Thyristor $T_{1}$ is triggered at an angle $\alpha$ (in degree), and $T_{2}$ at angle $180^{\circ}+\alpha$, in each cycle of the sinusoidal input voltage. Assume both thyristors to be ideal. To control the load power over the range $0$ to $\text{2 k W}$, the minimum range of variation in $\alpha$ is:
- $0^{\circ}$ to $60^{\circ}$
- $0^{\circ}$ to $120^{\circ}$
- $60^{\circ}$ to $120^{\circ}$
- $60^{\circ}$ to $180^{\circ}$