A circuit has a line of $5\text{ A}$. How many lamps of rating $40\text{ W}$; $220\text{ V}$ can simultaneously run on this line safely?

In domestic circuits, appliances are connected in parallel across the supply voltage. The total power consumed by $n$ parallel lamps is the sum of their individual powers ($n \times P$). The maximum current the line can safely carry is $5\text{ A}$ at $220\text{ V}$, which corresponds to a maximum power limit of $1100\text{ W}$. Dividing this total power limit by the power of a single lamp ($40\text{ W}$) gives $27.5$. Since we cannot have a fraction of a lamp, we must round down to $27$ to keep the current strictly within the safe limit of $5\text{ A}$.