In this physics video for iit jee, we will discuss the topic current electricity. In the above physics video, we have talked about the following topics,
- Electric current
- Direct electric current
- Drift velocity
- Relation between current, drift velocity and current density
- E ̅ inside a conductor
- Resistance, resistivity, conductivity
- And some exemplar problems
So let’s begin with our first topic, which is electric current. Current is nothing but the flow of charge in unit time. And it is denoted by i. So how does the charge flow? It flows by,
- Suppose the electron or proton moves in a particular direction, at a particular point if we see from a point or a cross sectional area the charge passes.
- The electron moving around the nucleus, it posses e charge and supposes n is the frequency of revolution around the nucleus. The electronic charge moves around the nucleus n times in one second. The current here is i= en.
- Current can be seen in an electrolytic cell, between two electrodes the current flows. In the video, the flow of current is mentioned.
In a metal, there are large numbers of electrons and they move randomly. The RMS speed of the electron is, Vrms = and its value is 105 m/s at normal temperature.
The next topic is direct electric current. In direct current, the graph is a straight line as its direction is constant in i-t graph. Further, we have discussed an exemplary problem.
Next topic discussed is drift velocity. The electrons in a metal are in random motion. But when we apply potential difference with the help of a battery, inside the metal an electric field is developed. The electric field will be EMF divided by the length. The electrons will experience a force where the electric field is present, and the electrons move in a zig-zag manner. This is known as drift and its velocity is called drift velocity and it is nearly equal to 0.1 mm. Instantaneous current is defined as the rate of flow of current at an instant of time. Average current is defined i= q/t.
Further moving, we have discussed Relation between current, drift velocity and current density. Suppose w have taken a uniform conductor with an area of cross section as A. The electrons are the charged particles and are moving. Let’s take ‘n’ as the number of electrons per unit volume. Under the potential difference, the electron starts moving. The charge flow per second is i, Vd is displacement per second. In the end, we found that i = neAVd
Current density ( J ̅) is a vector. It is the current per unit area. = neV ̅d, where is the current density.
Then we have discussed few more exemplary problems. Next, we have E ̅ inside a conductor, which is the electric field inside the conductor. In any conductor, if there is flow of current then an electric field is produced inside the conductor. The length of the electric field is V/l and will be inside the conductor. If the thickness of wire is uniform, then the valise of the electric field is constant. The last topic discussed is the relation between Resistance, resistivity, conductivity. For normal conductors like metal, the current density is directly proportional electric field inside the conductor. Its ratio is,
Resistivity = ϱ
In the end, we have discussed resistance. Resistivity is an intrinsic property of the material. Conductivity is denoted σ and is, σ= for the ohmic conductors, J∝ E