Section 5.2 Electricity
It is a branch of physics which deals with the motion of charges in a conductor. When charge flows from one place to another, an electrical current is formed. An electric current is defined as the rate of flow of charge. If a net charge \(q\) passes through any conductor in time \(t\text{,}\) then the electric current is given by
\begin{equation}
I=\frac{q}{t}\tag{5.2.1}
\end{equation}
Its unit is Ampere (A). One ampere of current represents one coulomb of charge passes through a conductor in one second. It is a scalar quantity and its conventional direction is taken as the direction of flow of positive charges. In conductor, current flows solely due to motion of electrons, hence the direction of current is opposite to electrons flow. From the law of conservation of charges current remains constant in a conductor irrespective of the local area of cross-section. When the direction of motion of charge does not change with time, the current is said to be direct current, or DC current. It is commonly used in electronic devices like cell phones and computers. If the direction of motion of charges reverses periodically, the current is known as an alternating current, or AC current. It is commonly used in the electrical power systems that supply to homes and commercial applications. AC current goes from positive to negative in a cycle, while DC current is always in the same direction. Current can only exist between two points of different potential (voltage) connected by a conductor and can only exist whenever a conductive path with no breaks is provided.
Flow of charges in DC current is similar to flowing water, but in AC current, charges do not go anywhere rather they are oscillating about the mean position at their respective position. Check the simulation link to visualize DC and AC current. DC & AC AC is more efficient to transmit over long distances than DC. This is the reason why AC is used in power transmission and distribution as well as in motors and other equipment. It is also used in many household appliances, such as refrigerators, air conditioners, and washing machines. AC can also be easily transformed to different voltages using a transformer, while this is not easy to achieve with DC. DC voltage can be stored in a device called a battery, while AC voltage cannot be stored.
1
javalab.org/en/dc_and_ac_en/
