<Dd> F A = B s a t 2 2 μ 0 ≈ 1000 k P a = 10 6 N / m 2 = 145 l b f ⋅ i n − 2 (\ displaystyle (\ frac (F) (A)) = (\ frac (B_ (sat) ^ (2)) (2 \ mu _ (0))) \ approx 1000 \ \ mathrm (kPa) = 10 ^ (6) \ mathrm (N / m ^ (2)) = 145 \ \ mathrm (lbf) \ cdot \ mathrm (in) ^ (- 2) \,) </Dd> <P> In more intuitive units it's useful to remember that at 1T the magnetic pressure is approximately 4 atmospheres, or kg / cm . </P> <P> Given a core geometry, the B field needed for a given force can be calculated from (2); if it comes out to much more than 1.6 T, a larger core must be used . </P> <P> For a closed magnetic circuit (no air gap), such as would be found in an electromagnet lifting a piece of iron bridged across its poles, equation (1) becomes: </P>

Write the difference between bar magnet and electromagnet