PHY101 Final Term Lecture-wise Short Questions

Lecture # 19

What do sound waves correspond to?

Longitudinal oscillations of density.

How does density vary in sound waves?

Density of air is greater in some places and less in others as sound waves move.

What is the minimum energy humans can hear?

About 10 watts per cm, known as the threshold of hearing.

What unit is used to measure sound intensity?

What is the sound level on a quiet street?

About 30 dB.

What sound level does a pressure horn create?

About 90 dB.

At what sound level does serious ear damage occur?

Around 120 dB.

How is a sound wave moving in a certain direction described?

By the equation 2 * sin(π * x/λ - ω * t).

What does the variable "u" represent in the formula?

The displacement of air particles due to sound wave propagation.

If speed "v" is kept constant, what happens to density over time?

Density remains constant, requiring movement at the speed of sound.

What happens when "x" is replaced by "x + λ" in the formula?

What does "T" represent in the context of a sound wave?

Time period of the sound wave, the time it takes to repeat itself.

What is the relationship between frequency and time period?

Frequency (f) is inversely related to time period (T) through f = 1/T.

What are wavenumber and angular frequency?

Wavenumber (k) and angular frequency (ω) are introduced in wave equations.

What causes the Doppler Effect in sound?

Relative motion between source and observer.

What happens when an observer is moving toward a source?

The observer receives more waves, resulting in a higher frequency (pitch).

How does the frequency actually heard change when an observer moves toward the source?

Frequency increases as the observer moves toward the source.

What happens to wavelength as the source moves toward the observer?

Wavelength is reduced.

What frequency does an observer hear when a source and observer both move?

A complex relationship between their motions affects the frequency heard.

What are the key considerations for the Doppler Effect?

Observer's motion, source's motion, and the change in frequency.

What term describes the energy carried by sound waves?

Intensity.

What is the unit for measuring intensity?

What sound level is typical on a quiet street?

About 30 dB.

What sound level can cause ear damage?

Around 120 dB.

How is a sound wave described mathematically?

Through equations involving density, speed, displacement, and time.

What does the displacement "u" represent in sound wave equations?

The variation of air particle positions caused by the sound wave.

What happens to density when "x" is replaced by "x + λ"?

What is the relationship between frequency and time period in a sound wave?

Inversely proportional, with frequency (f) = 1/time period (T).

What is the significance of wavenumber and angular frequency?

Introduced as mathematical terms in sound wave equations.

What causes the Doppler Effect in sound, and what does it influence?

Relative motion between source and observer; it affects perceived frequency.

Lecture # 20

What is wave motion?

Self-repeating motion transporting energy from one point to another.

Name two basic kinds of waves and their examples. (a) Longitudinal Waves: Examples include sound and "P-type" earthquake waves. (b) Transverse Waves: Examples include light waves and "S-type" earthquake waves.

How is energy transported by waves?

Waves transport energy, not matter.

Define amplitude and its relation to intensity. Amplitude is the wave height; intensity is proportional to the square of the amplitude.

What kind of waves does a sound source at the origin radiate?

Spherical waves.

How is total radiated power related to intensity?

Intensity is inversely proportional to the square of the distance from the source.

What happens when waves interfere constructively and destructively?

Constructive interference: In-phase waves amplify; destructive interference: out-ofphase waves reduce amplitude.

How is the speed of sound in a medium related to density and bulk modulus?

Speed of sound (v) = √(Bulk modulus (B) / Density (ρ)).

What is a pulse in wave motion?

A burst of energy with various shapes, mathematically represented as y(x, t) = f(x - vt).

What does the shape of a pulse look like at time 0 and a later time t?

The shape remains the same but shifts to the right.

How is velocity related to the shape of a pulse?

The velocity of the pulse equals the rate of change of phase.

What is the term for a wave's maximum displacement?

Amplitude.

Longitudinal waves have oscillation parallel to wave travel, while transverse waves have perpendicular oscillation.