the experimental observations when the electron is free to move, or when the containing size is extensive.

8) Classical physics applies when an electron is trapped whithin a limited confinement.

9) A photon has a mass, a linear momentum and a constant speed which is the speed of light and it has a size denoted by the wave length.

10) An evidence of photons is the photoelectric effect.

11) When n of indienet photons is greater than n c, no photocurrent flows.

12) As long as n of incident photon is greater than n c, the KE of the electron freed by the photoelectric effect (photoelectron) depends on the light intensity.

13) The electron freed by the photoelectric effect (photoelectron) is barely freed when hn of incident photon = h nc = Ew

14) The photocurrent increases by the increase of the intensity of light as longer as n is greater

15) The practiacle observations of photoelectric effect agrees with the classical physics.

16) The surface potential barrier prevents free electrons from leaving the metal due to the attractive forces of the surface.

17) In cathode ray tube (CRT) some electrons may overcome the forces of attraction at the cathode, surface due to heat.

18) De Broglie's equation is applied only on photons.

19) High resolving power of e-microscope is due to the low KE of electrons and hence very large wavelength l

20) The lenses used in e-microsocope are usually magnetic.

21) Optical microscope uses light, while e-microsocpe uses an electron beam.

22) In blackbody radiation curves (Planck's distribution) the wave length lm at which the peak of the curve occurs is inversely proportional to temperature.

II) Write the scientific term or concept: 1) The critical value of the frequency of the incident photon on a metal surface causing the emission of electrons. - Threshold frequency nc

2) The energy needed to free an electron from a metal surface in the photoelectric effect. - Work function Ew = hnc

3) When a photon (X or g) collids with a free electron, the photon frequency decreases and it changes its direction. Also the electron velocity increases and it changes its direction. (i.e the photon applies a force on the electron and the electron will be thrown off and a change in the linear momentum of the photon takes place). - Compton effect

4) A new set of laws of mechanics based on the assumptions formed by schrodinger and can interpret the observations of photoelectric effect, wave particle duality, blackbody radiation. - Quantum mechanics

5) The wave length lm at which the curve of balckbody radiation occurs is inversely proportional to temperature. - Wein's Law

6) The attractive forces of the surface of metal which prevents the free electrons from leaving it. - Surface potential barrier.

7) Small packets of energy radiated from the vibrating atoms when they are shifted from a high energy level to a lower energy level. - Quantum or photon.

8) The emission of electrons due to light falling on a metallic surface. - Photoelectric effect.

9) The distribution of the radiation intensity with wave length in blakcbody radiation. - Planck's distribution

III) Choose the correct answer: 1) A black body is a perfect ……….. absorber - emitter - absorber and emitter. - abosorber and emitter.

2) Wien's law explains that the increase in temperature of a blackbody cause ……… - The increase of intensity of black body radiation. - The intensity of radiation go down at the high frequency end in Planck's distribution. - The decrease in wavelelngth (l m) at which the peak of the curve occurs in Planck's distribution. - The intensity of radiation go down at the high frequency end in Planck's distribution.

3) Hot bodies emit light and heat as ……… - The sun - other stars - a glowing incandescent lamp. - all the previous - all the previous

4) Electromagnetic (em) radiation from the Earth lies within the region of ………. Of the electromagnetic spectrum. - Infrared - visible light - ultraviolet. - Infrared.

5) Cathode ray tube (CRT) is used in …………. - TV and computer monitors. - Studying photoelectric effect. - Studying compton effect - TV and computer monitors.

6) When the frequency of the incident photon on a metallic surface is greater than the threshold frequency (n > nc - Photoelectrons can not be emitted. - Photoelectrons are barely emitted. - Photoelectrons are emitted and have K E = hn - nc - Photoelectrons are emitted and have K E = hn - nc

7- Threshold frequency of the incident photon (nc) and the work function needed to free an electron from the metallic surface (Ew) in photoelectric effect both depend on ……… - Kind of metallic surface. - Time of exposure of light. - Intensity of incident light. - Kind of metallic surface.

8- Photoelectric current achieved by absorbing photons on a metal surface increases by the increase of light intensity when the frequency of incident photon ………. - n < nc - n = nc - n > nc - n < nc

9) Natural Earth resources are detected by satellites airborn as well as terrestrial equipments which map and photograph the surface of the Earth using (em) waves as....... - Infrared radiation emitted by the surface of the Earth. - Reflected visible light. - microwaves used in radars. - all the previous - all the previous.

10) The mass of photon while in motion is.......... which proves the wave particle duality of photon. - m c^2 -

11) The wavelength of a particel which proves the wave particle duality was proposed by............ - Einstien. - Planck - De Broglie - De Broglie

12) The particle nature of photons is proved by.............. - Compton effect. - Blackbody radiation. - Electron microscope. - Compton effect.

13) The wave nature of particles (electrons) is proved by............. - Compton effect. - Photoelectric effect. - Electron microscope - Electron microscope

14) The magnification of the electronmicroscope is so high (high resolving power), because of................ - The electromagnetic lenses. - the use of light beam. - high kinetic energy and hence very short wave length of electron beam. - high kinetic energy and hence very short wave length of electron beam.

15) "Relaxation and excitation are simultaneous processes, at thermal equilibrium the atom is stable due to the balance and simultaneity of these processes." This is one of the assumptions of................. science, formed by................. - Classical mechanics - Newton - Quantum mechanics - schordinger. - Quantum mechanics - Wein. - Quantum mechanics - schordinger.

IV) Give reasons: 1) Dominant color of light emitted from sun, a burning charcoal and glowing incandescent lamp varies from one to aother. - Because an (em) source does not emit all wavelengthes equally.

