Question

1. Dry hands have a resistance of 1 Megaohm or more. If you happen to stick your hands in a live socket with 120 V you will feel a mild buzzing sensation in your hands, but you will remain unharmed. Why? Why is it that using a hairdryer is so hazardous in the shower, when you are wet? (Estimate the current in each case)

2. Is Ohm’s law really a law? If it was a law, it would have to apply universally to all electrical components. Does it? Explain.

Answer 1

1)

Resistance of dry hands, R_dry = 1 Megohm = 1* 10⁶ ohm,

Given, Voltage, V = 120 V

so, Current, I₁ = V/  R_dry = 120 / (1* 10⁶) = 1.2 * 10^-4 A

When our body is wet while using hairdryer in shower, then net resistance is the parallel combination of our body and water, which is nearly equal to 1000 ohm

so, Current in this case, I₂ = 120/ 1000 = 0.12 A and this value of current is enough to effect our body. So, it is hazardous to use hairdryer in the shower.

B)

Ohm's law is not a fundamental law, but a simple and powerful mathemetical tool to analize the electric circuit and calculate Constant resistance of the circuit. Ohm's law is not universally applied to all material . Therefore sometimes material are also classifed on the basis of material Obeying Ohm's law(linear graph ) called Ohmic and matrial not obeying Ohm's law(non-linear graph), Example - P-n junction diodes. In certain cases, Ohm's law can not be applied when resistance is of varying nature. Example - Incandescent bulbs