To solve this problem it is necessary to apply the concepts related to optical magnification (is the process of enlarging the apparent size, not physical size, of something.). Specifically the angular magnification of an optical telescope is given by

Where,
Focal length of the objective lens in a refractor
Focal length of the eyepiece
Our values are given as
71cm
2.1cm
Replacing we have



Therefore the magnification of this astronomical telescope is -33.81
A needle valve and collar.
Answer:
-5 V
Explanation:
The charged particle (which is positively charged) moves from point A to B, and its kinetic energy increases: it means that the particle is following the direction of the field, so its potential energy is decreasing (because it's been converted into potential energy), therefore it is moving from a point at higher potential (A) to a point at lower potential (B). This means that the value
vb−va
is negative.
We can calculate the potential difference between the two points by using the law of conservation of energy:

where:
is the change in kinetic energy of the particle
is the charge of the particle
is the potential difference
Re-arranging the equation, we can find the value of the potential difference:

Answer:
density is defined as the amount of mass contained in unit volume of a body .its si unit is kg/m*3