A material has N spins per m3. If Np are the dipoles per m3 parallel to field and Na are the dipoles per m3 anti-parallel to field, the magnetisation is

• A. <img src="/_files/images/electronics-and-communication-engineering/materials-and-components/87-1.png">
• B. <img src="/_files/images/electronics-and-communication-engineering/materials-and-components/87-2.png">
• C. <img src="/_files/images/electronics-and-communication-engineering/materials-and-components/87-3.png">
• D. <img src="/_files/images/electronics-and-communication-engineering/materials-and-components/87-4.png">