The strength of a bar magnet's magnetic field decreases with distance according to what is known as an inverse cube law; multiplying the distance from the magnet by a factor of k divides the magnetic field strength by a factor of \(k^3\) .Suppose the magnetic field strength of the magnet is 64 Gauss at a distance of 10cm away. What is the magnetic field strength of the magnet, 20cm away?
Since the strength of the magnet decreases as the inverse cube of the distance, therefore:
64 x 1/(20/10)^3 =
64 x 1/2^3 =
64 x 1/8 =8 gauss - the strength of the magnet at 20 cm.