Both Panasonic ZS3 and Nikon 1 J2 have 10.0 MP resolution sensors but Panasonic ZS3's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Nikon 1 J2's sensor is 1-inch (13.2 x 8.8 mm ).
Since Nikon 1 J2's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Panasonic ZS3.
Below you can see the ZS3 and 1 J2 sensor size comparison.
As seen above, Nikon 1 J2 has a 4.2x Larger sensor area than Panasonic ZS3. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.