Question

A spark of static electricity, such as that you might receive from a doorknob on a cold dry day, may carry a few hundred watts of power. Explain why you are not injured by such a spark.

Short answer

The energy contained in a spark of static electricity is very less; therefore, we are not injured by such spark.

Step-by-step solution

Definition of Concepts

Power consumption: Power consumption is defined as the rate at which energy is being consumed.

Mathematically power is given as,

$P=\frac{E}{t}$ (1.1)

Here, P stands for power, E stands for energy used, and t stands for time.

Power is a scalar quantity measured in terms of watts.

The expression for energy can be obtained by rearranging equation (1.1),

$E=Pt$

Explain the spark of static electricity

In a spark of static electricity, the power is high (approximately a few hundred watts) but it lasts only for fractions of a second. Therefore, the product of high power and time equivalent to a fraction of a second is equivalent to very less energy.

Hence, the energy contained in a spark of static electricity is very less; therefore, we are not injured by such a spark.