Dual Nature Of Matter And Radiation

Question 1

What is electromagnetic radiation?

Answer 1

Electromagnetic radiation consists of mutually perpendicular oscillating electric and magnetic fields, both being perpendicular to the direction in which the wave and energy are travelling.

Question 2

What are the characteristics of a wave?

Answer 2

Characteristics of a wave include frequency, wavelength, amplitude, and speed.

Question 3

Define frequency and wave number associated with a wave.

Answer 3

Frequency is the number of oscillations per unit time, while wave number is the number of wavelengths per unit distance.

Question 4

How do we define momentum of a particle?

Answer 4

Momentum of a particle is defined as the product of its mass and velocity (p = mv).

Question 5

What is the concept of quantization of energy?

Answer 5

Quantization of energy refers to the idea that energy is emitted in discrete packets or quanta.

Question 6

Who first proposed the idea of quantization of energy?

Answer 6

Planck first proposed the idea of quantization of energy.

Question 7

What is the relationship described by Planck’s model for energy emission?

Answer 7

Energy is emitted in packets, and at higher frequencies, the energy of a packet is larger (E = nhν).

Question 8

What phenomenon did Heinrich Hertz discover in 1887?

Answer 8

Heinrich Hertz discovered photoelectric emission.

Question 9

What is the photoelectric effect?

Answer 9

The photoelectric effect is the emission of electrons from a metal surface when radiation of appropriate frequency is incident on it.

Question 10

What is required for the photoelectric effect to occur in metals like zinc and magnesium?

Answer 10

Ultraviolet radiation is necessary for the photoelectric effect to occur in metals like zinc and magnesium.

Question 11

What are the two ways electrical energy can be obtained from light?

Answer 11

• Photo-emissive effect
• Photo-voltaic effect

Question 12

What is the typical experimental setup for the photoelectric effect?

Answer 12

An evacuated glass tube with a quartz window containing a photosensitive metal plate (emitter) and a collector plate.

Question 13

What happens when the anode potential is positive in the photoelectric effect setup?

Answer 13

It accelerates the electrons.

Question 14

What is the role of the stopping potential in the photoelectric effect?

Answer 14

The stopping potential indicates the maximum energy needed to prevent photoelectrons from reaching the collector.

Question 15

What is the work function of a metal?

Answer 15

The minimum amount of energy required to remove an electron from the surface of the metal.

Question 16

True or False: The maximum kinetic energy of emitted photoelectrons depends on the intensity of the incident radiation.

Answer 16

False.

Question 17

What does the photoelectric equation relate?

Answer 17

It relates the energy of incident light to the kinetic energy of emitted electrons.

Question 18

What is the value of Planck’s constant?

Answer 18

6.626 × 10^-34 J s.

Question 19

Fill in the blank: The equation E = hν is known as _______.

Answer 19

Einstein’s relation.

Question 20

What phenomenon cannot be explained by wave theory regarding the photoelectric effect?

Answer 20

The instantaneous emission of electrons upon incidence of light.

Question 21

What is the threshold frequency in the context of the photoelectric effect?

Answer 21

The minimum frequency of incident radiation required to emit photoelectrons from a metal surface.

Question 22

What is the relationship between maximum kinetic energy and incident frequency?

Answer 22

Maximum kinetic energy increases with increasing incident frequency.

Question 23

What is the significance of the stopping potential V0?

Answer 23

It indicates the point at which the photocurrent becomes zero despite the incident radiation.

Question 24

How does the saturation current depend on intensity of incident radiation?

Answer 24

The saturation current increases proportionally with the intensity of the incident radiation.

Question 25

What is Planck's constant and its value?

Answer 25

Planck's constant is a fundamental constant used in quantum mechanics, defined as h = 6.626 × 10^-34 J s.

Question 26

What does Einstein's relation E = hν represent?

Answer 26

It represents the relationship between energy (E) and frequency (ν) of electromagnetic radiation.

Question 27

What does Einstein's relation indicate about energy and frequency?

Answer 27

Energy is directly proportional to frequency and inversely proportional to wavelength.

Question 28

Fill in the blank: High frequency radiation means _______ radiation.

Answer 28

high energy

Question 29

What are the energy values for various photon energies given in the example?

Answer 29

10^-12 J, 10^-15 J, 10^-18 J, 10^-21 J, 10^-24 J.

Question 30

What is the formula for energy of electromagnetic radiation?

Answer 30

E = hν.

