Physics Chapter: Quantum and Photoelectric Effect
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Questions and Answers

What concept does Planck's quantum hypothesis primarily explain?

  • The emission of light by glowing lightbulbs (correct)
  • The interference of light waves
  • The diffraction patterns of light
  • The behavior of electromagnetic waves

Which phenomenon is associated with Maxwell's electromagnetic wave theory?

  • Radioactive decay
  • Thermal conduction
  • Chemical reactions
  • Interference and diffraction (correct)

At what condition does a blackbody begin to emit visible light?

  • At room temperature
  • In a vacuum
  • When exposed to radiation
  • When heated (correct)

What relationship does the document suggest exists between temperature and emitted light?

<p>Higher temperature increases the amount of emitted light (A)</p> Signup and view all the answers

Which of the following is a potential query left unanswered in the discussion?

<p>How does a glowing lightbulb emit light? (C)</p> Signup and view all the answers

What is the primary effect observed when electromagnetic radiation strikes the cathode in a photocell?

<p>Electric current is generated immediately. (D)</p> Signup and view all the answers

Which statement best describes the energy transfer during the photoelectric effect?

<p>Energy is transferred in discrete or quantized amounts. (C)</p> Signup and view all the answers

What happens when no electromagnetic radiation is incident on the cathode of a photocell?

<p>No current is observed in the ammeter. (C)</p> Signup and view all the answers

What role does the low voltage from the DC power source in a photocell serve?

<p>To prevent the spontaneous emission of electrons from the cathode. (A)</p> Signup and view all the answers

Which observation indicates the nature of light in the context of the photoelectric effect?

<p>Light exhibits no wave nature in the process. (A)</p> Signup and view all the answers

What happens when electromagnetic radiation is below the threshold frequency?

<p>No current is produced regardless of light intensity. (D)</p> Signup and view all the answers

Which statement reflects the relationship between frequency and the speed of emitted electrons?

<p>Higher frequency above the threshold increases the speed of emitted electrons. (B)</p> Signup and view all the answers

Why could Maxwell's wave theory not explain the photoelectric effect?

<p>It claimed that intensity affects electron emission energy. (C)</p> Signup and view all the answers

What characterizes the threshold frequency for different metals?

<p>It is specific to each metal and depends on its properties. (A)</p> Signup and view all the answers

What concept did Einstein introduce to explain the photoelectric effect?

<p>Light consists of discrete packets of energy called photons. (D)</p> Signup and view all the answers

What represents the relationship between the photon energy and the kinetic energy of the emitted photoelectron?

<p>$E_{photon} = E_k + E_{ext}$ (B)</p> Signup and view all the answers

Which statement accurately describes the effect of brightness on current in photoelectric emission?

<p>Brightness increases current if $f &lt; f_0$ (D)</p> Signup and view all the answers

What is the correct expression for the maximum kinetic energy of the emitted photoelectron?

<p>$E_{k_{max}} = hf - W$ (A)</p> Signup and view all the answers

What occurs when a photon interacts with an electron on a cathode in photoelectric effect?

<p>The electron can accumulate energy to eventually leave (C)</p> Signup and view all the answers

Which of the following correctly describes the conditions necessary for photoelectrons to be emitted from a metal surface?

<p>The incoming light must exceed a certain photon energy corresponding to frequency $f_0$ (C)</p> Signup and view all the answers

What does the maximum kinetic energy ($E_{max}$) of a photoelectron depend on?

<p>The energy of the photon minus the work function (B)</p> Signup and view all the answers

What happens when the voltage of the battery in the photoelectric cell is increased sufficiently?

<p>Electron repulsion becomes too strong for movement (D)</p> Signup and view all the answers

Which component of the photoelectric effect does the work function ($W$) represent?

<p>The minimum energy needed to release an electron from the surface (B)</p> Signup and view all the answers

Based on the graph of the photoelectric effect, how does the maximum kinetic energy of photoelectrons change with frequency?

<p>It increases linearly with increasing frequency (B)</p> Signup and view all the answers

What is the formula to calculate the maximum kinetic energy ($E_{max}$) of a photoelectron?

<p>$E_{max} = E_{photon} - W$ (A)</p> Signup and view all the answers

What did Einstein propose about photons in 1916?

<p>Photons can have momentum. (D)</p> Signup and view all the answers

What evidence did Arthur Compton provide in 1922?

<p>That scattered x-rays exhibit changes in wavelength. (B)</p> Signup and view all the answers

Which equation relates to kinetic energy in the context of the Compton effect?

<p>$E_k = rac{1}{2} mv^2$ (C)</p> Signup and view all the answers

What does the slope of the graph related to the Compton effect represent?

<p>Planck's constant. (D)</p> Signup and view all the answers

Which of the following statements about photons is NOT correct based on the Compton effect?

<p>Photons possess mass. (D)</p> Signup and view all the answers

What occurs to a photon when it interacts with an electron during the Compton effect?

