Question : You are measuring the current in a circuit that is operated on an 18 V battery. The ammeter reads 40 mA. Later you notice the current has dropped to 20 mA. How much has the voltage changed?
a) 9V
b) 36 V
c) 0 V
d) 18 V
Doubt by Tanya
Solution :
V = 18 V
I = 40 mA
V'= ?
I' = 20 mA
We know, According to Ohm's Law
V = IR
V∝I
V'/V = I'/I
V' = (I'×V)/I
V' = (20 mA × 18 V)/ 40 mA
V' =18/2
V' = 9 V
Hence, a) 9V is correct.
