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Measuring Electrical Resistance

Measuring Electrical Resistance. The most common component in a computer is a resistor The filament of a light bulb is also a resistor Remember** A resistor is used in a circuit to decrease the current Energy is transferred into heat by resistors which is why devices get warm when being used.

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Measuring Electrical Resistance

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  1. Measuring Electrical Resistance

  2. The most common component in a computer is a resistor • The filament of a light bulb is also a resistor Remember** A resistor is used in a circuit to decrease the current Energy is transferred into heat by resistors which is why devices get warm when being used.

  3. Ohm’s Law • Georg Ohm (German physicist) discovered that for most wires, the ratio of potential difference (V) to current (I) is constant. The constant is called resistance (R) • R=V/I

  4. Based on Ohm's Law, the larger the resistance in a circuit, the smaller the current • A resistor therefore resists, of reduces the current in a circuit • A resistor is an electronic component with a precise resistance

  5. Methods for Changing Potential Difference • One way to vary to change potential difference is to change the number of cells in a circuit, or connect a variables power supply Units of Resistance: • Since R = V/I, the unit of resistance is Volt/ampere or Ohm Ω (the Greek letter Omega) • Example #1: If a potential Difference of 1V across the ends of a load results in a current of 1A, then what is the resistance?

  6. Example #2: A technician is checking the circuits on a car. The technician measures the current entering a component as 0.47 A. The potential difference across the component is 12V. What is the resistance?

  7. Example #3: • An electric Toy has a resistance of 120 Ω and requires a current of 0.05A to work properly. How many 1.5 V cells does this toy use?

  8. Factors that Affect the Resistance of Wires • Resistance is caused when a current of electrons collides with ions and other electrons • Ohm found that that resistance of different wires of the same length are different • Type of material: Copper is a better conductor than iron and thus has less resistance • Length of Wire: Resistance is directly proportional to the length of a wire (doubling the length of a wire doubles its resistance) • Diameter of Wire: Resistance and diameter are inversely proportional; resistance decreases as the diameter of wire increases • Temperature: Resistance increases as temperature increases

  9. Superconductors • When electric charge can flow through a material with no resistance, the material is called a superconductor • A superconducting wire does not transform electrical energy into heat. • Example: When mercury is cooled to -270 ºC, it becomes a superconductor

  10. Non-Ohmic Conductors • A non-ohmic conductor is a material that is able to change its resistance (R, Ω) in response to changes in potential difference (Volts, V). • The filament inside a light bulb is a non-ohmic conductor since its resistance changes with temperature - The more resistance, the brighter and hotter the light

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