The average intensity a distance d₁ = 1.6 m from an omni-directional light bulb is el1 = (a) Write a symbolic expression for the intensity a distance d₂ = 2.5 m from the same bulb, in terms of ₁, d₁ and d₂, and calculate its numeric value. d2 (32 (d₂.)³7₁ 0.533 .3 W/m². W/m² (Don't worry about the font -- use 1₁ for 1.) (b) Calculate the maximum output power of the light bulb. Pmax = 41.82 x W
The average intensity a distance d₁ = 1.6 m from an omni-directional light bulb is el1 = (a) Write a symbolic expression for the intensity a distance d₂ = 2.5 m from the same bulb, in terms of ₁, d₁ and d₂, and calculate its numeric value. d2 (32 (d₂.)³7₁ 0.533 .3 W/m². W/m² (Don't worry about the font -- use 1₁ for 1.) (b) Calculate the maximum output power of the light bulb. Pmax = 41.82 x W
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Transcribed Image Text:The average intensity a distance d₁ = 1.6 m from an omni-directional light bulb is ₁ = 1.3 W/m²2.
(a) Write a symbolic expression for the intensity a distance d₂ = 2.5 m from the same bulb,
in terms of ₁, d₁ and d₂, and calculate its numeric value.
I₂ =
2
= 0.533
W/m² (Don't worry about the font -- use 11 for 1.)
(b) Calculate the maximum output power of the light bulb.
P₁ = 41.82
max
X W
Transcribed Image Text:EM waves, like all other waves, are generated a source. The power of a source measures the rate that it radiates EM energy. The energy spreads
outward as the wave carries it away from the source so the amount crossing a given area decreases with distance.
The intensity at a given point measures the rate per unit area
that EM energy is being transported to that point (i.e. received).
Intensity = Source Power/Surface Area
The surface area takes into account the specific details of how
energy spreads outward as it radiates away from the source.
A light source that radiates uniformly in all directions like the
one shown in the figure is called isotropic or omni-directional.
The energy is spread uniformly across spherical surfaces that
are centered on the source so the intensity, , a distance, d,
from an isotropic source that with power, P, is given by:
I =
P
4nd²
Observation
Point
Surface Area4d²
The power rating of a light bulb indicates the average power that it consumes when plugged into standard wall outlet.
In other words, a "60-W bulb" radiates an average power of 60-W when supplied with an average AC voltage of 120-V.
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