Question

Why is a 12-volt household battery harmless, but the shock from a 12-volt car battery will kill you?​

Answer 1

The shock from a car battery will not kill you. In fact, under normal conditions, a 12-volt car battery will usually not even shock you. Car batteries are not harmless, though.

Answer 2

Answer:

Given conditions ⇒

Resistance = 16 Ω

Potential = 12 V.

∴ I = 12/16 [By Ohm's law]

⇒ I = 0.75 A.

Now, Using the Formula, 

ε = I(R + r)

where r is the Internal Resistance of the Battery and ε is the e.m.f. of the battery. 

ε = 0.75(16 + r)  ----eq(i)

We know that the e.m.f. of the battery will never change if the resistance or the potential will change. 

∴ ε = I (10 + r)

ε = 11/10 (10 + r)  ------eq(ii) 

From  equations (i) and (ii), 

0.75(16 + r) = 1.1(10 + r)

⇒ 12 + 0.75r = 11 + 1.1r

⇒ 1.1r - 0.75r = 12 - 11

⇒ 0.35r = 1

∴ r = 1/0.35

∴ r = 2.86 Ω

Hence, the Internal Resistance of the Battery is 2.86 Ω.

Hope it helps.