10.6 Household wiring and electrical safety  (Page 4/11)

Why isn’t a short circuit necessarily a shock hazard?

We are often advised to not flick electric switches with wet hands, dry your hand first. We are also advised to never throw water on an electric fire. Why?

(a) How much power is dissipated in a short circuit of 240-V ac through a resistance of $0.250\text{Ω}$ ? (b) What current flows?

What voltage is involved in a 1.44-kW short circuit through a $0.100\text{-}\text{Ω}$ resistance?

Find the current through a person and identify the likely effect on her if she touches a 120-V ac source: (a) if she is standing on a rubber mat and offers a total resistance of $300\text{k}\text{Ω}$ ; (b) if she is standing barefoot on wet grass and has a resistance of only $4000\text{k}\text{Ω}$ .

While taking a bath, a person touches the metal case of a radio. The path through the person to the drainpipe and ground has a resistance of $4000\text{Ω}$ . What is the smallest voltage on the case of the radio that could cause ventricular fibrillation?

A man foolishly tries to fish a burning piece of bread from a toaster with a metal butter knife and comes into contact with 120-V ac. He does not even feel it since, luckily, he is wearing rubber-soled shoes. What is the minimum resistance of the path the current follows through the person?

(a) During surgery, a current as small as $20.0\mu \text{A}$ applied directly to the heart may cause ventricular fibrillation. If the resistance of the exposed heart is $300\text{Ω},$ what is the smallest voltage that poses this danger? (b) Does your answer imply that special electrical safety precautions are needed?