Question

There are 11 lights in series, and they are in series with 2 lights in parallel. If the 13 lights are identical, which of them will burn brightest?
11 lights
2 lights
all 13 lights
none will be brightest

Answer 1

Answer: 2 lights (in parallel)

Explanation:

When light bulbs are connected in series the total voltage $V_{s}$ will be:

$V_{s}=V_{1}+V_{2}+...+V_{n}$  (1)

This means the total voltage will be distributed among each of the bulbs in series, therefore the luminosity will be also divided among the bulbs.

When lights are connected in parallel the total voltage $V_{p}$ will be:

$V_{p}=V_{1}=V_{2}=...=V_{n}$  (2)

This means the total voltage will be the same for each bulbs in parallel, therefore the luminosity will be the same.

Now, if we combine this two types of connections, as in this problem with 11 lights in series, which are also in series with 2 lights in parallel; the 2 lights in parallel will be brighter than the 11 lights in series.