2A3 Absorption and Emission

Question 1

Define:

electromagnetic radiation

Answer 1

A wave propagating through space, carrying energy at the speed of light.

It consists of oscillating electric and magnetic fields.

Electromagnetic radiation travels at the speed of light since it does not require a medium to travel.

Question 2

How does light behave according to quantum theory?

Answer 2

It behaves as both a particle and a wave.

This dual nature is central to quantum mechanics.

Question 3

What is the electromagnetic spectrum?

Answer 3

The range of all types of electromagnetic radiation.

It includes all seven types of light listed from the lowest to the highest frequency.

Question 4

List seven types of electromagnetic waves in order of decreasing wavelengths.

Answer 4

1. Radio waves
2. Microwaves
3. Infrared light
4. Visible light
5. Ultraviolet light
6. X-rays
7. Gamma rays

Gamma rays have the shortest wavelength and highest frequency, while radio waves have the longest wavelengths and shortest frequency.

Question 5

What is the visible spectrum range?

Answer 5

400 to 700 nm

It spans from violet (shorter wavelength) to red (longer wavelength) light.

The frequency range of visible ranges from 400 to 750 trillion Hertz.

Question 6

What are radio waves characterized by?

Answer 6

• Low frequency
• Long wavelength

Wavelength above 1 millimeter.

Frequency below 300 billion Hz.

Question 7

List four uses of microwaves.

Answer 7

1. Microwave ovens
2. Radar
3. GPS
4. Wi-Fi

They have wavelengths between 1 millimeter and 25 micrometers.

Question 8

Fill in the blank:

The energy of light is directly proportional to __________?

Answer 8

frequency

Energy increases with an increase in frequency, according to the energy equation where E=hc/λ. Gamma rays are high frequency and are therefore contain huge amounts of energy.

Question 9

Fill in the blanks:

Infrared light is defined as having wavelengths between _______ and _________ micrometers.

Answer 9

25; 2.5

Infrared means ‘below red’ in Latin.

Question 10

Fill in the blanks:

Ultraviolet light wavelengths range from ______ to _______ nanometers.

Answer 10

1; 400

Ultraviolet light can cause sunburns.

Question 11

Which types of electromagnetic waves are generally harmless to humans?

Answer 11

• Radio waves
• Microwaves
• Infrared light
• Visible light

These have low frequencies and long wavelengths.

High-frequency waves like ultraviolet light, X-rays, and gamma rays strip electrons from materials and damage human cells.

Question 12

Explain why X-rays have higher energy than visible light.

Answer 12

• Higher frequencies
• Shorter wavelengths

Higher-frequency waves carry more energy.

X-rays are capable of damaging human cells but are useful in medical diagnostics with proper protection.

Question 13

What is a wave?

Answer 13

A propagating and oscillating deformation of some quanta or medium.

Waves can take various forms such as water, sound, and electromagnetic waves.

Question 14

List five parameters used to describe waves.

Answer 14

1. Amplitude
2. Frequency
3. Wavelength
4. Speed
5. Period

These characteristics help quantify and understand wave behavior.

Question 15

Define:

wavelength

Answer 15

The distance between two consecutive peaks or troughs of a wave.

This value is often measured in meters or nanometers.

Question 16

Define:

frequency

Answer 16

The number of completed wave cycles in a given period of time.

It is measured in hertz (Hz), where 1 Hz equals 1 wave per second or 60 revolutions per minute.

A frequency of 15 Hz indicates 15 wave cycles per second.

Frequency (ν) is given by the formula ν = 1/T, where T is the period of the wave.

Question 17

What is the relationship between frequency and wavelength?

Answer 17

The two are inversely proportional.

Higher frequency results in shorter wavelengths while lower frequency results in longer wavelengths.

The relationship is described by the formula λ = c /ν, where λ is the wavelength, c is the speed of light, and ν is the frequency.

Question 18

Define:

period

Answer 18

The amount of time it takes to complete a wave cycle.

Periods can be calculated by taking the inverse of the frequency, which means dividing 1 by the frequency value.

Question 19

What is the formula for calculating the wavelength (λ) of light?

Answer 19

λ = v / f

v refers to the speed of light, and f is the frequency of the wave. When calculating the wavelength of other kinds of waves, v will refer to the wave speed, not the speed of light.

Question 20

Define:

amplitude

Answer 20

The distance from the midline of a wave to its crest or trough.

