Answer:
From the formula of force:

since AB and k are constants:

x is a constant of proportionality
• when force is 4N, separation distance is 1

therefore, equation becomes

when r is doubled, r becomes 2. find F:

A "screen" or even just a set of parallel bars are highly reflective to electromagnetic waves as long as the open spaces are small compared to the wavelengths.
"Grid" dishes work fine ... with less weight and less wind resistance ... for frequencies below about 3 GHz. (Wavelengths of at least 10 cm.)
(I even worked on a microwave system in South America where huge grid dishes were used on a 90-mile link.)
Answer:
Magnetic field, B = 0.275 T
Explanation:
Given that,
Length of the wire, L = 35 cm = 0.35 m
Current carried in the wire, I = 2.6 A
The segment makes an angle of 53∘ with the direction of the magnetic field, 
Magnetic force, F = 0.2 N
To find,
The magnitude of the magnetic field.
Solution,
The magnetic force acting on the wire is given by :

is the angle between the length of wire and the magnetic field.

B = 0.275 T
Therefore, the magnitude of the magnetic field is 0.275 T. Hence, this is the required solution.