Physics Chapter: Photoelectric Effect

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Questions and Answers

What is the relationship between photon energy and wavelength?

Photon energy is dependent on the surface area of the metal.

Photon energy is directly proportional to wavelength.

Photon energy is inversely proportional to wavelength. (correct)

Photon energy remains constant regardless of wavelength.

What determines the minimum energy required for an electron to be emitted from a metal surface?

Work function. (correct)

Stopping potential.

Threshold frequency.

Photon emission rate.

Which of the following statements about the photoelectric effect is true?

Only light with a wavelength shorter than the threshold wavelength can emit electrons. (correct)

Electrons can be emitted even if the photon energy is lower than the work function.

The photoelectric effect can be observed with any type of metal.

Increasing the light intensity alone guarantees electron emission.

What happens to the kinetic energy of emitted electrons if the frequency of incident light exceeds the threshold frequency?

It increases proportionally to the frequency minus the work function. Signup and view all the answers

Which metal type is preferred for demonstrating the photoelectric effect?

Alkali metals. Signup and view all the answers

What is the formula that relates the energy of a photon to its frequency?

E = hf. Signup and view all the answers

What does Planck's constant relate to in the context of photons?

It relates energy to frequency. Signup and view all the answers

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

The maximum kinetic energy of emitted electrons. Signup and view all the answers

What is the result of adding trivalent atoms to an intrinsic semiconductor?

It becomes a p-type semiconductor. Signup and view all the answers

What does the depletion region in a PN junction signify?

It is an area with few free charge carriers. Signup and view all the answers

Which type of rectifier uses a single diode to convert input AC to DC?

Half-wave rectifier Signup and view all the answers

What is the primary function of a transistor?

To amplify or switch electronic signals Signup and view all the answers

In which condition is a PN junction said to be in forward bias?

Positive voltage applied to the p-type side Signup and view all the answers

Which statement about the electrical conductivity of semiconductors is correct?

It increases with increasing temperature. Signup and view all the answers

What defines the barrier potential in a PN junction?

The potential difference across the depletion region Signup and view all the answers

What condition is required for a full-wave rectifier to operate effectively?

Multiple diodes connected in series Signup and view all the answers

Which equation represents the relationship between emitter current, base current, and collector current in a transistor?

$IE = IB + IC$ Signup and view all the answers

What materials are commonly used to create n-type semiconductors?

Phosphorus and arsenic Signup and view all the answers

What happens to the mass number of an atom during alpha emission?

It decreases by 4 Signup and view all the answers

Which of the following correctly defines the half-life of a radioactive substance?

The time taken for the concentration to fall to half its initial value Signup and view all the answers

How does the de Broglie wavelength of a particle relate to its mass?

Inversely proportional to the square root of its mass Signup and view all the answers

What characterizes intrinsic semiconductors?

They are pure semiconductors with equal electrons and holes Signup and view all the answers

The uncertainty principle implies that which of the following must be true?

The product of the uncertainties must be greater than or equal to Planck's constant divided by 4π Signup and view all the answers

What is the significance of Moseley's law in X-ray emissions?

It shows the square root of frequency is directly proportional to atomic number Signup and view all the answers

During beta emission, what change occurs in the atomic number of an atom?

It increases by 1 Signup and view all the answers

Which formula expresses the law of radioactive decay?

N = N0e^(-λt) Signup and view all the answers

What does Bragg's law describe?

The conditions for maximum intensity of diffracted X-rays Signup and view all the answers

In the context of Compton scattering, what occurs during the collision of a high-energy photon with a free electron?

The electron gains kinetic energy and the photon is scattered Signup and view all the answers

Which statement is true about nuclear binding energy?

It requires energy to separate the nucleons in a nucleus Signup and view all the answers

Which of the following best describes a conductor's forbidden energy gap?

It has no energy gap Signup and view all the answers

What is the primary reason for the high energy requirement in nuclear fusion?

Protons repel due to electromagnetic forces Signup and view all the answers

What effect does increasing the intensity of light have on photoelectric current?

It increases the photoelectric current Signup and view all the answers

Signup and view all the answers

Study Notes

Photoelectric Effect

Light is composed of energy packets called photons.
Photon energy (E) is inversely proportional to its wavelength (λ): E = hc/λ, where h is Planck's constant, and c is the speed of light.
The photoelectric effect occurs when light of a suitable wavelength strikes a metal surface, causing electron emission.
The work function (Φ) is the minimum energy needed for an electron to escape a metal's surface.
Threshold frequency is the minimum frequency needed for electron emission from a metal.
Maximum kinetic energy (KE) of emitted electrons is related to the incident light frequency and work function: KE = hf - Φ.
Alkali metals are good for demonstrating the photoelectric effect due to their low work functions.
Einstein's photoelectric equation: hf = Φ + KE (energy of the incident photon equals the work function plus the emitted electron's kinetic energy).
Planck's constant (h) relates a photon's energy to its frequency, approximately 6.63 × 10^-34 joule-seconds.
De Broglie wavelength (λ) of a particle is related to its momentum (p): λ = h/p.

Key Points for Photoelectric Effect

Incident light energy must exceed the metal's work function to eject electrons.
Shorter wavelengths (higher frequencies) of light are needed for the photoelectric effect than longer wavelengths (lower frequencies).
Planck's constant (h) has dimensions of joule-seconds (J·s), equivalent to kg·m²/s.
Energy and wavelength are inversely related: higher energy corresponds to shorter wavelengths, and vice versa.
Calculations for photon energy or wavelength use the equation E = hc/λ.

