# How many batteries with EMF 2 in parallel-connected batteries are there if a current of 0.4 A

How many batteries with EMF 2 in parallel-connected batteries are there if a current of 0.4 A flows through the bulb? Bulb resistance 4.98 ohm, battery internal resistance 0.06 ohm

Let’s use the formula:
I = E / (R + r);
Let’s transform the formula to the form in which we need it:
I = (R + r) * E;
E = I * R + I * r;
I * r = E – I * R;
Thus, we get the formula:
r = (E – I * R) / I;
Let’s substitute the values into the formula:
r = (2 – 0.4 * 4.98) /0.4;
r = (2 – 1.992) / 0.4;
r = 0.008 / 0.4;
r = 0.02 (Ohm) is the resistance of the battery, all batteries.
T to they are connected in parallel and their resistances are the same, then r = r1 / n, we find n:
n = r1 / r;
n = 0.06 / 0.02;
n = 3.
Answer: from 3 batteries.

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