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Praxis (5266) - Physics > 5B1 Electromagnetic Waves > Flashcards

5B1 Electromagnetic Waves Flashcards

Explain the properties of electromagnetic waves, including the electromagnetic and visible light spectra.

1
Q

Define:

Electromagnetic waves

A

Waves composed of oscillating electric and magnetic fields.

The fields propagate perpendicular to each other and to the direction of wave propagation.

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2
Q

True or False:

Electromagnetic waves require a medium for propagation.

A

False

EM waves can travel through the vacuum of space.

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3
Q

What is the speed of electromagnetic waves in a vacuum?

A

c=3.00×10^8 m/s

The speed c is a fundamental constant of nature.

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4
Q

Why does light travel at a constant speed in a vacuum?

A

Speed is consistent due to electromagnetic induction and energy conservation.

If light slowed down, weakening electric and magnetic fields would extinguish the wave, preventing energy transfer. If it sped up, fields would grow uncontrollably, violating energy conservation.

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5
Q

What makes electromagnetic waves different from mechanical waves?

A

EM waves do not require a medium; mechanical waves do.

This makes EM waves capable of traveling through space.

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6
Q

Why does the speed of light decrease in glass?

A

Light interacts with the material’s atoms, causing delays in its propagation.

These interactions lead to refraction.

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7
Q

What happens to the frequency of a wave when it passes from a vacuum into a medium?

A

The frequency remains the same, but the wavelength decreases.

Frequency is constant across different media.

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8
Q

Why are electromagnetic waves considered transverse waves?

A

Because their electric and magnetic fields oscillate perpendicular to the direction of wave propagation.

Transverse waves have oscillations perpendicular to their direction of travel.

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9
Q

How are wavelength and frequency related in electromagnetic waves?

A

c=λf

They are inversely related: c = λf.

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10
Q

What differentiates one type of EM wave from another?

A

Wavelength and frequency.

Higher frequency waves, like X-rays, have shorter wavelengths than lower frequency waves, like radio waves.

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11
Q

Fill in the blank:

The range of all possible frequencies of electromagnetic waves is called the _______ _____.

A

Electromagnetic spectrum

The spectrum includes gamma rays, X-rays, visible light, and radio waves.

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12
Q

Define:

light

in terms of electromagnetic waves

A

A specific type of electromagnetic wave that falls within the visible spectrum and can be detected by the human eye.

While all light is electromagnetic radiation, not all electromagnetic waves are light.

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13
Q

What are the types of electromagnetic waves?

A
  • Radio waves
  • Microwaves
  • Infrared light
  • Visible light
  • Ultraviolet light
  • X-rays
  • Gamma rays

These types are categorized based on their frequency and wavelength.

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14
Q

Which type of electromagnetic wave has the lowest frequency?

A

Radio waves

They have the longest wavelength and are used for various communication technologies.

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15
Q

Fill in the blank:

The frequency of a radio wave is the _____ compared to the frequency of the vibrating electrons that produce it.

A

same

The frequency of the emitted wave matches that of the source.

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16
Q

True or False:

Infrared light has longer wavelengths than visible light.

A

True

Infrared wavelengths range from approximately 700 nm to 1 mm.

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17
Q

True or False:

Microwaves have a higher frequency than radio waves but lower than infrared waves.

A

True

Microwaves range from about 1 mm to 1 m in wavelength.

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18
Q

What property determines the energy of an electromagnetic wave?

A

Frequency

Higher frequency waves carry more energy.

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19
Q

What formula relates the energy of an electromagnetic wave to its frequency?

A

E=hf

h is Planck’s constant [6.626×10^(−34) J⋅s].

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20
Q

True or False:

The energy of electromagnetic waves increases with decreasing wavelength.

A

True

Shorter wavelengths correspond to higher frequencies and more energy.

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21
Q

What happens to the energy of a photon if its wavelength doubles?

A

The energy is halved.

Energy and wavelength are inversely related by E=(hc)/λ

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22
Q

Explain why gamma rays are more dangerous than radio waves.

A

Gamma rays have much higher frequencies and energy, which can damage biological tissue.

High-energy photons can ionize atoms and molecules.

