Answer:
(a): The magnitude of the electric force on the small sphere = 
(b): Shown below.
Explanation:
<u>Given:</u>
- m = mass of the small sphere.
- q = charge on the small sphere.
- L = length of the silk fiber.
= surface charge density of the large vertical insulating sheet.
<h2>
(a):</h2>
When the dimensions of the sheet is much larger than the distance between the charge and the sheet, then, according to Gauss' law of electrostatics, the electric field experienced by the particle due to the sheet is given as:

<em>where,</em>
is the electrical permittivity of the free space.
The electric field at a point is defined as the amount of electric force experienced by a unit positive test charge, placed at that point. The magnitude electric field at a point and the magnitude of the electric force on a charge q placed at that point are related as:

Thus, the magnitude of the electric force on the small sphere is given by

The sheet and the small sphere both are positively charged, therefore, the electric force between these two is repulsive, which means, the direction of the electric force on the sphere is away from the sheet along the line which is perepndicular to the sheet and joining the sphere.
<h2>
(b):</h2>
When the sphere is in equilibrium, the tension in the fiber is given by the resultant of the weight of the sphere and the electric force experienced by it as shown in the figure attached below.
According to the fig.,

<em>where,</em>
= electric force on the sphere, acting along left.
= weight of the sphere, acting vertically downwards.
<em />

g is the acceleration due to gravity.
A car making a turn is accelerating. Acceleration is defined as a change in speed or direction.
Answer:
Minimum distance needed to move one of the mirrors = 125 nm
Explanation:
Constructive interference occurs when the maxima (trough or crest) of two waves that are in phase add together so that the amplitude of the resulting wave is equal to the sum of the individual amplitudes.
Destructive interference occurs when the maxima (trough or crest) of two waves that are out of phase by 180⁰ or half a wavelength combine to produce a smaller amplitude than the individual amplitudes that combine. It can even produce a wave of zero amplitude.
Since the spot of constructive interference has been changed to destructive interference, Path difference = Wavelength/2
Path difference = 500nm/2 = 250 nm
Path difference = 250 * 10⁻⁹ m
Since there are two interferometer's mirrors and only one is moved, the minimum distance will be a half of the path difference.
That is, minimum distance = (path difference)/2
Minimum distance = (250 * 10⁻⁹)/2
Minimum distance = 125 * 10⁻⁹ m
Minimum distance = 125 nm