2A4 Basic Quantum Physics

Question 1

What is wave-particle duality?

Answer 1

The concept that light and all particles can be described as both a particle and a wave.

For example, light can act as a wave (diffraction) or as particles (photons).

Question 2

Define:

Photon

Answer 2

A massless particle that carries light energy.
## Footnote

They are massless particles that travel at the speed of light in a vacuum and belong to the class of boson particles.

Question 3

Define:

Electromagnetic radiation

Answer 3

A form of energy that travels through space as oscillating electric and magnetic fields.

Electromagnetic radiation includes light, radio waves, and X-rays, and it propagates at the speed of light in a vacuum.

Question 4

Define:

Electromagnetic spectrum

Answer 4

The full range of electromagnetic radiation, sorted by wavelength or frequency.

Each type differs in energy and applications.

Question 5

How does wave-particle duality connect matter and electromagnetic radiation?

Answer 5

Both matter and electromagnetic radiation exhibit wave-like and particle-like behaviors.

Electromagnetic radiation (like light) behaves as waves in diffraction and interference, but as particles (photons) in the photoelectric effect. Matter, such as electrons, also shows wave-like behavior in experiments like diffraction.

Question 6

Fill in the blank:

The energy of a photon is directly proportional to its ________.

Answer 6

frequency

Higher frequency corresponds to higher energy, as described by E=hν.

Question 7

What is the relationship between wavelength and frequency?

Answer 7

They are inversely related.

A higher frequency means shorter wavelength, and vice versa. The relationship is represented as c = λ * f, where λ represents the wavelength and f represents frequency.

Question 8

What is the significance of Planck’s constant in quantum physics?

Answer 8

It relates the energy of a photon to its frequency:
E=hv

h (Planck’s constant) is a fundamental constant in quantum mechanics. It respresents 6.62607015 × 10^-34 m² kg / s

Question 9

Who proposed the idea of wave-particle duality for electrons?

Answer 9

Louis de Broglie

He suggested that particles like electrons have a wavelength, described by λ = h/p, whwere p is momentum.

Question 10

How does the wave-particle duality relate to the development of quantum mechanics?

Answer 10

Electrons & photons behave as both waves and particles, forming a core principle of quantum mechanics.
## Footnote

This dual behavior was demonstrated in experiments like electron diffraction and the photoelectric effect, challenging classical physics.

Question 11

What is the relationship between the wavelength of light and its energy?

Answer 11

Energy is inversely proportional to wavelength.

Shorter wavelengths have higher energy (E=hc/λ).

Question 12

Which experiment proved the wave nature of light?

Answer 12

The Double Slit Experiment

This experiment, conducted by Thomas Young, showed interference patterns.

Question 13

True or false:

Young’s double-slit experiment, originally for light, was later replicated with electrons to show wave-particle duality.

Answer 13

True

This demonstrated that even particles like electrons can create interference patterns, behaving as waves.

Question 14

Fill in the blank:

Isaac Newton proposed that light is made of particles, while Christian Huygens suggested that light behaves as a _____.

Answer 14

wave

Newton’s particle theory explained reflection and refraction, while Huygens’ wave theory accounted for phenomena like diffraction and interference.

Question 15

What is the phenomenon where light bends around obstacles or spreads after passing through a narrow slit?

Answer 15

Diffraction

Diffraction demonstrates the wave nature of light, as it cannot be explained by particle behavior alone.

Question 16

Fill in the blanks:

Newton’s particle theory failed to explain _______ and _______, supporting the wave theory.

Answer 16

diffraction; interference

These phenomena involve the bending and overlapping of light waves, which cannot be accounted for by a purely particle-based theory.

Question 17

True or false:

The concept of wave-particle duality explains why particles can interfere with each other, similar to waves.

Answer 17

True

Quantum mechanics uses the wave-particle duality to explain phenomena such as interference patterns observed in the double-slit experiment with particles like electrons.

