physics-class-12-unit-07-chapter-02-electric-current-current-density-current-electricity-l-2-10-7rndxyupqxm

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Aurora Borealis (Northern Light) </primary>
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- Image from international space station of NASA (Image Credit NASA)
 
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<footer style = "font-size: 18px">Electric Current and Current Density $\rightarrow$ Current Electricity $\rightarrow$ <span style = "color:blue"> Aurora Borealis (Northern Light) </span> $\rightarrow$ Electric Current $\rightarrow$ Current </footer>

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Electric Current </primary>
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- We have an arbitrary surface with some area.

- The net amount of charge Q which is flowing: $ Q = Q_+ - Q_-$

- These charges were steadily flowing through that surface, then the amount of charge that is going through that surface would be $\propto \text{time} ~t$.

- The rate at which the charge flows, $I = \frac{Q}{t}$.

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<footer style = "font-size: 18px">Current Electricity $\rightarrow$ Aurora Borealis (Northern Light) $\rightarrow$ <span style = "color:blue"> Electric Current </span> $\rightarrow$ Current $\rightarrow$ Current </footer>

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Current </primary>
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- Take a small time interval, $ \Delta t$.

- The amount of charge that is flows through that surface, $\Delta Q $.

- $I(t)=\operatorname{Lim}_{\Delta t \mapsto 0} \frac{\Delta Q}{\Delta t}=\frac{d Q}{d t}$

- Unit of current: $\frac{\text{Coulomb}}{\text{Second}}$ =Ampere

- $220 - 240 V$ Household appliances. $\sim5 A.$

- Lightening : Several Thousand Amps.

- Fish $\sim 1A$.

- Human Nervous System $\mu A.$

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<footer style = "font-size: 18px">Aurora Borealis (Northern Light) $\rightarrow$ Electric Current $\rightarrow$ <span style = "color:blue"> Current </span> $\rightarrow$ Current $\rightarrow$ Conductor </footer>

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Conductor </primary>
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- All material consists of atoms and molecules and their interaction.

- Ability to conduct also depends upon physical condition of the material, for example pressure, temperature etc.

- For the purpose of electric current, we use conductors such as silver, copper, aluminum, mercury, etc. So these are materials which readily conduct electricity.

- Electrostatics: $\vec{E}_{inside} = 0$

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<footer style = "font-size: 18px">Current $\rightarrow$ Current $\rightarrow$ <span style = "color:blue"> Conductor </span> $\rightarrow$ Electrolyte $\rightarrow$ Insulators </footer>

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Dynamic Condition </primary>
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- No internal electric field will be created $E_{int}=0$, for conductor.

- Current is flow of charge.

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<footer style = "font-size: 18px">Electrolyte $\rightarrow$ Insulators $\rightarrow$ <span style = "color:blue"> Dynamic Condition </span> $\rightarrow$ Direction of Current $\rightarrow$ Current Density </footer>

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Direction of Current </primary>
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- Direction of flow of positive charge.

- I has a direction but is a scalar.

- $\frac{dQ}{dt}=I$

- Q through a surface $ = \int Idt$

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<footer style = "font-size: 18px">Insulators $\rightarrow$ Dynamic Condition $\rightarrow$ <span style = "color:blue"> Direction of Current </span> $\rightarrow$ Current Density $\rightarrow$ Electrostatic Condition </footer>

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Current Density </primary>
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- Current Density is a Vector.

- $|J| = \frac{I}{Area}$.

- Since $\vec{J}$ is a vector, we need to give a direction.

- $\vec{ds}:$ a direction perpendicluar to the cross section.

- $\vec{J}:$ In the direction of current flow, $\vec{J}.\vec{ds} > 0$ For Positive Current.

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<footer style = "font-size: 18px">Dynamic Condition $\rightarrow$ Direction of Current $\rightarrow$ <span style = "color:blue"> Current Density </span> $\rightarrow$ Electrostatic Condition $\rightarrow$ Dynamic Conditions </footer>

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Electrostatic Condition </primary>
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- Under electrostatic condition there is no field inside a conductor.

- $\vec{E}_{inside}=0$.

- Thermal Velocity $\sim 10^6 m/s.$

- Electron is continuously colliding with atoms or ions and then bouncing back, collision is elastic in nature.

- Velocities of different electrons are uncorrelated.

- $\frac{1}{N} \sum_{i=1}^N\left\langle\vec{v}_i\right\rangle=0$

- Average velocity of the collection of electrons is zero.

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<footer style = "font-size: 18px">Direction of Current $\rightarrow$ Current Density $\rightarrow$ <span style = "color:blue"> Electrostatic Condition </span> $\rightarrow$ Dynamic Conditions $\rightarrow$ Thank You </footer>

### <Success style="font-size:25px"> Electric Current Current Density Current Electricity L-2 </Success>
### <primary style="font-size:24px"> Dynamic Conditions </primary>
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- $\vec{E}_{inside} \neq 0$
- Electrons are accelerated. The collection of electrons would move in a direction opposite to $\vec{E}.$
- The concept of drift velocity.
- All electrons within a volume AL will pass through the right face.
- $n=$ electron density
- $Q = (en)LA$
- $e=$ magnitude of electron charge $=1.6\times 10^{-19}c.$
- $|J| = \frac{Q}{At} = en (\frac{L}{t}) = env_ d \vec{J} = -en\vec{v}_d.$

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<footer style = "font-size: 18px">Current Density $\rightarrow$ Electrostatic Condition $\rightarrow$ <span style = "color:blue"> Dynamic Conditions </span> $\rightarrow$ Thank You $\rightarrow$  </footer>