Electric Current Study Notes

Electric Current

Definition of Electric Current

• Electric current is defined as the flow of electrons through a wire.

• It can also be described as the rate at which electric charge flows in a circuit.

Key Components of Electric Current

• Current (I): Represents the flow of electric charge.

• Charge (Q): The quantity of electricity that flows.

• Time (t): The duration over which the charge flows.

Formula for Electric Current

• The relationship between current, charge, and time is given by the equation: $I=\frac{\Delta Q}{\Delta t}$ where:

  • $I$ is the current in Amperes (A)

  • $Q$ is the charge in Coulombs (C)

  • $t$ is the time in seconds (s)

Units of Electric Current

• The Ampere (A) is the unit of electric current, defined as:

  • 1 Ampere = 1 Coulomb/second
    $1A=\frac{C}{s}$

• The Ampere is named after André-Marie Ampère, who contributed to the understanding of electromagnetism in 1819.

Examples of Electric Current Calculations

Example 1

• Problem: What is the electric current if 10 C of charge passes through a wire in 2 seconds?

• Solution: Using the formula, we calculate:
  $I=\frac{10C}{2s}=\frac{5C}{s}$
  Thus, the electric current is 5 A.

Fundamental Units of Measurement

• Example 2: What are the 7 fundamental units of measurement? (Answer not provided in the transcript)

• Example 3: What are the fundamental units of a Coulomb?

• Example 4: What are the fundamental units for electric field strength?

  • Answer: $\frac{\operatorname{kg}m}{As^3}$

• Example 5: What are the fundamental units of a Volt?

  • Answer: $\frac{\operatorname{kg}m}{As^3}$

• Example 6: What are the fundamental units of a Farad?

  • Answer: $\frac{A^2s^4}{\operatorname{kg}m}$

• Example 7: What are the fundamental units for electric flux?

  • Answer: $\frac{\operatorname{kg}m^3}{As^3}$

• Example 8: What are the fundamental units for the permittivity of free space?

  • Answer$\frac{A^2s^4}{\operatorname{kg}m}$

Additional Examples and Applications of Electric Current

Example 9

• Challenge: How many electrons go through a light bulb in 15 seconds if the current is 0.5 A?

• Solution approach: Use the relationship between current, charge, and the fundamental charge of an electron, which is approximately 1.6 x 10^-19 C.

Example 10

• Challenge: A defibrillator has square pads of 35 cm sides, separated by a distance of 5 cm, and connected to a voltage source 10 times greater than a household outlet (approx. 120 V). It discharges in a millisecond. Calculate the current that runs through the heart and the number of electrons discharged.

• Solution approach: The exact calculations would require additional information like capacitance and are to be based on the voltage and time of discharge.

• Note: The solution would use the fundamental equations related to current, capacitance, and the properties of the defibrillator setup.