Some light bulbs are connected in parallel to a 120 V source as shown in the figure.Each bulb dissipates an average power of 60 W.The circuit has a fuse F that burns out when the current in the circuit exceeds 9 A.Determine the largest number of bulbs,which can be used in this circuit without burning out the fuse.
A)9
B)17
C)25
D)34
E)36

Question

Some light bulbs are connected in parallel to a 120 V source as shown in the figure.Each bulb dissipates an average power of 60 W.The circuit has a fuse F that burns out when the current in the circuit exceeds 9 A.Determine the largest number of bulbs,which can be used in this circuit without burning out the fuse. 
A)9 
B)17 
C)25 
D)34 
E)36

Quizplus · Accepted Answer

First, we need to find the total current drawn by the circuit when all the bulbs are connected.
Total power dissipated by all bulbs = power dissipated by one bulb x number of bulbs
Total power = 60 W x N (where N is the number of bulbs)
Total current (I) drawn by the circuit = Total power / Voltage of the source
I = (60N / 120) = 0.5N amps

To prevent the fuse from burning out, the total current should not exceed 9 A. So,
0.5N <= 9
N <= 18

Therefore, the largest number of bulbs that can be used without burning out the fuse is 17 (since adding an 18th bulb would cause the current to exceed the limit).

Some Light Bulbs Are Connected in Parallel to a 120