Two charges equal in magnitude and opposite in polarity are placed at a certain distance apart and force acting between them is F. If 75% charge of one is transferred to another, then the force between the charges becomesF

The initial situation is that we have two charges, let's call them Q and -Q, and the force between them is F. This force can be calculated using Coulomb's law:

F = k * Q * -Q / r^2

where k is Coulomb's constant and r is the distance between the charges.

Now, 75% of the charge of one is transferred to the other. This means that one charge now has 25% of the original charge and the other has -175% of the original charge. So, we have 0.25Q and -1.75Q.

The new force F' between the charges can be calculated using the same formula:

F' = k * 0.25Q * -1.75Q / r^2

To find the ratio of the new force to the old force, we divide the new force by the old force:

F'/F = (k * 0.25Q * -1.75Q / r^2) / (k * Q * -Q / r^2)

The k, Q, and r^2 terms cancel out, leaving us with:

F'/F = 0.25 * -1.75 = -0.4375

So, the new force is -0.4375 times the old force. The negative sign indicates that the direction of the force has reversed, because the charges have switched from being opposite to being the same.