Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 8.3 Resistance and Ohm`s Law
Document related concepts
Transcript
8.3 RESISTANCE AND OHM’S LAW BC Science 9: p. 290-301 Resistance • Resistance is the property of any material that slows down the flow of electrons. • Some resistant materials (ie. loads) are able to convert electrical energy into other forms (eg. lamps). Measuring Resistance • Resistance can be measured in circuit using an ohmmeter. • The unit of measurement for resistance is the ohm (Ω). Ohm’s Law • Ohm’s law is an equation that shows how voltage, current, and resistance are related. • As the resistance in a circuit increases, the current decreases (ie. slows down). • Ohm’s Law: – Voltage (V) = Current (I) x Resistance (R) Ohm’s Law • Example Problems: 1. The current through a load in a circuit is 1.5 A. If the potential difference across the load is 12 V, what is the resistance of the load? Ohm’s Law • Example Problems: 2. The resistance of a car headlight is 15 Ω. If there is a current of 0.80 A through the headlight, what is the voltage across the headlight? Ohm’s Law • Examples Problems: 3. A 60 V potential difference is measured across a load that has a resistance of 15 Ω. What is the current through this load? Applications of Resistance • Specific resistors are used to control the amount of current in an electrical circuit. – Eg. Volume controls, coils in electric stoves. • Circuit resistors are marked with coloured bands to indicate their resistance in ohms. • The colours indicate different values of the resistance. Applications of Resistance • The colour of the first band indicates the first digit. • The colour of the second band indicates the second digit. • The colour of the third band indicates the number of zeros. • The fourth band indicates the percentage accuracy of the resistor. – Gold is 5%, silver is 10%, no colour is 20%. Applications of Resistance • Examples: – Violet, White, Red, Silver • 7 900 ± 10% Ω – Orange, Red, Brown, Gold • 320 ± 5% Ω – Red, Blue, Green • 2 600 000 ± 20% Ω Reducing Resistance • Semiconductors have conductivity that varies with temperature. • Eg. Silicon • Superconductors have zero resistance but require very low temperatures. • Eg. Mercury or lead alloys • Variable resistors allow resistance to be adjusted. • Eg. Dimmer switches and volume dials. – Orange, Red, Brown, Gold • 320 ± 5% Ω – Red, Blue, Green
