Electric Current And Current Density - Introduction of Electric Current

• Electric current is the flow of electric charge.
• It can be defined as the rate of flow of electric charges through a conductor.
• Electric current is a scalar quantity.
• The SI unit of electric current is the Ampere (A).
• Electric current is denoted by the symbol ‘I’.

Factors Affecting Electric Current

• Electric current depends on the following factors:
  • Voltage applied - The potential difference across the conductor.
  • Resistance of the conductor - The opposition offered to the flow of current.
  • Length of the conductor - Longer the conductor, more the resistance.
  • Cross-sectional area of the conductor - Wider the conductor, less the resistance.

Equation for Electric Current

• The equation for electric current is given by Ohm’s law:
  • I = V/R
  • Where I is the current in Amperes, V is the voltage in Volts, and R is the resistance in Ohms.

Current Density

• Current density is a measure of the density of current flow in a conductor.
• It is defined as the current per unit area perpendicular to the direction of current flow.
• Current density is denoted by the symbol ‘J’.
• SI unit of current density is Amperes per square meter (A/m^2).

Equation for Current Density

• The equation for current density is given by:
  • J = I/A
  • Where J is the current density in A/m^2, I is the current in Amperes, and A is the cross-sectional area in square meters.

Relation between Electric Current and Current Density

• Electric current can be calculated using current density and cross-sectional area:
  • I = J * A

Example

• Consider a wire of cross-sectional area 0.001 m^2 carrying a current of 2 A. Calculate the current density.
• Solution:
  • Given:
    • Current (I) = 2 A
    • Cross-sectional area (A) = 0.001 m^2
  • Using the formula:
    • J = I/A
    • J = 2 A / 0.001 m^2 = 2000 A/m^2

Effect of Length and Area on Electric Current and Current Density

• As the length of the conductor increases, the resistance increases, resulting in a decrease in electric current and current density.
• As the cross-sectional area of the conductor increases, the resistance decreases, resulting in an increase in electric current and current density.

Example

• Consider two wires of the same material and length. Wire 1 has a cross-sectional area of 0.001 m^2, while wire 2 has a cross-sectional area of 0.002 m^2. If both wires have the same current flowing through them, which wire will have a higher current density?
• Solution:
  • Given:
    • Cross-sectional area of wire 1 (A1) = 0.001 m^2
    • Cross-sectional area of wire 2 (A2) = 0.002 m^2
    • Current flowing through both wires (I) = Same
  • Since current density is given by J = I/A, wire 1 will have a higher current density as its cross-sectional area is smaller compared to wire 2.

Electric Current And Current Density - Introduction of Electric Current

• Electric current is the flow of electric charge.
• It can be defined as the rate of flow of electric charges through a conductor.
• Electric current is a scalar quantity.
• The SI unit of electric current is the Ampere (A).
• Electric current is denoted by the symbol ‘I’.

Factors Affecting Electric Current

• Electric current depends on the following factors:
  • Voltage applied - The potential difference across the conductor.
  • Resistance of the conductor - The opposition offered to the flow of current.
  • Length of the conductor - Longer the conductor, more the resistance.
  • Cross-sectional area of the conductor - Wider the conductor, less the resistance.

Equation for Electric Current

• The equation for electric current is given by Ohm’s law:
  • I = V/R
  • Where I is the current in Amperes, V is the voltage in Volts, and R is the resistance in Ohms.

Current Density

• Current density is a measure of the density of current flow in a conductor.
• It is defined as the current per unit area perpendicular to the direction of current flow.
• Current density is denoted by the symbol ‘J’.
• SI unit of current density is Amperes per square meter (A/m^2).

Equation for Current Density

• The equation for current density is given by:
  • J = I/A
  • Where J is the current density in A/m^2, I is the current in Amperes, and A is the cross-sectional area in square meters.