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23
Q

Fill in the blanks:

The wavelength range for visible light is approximately ____ to ____ nanometers.

A

400; 700

Violet light is at the lower end (400 nm), and red light is at the higher end (700 nm).

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24
Q

What are the three electromagnetic waves with wavelengths that shorter than visible light?

A
  1. Ultraviolet
  2. X-rays
  3. Gamma rays

These waves generally carry higher energy.

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25
What **percentage** of the electromagnetic spectrum does visible light occupy?
Less than 1%. ## Footnote The electromagnetic spectrum spans a vast range, with visible light occupying only a tiny fraction.
26
What is **white light**?
It contains all wavelengths of the visible spectrum combined, appearing colorless to the human eye. ## Footnote White light can be dispersed into individual colors using a prism.
27
Which color in the **visible spectrum** has the **longest wavelength**?
**Red** has the longest wavelength. ## Footnote Red wavelengths carry less energy compared to blue or violet.
28
Which color in the **visible spectrum** has the **shortest wavelength**?
**Violet** has the shortest wavelength. ## Footnote Shorter wavelengths have higher energy.
29
# True or False: **Blue light** has a higher frequency than yellow light.
True ## Footnote Frequency is inversely proportional to wavelength.
30
What happens when a **prism** interacts with **white light**?
The prism disperses white light into its constituent colors, creating a spectrum. ## Footnote This phenomenon is called **dispersion**.
31
What determines the **color** an object appears?
The wavelengths of light that are **reflected or transmitted** by the object. ## Footnote Objects absorb some wavelengths and reflect others.
32
What happens when an **object absorbs all wavelengths** of visible light?
It appears **black**. ## Footnote Black objects do not reflect visible wavelengths.
33
What color do we perceive when all wavelengths of **visible light** are **reflected** equally?
White ## Footnote White is the combination of all colors in the visible spectrum.
34
Which **visible color** carries the most **energy**?
Violet ## Footnote Higher frequency corresponds to greater energy.
35
Name a **natural phenomenon** that showcases the entire **visible spectrum**.
A rainbow. ## Footnote Rainbows form when sunlight is refracted, reflected, and dispersed by raindrops.
36
What role does the **retina** play in color perception?
The retina contains cone cells that detect different wavelengths of light, enabling color vision. ## Footnote There are three types of cone cells, sensitive to red, green, and blue light.
37
# Define: Transparent material
Allows **light to pass through** in a straight line without significant scattering. ## Footnote Examples include clear glass and clean water.
38
# Define: opaque material
A material that **absorbs light without re-emitting it**, preventing light from passing through. ## Footnote Opaque materials often appear dark or colored due to their absorption properties.
39
# True or False: A **shadow** forms when an object completely blocks light.
True ## Footnote A complete shadow is called an **umbra**.
40
What is a **penumbra**?
A **partial shadow** that appears when only part of the light is blocked. ## Footnote Penumbras are common in astronomical events like solar eclipses.
41
In what region of the electromagnetic spectrum is the **resonance frequency** of electrons in glass?
In the **ultraviolet** region. ## Footnote This resonance leads to the absorption of ultraviolet light by glass.
42
What is the **Doppler effect** in **electromagnetic waves**?
**Apparent change in the frequency or wavelength** of electromagnetic waves **due to the relative motion** between the source and the observer. ## Footnote The Doppler effect can shift light towards the blue or red end of the spectrum.
43
# Define: Blueshift
A **decrease in wavelength**, making light appear bluer. ## Footnote This occurs when a light source approaches the observer.
44
What is a **redshift**?
An **increase in wavelength**, making light appear redder. ## Footnote This occurs when a light source moves away from the observer.
45
# True or False: A **higher relative speed** between a star and Earth causes a greater Doppler shift.
True ## Footnote Speed determines the magnitude of the frequency shift.
46
How does **Earth's motion** affect the Doppler shift?
The Earth's motion towards or away from a star **affects whether the shift is a blueshift or redshift**. ## Footnote Earth moving towards a star results in blueshift; moving away results in redshift.
47