Question 18

What phenomenon, observed in the Compton scattering experiment, provided evidence for light’s particle nature?

Answer 18

A decrease in wavelength when X-rays scatter off electrons.

Arthur Compton showed photons transfer momentum to electrons, supporting wave-particle duality.

Question 19

Fill in the blank:

Electromagnetic energy travels at the speed of _______ in a vacuum.

Answer 19

light

3×10⁸ m/s² is the universal speed limit for electromagnetic waves.

Question 20

Which type of electromagnetic radiation is considered the least dangerous?

Answer 20

Radio waves

Radio waves have the longest wavelength and lowest frequency in the Electromagnetic spectrum.

Question 21

Fill in the blanks:

The visible spectrum ranges from approximately ____ nm (violet) to ____ nm (red).

Answer 21

400 nm to 700 nm

The visible spectrum represents the small portion of the electromagnetic spectrum detectable by the human eye.

Question 22

What type of electromagnetic radiation is used in medical imaging to view bones?

Answer 22

X-rays

X-rays have high energy and short wavelengths, allowing them to penetrate soft tissues but not dense materials like bones.

Question 23

What kind of electromagnetic waves are commonly used in communication technologies, such as television and radio?

Answer 23

Radio waves

Their long wavelengths and low frequencies make them suitable for transmitting signals over long distances.

Question 24

Fill in the blanks:

Gamma rays are the most energetic form of electromagnetic radiation and are produced by ______ _______.

Answer 24

Nuclear reactions

or radioactive decay

Gamma rays have extremely short wavelengths and high energy, making them useful in cancer treatments and astrophysics.

Question 25

Which type of radiation is responsible for **sunburns** and can also help the body produce **vitamin D**?

Answer 25

Ultraviolet (UV) radiation ## Footnote UV radiation has higher energy than visible light but can damage skin cells with overexposure.

Question 26

# True or false: **Microwaves** are used in radar systems and to heat food by causing water molecules to vibrate.

Answer 26

True ## Footnote Microwaves interact with water and fat molecules, generating heat in materials with these components.

Question 27

# Define: Photoelectric effect

Answer 27

The **emission of electrons** from a material when it absorbs light of sufficient energy. ## Footnote This phenomenon is essential for the operation of devices like solar panels.

Question 28

# True or false: The **photoelectric effect** demonstrates the particle nature of light.

Answer 28

True ## Footnote The ejection of electrons from a surface occurs because light delivers energy in discrete quanta (photons).

Question 29

Who proposed the theory of the **photoelectric effect**?

Answer 29

Albert Einstein ## Footnote Einstein's theory was published in 1905 in his paper titled 'On a Heuristic Point of View Concerning the Production and Transformation of Light.'

Question 30

How did **J.J. Thomson** contribute to the study of the photoelectric effect?

Answer 30

He demonstrated that the **particles emitted** in the photoelectric effect were **electrons**. ## Footnote His experiments with **cathode rays** led to the discovery of the electron and its behavior in various processes.

Question 31

# True or false: Increasing the **intensity of light** increases the **kinetic energy** of ejected electrons in the photoelectric effect.

Answer 31

False ## Footnote The energy of ejected electrons depends on the **frequency** of light, not its intensity.

Question 32

What did **Philipp Lenard** discover about the photoelectric effect?

Answer 32

He found that the **energy** of emitted electrons **depends on the frequency** of light, not its intensity. ## Footnote Lenard's experiments laid the groundwork for Einstein's quantum explanation.

Question 33

# Fill in the blank: In the **photoelectric effect**, photons transfer \_\_\_\_\_\_\_ to electrons.

Answer 33

energy ## Footnote The energy must exceed the material’s work function to eject electrons.

Question 34

What does **work function** mean in the photoelectric effect?

Answer 34

The **minimum energy needed to eject an electron** from a material’s surface. ## Footnote Light with frequency below the threshold cannot cause electron emission.

