Big Bang Theory Notes

Evidence for the Big Bang

Cosmic Microwave Background Radiation (CMBR)

• CMBR is a faint glow of leftover heat from the Big Bang, which occurred around 13.8 billion years ago.
• The uniformity of CMBR in every direction and its temperature are consistent with a universe expanding over billions of years.
• The discovery of CMBR in the 1960s matched predictions of what should remain from the initial explosion, supporting the Big Bang theory.

Redshifting

• Redshifting is the stretching of light waves, making them appear more red, which occurs when objects emitting light move away from us.
• This indicates that the universe is expanding, supporting the Big Bang theory.
• The redshift of light from distant galaxies and the Cosmic Microwave Background Radiation provides evidence for cosmic expansion and the Big Bang origin of the universe.

Composition of Stars in our Universe

• Stars are primarily composed of hydrogen and helium, with smaller amounts of other elements like carbon and oxygen.
• The abundance of hydrogen and helium in the universe supports the Big Bang theory, as they formed during the universe's expansion from a hot, dense point.
• The formation of heavier elements like carbon and oxygen through stellar nucleosynthesis and their scattering throughout the universe also supports the Big Bang theory.

Anatomy of a Wave

• A wave is the movement of energy through a medium, such as air, water, or space.
• Frequency is the amount of complete wave cycles in one second, measured in Hertz (Hz).

Wavelength

• Wavelength is the distance between two equal points on a wave.
• It is denoted by the Greek letter 'lambda' (λ) and measured in meters.
• It is the distance between two successive crests or troughs.

Amplitude

• Amplitude is the distance between the equilibrium line (EL) and the trough or crest.
• Units depend on the type of wave (e.g., sound waves in decibels (Db)).
• It is the height of the wave from the equilibrium line to the crest or trough.

Period

• Period is the time taken to complete one wave cycle.
• It is denoted as 1/t and measured in seconds (s).

Key Concepts

• Equilibrium line: The central line around which the wave oscillates.
• Trough: The lowest point of the wave below the equilibrium line.
• Crest: The highest point of the wave above the equilibrium line.
• Frequency (Hz): The number of complete wave cycles per second.

Wave Types

• Transverse wave: A wave in which the energy moves perpendicular to the direction of the wave.
• Examples: Light waves, electromagnetic waves.
• Longitudinal wave: A wave in which the energy moves parallel to the direction of the wave.
• Example: Sound waves.

Wave Speed

• Wave speed (v) = Frequency (f) × Wavelength (λ).
• Waves carry energy.

Speed of Sound and Its Mediums

• The speed of sound in air is approximately 340 meters per second (m/s).
• Sound travels fastest in solids, slower in liquids, and slowest in gases due to the close proximity of particles in solids, which allows for efficient transmission of vibrations.

Factors Affecting Speed of Sound

• Sound travels faster in steel than in wood because steel is denser and more elastic, allowing sound waves to travel more quickly.
• Particles in solids are very close together, enabling them to pass on vibrations more efficiently than particles in gases, which are farther apart.

Amplitude and Loudness of Sound

• A sound wave with a larger amplitude is perceived as louder because it carries more energy.

Frequency and Wavelength

• The wave with the most cycles per second has the highest frequency, which corresponds to a higher pitch.
• Frequency is directly related to pitch, with higher frequency corresponding to a higher pitch.
• Frequency is measured in Hertz (Hz), with 1 Hz representing one cycle per second.

Speed of Sound and Its Mediums

• Sound travels fastest in solids, slower in liquids, and slowest in gases because particles are closer together in solids, allowing vibrations to transmit more efficiently.
• The speed of sound in air is approximately 340 meters per second (m/s).

Transmission of Sound through Materials

• Sound travels through materials by passing vibrations from particle to particle.
• Particles in solids are very close together, allowing them to pass on vibrations more efficiently than particles in gases, which are farther apart.

Speed of Sound in Different Materials

• Sound travels faster in steel than in wood because steel is denser and more elastic, allowing sound waves to travel more quickly.

Amplitude and Loudness of Sound

• A sound wave with a larger amplitude is perceived as louder because it carries more energy.

Frequency and Wavelength

• The wave with the most cycles per second (highest frequency) has the highest pitch.
• Frequency is directly related to pitch, with higher frequency corresponding to a higher pitch.
• Frequency is measured in Hertz (Hz) and represents the number of cycles per second.
• A wave with the same frequency but higher amplitude represents a louder sound.
• To determine the time period of a wave, count the number of squares between peaks and multiply by the time each square represents (0.001 s).
• Frequency is the inverse of the time period (Frequency = 1 / Time Period).

Wave Terminology

• A wave is a vibration that transfers energy.
• Amplitude is the height from the middle of the wave to the crest or trough, and wavelength is the distance between two consecutive crests or troughs.
• Loudness depends on amplitude, and sound waves are longitudinal waves, meaning the vibration direction is the same as the wave direction.

Practical Applications

• Sound travels faster in solids because the particles are more closely packed, allowing vibrations to transmit more efficiently.
• The amplitude of a sound wave affects its loudness, with larger amplitude meaning louder sound.
• Frequency refers to the number of wave cycles per second, while wavelength is the distance between two consecutive points on a wave, with higher frequency meaning shorter wavelength.