Originally Posted by

**Alias_NeO** ...

Q2:

A circuit breaker is designed to stop fault current flowing in a circuit at a point in time where the current in the circuit is 0.

If the fault curent in the circuit is: $\displaystyle i(t) = 50cos(314t - 60^\circ)$ Amperes

i) At what time would the first current 0 in the circuit occur?

ii) Given the circuit breaker will take 40mS to operate, at what time would the next current 0 occur after that?

For the first part I am assuming i should make i(t) = 0 so:

$\displaystyle 50cos(314t - 60^\circ) = 0$

Now since I am unsure how one should correctly manipule the cos trig function in this case, i would do the following ... is this correct?:

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