Answer:

Explanation:
The electric flux through a certain surface is given by (for a uniform field):

where:
E is the magnitude of the electric field
A is the area of the surface
is the angle between the direction of the field and of the normal to the surface
In this problem, we have:
is the electric field
L = 2.0 m is the side of the sheet, so the area is

, since the electric field is perpendicular to the surface
Therefore, the electric flux is

If the substance doesn't change chemically, it is a physical reaction.
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
D is the correct answer!!