b) between poles M1 and M2
Explanation:
From the expression, we can deduce that r is the distance between two magnetic poles M1 and M2.
The law of attraction between two magnetic poles states that:
<em> the force of attraction or repulsion between two magnetic poles is a function of the product of the strength of the magnetic poles and the square of the distance between the pole</em>s
Mathematically:
FM = K
here r is the distance between the poles
FM is the magnetic force between the poles
M1 is the strength of the first magnetic pole
M2 is the strength of the second pole
K is the magnetic field constant
learn more:
magnetic pole brainly.com/question/2191993
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