Your answer is electricity, light and magnetism. They can be determined usinf elecromagnetic radioation.
<span>
Even the energy can't be detected by our eyes, there are a lot of measurement instruments that can measure infrared (IR), gamma rays, radio or X-rays or ultraviolet (UV)</span>
1.Density of the material building the raft must be lower than the water.
<span>2. Material must not react with water. </span>
<span>3.Material must have high strength. </span>
<span>4.Raft must be wide in-order to avoid drawing in the river.</span>
Answer:
B. Solids, liquids, and gases.
Explanation:
I have no explanation.
Answer:
145 m
Explanation:
Given:
Wavelength (λ) = 2.9 m
we know,
c = f × λ
where,
c = speed of light ; 3.0 x 10⁸ m/s
f = frequency
thus,
substituting the values in the equation we get,
f = 1.03 x 10⁸Hz
Now,
The time period (T) = 
or
T = 
= 9.6 x 10⁻⁹ seconds
thus,
the time interval of one pulse = 100T = 9.6 x 10⁻⁷ s
Time between pulses = (100T×10) = 9.6 x 10⁻⁶ s
Now,
For radar to detect the object the pulse must hit the object and come back to the detector.
Hence, the shortest distance will be half the distance travelled by the pulse back and forth.
Distance = speed × time = 3 x 10^8 m/s × 9.6 x 10⁻⁷ s) = 290 m {Back and forth}
Thus, the minimum distance to target = 
= 145 m
Electroreception is limited to aquatic environments because on here is the resistivity of the medium is low enough for electric currents to be generated as the result of electric fields of biological origin. In air, the resistivity of the environment is so high that electric fields from biological sources do not generate a significant electric current. Electroreceptor are found in a number of species of fish, and in at least one species of mammal, the Duck-Billed platypus.
