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Electric current


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The slides present a very brief introduction to Electric Current.

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Electric current

  1. 1. Electric Current by SBR
  2. 2. Electric Current β€’ Electric current is the rate of flow of charge through a conductor of cross-sectional area 𝑨. β€’ In electric circuits this charge is often carried by electrons moving through a wire. β€’ It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionized gas (plasma).
  3. 3. Unit of Current β€’ The conventional symbol for current is 𝑰 β€’ If βˆ†π‘Έ is the amount of charge passing through an area in a time interval βˆ†π’•, then the average current 𝑰 𝒂𝒗𝒆 is defined as: 𝑰 𝒂𝒗𝒆 = βˆ†π‘Έ βˆ†π’• = 𝒅𝑸 𝒅𝒕 β€’ The unit of current is coulomb per second. β€’ also called the ampere (𝑨). πŸπ‘¨ = 𝟏π‘ͺ πŸπ’”
  4. 4. Unit of Current β€’ Ampere is a large unit. β€’ Therefore, the current is usually expressed in: π‘šπ‘–π‘™π‘™π‘–π‘Žπ‘šπ‘π‘  (1 π‘šπ΄ = 1 Γ— 10βˆ’3 𝐴) π‘šπ‘–π‘π‘Ÿπ‘œπ‘Žπ‘šπ‘π‘  (1 ¡𝐴 = 1 Γ— 10βˆ’6 𝐴) π‘›π‘Žπ‘›π‘œπ‘Žπ‘šπ‘π‘  (1 𝑛𝐴 = 1 Γ— 10βˆ’9 𝐴)
  5. 5. Conventions β€’ In a conductive material, the moving charged particles that constitute the electric current are called charge carriers. β€’ In metals, which make up the wires and other conductors in most electrical circuits, the positively charged atomic nuclei of the atoms are held in a fixed position, and the negatively charged electrons are the charge carriers, free to move about in the metal. β€’ In other materials, notably the semiconductors, the charge carriers can be positive or negative, depending on the dopant used. β€’ Positive and negative charge carriers may even be present at the same time, as happens in an electrolyte in an electrochemical cell.
  6. 6. Conventions β€’ A flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. β€’ Since current can be the flow of either positive or negative charges, or both, a convention is needed for the direction of current that is independent of the type of charge carriers. β€’ The direction of conventional current is arbitrarily defined as the same direction as positive charges flow.
  7. 7. Conventions β€’ The electrons, the charge carriers in an electrical circuit, flow in the opposite direction of the conventional electric current. Flow of Positive Charge Flow of Electrons
  8. 8. What is enough current? Note: around 100 mA to 1 A of current is sufficient to induce cardiac/respiratory arrest. Device Current (A) (A) 100-W lightbulb 1 Microwave 8 – 13 Laptop 2 – 3 Electric Fan 1 Television 1 – 3 Toaster 7 – 10 Fluorescent Light 1 – 2 radio/stereo 1 – 4 typical LED 20 X 10-3 Smart Phone 200 X 10-3 automobile starter 200 Lightning 1000