<p>It loses energy and transfers momentum to the electron. (D)</p> Signup and view all the answers

Which statement accurately summarizes the Compton effect's demonstration of light properties?

<p>Light can scatter and transfer momentum, indicating particle-like behavior. (A)</p> Signup and view all the answers

In the context of the Compton effect, what happens to photons that are not scattered?

<p>They remain unscattered and pass through the target material. (A)</p> Signup and view all the answers

What role does the target material play in the Compton effect?

<p>It allows some photons to pass through unscattered and interacts with others. (B)</p> Signup and view all the answers

During the scattering process in the Compton effect, what happens to a photon in terms of its energy?

<p>It loses energy when interacting with electrons. (D)</p> Signup and view all the answers

What is the energy of a single photon emitted by a handheld laser with a wavelength of 630 nm?

<p>3.166 x 10^-19 J (C)</p> Signup and view all the answers

In electron volts, what is the energy of a photon emitted by a handheld laser with a wavelength of 630 nm?

<p>1.97 eV (C)</p> Signup and view all the answers

How many photons are emitted by a handheld laser with 100 mW power over 25 seconds?

<p>7.96 x 10^16 (A)</p> Signup and view all the answers

Who discovered the photoelectric effect and which device did he use?

<p>J.J. Thomson; cathode ray tube (D)</p> Signup and view all the answers

What is a necessary condition for the photoelectric effect to occur?

<p>Sufficiently high voltage (C)</p> Signup and view all the answers

What does Planck's constant represent in the equation $E = h u$?

<p>A proportionality factor for quantized energy (A)</p> Signup and view all the answers

How does Einstein's quantum theory differ from Planck's theory?

<p>Einstein applied quantization to light rather than just to atoms. (D)</p> Signup and view all the answers

In the equation $E = h f$, what does the variable f represent?

<p>The frequency of the light (B)</p> Signup and view all the answers

What is the significance of the equation $c = f au$ in relation to electromagnetic radiation?

<p>It demonstrates the relationship between speed, frequency, and wavelength. (B)</p> Signup and view all the answers

Which equation expresses the energy of a photon in relation to its wavelength?

<p>$E = rac{hc}{ au}$ (D)</p> Signup and view all the answers

What was the primary issue with classical physics in explaining blackbody radiation?

<p>It failed to account for energy distribution at higher frequencies. (A)</p> Signup and view all the answers

What does Planck's curve illustrate in the study of blackbody radiation?

<p>The prediction of emitted intensity across different frequencies at a certain temperature. (B)</p> Signup and view all the answers

What resolution did Planck provide to the mismatch between classic theory and observed data of blackbody radiation?

<p>Introduced the concept of quantized energy levels. (C)</p> Signup and view all the answers

How does the intensity of emitted radiation change as an object increases in temperature?

<p>It shifts to higher frequencies with greater intensity. (A)</p> Signup and view all the answers

What underlying concept did the UV catastrophe challenge in classical physics?

<p>The belief that all objects radiate energy in excess as temperature rises. (D)</p> Signup and view all the answers

Flashcards

Planck's Quantum Hypothesis

Explains light emission from objects by proposing light exists in small packets called quanta.

Maxwell's EM Wave Theory

Describes light as waves of electric and magnetic fields.

Blackbody

An object that absorbs all radiation and emits light based on its temperature.

Temperature & Emitted Light

The amount of light emitted by an object is related to its temperature.

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Lightbulb Filament

The part of the lightbulb that glows when heated.

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Blackbody Radiation

The electromagnetic radiation emitted by an idealized object that absorbs all incident radiation.

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UV Catastrophe

The discrepancy between classical physics predictions and observed blackbody radiation, specifically the predicted infinite energy at high frequencies, particularly in the UV.

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Planck's Curve

A theoretical curve representing the intensity vs. frequency of blackbody radiation. It's a solution to the UV Catastrophe.

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Max Planck

A physicist who proposed quantum theory to solve the UV Catastrophe.

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Classical Physics

Traditional physics frameworks that predicted infinite energy at higher frequencies, not true for blackbody radiation.

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What is the photoelectric effect?

When light shines on a metal surface, electrons can be emitted. This is the photoelectric effect.

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Threshold Frequency (f₀)

The minimum frequency of light needed to cause electron emission in the photoelectric effect.

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Intensity & Photoelectric Effect

The intensity of light does not affect the energy of emitted electrons, only the number of electrons released.

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Frequency & Electron Speed

Higher frequency light, as long as it's above the threshold, causes emitted electrons to travel faster.

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Einstein's Explanation

Einstein explained the photoelectric effect by proposing light exists as packets of energy called photons, each with energy proportional to its frequency.

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Photoelectric effect

The release of electrons from a metal surface when electromagnetic radiation (light) hits it.

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What is a photocell?

A device containing two electrodes in a vacuum tube used to study the photoelectric effect. Light shines on the cathode, causing electrons to be emitted and travel to the anode.

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What happens in the photoelectric effect?

