The beam from a small laboratory laser typically has an intensity of about
. Assuming that the beam is composed of plane waves, calculate the amplitudes of the electric and magnetic fields in the beam.
Strategy
Use the equation expressing intensity in terms of electric field to calculate the electric field from the intensity.
A 60-kW radio transmitter on Earth sends its signal to a satellite 100 km away (
[link] ). At what distance in the same direction would the signal have the same maximum field strength if the transmitter’s output power were increased to 90 kW?
In three dimensions, a signal spreads over a solid angle as it travels outward from its source.
Strategy
The area over which the power in a particular direction is dispersed increases as distance squared, as illustrated in the figure. Change the power output
P by a factor of (90 kW/60 kW) and change the area by the same factor to keep
the same. Then use the proportion of area
A in the diagram to distance squared to find the distance that produces the calculated change in area.
Solution
Using the proportionality of the areas to the squares of the distances, and solving, we obtain from the diagram
Significance
The range of a radio signal is the maximum distance between the transmitter and receiver that allows for normal operation. In the absence of complications such as reflections from obstacles, the intensity follows an inverse square law, and doubling the range would require multiplying the power by four.
The energy carried by any wave is proportional to its amplitude squared. For electromagnetic waves, this means intensity can be expressed as
where
I is the average intensity in
and
is the maximum electric field strength of a continuous sinusoidal wave. This can also be expressed in terms of the maximum magnetic field strength
as
and in terms of both electric and magnetic fields as
The three expressions for
are all equivalent.
Conceptual questions
When you stand outdoors in the sunlight, why can you feel the energy that the sunlight carries, but not the momentum it carries?
The amount of energy (about
) is can quickly produce a considerable change in temperature, but the light pressure (about
) is much too small to notice.
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
Hilary
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