Electric current in a circuit is given by $i = i _ { 0 } \left( \frac { t } { T } \right)$, find rms current for period $\mathbf { t } \boldsymbol { = } \mathbf { 0 }$ to $\mathbf { t } \boldsymbol { = } \mathbf { T }$.
(A) $\frac { 1 _ { 0 } } { \sqrt { 3 } }$
(B) $\frac { \mathrm { i } _ { 0 } } { \sqrt { 2 } }$
(C) $\frac { \mathrm { i } _ { 0 } } { \sqrt { 5 } }$
(D) $\frac { \mathrm { i } _ { 0 } } { \sqrt { 7 } }$