Example Calculation

If an electron has a wavelength of 1.24 x 10^-10 m, its energy is 1 eV.

Energy of an Electron

One electron volt (eV) is the energy gained by an electron when a potential difference of one volt is applied across it.

Photoelectric Effect (continued)

Compton scattering occurs when a high-energy photon collides with a free electron, causing scattering.
The photoelectric effect arises from the principle of energy conservation.

Uncertainty Principle

The product of the uncertainty in position (Δx) and the uncertainty in momentum (Δp) of a particle is greater than or equal to Planck's constant divided by 4π: ΔxΔp ≥ h/4π.
Minimum momentum uncertainty for a proton with a 1.6 x 10^-8 m position uncertainty is roughly 1 m/s.

Photoelectric Current

Photoelectric current increases as light intensity increases.

De Broglie Wavelength

De Broglie wavelength is inversely proportional to the square root of a particle's mass and directly proportional to the square root of kinetic energy.

Radioactive Decay

Half-life is the time it takes for a radioactive substance to decay to half its initial concentration.
Half-life is independent of the initial concentration.
Radioactive decay is a spontaneous process continuing indefinitely.

Radioactive Emission

Radioactive decay products include alpha, beta, and gamma emissions.
Alpha particles are helium nuclei, beta particles are electrons, and gamma rays are electromagnetic radiation.

Alpha Emission

Alpha emission reduces the atomic number by 2 and mass number by 4.

Beta Emission

Beta emission doesn't change the mass number but increases the atomic number by 1.

Gamma Emission

Gamma emission has no effect on the mass or atomic number.

Law of Radioactive Decay

Radioactive decay is described by the equation: N = N₀e^-λt, where N is the number of nuclei at time t, N₀ is initial nuclei, and λ is the decay constant.

Bragg's Law

Bragg's law describes the maximum intensity of diffracted X-rays when the path difference between reflected waves from adjacent crystal planes is an integer multiple of the wavelength.
The maximum wavelength for Bragg's law solution: λ_max = 2d, where d is crystal plane separation.

X-Ray Wavelength

The lower limit of X-ray wavelength (λ) produced in an X-ray tube operating at voltage V is given by λ = 12,400/V (λ in Å, V in eV).

Moseley's Law

Moseley's law relates the square root of X-ray frequency to the target material's atomic number.

Interference

Constructive interference occurs when the path difference between waves is an integer multiple of the wavelength.
Destructive interference occurs when the path difference between waves is an odd multiple of half the wavelength.

Nuclear Physics

Rutherford's alpha-scattering experiment led to the discovery of the atomic nucleus.
James Chadwick discovered the neutron.
Rutherford discovered protons and the concept of the nucleus.
Nuclear size is around 10^-15 meters.
Nuclear density, roughly 10¹⁷ kg/m³, is independent of mass number.
Nuclear mass is the total mass of protons and neutrons within the nucleus.
Atomic mass unit (amu) is 1/12th of the mass of a carbon-12 atom, approximately 1.67 x 10^-27 kg.
Isotopes are atoms of the same element with the same atomic number but different mass numbers.
Isotones have the same number of neutrons but different atomic and mass numbers.
Isomers have the same atomic number and mass number but different nuclear configurations and energy states.
Nuclear binding energy is the energy needed to separate nucleons in a nucleus; equivalent to the mass defect.
Binding energy calculation: E = Δm c² (Δm is mass defect, c is the speed of light).
Nuclear fusion occurs when multiple atomic nuclei combine to form a heavier nucleus, releasing considerable energy, needing extremely high temperatures.

Semiconductors

Forbidden energy gap is the energy difference between the valence and conduction bands in a semiconductor.
It dictates electrical conductivity; small gap (conductors), large gap (insulators), moderate gap (semiconductors).
Intrinsic semiconductors are pure, having equal electron and hole numbers, with lower conductivity than extrinsic semiconductors.
Extrinsic semiconductors are produced by adding impurities (doping) to intrinsic semiconductors.
N-type semiconductors add pentavalent atoms (e.g., phosphorus), increasing electron numbers.
P-type semiconductors add trivalent atoms (e.g., boron), increasing hole numbers.

Diodes

PN junction forms from joining p-type and n-type semiconductors.
Depletion region near the PN junction has few charge carriers.
Barrier potential is the potential difference across the depletion region.
Forward bias (positive to p-type, negative to n-type).
Reverse bias (negative to p-type, positive to n-type).

Rectifiers

Rectifiers convert AC to DC.
Half-wave rectifiers use a single diode.
Full-wave rectifiers use multiple diodes.
Step-down transformers reduce AC voltage before rectification.

Transistors

Transistors amplify or switch electronic signals.
Bipolar junction transistors (BJTs) have three layers (base, collector, emitter).
NPN transistors have a p-type base between two n-type regions.
PNP transistors have an n-type base between two p-type regions.
Emitter current (IE), base current (IB), and collector current (IC) relate in IE = IB + IC.

General Information

Amplifier voltage gain depends on load resistance, transistor type, and biasing.
Semiconductor conductivity increases with temperature.
Silicon is a common semiconductor material.

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