# Fill in the blank: **Redshift** provides key evidence for the \_\_\_\_\_\_ of the universe.
expansion ## Footnote The discovery of redshift in galaxies supported the **Big Bang theory**.
48
What type of shift would occur if a star moves **perpendicularly** to Earth’s line of sight?
No Doppler shift. ## Footnote Only motion along the line of sight affects wavelength.
49
Which electromagnetic wave **applications** use the Doppler effect?
* Astronomy * Radar systems * Doppler weather monitoring ## Footnote Astronomers use it to study star motion; radar measures vehicle speed.
50
# Fill in the blanks: Astronomers use **redshift** to determine the \_\_\_\_\_\_ and \_\_\_\_\_\_ of **distant galaxies**.
velocity; direction ## Footnote Redshift measurements provide information about cosmic movement.
51
How is the **Doppler effect** used in **radar speed guns**?
Radar speed guns measure the speed of moving vehicles by **detecting the frequency shift** of reflected electromagnetic waves. ## Footnote A higher frequency shift indicates a faster approaching vehicle.
52
# True or False: The **Doppler effect** is used in **medical imaging**.
True ## Footnote Doppler ultrasound is used to visualize and measure blood flow within the body by detecting frequency changes.
53
# Fill in the Blank: In telecommunications, the **Doppler effect** is important for maintaining stable signals in \_\_\_\_\_\_\_ communication systems.
satellite ## Footnote The motion of satellites relative to Earth causes frequency shifts that need to be corrected for accurate signal transmission.
54
How does the **Doppler effect** help in **weather radar systems**?
It detects the motion and speed of raindrops, helping to track storms and measure wind speeds. ## Footnote Shifts in frequency indicate whether precipitation is moving toward or away from the radar.
55
Why is the **Doppler effect** significant in wireless **communication for high-speed trains**?
The movement of the train causes frequency shifts that must be compensated to maintain clear communication signals. ## Footnote This ensures stable internet and communication services onboard.
56
What does a **light-year** measure?
Distance ## Footnote A light-year is the distance a photon travels in one year in a vacuum.
57
Why is the **light-year** a useful **unit** in astronomy?
It **simplifies** the expression of immense distances across space. ## Footnote Instead of billions of kilometers, distances are given in light-years for clarity.
58
What is **lookback time**?
The time that has **passed between the emission of light and when it is detected** on Earth. ## Footnote Observing distant galaxies allows astronomers to look into the past.
59
What is an application of **radio waves** in **communication**?
They are used in **broadcasting**. ## Footnote Examples include AM/FM radio, television signals, and mobile phone communications. Radio waves have long wavelengths and low frequencies, making them ideal for transmitting signals over long distances.
60
# True or False: Infrared radiation is used for **night vision** equipment.
True ## Footnote Infrared radiation allows the detection of heat emitted by objects, even in total darkness.
61
# Fill in the blank: ____ waves are commonly used in **medical imaging**, such as MRI scans.
Radio ## Footnote Radiofrequency waves interact with the magnetic fields in MRI to produce detailed images of the body's internal structures.
62
Why are **microwaves** used in cooking?
They cause **water molecules** in food to vibrate, generating heat and cooking the food. ## Footnote This process is efficient for heating food quickly.
63
Which type of wave is commonly used for **sterilizing medical equipment**?
Gamma rays ## Footnote Gamma rays destroy bacteria and viruses through high-energy radiation.
64
How are **X-rays** useful in the medical field?
They are used to visualize internal structures of the body, such as bones, by passing through soft tissues but being absorbed by denser materials. ## Footnote Xrays pass through soft tissues but are absorbed by denser materials, like bone. X-rays revolutionized diagnostics by allowing non-invasive imaging.
65
What are two common applications of **ultraviolet light**?
1. Water purification 2. Sterilization systems ## Footnote UV light kills microorganisms by disrupting their DNA.
66
# Fill in the blank: **Terahertz radiation** is being explored for use in \_\_\_\_\_\_ screening.
Security ## Footnote Terahertz waves can detect concealed objects without harmful radiation exposure.
67
Why are **gamma rays** effective in cancer treatment?
They **target and destroy cancerous cells** due to their high energy. ## Footnote This process is known as radiation therapy.

Praxis (5266) - Physics (38 decks)

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