2) Free electrons in metals cannot leave the surface of metal. - Because of the surface potential barrier, i.e the attractive forces of the surface which is formed of positive ions.

3) An enclosed cavity with a small hole is considered as a black body. - because radiation inside the cavity is trapped due to multiple reflections, only a small part of it leaks out, which is called black body radiation, and the cavity appears black.

4) Classical physics expectations failled in explaining Planck's distribution of black body radiation. - Because classical physics states that since the radiation is an (em) wave, the intensity of radiation increases with frequency which fails to explain, why the intensity of radiation go down in plancks distribution curves of blackbody radiation

5) Planck succeeded in explaining the blackbody distribution for all hot bodies (black body radiation) - Because he proposed that radiation was made up of small units or packets of energy each he called quantum or photon. The photon energy increases by the increase of frequency but their number decreases with increasing energy.

6) When the frequency of incident photon n is less than nc no photocurrent is obtained, no matter how intense the light might be. - Because according to Einstein interpretion of the photoelectric effect, he proposed that when the energy of the incident photon hn is less than the energy needed to free an electron from the metal surface which is called the work function Ew = hnc. If hn < Ew, the electron would not be emitted at all no matter how intense the light might be.

7) Increasing n of incident photons than nc (n > nc), increases the photocurrent intensity. - because of increasing KE of freed electrons according to Einstein intepretion of the photoelectric effect, he proposed that when the energy of incident photon hn exceeds the limit of the work furnction of the surface metal (Ew = hnc), the electron is freed and the enegry difference (hn - Ew) carried by the electron as KE. i.e it moves faster as hn increases.

8) Photons have wave particle duality. - Because photon has energy E = hn and it always moves at the speed of light c = 3 x 10^8 m/s regardless of its frequency, it has a mass of while in motion its mometum . Compton effect proved the particle nature of photon. When a photon falls on a free electron, it applies a force on it, the electron will be thrown off and a change in the linear mometum of the photon takes place. (i.e the wave length of the photon decreases and it changes its direction and the velocity of the electron icreases and it changes its direction).

9) Particles have wave particle duality. - electron microscope proved the wave nature of particles and De Broglie's equation proved the wave nature of particles where l is the wave length of a prticle which is in analoge with photon.

10) Electronmicrosocpe has high resolving power. - Because the electron beam can carry high kinetic energy and hence very short wave length . Thus its magnification is so high that it can detect very small objects.

V) Examine the corresponding graph then answer the following: a- These curves are known by............. b- The wavelength at the peak is.......... propertional to.............. which is........... law. c-.............. physics cannot explain the phenomenon of............. d- Planck's assumption to expalin this phenomenon is that he proposed........... a- Planck's distribution. b- inversely - temperature - Wien's. c- classical - blackbody radiation. d- quantum or photon.

VI) Examine the corresponding figure, then answer the following: a- This figure represents the construction of............. b- labell the constructions in the fig. c- State the idea behind this apparatus.......... d- This is used in............. and.............. a- cathode ray tube (CRT) b- 1. cathode - 2. gride - 3. anode - 4. E-gun - 5. flouresceent screen. c- electrons can be emitted from the metal of cathode when given enough energy in the form of heat. d- TV - computer monitors.

VII) Examine the corresponding figure then answer the following: 1- Label the diagram. 2- State its function. 3- How can you increase the obtained current? 1) 1. photo electrons. 2. ammeter. 3. voltmeter. 4. battery. 5. cold metallic cathode. 2) Get electrons freed from metal cathode due to light. 3) by increasing n of incident light than nc.

VIII) These two graphes are related to the pervious question. How can you explain these two curves? (1) n incident light < nc (2) n of incident light is > nc [ nc is the critical frequency].

IX) Examine the following figure then answer the following: 1- This is........... which states that................... 2- This phenomenon can be explained by the following relation: 1- compton effect - when a photon falls on a free electron, it applies a force on its the electron will be thrown off end a change in the linear momentum of the photon takes place. 2-

XI) Examine the corresponding figures (a), (b) and (c) then answer the following 1- These experimental results prove the.............. of both.............. and................. Then a beam of electrons can be used in.............. microscope. - duality - electrons - photons - electron

XI) Examine the corresponding figure then answer the following: 1- These two apparatuses are................ and.............. 2- Complete labeling both of them. 1- oplical microscope - electronic microscope 2-

XII) Show the difference between the emission of electrons in both, photoelectric cell and cathode ray tube. - emission of electrons in photo electric cell due to light, but in (CRT) due to heat energy.

XIII) Write the following important relation of modern physics: a- Einstein's law of concervation of mass and energy. b- Planck's relation of the photon energy. c- De Broglie's relation of the duality of both photon and particle. d- The relation which explain's compton effect.

Problems: 1) Calculate the energy of a photon whose wavelength is 800 nm and find its mass and linear momentum.

2) Calculate the mass of an x-ray photon and a - g - ray photon if the wavelength of x-ray is 90 nm and that of g - ray is 0.05 nm.

3) Calculate the wavelength of a ball whose mass is 200 kg which moves at velocity 30 m/s. Also calculate the wavelength of an electron if it has the same velocity.

4) A radio station emits a wave whose frequency is 82.4 MHz. Calculate the energy of each photon emitted from this station. Also calculate the rate of photons j L if the power of station is 100 kw

5) An electron is under a potential difference 10 kv. Calculate its velcoity upon collision with the anode from the low of conservation of energy. then calculate l and PL

6) If the least distance detected with an electron microscope is 0.1 nm, calculate the velocity of electrons and the potential of anode

7) Calculate the force by which an e-beam whose power is 200 kw affects an object whose mass is 50 kg. What happens if the object is an electron and why? This force is too diminutive to affect the object. But if the object is an electron, due its small mass and size, so this force throws it off.

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