An industrial step-down transformer is used in a laboratory to power a high-intensity plasma lamp. The primary coil of the transformer has 800 turns, and the secondary coil has 40 turns. An alternating voltage supply is connected to the primary coil. A plasma lamp that dissipates 75 W75\text{ W}75 W at its operating potential difference of 15 V15\text{ V}15 V is connected across the secondary coil. The transformer is 100%100\%100% efficient.
Calculate the current in the primary coil.
The alternating voltage supply is replaced by a 24 V24\text{ V}24 V DC power supply and an open switch in series. The switch is closed. Explain why the plasma lamp is only illuminated briefly and then remains unlit.
