If the instantaneous current in a circuit is given by $\mathrm{i}=2\cos (\mathrm{\omega t}-\mathrm{\varphi })$ amperes, the r.m.s. value of the current is

• A

  2 amperes

• B

  $\sqrt{2}\text{ amperes }$

• C

  $2\sqrt{2}\text{ amperes }$

• D

  zero