Sony a3500 has a
20.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features BIONZ processor. On the other hand, Sony A6000 has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Bionz X processor.
Below you can see the a3500 and A6000 sensor size comparison.
Sony a3500 and Sony A6000 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Sony a3500 has 21% larger pixel area compared to Sony A6000, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.