Three similar light bulbs are connected to a constant voltage d.c. supply as shown in Figure. Each bulb operates at normal brightness and the ammeter (of negligible resistance) registers a steady current
The filament of one of the bulbs breaks. What happens to the ammeter reading and to the brightness of the remaining bulbs?
Ammeter reading - increases, Bulb brightness - increases
Ammeter reading - increases, Bulb brightness - unchanged
Ammeter reading - unchanged , Bulb brightness - unchanged
Ammeter reading - decreases, Bulb brightness - unchanged
Suppose V is the voltage of the supply and R is the resistance of each bulb
Now, and current in ammeter,
,
Provided all three bulbs are working properly
If one bulb has broken down, then
Therefore, current decreases and since current through each bulb is the same as before, brightness of bulbs is not affected