Question 31

What is the threshold frequency for photoemission?

Answer 31

The minimum frequency (ν₀) required to eject electrons from a metal surface.

Question 32

True or False: Electrons will be emitted if the energy gained by them is less than the work function.

Answer 32

False.

Question 33

What does the equation KEmax = hν - φ₀ represent?

Answer 33

It describes the maximum kinetic energy of emitted electrons in the photoelectric effect.

Question 34

Fill in the blank: Photocurrent depends on the intensity of incident radiation through the number of _______ emitted.

Answer 34

photoelectrons

Question 35

What happens to photocurrent when the intensity of incident radiation increases?

Answer 35

The number of emitted photoelectrons increases, leading to a higher photocurrent.

Question 36

What is the significance of the stopping potential (V₀)?

Answer 36

It indicates the potential required to stop the most energetic emitted electrons from reaching the collector.

Question 37

What relationship does V₀ have with incident frequency (ν)?

Answer 37

V₀ varies linearly with incident frequency.

Question 38

Fill in the blank: The energy of a photon is given by _______.

Answer 38

hν

Question 39

What did Einstein argue about the interaction of photons with electrons?

Answer 39

A photon gives all its energy to an electron upon collision, and the photon ceases to exist.

Question 40

What is the formula to calculate the number of photons incident per second?

Answer 40

N = Power / Energy of a single photon.

Question 41

How does the energy of emitted electrons vary?

Answer 41

Electrons have different kinetic energies due to varying depths of ejection and collisions.

Question 42

What is the relationship between wavelength and energy for photons?

Answer 42

Wavelength (in Å) × energy (in eV) ≈ 12500.

Question 43

What does the Compton shift relate to?

Answer 43

It relates the change in wavelength of photons due to scattering with electrons.

Question 44

True or False: Photons can be absorbed or created during collisions.

Answer 44

True.

Question 45

What is the relationship between intensity and electron energy in the photoelectric effect?

Answer 45

Intensity affects the number of emitted electrons but not their energy.

Question 46

What is a key conclusion from the experiments on the photoelectric effect?

Answer 46

Light behaves as packets of energy called quanta.

Question 47

Fill in the blank: A photon of low frequency light will not have sufficient energy to _______ an electron.

Answer 47

release

Question 48

What is the effect of increasing the frequency of incident light?

Answer 48

It increases the maximum kinetic energy of the emitted electrons.

Question 49

What did Compton demonstrate about photons?

Answer 49

Photons have associated momentum along with the energy they carry ## Footnote This was established through experiments showing that photons interact with matter.

Question 50

What is the rest mass of a photon?

Answer 50

Zero ## Footnote Photons are massless particles and always move at the speed of light.

Question 51

In photon-particle collisions, what quantities are conserved?

Answer 51

Energy and momentum ## Footnote However, the number of photons is not conserved as photons can be absorbed or created.

Question 52

What is Compton shift?

Answer 52

The change in wavelength of scattered photons, denoted as Δλ ## Footnote It depends on the scattering angle during photon-electron collisions.

Question 53

What experiments demonstrate the particle nature of radiation?

Answer 53

Black body radiation and photoelectric effect ## Footnote These phenomena can only be explained by considering radiation as consisting of photons.

Question 54

What does wave-particle duality imply?

Answer 54

Both wave and particle characteristics are necessary to describe electromagnetic radiation ## Footnote This concept applies to both light and the entire electromagnetic spectrum.

Question 55

What is a photocell?

Answer 55

A device that converts light energy into electrical energy ## Footnote It operates using the photoelectric effect and is used in various applications like light meters.

Question 56

How does a photocell work?

Answer 56

When suitable light falls on the cathode, photoelectrons are emitted and create a photocurrent ## Footnote This current can be measured and used to trigger other devices.

Question 57

What did de Broglie hypothesize about matter?

Answer 57

Matter may also possess dual nature, exhibiting both wave and particle properties ## Footnote This was based on the observed symmetry in nature.

Question 58

What is the de Broglie wavelength formula?

Answer 58

λ = h/p ## Footnote Where h is Planck's constant and p is momentum.

Question 59

What confirms the wave nature of electrons?

Answer 59

The Davisson and Germer experiment ## Footnote It demonstrated electron diffraction patterns, similar to wave interference.

Question 60

What is the significance of the Davisson and Germer experiment?

Answer 60

It substantiated de Broglie's hypothesis of wave-particle duality ## Footnote The experiment showed that electrons exhibit wave-like behavior.

