Solve the following questions given below hera

Question

A string of twenty 15 Ω Christmas tree lights is used for a party. One burns out, they all burns out. Calculate the resistance Also what will be the current flowing through it if 150 V battery is used.(2)

Answer 1

total resistance=15*20=300ohm

voltage=150V

Current =voltage/resistance

150/300=0.5A

Answer 2

given one burns out and all burns out means connection is series. 

So Rnet = R1 +R2..... +R20 =20R = 20(15)

= 300 ohm. 

as R1= R2 = R3= .......... R20= 15 ohm

From ohms law 

V=IR 

Given V= 150 V

R= 300 ohm

Thus I= V/R = 150/300 = 0.5 A