When light hits the cathode, electrons are instantly emitted and travel to the anode, creating an electric current.

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What does the photoelectric effect suggest about light?

It supports the idea that light is made up of small packets of energy called photons, not just a continuous wave.

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Energy transfer in the photoelectric effect

The energy transfer from light to electrons is 'all or none' meaning either a photon gives all its energy to an electron, or it doesn't. No partial energy transfer happens.

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What is the role of photons in the photoelectric effect?

Photons transfer their energy to electrons on the metal's surface, causing some electrons to gain enough energy to escape.

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What is the relationship between photon energy and electron kinetic energy?

The photon's energy (hf) is equal to the work function (W) required to free the electron plus the electron's kinetic energy (Ek).

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How does the frequency of light affect the photoelectric effect?

The frequency of light determines the energy of the photons. Only frequencies above a threshold frequency (f0) can eject electrons.

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What is the relationship between brightness and photoelectric current?

Brightness determines the number of photons hitting the metal, which increases the photoelectric current. However, only if the frequency is above the threshold frequency.

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What is the maximum kinetic energy of a photoelectron?

The maximum kinetic energy of a photoelectron ($E_{max}$) is calculated as the difference between the energy of the incoming photon ($E_{photon}$) and the work function of the material ($W$). The formula is: $E_{max} = E_{photon} - W$

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What happens when the voltage in the circuit is increased?

Increasing the voltage in the circuit increases the repulsion of electrons, making it harder for them to move. If the voltage is high enough, the electrons will be repelled so strongly that they won't be able to move from the anode to the cathode.

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What is the relationship between frequency of light and maximum kinetic energy?

The maximum kinetic energy of photoelectrons increases linearly with the frequency of the incident light. This means that higher frequency light produces photoelectrons with greater energy.

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What is the work function?

The work function ($W$) is the minimum amount of energy required to remove an electron from the surface of a material.

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Compton Effect

A phenomenon where X-rays scatter off electrons, resulting in a change in their wavelength and energy, demonstrating the particle-like nature of light.

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Scattered X-ray

In the Compton Effect, this refers to the X-ray photon that has interacted with an electron and changed its direction and energy.

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Unscattered X-ray

In the Compton Effect, this refers to the X-ray photon that passed through the target material without interacting with any electrons.

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Energy Transfer in Compton Effect

During the Compton Effect, the scattered X-ray photon loses energy, which is transferred to the electron it interacts with.

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What does the Compton Effect tell us about light?

The Compton Effect provides evidence that light has particle-like properties (photons) and can interact with electrons, transferring momentum and energy.

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Handheld Laser Power

The amount of energy emitted by a handheld laser per unit time, typically measured in milliwatts (mW).

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Energy per Photon

The amount of energy carried by a single photon of light, calculated using Planck's constant, the speed of light, and the wavelength of the light.

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Electron Volts (eV)

A unit of energy often used to describe energy at the atomic and subatomic levels. One electron volt is equal to the energy gained by an electron when it moves through an electric potential difference of one volt.

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Threshold Frequency

The minimum frequency of light required to cause the photoelectric effect. Below this frequency, no electrons will be emitted, no matter how intense the light is.

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What is the Compton Effect?

The Compton Effect is when a photon collides with an electron and transfers some of its energy to the electron, causing the photon to lose energy and increase in wavelength. This demonstrates the particle nature of light as photons behave like particles with momentum.

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What does the Compton Effect prove?

The Compton Effect proves that photons, despite being wave-like, also behave as particles with momentum. This reinforces the dual nature of light, which can act as both a wave and a particle depending on the situation.

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What is the significance of Compton's discovery?

Compton's discovery provided strong evidence supporting the particle nature of light. It extended the understanding of light beyond Maxwell's wave theory and supported Einstein's earlier proposal about photon momentum.

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How do photons transfer energy in the Compton Effect?

Photons transfer energy to electrons during collisions, causing them to lose energy and increase in wavelength. This energy transfer is quantized, meaning the energy is transferred in discrete packets called quanta, just like in the photoelectric effect.

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What is the relationship between wavelength and energy in the Compton Effect?

In the Compton Effect, the scattered photon has a longer wavelength than the incident photon. This means the photon loses energy due to the collision with the electron. The amount of energy lost is directly proportional to the change in wavelength.

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Planck's Constant (h)

A fundamental constant in physics, representing the smallest unit of energy that can be emitted or absorbed by an object, related to the frequency of light.

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Photon

A tiny packet of light energy, like a particle, with energy proportional to its frequency.

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What is the relationship between light's energy and frequency?

The energy of a photon (light particle) is directly proportional to its frequency, meaning higher frequency light carries more energy.

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What is the equation for the energy of a photon?

E = h * f where E is the energy of the photon, h is Planck's constant, and f is the frequency of the light.

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How are frequency, wavelength, and the speed of light related?

The speed of light (c) is a constant, and it equals the product of frequency (f) and wavelength (λ). This means that higher frequency light has a shorter wavelength, and vice versa.

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