Amplitude also measures the amount of energy transported by the wave.

Higher amplitude means more energy carried by the mechanical and electronegative waves.

It is measured in meters for transverse waves and in units of pressure for longitudinal waves.

Question 21

What is the difference between amplitude and frequency?

Answer 21

Amplitude measures energy, while frequency measures how often waves occur.

Two waves can have the same frequency but different amplitudes.

Question 22

What is emitted when an electron transitions from a higher energy level to a lower energy level?

Answer 22

A photon

It can be defined as a quantum of electromagnetic radiation, representing a particle of light.

The emitted photon varies in frequency and can be in the range of ultraviolet, visible, or infrared light.

Question 23

What is the relationship between energy and frequency of a photon?

Answer 23

Energy is directly proportional to frequency.

Higher-frequency photons have more energy.

This is described by Planck’s equation, E=hν, where E is the energy, ν is the frequency, and h is Planck’s constant.

Question 24

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

Answer 24

3.31×10^-19  J

Using E=hν, where h=6.626×10^-34 J and ν = 5×10^14 Hz.

Question 25

# Fill in the blank. The **photoelectric effect** involves the emission of \_\_\_\_\_\_\_\_\_\_\_ from a metal surface.

Answer 25

electrons ## Footnote Electrons are emitted when light of sufficient energy strikes a metal surface.

Question 26

How does the photoelectric effect support the **particle nature of light**?

Answer 26

Light ejects electrons from a material **only if its frequency is above a threshold**. ## Footnote This demonstrates that light is quantized into photons. Photon quantization implies that light is emitted or absorbed in discrete packets called photons.

Question 27

What is the relationship between **energy quantization and electron transitions**?

Answer 27

Energy is quantized, meaning electrons **can only occupy specific allowed energy levels**. ## Footnote This quantization restricts the energies that can be absorbed or emitted.

Question 28

What **type of spectrum** is produced by electronic transitions?

Answer 28

Line spectrum ## Footnote Each element's spectrum is unique due to specific energy level differences.

Question 29

What happens to electrons when an atom **absorbs energy**?

Answer 29

Electrons **become excited** and move to higher energy orbitals. ## Footnote Excited electrons carry more energy and oscillate quicker than ground state electrons.

Question 30

What determines the **color of light emitted** by an atom?

Answer 30

The **energy difference** between two electronic levels. ## Footnote Larger energy gaps produce shorter wavelengths. The specific wavelengths correspond to different colors in the visible spectrum.

Question 31

Explain why **visible spectra** are limited to certain colors.

Answer 31

Only **specific wavelengths** correspond to energy differences in visible transitions. ## Footnote Visible transitions occur in the range of *400* to *700* nm.

Question 32

What is the significance of **temperature and pressure** in electronic transitions?

Answer 32

They **affect energy changes** within an atom. ## Footnote Due to this, experiments should be conducted at sea level and room temperature unless otherwise specified.

Question 33

How do spectral lines **correlate** with electronic transitions?

Answer 33

Each line corresponds to a **specific transition** between energy levels. ## Footnote Lines indicate emitted or absorbed photons.

Question 34

List *three* **series named after physicists** that describe electronic transitions in hydrogen.

Answer 34

1. **Lyman series** that correspond to transitions ending at *n=1*. 1. **Balmer series** that correspond to transitions ending at *n=2*. 1. **Paschen series** that correspond to transitions ending at *n=3*. ## Footnote Lyman transitions occur in the ultraviolet region. Balmer transitions occur in the visible region. Paschen transitions occur in the infrared region.

Question 35

# Fill in the blank: **Higher energy transitions** correspond to \_\_\_\_\_\_\_\_\_\_\_ wavelengths.

Answer 35

shorter ## Footnote Energy and wavelength are inversely proportional.

Question 36

# Define: spectroscopy

Answer 36

The process of **identifying** a compound **by its electron emission spectrum**. ## Footnote It involves analyzing atomic spectra. This relies on the specific colors of light emitted when electrons return to ground state. Spectroscopy applies spectrometers to measure spectral lines to determine chemical composition.

Question 37

# True or False: All elements produce the **same spectral lines**.

Answer 37

False ## Footnote Each element has unique spectral lines due to specific energy levels. The unique spectral lines act as fingerprints for elements allowing atomic identification.