Resistance and Resistivity Resistance and Resistivity what is
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Resistance and Resistivity
Resistance and Resistivity, what is it? Resistivity is the opposite of conductivity, it’s a measure of how effectively a material slows down the flow of electricity. Insulators have a high resistivity rating. Materials such as metals and other conductors have a low resistivity rating.
Resistance and Resistivity A conductor’s Resistance is defined as the ratio of the Applied Voltage to the Current produced. R = V/I Scalar Units: Ohm [Ω] = [V/A]
Resistance and Resistivity Resistance can be calculated for any object. Good conductor – low resistance Poor conductor –high resistance All circuit elements have some resistance. The resistance of connecting wire leads is considered negligible.
Resistance and Resistivity Resistance Ø The geometry of the resistor matters Length Area Resistivity: (units m) Ø Increase the Length, flow of electrons impeded Ø Increase the cross-sectional Area, flow enhanced
Resistance and Resistivity For a wire of length l and cross-sectional area A the resistance R: ØIs proportional to l ØAnd inversely proportional to A ØThe constant ρ (rho) ØIs known as the resistivity.
Resistance and Resistivity Increasing the cross-sectional area increases the number of available electrons.
Resistance and Resistivity
Resistance and Resistivity Therefore, the units of resistance are: Resistivity has units of Ohm· meters ( · m)
Resistance and Resistivity
Resistance and Resistivity
Resistance and Resistivity and temperature. The resistance and resistivity changes with temperature, therefore resistivity at quoted at a specific temperature The resistance is proportional to the length l and inversely proportional to the cross-sectional area A, the material the conductor is made from, and the temperature.
Resistance and Resistivity Superconductivity Below a certain critical temperature, Resistance becomes ZERO, allowing current to exist without energy wasted. Superconductivity, although predicted and discovered a century ago has only become useful recently due to the development of rare-earth conductive ceramics. Superconductive wires are used in the electromagnets of MRI machines.
Resistance and Resistivity Two wires, A and B, are made of the same metal and have equal length, but the resistance of wire A is four times the resistance of wire B. How do their diameters compare? a. b. c. d. e. d. A = 4 d. B d. A = 2 d. B d. A = ½ d. B d. A = ¼ d. B
Resistance and Resistivity A wire of resistance R is stretched uniformly (keeping its volume constant) until it is twice its original length. What happens to the resistance? a. it increases by a factor 4 b. it increases by a factor 2 c. it stays the same d. it decreases by a factor 2 e. it decreases by a factor 4
Resistance and Resistivity Find the resistance of a piece of copper with a diameter of 1 mm and a length of 1 cm
Resistance and Resistivity Bolbo the gold broker from Baghdad has just received a gold bullion bar for his birthday from his brother Bob. The face of the bar is 5 cm on both sides, and the length is 20 cm. The resistance between faces A and B is measured to be 0. 8 micro-ohms. Bolbo the broker assumes that the bullion is gold if the measured resistance is within +/- 10% of theoretical value. Is the material gold or is it bogus? 20 c m =1. 92 u don’t try to cash it in! 5 cm B A
Resistance and Resistivity A wire 10 m long consists of 5 m of copper followed by 5 m of aluminum of equal diameter of 1 mm. A voltage difference of 80 V is placed across the composite wire. a. b. What is the total resistance of the wire? What is the current flow through the wire?
Resistance and Resistivity Summary
- Resistance is futile if 1 ohm
- Resistance from resistivity
- Copper conductivity s/m
- Specific resistance formula
- What is a force that opposes motion through direct contact
- Resistivity log
- Is 121
- Resistivity of human body
- Cz silicon wafer with high resistivity
- Factors affecting resistivity of rocks
- Current density resistivity
- Regents physics work power energy
- Resistivity unit
- Resistivity by four probe method
- Measurement of dc resistivity
- Joule solar problems
- Does everything fall at the same speed
- Biotic potential
- Levers in everyday life
- Primary retention