Electric Current And Current Density

Slide 1

Topic: Electric Current and Current Density - Drift Velocity
Definition: Electric current is the rate of flow of electric charge. It is denoted by ‘I’ and measured in Amperes (A).
Symbol: I
Unit: Ampere (A)
Formula: I = ΔQ/Δt, where ΔQ is the change in charge and Δt is the change in time.

Slide 2

In a conductor, electric current is caused by the movement of electrons.
Electrons move from the negatively charged terminal (cathode) to the positively charged terminal (anode).
This flow of electrons constitutes the electric current.
Electric current can also occur in the opposite direction, where positively charged particles (e.g., ions) move towards the negatively charged terminal.

Slide 3

Current Density (J) represents the amount of current flowing per unit area of a conductor.
It is denoted by the symbol ‘J’ and measured in Amperes per square meter (A/m²).
Formula: J = I/A, where I is the current and A is the area of the conductor.
Higher current density implies a greater amount of current flowing per unit area.

Slide 4

Drift Velocity (v) is the average velocity of charge carriers (e.g., electrons) in a conductor due to an applied electric field.
It is influenced by the resistivity (ρ) and cross-sectional area (A) of the conductor and is inversely proportional to the number density (n) of charge carriers.
Formula: v = (I/nqA), where I is the current, n is the number density, q is the charge of the carrier, and A is the cross-sectional area.

Slide 5

Ohm’s law relates the electric current (I) flowing through a conductor with the voltage (V) applied across it.
Ohm’s law states that the current is directly proportional to the voltage and inversely proportional to the resistance (R) of the conductor.
Formula: V = IR, where V is the voltage, I is the current, and R is the resistance.

Slide 6

Resistance (R) is the opposition to the flow of electric current in a conductor.
It is represented by the symbol ‘R’ and measured in Ohms (Ω).
Higher resistance results in a lower current flow.
Resistance depends on the type of material, length (l) of the conductor, and its cross-sectional area (A).
Formula: R = ρ(l/A), where ρ is the resistivity, l is the length, and A is the cross-sectional area.

Slide 7

Resistivity (ρ) is the inherent characteristic of a material that determines its resistance.
It is denoted by the Greek letter ‘rho’ (ρ) and measured in Ohm-meter (Ω·m).
Resistivity depends on the nature of the material and its temperature.
Materials with high resistivity impede electric current flow more than materials with low resistivity.

Slide 8

Conductors are materials that allow the easy flow of electric current.
Examples of conductors include metals like copper, silver, aluminum, etc.
Conductors have low resistivity and high electrical conductivity.
This is because they have a large number of free electrons that can move easily in response to an electric field.

Slide 9

Insulators are materials that do not allow the flow of electric current.
Examples of insulators include rubber, wood, glass, plastic, etc.
Insulators have high resistivity and low electrical conductivity.
They do not have many free electrons available for current flow.

Slide 10

Semiconductors are materials whose conductivity lies between that of conductors and insulators.
Examples of semiconductors include silicon (Si), germanium (Ge), etc.
The conductivity of semiconductors can be altered by the addition of impurities or by applying an external electric field.
Semiconductors are essential components of electronic devices like transistors, diodes, and integrated circuits.

Slide 11

Electric Current And Current Density - Drift Velocity

Drift velocity is influenced by the magnitude of electric field (E) applied to the conductor.
Formula: v = μE, where v is the drift velocity, μ (mu) is the mobility of charge carriers.
Mobility (μ) is the average speed of charge carriers per unit electric field.
Charge carriers experience collisions with atoms or other carriers, limiting their velocity.
Collisions cause the charge carriers to change direction and randomize their motion.

Slide 12

Current flows due to the continuous motion of charge carriers.
The actual motion of charge carriers is random in direction and magnitude.
However, the average velocity contributes to the net drift velocity.
The drift velocity is very small, on the order of millimeters per second.
Example: In a copper wire, the drift velocity of electrons is around 0.01 mm/s when a current of 1 A is flowing.

Slide 13

Current density plays a significant role in determining the flow of current through a conductor.
For a uniform current density, the current flowing through a given cross-sectional area is constant.
Formula: J = nqv, where J is the current density, n is the number density of charge carriers, q is the charge of the carrier, v is the drift velocity.
Higher current density implies a greater number of charge carriers passing through a given area per unit time.

Slide 14

Resistivity is a fundamental property of a material related to its electrical conductivity.
Resistivity determines how effectively a material resists the flow of electric current.
Different materials have different resistivities.
Example: Copper has a low resistivity of 1.7 x 10^-8 Ω·m, while rubber has a high resistivity of 10^13 Ω·m.

Slide 15

Resistance can be calculated using the formula R = ρ(l/A).
Longer conductors have higher resistance due to increased collision probability with charge carriers.
Thinner conductors have higher resistance because the cross-sectional area is reduced, limiting the flow of charge carriers.
Resistance can also be influenced by temperature, as resistivity changes with temperature for most materials.

Slide 16

Ohm’s law relates the current flowing through a conductor to the voltage applied.
Ohm’s law holds true for conductors with a constant resistance.
Ohm’s law becomes invalid for non-ohmic conductors and non-linear circuit components like diodes and transistors.
Ohm’s law can be represented using the equation V = IR.

