A parallel plate capacitor is formed by two plates each of area 30$\pi cm
2
separated by 1 mm. A material of dielectric strength 3.6 \times 10
7
Vm
-1
is filled between the plates. If the maximum charge that can be stored on the capacitor without causing any dielectric breakdown is 7 \times 10
-6
C, the value of dielectric constant of the material is :
[Use {1 \over {4\pi {\varepsilon _0}}} = 9 \times {10^9} Nm
2
C
-$2
]