Question 61

What is the relation between kinetic energy and de Broglie wavelength for a charged particle?

Answer 61

λ = h / √(2mEK) ## Footnote Where EK is the kinetic energy and m is the mass of the particle.

Question 62

True or False: The de Broglie wavelength of larger objects like cars or humans is significant.

Answer 62

False ## Footnote The calculated wavelengths are extremely small and not observable.

Question 63

Fill in the blank: The phenomenon of light exhibiting both wave and particle characteristics is known as _______.

Answer 63

wave-particle duality

Question 64

What defines the momentum of a photon?

Answer 64

p = E/c ## Footnote This relationship is valid for massless particles traveling at the speed of light.

Question 65

What is the formula for de Broglie wavelength?

Answer 65

λ = h/p

Question 66

What is the value of Planck's constant h?

Answer 66

6.63 × 10^-34 J s

Question 67

What is the de Broglie wavelength of a car moving with a momentum of 20000 kg m/s?

Answer 67

3.32 × 10^-38 m

Question 68

What phenomenon describes the wave-like nature of material particles?

Answer 68

Wave-particle duality of matter

Question 69

What are the classical terms used to describe waves?

Answer 69

* Frequency (ω) * Wave number (k)

Question 70

Why are the wavelengths associated with macroscopic particles negligible?

Answer 70

They are negligible compared to the size of the moving objects and the widths of their paths.

Question 71

What is the significance of the de Broglie wavelength for an electron passing through a small aperture?

Answer 71

It is comparable to the size of the hole.

Question 72

What is the de Broglie wavelength of an electron with kinetic energy of 100 eV?

Answer 72

1.228 Å

Question 73

What effect does the wavelength of the characterizing probe have on the resolution of a microscope?

Answer 73

The shorter the wavelength, the better the resolution.

Question 74

What is thermionic emission?

Answer 74

The process of emitting electrons by heating a material to high temperatures (~2000 ºC).

Question 75

What is field emission?

Answer 75

The process of emitting electrons by applying strong electric fields (~10^6 V/m) at the surface of a metal tip.

Question 76

What is photo-electron emission?

Answer 76

The process of emitting electrons by shining suitable frequency radiation (ultraviolet or visible) on a metal surface.

Question 77

What is the primary advantage of electron microscopes over optical microscopes?

Answer 77

Higher resolution due to shorter wavelengths associated with electrons.

Question 78

Who developed the first electron microscope and when?

Answer 78

Herald Ruska in 1929.

Question 79

What is the relationship between stopping potential and incident wavelength in the photoelectric effect?

Answer 79

The stopping potential is inversely linear with the incident wavelength.

Question 80

What happens to the extra energy of incident radiation in the photoelectric effect when intensity increases?

Answer 80

It does not change the maximum kinetic energy of the electrons.

Question 81

What is the work function in the context of photoelectric effect?

Answer 81

The minimum energy needed to remove an electron from a material.

Question 82

What is the stopping potential if the photocurrent vanishes?

Answer 82

It is the maximum retarding potential that prevents photoelectrons from reaching the anode.

Question 83

What is the threshold wavelength for tungsten?

Answer 83

2.76 × 10^-5 cm

Question 84

What is the energy of a photon with a frequency of 5×10^14 Hz?

Answer 84

3.315 × 10^-19 J (or 2.071 eV)

Question 85

What is the significance of the Davisson and Germer experiment?

Answer 85

It demonstrated the wave nature of electrons through diffraction.

Question 86

Fill in the blank: The de Broglie wavelength of an electron is _______.

Answer 86

λ = h/p

Question 87

True or False: Electrons can behave as waves.

Answer 87

True

Question 88

What is the typical resolution of electron microscopes compared to optical microscopes?

Answer 88

Several hundred times higher.

Question 89

What happens to photoelectrons when radiation of wavelength greater than the threshold wavelength is incident on a metal surface?

Answer 89

No photoelectrons are emitted.

Question 90

What is the maximum kinetic energy of photoelectrons when ultraviolet radiation of wavelength 1.80 × 10^-5 cm is incident on tungsten?

Answer 90

2.40 eV

Question 91

What is the expected behavior of an electron at rest in relation to de Broglie wavelength?

Answer 91

An electron at rest does not have an associated de Broglie wavelength.

Question 92

What is the significance of the wavelength being comparable to atomic dimensions in electron diffraction?

Answer 92

It allows for the study of atomic structures.