Subsection 5.2.2 Ohm’s Law
Ohm’s law states that the current flowing through a conductor is directly proportional to the voltage across the two ends of the conductor, and inversely proportional to the resistance between them. It can be mathematically expressed as
\begin{equation*}
I = V/R
\end{equation*}
or,
\begin{equation}
V=IR\tag{5.2.3}
\end{equation}
here I is the current, V is the voltage, and R is the resistance of the conductor. Resistance: is a restriction imposed by a conductor on the motion of a current. Motion of charge carriers (electrons) are not very smooth in a conductor as they bump onto the other electrons and positive charge residual atoms during their motion. Such restrictions in flow of electrons are measured as a resistance of a conductor in current flow. It is denoted by \(R\) and its unit is Ohm (\(\Omega\)) . Electrical Power: It is the measure of energy transferred or consumed per unit time i.e.,
\begin{equation}
P=\frac{W}{T}\tag{5.2.4}
\end{equation}
\begin{align*}
or, P \amp = \frac{Energy}{time}\\
or, \quad P \amp = \frac{qV}{t}
\end{align*}
\begin{equation}
\therefore \quad P = IV\tag{5.2.5}
\end{equation}
Hence power is also defined as the product of current and voltage. Its unit is Watts (W). One watt means consuming one joule of energy every second.
Now from Ohm’s law, (5.2.3)
\begin{equation*}
V=IR
\end{equation*}
Hence, the power of electrical circuit is given as
\begin{equation}
P = IV = I\times IR = I^2R\tag{5.2.6}
\end{equation}
\begin{equation}
P = IV = \frac{V^2}{R}\tag{5.2.7}
\end{equation}
Electrical Shock: According to Ohm’s law if resistance of the conductor is low then the higher current can flow through it. High current can be deadly. Actually, a “voltage” does not go “into” your body rather current can pass through it when charges flow toward a lower potential. In order to get an electric shock at least \(1mA\) of current must pass through our body. In dry conditions, the human body has a resistance of about \(50000\Omega\text{,}\) so to have \(1mA\) current flowing through our body we need to touch the voltage source of about \(50 V\text{,}\) as shown in the calculation below.
\begin{align*}
V\amp =IR \\
or, \quad V \amp = 1\times 10^{-3}\times 50000\\
\therefore \quad V \amp =50
\end{align*}
In wet condition, human body resistance becomes only \(10000\Omega\text{,}\) so to get \(1mA\) current through our body we need to touch the voltage source of about \(10 V\text{.}\)
