Electrical Engineering: Basic Laws (1 of 31) Resistance and Resistivity

Michel van Biezen

27 Oct 201503:46

Summary

TLDRThis section of Electro Line introduces the fundamental concepts of electrical engineering, focusing on resistance and resistivity. Resistance is the property of a material that opposes the flow of electrical current, measured in ohms. The relationship between current and resistance is inversely proportional. Resistivity, measured in ohm-meters, is a material property influencing resistance. The video highlights how length and cross-sectional area affect resistance and compares materials like copper, aluminum, and semiconductors based on their resistivity. Copper is favored for wiring due to its low resistivity, while aluminum has drawbacks due to higher energy loss.

Takeaways

⚡ Resistance is the property of a material that resists the flow of current or electrical charges in a circuit.
📉 The amount of current flowing through an object is inversely proportional to its resistance. Doubling the resistance halves the current.
🧮 The unit of resistance is ohms (Ω).
🧲 Resistivity is the property of a material that determines its resistance. Higher resistivity means higher resistance.
📏 The formula for resistance is resistivity times length divided by cross-sectional area. Longer objects or smaller cross-sectional areas increase resistance.
🔗 Materials like copper and silver have low resistivity, making them excellent conductors, but copper is preferred over silver due to cost.
💡 Aluminum is cheaper than copper but has higher resistivity, leading to higher energy loss and heat dissipation.
🏠 Aluminum wiring is less favored by insurance companies for homes and buildings due to its higher resistivity.
⚙️ Semiconductors like carbon and germanium have much higher resistivity than metals, making them less conductive.
🔄 Current is inversely proportional to resistance: increasing resistance decreases current flow proportionally.

Q & A

What is resistance in electrical engineering?
-Resistance is the property of a material that resists the flow of electrical current or charges in a circuit. It limits the amount of current that can flow through an object.
How is resistance related to current in a circuit?
-The amount of current that flows through an object is inversely proportional to its resistance. If resistance increases, the current decreases proportionally.
What is the unit of resistance?
-The unit of resistance is ohms (Ω).
What is resistivity, and how is it different from resistance?
-Resistivity is a material's inherent property that determines how much resistance it offers to current flow. Resistance depends on resistivity, but also on the physical dimensions (length and cross-sectional area) of the object.
What is the equation to calculate resistance in terms of resistivity?
-The resistance of an object is calculated using the equation: Resistance (R) = Resistivity (ρ) × Length (L) / Cross-sectional Area (A).
How does the cross-sectional area of an object affect its resistance?
-If the cross-sectional area increases, there are more paths for the current to flow, lowering the resistance. If the area decreases, resistance increases due to fewer paths for current.
How does the length of an object affect its resistance?
-The longer the object, the higher the resistance, as the current has to travel through a longer path, which increases opposition.
What are the units of resistivity?
-The units of resistivity are ohm-meters (Ω·m), as resistivity involves both resistance (ohms) and dimensions (meters).
Why is copper preferred over aluminum for electrical wiring?
-Copper is preferred because it has a lower resistivity compared to aluminum, allowing for better current flow and less energy loss. Aluminum, with higher resistivity, causes more energy dissipation and can lead to heating.
How do metals like copper and silver compare to semiconductors in terms of resistivity?
-Metals like copper and silver have much lower resistivity, making them better conductors of electricity. Semiconductors like carbon and germanium have higher resistivity, meaning they oppose the flow of current more.