Question

Magnet A has thrice the magnetic field strength of magnet B and at a certain distance pulls on magnet B with a force of 100 Newtons. With how much force, then, does magnet B pull on magnet A? What is the force if the distance between the magnets is doubled?

Answer 1

- The force that magnet B pulls on the magnet A is equal to the force that magnet A pull on B. That is , 100N.

- F'B = 25N

Step-by-step explanation:

- You have that the magnet A pulls on the magnet B with a force of 100N.

By the third Newton law you have that any force has a reaction, that is, the force that magnet B pulls on the magnet A is equal to the force that magnet A pull on B. That is , 100N.

- In order to calculate the force, if the distance between magnets is twice, you first take into account that the magnetic force is inversely proportional to the force between magnets, as follow:

`F_B\ \alpha\ (1)/(r^2)` (1)

FB: magnetic force between the magnets = 100N

If the distance is twice, you obtain:

`F_B'\ \alpha\ (1)/((2r)^2)=(1)/(4r^2)\\\\F_B'\ \alpha\ (1)/(4)F_B`

The new force is a quarter of the initial force, that is:

`F_B'=(1)/(4)(100N)=25N`

If the distance is twice the force is a quarter of the initial force.