Answer:
A) I = 0.09947 W
, β = 109 db
, B) β = 116 db
, β = 116 db
, c) Δβ = 7 dB,
D) P = 50.27 W
Explanation:
A) The intensity of a spherical sound wave is
I = P / A
where A is the area of the sphere where the sound is distributed
A = 4π R²
we substitute
I = P / 4πR²
let's calculate
I = 500 / (4π 20²)
I = 0.09947 W
to express this quantity in decibels we use relate
β = 10 log (I / I₀)
The detectivity threshold is I₀ = 1 10⁻¹² W / m²
β = 10 lob (0.09947 / 10⁻¹²)
β = 10 (10.9976)
β = 109 db
B) intensity at r = 10m
I = 500 / (4π 10²)
I = 0.3979 W / m²
β = 10 log (0.3979 / 10⁻¹²)
β = 10 (11.5997)
β = 116 db
C) the change in intensity in decibles is
Δβ = β₁ - β₂
Δβ = 116 - 109
Δβ = 7 dB
D) let's find the intensity for 100 db
I = I₀ 10 (β / 10)
I = 10⁻¹² 10 (100/10)
I = 10⁻² W / m²
Thus
P = I A
P = I 4π R²
P = 10⁻² 4π 20²
P = 50.27 W
Given:
rod of circular cross section is subjected to uniaxial tension.
Length, L=1500 mm
radius, r = 10 mm
E=2*10^5 N/mm^2
Force, F=20 kN = 20,000 N
[note: newton (unit) in abbreviation is written in upper case, as in N ]
From given above, area of cross section = π r^2 = 100 π =314 mm^2
(i) Stress,
σ
=force/area
= 20000 N / 314 mm^2
= 6366.2 N/mm^2
= 6370 N/mm^2 (to 3 significant figures)
(ii) Strain
ε
= ratio of extension / original length
= σ / E
= 6366.2 /(2*10^5)
= 0.03183
= 0.0318 (to three significant figures)
(iii) elongation
= ε * L
= 0.03183*1500 mm
= 47.746 mm
= 47.7 mm (to three significant figures)
Half a wavelength must fit exactly into the length of a vibrating cord
Explanation:
A standing wave is a wave produced by the interference between a wave and its reflection. A standing wave is the wave produced, for instance, in the string of a guitar.
A standing wave is different from other types of waves because it does not propagate in space, but it only vibrate in a fixed region.
A standing wave is characterized by the presence of:
- Nodes: points where the amplitude of the wave is always zero (destructive interference)
- Antinodes: points where the amplitude of the wave is maximum (constructive interference)
The two ends of the string do not vibrate: this means that they always correspond to two nodes. If we take the fundamental mode of vibration of the string (so, no other nodes), we see that the length of the string corresponds to the distance between two consecutive nodes: however, this also corresponds to half the wavelength of the wave. Therefore, we can conclude that the correct option is
Half a wavelength must fit exactly into the length of a vibrating cord
Learn more about waves:
brainly.com/question/5354733
brainly.com/question/9077368
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The resistance between the opposite ends will be 3R/4.
