Question

The music system draws a current of 400 mA when connected to a 12 V battery.

1. What is the resistance of the music system?
2. The music system if left playing for several hours and finally the battery voltage drops and the music system stops playing when the current drops to 320 mA. At what battery voltage does the music system stop playing?

Answer 1

1. Given: I = 400 mA = 400 × 10^-3 A
   V = 12V
   V = IR
   `:. "R" = "V"/"I"`
   = `"12V"/(400 xx 10^(-3)A)`
   ∴ R = 30 Ω
2. Current drops to I = 320 mA = 320 × 10^-3 A
   The music stops playing at
   V = IR
   = 320 × 10^-3 × 30
   ∴ V = 9.6 V