The effective length of the first magnet is two times that of the second magnet. The effective length of the third magnet is one-third of the first magnet. If the effectiv length of the second magnet is 7.5 cm, the effective length of the third magnet is ______

Options

A. 5 cm
B. 15 cm
C. 2.5 cm
D. 7.5 cm

Explanation

Effective length of second magnet =7.5 cm.
Therefore, effective length of the first magnet =`2xx7.5`
`=15 cm `
Therefore, effective length of the third magnet `=1//3xx15 cm`
`= cm. `
Hence , the correct option is (a).