Relation between Electric Current and Current Density

• Electric current can be calculated using current density and cross-sectional area:
  • I = J * A

Example

• Consider a wire of cross-sectional area 0.001 m^2 carrying a current of 2 A. Calculate the current density.
• Solution:
  • Given:
    • Current (I) = 2 A
    • Cross-sectional area (A) = 0.001 m^2
  • Using the formula:
    • J = I/A
    • J = 2 A / 0.001 m^2 = 2000 A/m^2

Effect of Length and Area on Electric Current and Current Density

• As the length of the conductor increases, the resistance increases, resulting in a decrease in electric current and current density.
• As the cross-sectional area of the conductor increases, the resistance decreases, resulting in an increase in electric current and current density.

Example

• Consider two wires of the same material and length. Wire 1 has a cross-sectional area of 0.001 m^2, while wire 2 has a cross-sectional area of 0.002 m^2. If both wires have the same current flowing through them, which wire will have a higher current density?
• Solution:
  • Given:
    • Cross-sectional area of wire 1 (A1) = 0.001 m^2
    • Cross-sectional area of wire 2 (A2) = 0.002 m^2
    • Current flowing through both wires (I) = Same
  • Since current density is given by J = I/A, wire 1 will have a higher current density as its cross-sectional area is smaller compared to wire 2.

Slide 21

• Electric current is the flow of electric charges through a conductor.
• It can be caused by the movement of electrons or ions.
• In a solid conductor, such as a wire, the flow of electric charges is due to the movement of electrons.
• In a fluid conductor, such as an electrolyte, the flow of electric charges is due to the movement of ions.

Slide 22

• Electric current can also be classified into two types: direct current (DC) and alternating current (AC).
• In direct current, the flow of electric charges is in a constant direction.
• In alternating current, the flow of electric charges periodically changes direction.
• The standard household electrical outlets provide alternating current.

Slide 23

• Electric current can also be categorized as either a steady current or a transient current.
• Steady current refers to a constant flow of electric charges in a circuit.
• Transient current refers to a temporary or changing flow of electric charges, which occurs during the switching on or off of a circuit.

Slide 24

• Electric current is not always visible to the naked eye.
• However, it can be detected or measured using various instruments, such as ammeters or galvanometers.
• Ammeters are devices used to measure the electric current flowing through a circuit.
• Galvanometers can be used to detect and measure small electric currents.

Slide 25

• Electric current is essential for the functioning of various electrical devices and systems.
• It powers electrical appliances, lighting systems, and electronic devices.
• It is also used in industries for powering machinery and equipment.
• Moreover, electric current plays a crucial role in the transmission and distribution of electrical energy.

Slide 26

• Electric current produces various effects, including heating, magnetic effects, and chemical reactions.
• When a current passes through a conductor, it generates heat due to the resistance offered by the conductor.
• Electric currents also create magnetic fields around the conductors, leading to magnetic effects.
• In electrolytes, electric currents can cause chemical reactions, such as electrolysis.

Slide 27

• Understanding electric current is essential for studying circuit theory and analyzing electrical circuits.
• Circuit theory helps in designing and troubleshooting electrical circuits.
• It involves concepts like voltage, resistors, capacitors, inductors, and various circuit components.
• The study of electric current is crucial for engineering disciplines like electrical engineering and electronics.

Slide 28

• Let’s consider an example to apply the concepts of electric current.
• Suppose you have a circuit with a voltage source of 12 V and a resistor of 4 Ohms.
• Using Ohm’s law, we can find the current flowing through the circuit:
  • I = V/R
  • I = 12 V / 4 Ohms
  • I = 3 Amperes

Slide 29

• In this example, the electric current flowing through the circuit is found to be 3 Amperes.
• The current density can be determined by considering the cross-sectional area of the conductor.
• If the cross-sectional area is 0.05 square meters, we can calculate the current density:
  • J = I/A
  • J = 3 A / 0.05 m^2
  • J = 60 A/m^2

Slide 30

• In conclusion, understanding electric current and current density is crucial for various applications in physics and engineering.
• Electric current is the flow of electric charges and can be categorized as direct or alternating current.
• It has important effects, such as heating, magnetic effects, and chemical reactions.
• Current density provides a measure of the density of current flow in a conductor.
• Knowledge of electric current is essential for studying circuit theory and analyzing electrical circuits.