Slide 17

The relationship between current, voltage, and resistance can be understood using the analogy of water flow.
Current is similar to the flow rate of water, voltage is similar to the pressure difference, and resistance is similar to the narrowing of a pipe or obstruction.
Just as smaller pipes or obstructions in a pipe restrict water flow, resistance in a circuit restricts the flow of electric current.

Slide 18

Electric power (P) is the rate at which electric energy is transferred or consumed.
P = VI, where P is the power, V is the voltage, and I is the current.
Power is measured in Watts (W).
Higher power indicates higher energy consumption or transfer rate.

Slide 19

Electrical energy is commonly measured in kilowatt-hours (kWh).
1 kWh is equal to the energy consumed (or transferred) at a rate of 1 kilowatt (1000 watts) for 1 hour.
To calculate the energy consumed in kWh, the power consumption needs to be multiplied by the time in hours.
Example: If a device consumes 500 watts for 5 hours, the energy consumed is 2.5 kWh.

Slide 20

Electric circuits consist of interconnected components that allow the flow of electric current.
Series circuits have elements connected in a sequence where the same current flows through all components.
Parallel circuits have elements connected between common points, allowing different currents to flow through each component.
Combination circuits have a mix of series and parallel arrangements. They require a thorough analysis to determine the currents and voltages across each element.

Slide 21

Electric Current and Current Density - Drift Velocity

Drift velocity depends on the magnitude of the electric field applied to the conductor.
Formula: v = μE, where v is the drift velocity, μ (mu) is the mobility of charge carriers.
The direction of the drift velocity is opposite to the direction of the electric field.
Charge carriers experience collisions with atoms or other carriers, causing their velocity to change.
Collisions lead to random motion of charge carriers, but the average velocity contributes to the net drift velocity.

Slide 22

Electric field strength can be determined using the formula E = V/d, where E is the electric field strength, V is the voltage, and d is the separation between the two points.
The drift velocity of charge carriers in a conductor is directly proportional to the electric field strength.
Higher electric field strengths result in higher drift velocities.
Example: If the electric field strength is doubled, the drift velocity of charge carriers will also double.

Slide 23

Current density gives information about how the current is distributed across a conductor.
Current density can vary within a conductor, depending on its shape and cross-sectional area.
Formula: J = I/A, where J is the current density, I is the current, and A is the cross-sectional area.
Surface currents are often concentrated near sharp edges or points where the cross-sectional area is significantly reduced.
High current density areas can lead to localized heating and may require thicker conducting materials to handle the larger current flow.

Slide 24

The concept of resistance arises from the collisions of charge carriers with the atoms of the conductor.
Resistivity determines how effectively the material resists the flow of electric current.
Resistance increases with an increase in the length of the conductor.
Resistance decreases with an increase in the cross-sectional area of the conductor.
Materials with high resistivity have high resistance, while materials with low resistivity have low resistance.

Slide 25

Superconductors are materials that exhibit zero electrical resistivity at very low temperatures.
When cooled below a critical temperature, superconductors allow the flow of electric current with zero resistance.
Superconductors have various applications, including high-speed magnetic levitation trains and powerful electromagnets used in research and medical imaging.

Slide 26

Conductance (G) is the reciprocal of resistance and represents the ease with which electric current flows through a conductor.
Formula: G = 1/R, where G is the conductance and R is the resistance.
Conductance is measured in Siemens (S).
Conductivity (σ) is another term used to describe how effectively a material conducts electricity and is the reciprocal of resistivity.

Slide 27

Kirchhoff’s laws are essential tools for analyzing complex electrical circuits.
Kirchhoff’s current law (KCL) states that the total current entering a junction is equal to the total current leaving the junction.
Kirchhoff’s voltage law (KVL) states that the sum of the voltages in any closed loop of a circuit is equal to zero.
These laws enable the analysis of circuits with multiple branches and are widely used in circuit design and troubleshooting.

Slide 28

Application: Electric circuits are used in a wide range of devices, from simple household appliances to sophisticated electronic devices.
Examples include lighting systems, computers, televisions, smartphones, electric vehicles, and power distribution networks.
Understanding the principles of electric current and current density is crucial for designing safe and efficient electrical systems.

Slide 29

Charge carriers in a conductor experience resistance, which causes the production of heat.
This heat dissipation can be significant and needs to be considered in electrical system designs.
Joule’s law states that the heat dissipated per unit time (P) in a conductor is given by P = I²R, where I is the current and R is the resistance.
Large resistances or high current values can result in significant heat generation, which may require cooling measures or conductors with higher thermal capacities.

Slide 30

Summary:
- Electric current is the flow of charge carriers in a conductor.
- Current density represents the amount of current flowing per unit area.
- Drift velocity is the average speed of charge carriers due to an applied electric field.
- Resistance opposes the flow of current in a conductor.
- Ohm’s law relates current, voltage, and resistance.
- Kirchhoff’s laws are used to analyze complex electrical circuits.
Application:
- Electric circuits are widely used in various devices and systems.
- Understanding and applying the principles of current and resistance are essential for designing and troubleshooting electrical systems.
- Consideration of heat dissipation is important to ensure the safe and efficient operation of electrical systems.