Questions

Some more NPP Acronym stands for 

NPP New Patriotic Party

NPP Nuclear Power Plant

NPP Notice of Privacy Practices

NPP Non-Physician Practitioner

NPP New Progressive Party

NPP National Patriotic Party

NPP Notice of Proposed Procurement

NPP Neighbourhood Police Post (Singapore)

NPP Non-Paged Pool (memory)

NPP Nurse Practitioner in Psychiatry.

From the given data,

11+ 11 = 4 => 1 + 1  +  1 + 1 = 4

12 + 12 = 6 => 1 + 2  + 1 + 2 = 6

13 + 1 3 = 8 => 1 + 3  + 1 + 3 = 8

Similarly,

14 + 14 = 10 => 1 + 4  +  1 + 4  = 5 + 5 = 10

A Slip ring is a ring in a dynamo or electric motor which is attached to and rotates with the shaft, passing an electric current to a circuit via a fixed brush pressing against it.

Slip rings are usually made of Phosphor Bronze.

Slip ring motors usually have a 'phase-wound' rotor. This type of rotor has a 3-phase, double-layer, distributed winding consisting of coils used in alternators. The rotor core is made up of steel laminations which have slots to accommodate formed 3-single phase windings.

Hard disk is coated in both side with Magnetic metallic oxide.