In a closed switch, there is typically very little to no voltage across its terminals. When a switch is closed, it creates a complete electrical pathway, allowing current to flow freely between the two terminals of the switch. In an ideal closed switch with no resistance, the voltage across its terminals would be practically zero.
Voltage is the electrical potential difference between two points in a circuit. When a switch is open (off), there can be a voltage across its terminals, as there might be a potential difference between those points due to the rest of the circuit. However, when the switch is closed (on), it is designed to provide a low-resistance path for current, resulting in negligible voltage across its terminals.
Keep in mind that real-world switches might not be perfect conductors when closed, and they might have some resistance. This resistance could lead to a small voltage drop across the switch when it's closed, but under normal conditions, this voltage drop would be minimal and often neglected for practical purposes.