Question 35

What aspect of light does the photoelectric effect contradict about **classical physics**?

Answer 35

Classical physics **wrongly assumed intensity, not frequency**, controls ejection.' ## Footnote The photoelectric effect shows that this is not true. Quantum mechanics resolved this contradiction by introducing the concept of photons.

Question 36

How does the photoelectric effect support the principles of **quantum mechanics**?

Answer 36

The photoelectric effect demonstrates that light behaves as quanta of **energy (photons)**, supporting the idea that energy is quantized. ## Footnote This concept, introduced by Planck and Einstein, is a cornerstone of quantum mechanics, contrasting with the classical wave theory of light.

Question 37

# True or false: The **photoelectric effect** helped establish the idea that energy is emitted and absorbed in **discrete packets**, not continuously.

Answer 37

True ## Footnote Einstein’s explanation of the photoelectric effect provided evidence for the quantization of energy, a key principle in quantum mechanics.

Question 38

What range of the electromagnetic spectrum can cause the **photoelectric effect** in most materials?

Answer 38

**Ultraviolet** and higher frequencies. ## Footnote These frequencies have sufficient energy to overcome most work functions.

Question 39

# True or false: The photoelectric effect supports the **wave model of light**.

Answer 39

False ## Footnote It supports the particle model by showing light delivers energy in discrete photons.

Question 40

# Fill in the blank: The **photoelectric effect** supports the idea that electromagnetic radiation is made of discrete packets of energy called \_\_\_\_\_\_.

Answer 40

photons ## Footnote This concept was key to the development of quantum mechanics.

Question 41

What is the **threshold frequency** in the photoelectric effect?

Answer 41

The **minimum frequency of light required** to eject electrons from a material's surface. ## Footnote Light below this frequency will not cause electron emission, regardless of intensity.

Question 42

# True or false: Increasing the **intensity of light** above the **threshold frequency** will increase the number of emitted electrons.

Answer 42

True ## Footnote While **intensity does not affect the energy** of electrons, it increases the number of photons hitting the surface.

Question 43

# True or false: Infrared light **cannot trigger** the photoelectric effect.

Answer 43

True ## Footnote Infrared photons generally lack the energy needed to dislodge electrons, as their energy is below the threshold frequency required for the photoelectric effect.

Question 44

How did **Heinrich Hertz’s experiments** contribute to the discovery of the photoelectric effect?

Answer 44

He observed that **UV light enhanced electric sparks** between metal electrodes, providing the first evidence of the photoelectric effect. ## Footnote Hertz's experiments involved a source of electromagnetic radiation and a receiver that generated a spark.

Question 45

What is the purpose of **photoelectron spectroscopy (PES)**?

Answer 45

To **identify the elements** that make up a material by measuring ejected electron energy. ## Footnote This involves shining a monochromatic X-ray at the material.

Question 46

How does **nuclear medicine** utilize the **photoelectric effect**?

Answer 46

By using **radiation** to destroy cancer cells and shrink tumors. ## Footnote Typically, X-rays or gamma rays are employed in this treatment. Photoelectric effect helps in imaging & radiation therapy.

Question 47

# True or false: The photoelectric effect is used in **night vision devices**.

Answer 47

True ## Footnote Night vision devices amplify low-intensity light by converting photons into electrons using the photoelectric effect.

Question 48

How is the photoelectric effect used in **astronomy**?

Answer 48

In **photoelectric photometers**, which measure the intensity of starlight. ## Footnote This helps astronomers study the properties of stars and other celestial objects.

Question 49

What device uses the **photoelectric effect** to convert sunlight into electricity?

Answer 49

Solar panels | (photovoltaic cells) ## Footnote These cells convert light into electrical energy, a practical application of the photoelectric effect.

Question 50

What role does the **photoelectric effect** play in **photoelectric sensors**?

Answer 50

It **detects light and converts it** into an electrical signal. ## Footnote These sensors are used in automatic doors, burglar alarms, and other devices.