# A short magnet oscillating in vibration magnetometer with a frequency 10 Hz . A downward current of 15 A is established in a long vertical wire placed 20 cm to the west of the magnet. The new frequency of the short magnet is : ( The horizontal component of earth's magnetic field is 12 $\mu$ T)

$\begin {array} {1 1} (1)\;4\: Hz & \quad (2)\;2.5 \: Hz \\ (3)\;9\: Hz & \quad (4)\;5\: Hz \end {array}$

Ans : (4)
5 Hz