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Asked in NEET 2014 · Peak and instantaneous EMF
As the loop turns, the flux through it varies as φ=BA cos ω t and the emf as
ε=BAω sin ω t.
A sinusoid changes sign wherever it crosses zero, and sin ω t crosses zero twice in each
full cycle: once going up, once coming down.
One revolution is one full cycle, so the emf reverses direction twice per revolution.
This is exactly why a plain rotating loop produces alternating current and needs a commutator to
give direct current.
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