To solve this problem it is necessary to apply the concepts related to the principle of superposition and the equations of destructive and constructive interference.
Constructive interference can be defined as

Where
m= Any integer which represent the number of repetition of spectrum
= Wavelength
d = Distance between the slits.
= Angle between the difraccion paterns and the source of light
Re-arrange to find the distance between the slits we have,



Therefore the number of lines per millimeter would be given as



Therefore the number of the lines from the grating to the center of the diffraction pattern are 380lines per mm
The answer I found was parabola?
The free-body diagram of an apple falling through the air has weight of the apple pointing downwards and the air-resistance on the apple acting upwards.
When an object falls from up to the ground, the object falls under in the influence of acceleration due to gravity.
The vertical component of the force on the apple as it falls trough the air is given as;
∑Fy = 0
Fₙ - W = 0
Fₙ = W
where;
- <em>Fₙ is the frictional force on the apple acting upwards</em>
- <em>W is the weight of the apple acting downwards</em>
The free-body diagram of the apple is represented as follows;
↑ Fₙ
Ο
↓ W
Thus, the free-body diagram of an apple falling through the air has weight of the apple pointing downwards and the air-resistance on the apple acting upwards.
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