A waveguide consists of two infinite parallel plates (perfect conductors) at a separation of $10^{-4} \; \text{cm},$ with air as the dielectric. Assume the speed of light in air to be $3 \times 10^{8} \; \text{m/s}.$ The frequency/frequencies of $\text{TM}$ waves which can propagate in this waveguide is/are _________.
- $6 \times 10^{15} \; \text{Hz}$
- $0.5 \times 10^{12} \; \text{Hz}$
- $8 \times 10^{14} \; \text{Hz}$
- $1 \times 10^{13} \; \text{Hz}$