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8.3 – Resistance and Ohms Law

8.3 – Resistance and Ohms Law. Resistance – is the property of any material that slows down the flow of electrons (i.e. a load) and converts electrical energy into other forms of energy (i.e. light or heat).

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8.3 – Resistance and Ohms Law

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  1. 8.3 – Resistance and Ohms Law

  2. Resistance – is the property of any material that slows down the flow of electrons (i.e. a load) and converts electrical energy into other forms of energy (i.e. light or heat). Wires that connect the battery to a load have very little resistance; therefore, electrons can travel through the wire with almost no loss of electrical energy. Section 8.3 – Resistance and Ohm’s Law

  3. Voltage is directly proportional to current; therefore, as the voltage increases, so does the current (I). If an electric circuit has a large resistance, less current will flow if a battery with the same voltage is connected to a lower resistance circuit. Resistance and Current

  4. R = V/I R = resistance (ohm - Ω) V = voltage (volts – V) I = current (amperes – A) Ohm’s Law V R I

  5. Divide by 1000 to convert mA (m = milli)  A Times by 1000 to convert A  mA Example: 5 mA  ? A 5 mA/1000 = 0.005 A 0.095 A  ? mA 0.095 A x 1000 = 95 mA Conversions

  6. Divide by 1000 to convert Ω  k Ω (k = kilo) Times by 1000 to convert k Ω  Ω Example: 6000 Ω  ? k Ω 6000 Ω/1000 = 6 k Ω 20 k Ω  ? Ω 20 k Ω x 1000  20,000 Ω Conversions

  7. Divide by 1,000,000 to convert V to MV (mega) Times by 1,000,000 to convert MV to V Example: 25 MV  ? V 25 MV x 1,000,000 = 25, 000,000 4,000,000 V  MV 4,000,000 V/1,000,000 = 4 MV Conversions

  8. 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? R = V/I R = 12 V/1.5A R = 8.0 Ω The resistance of the load is 8.0 Ω. Sample Calculations Using the Ohm’s Formula

  9. 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? V = IR V = (0.80 A)(15 Ω) V = 12 V The voltage across the headlight is 12 V. Sample Calculations Using the Ohm’s Formula

  10. A 60 V potential difference is measured across a load that has a resistance of 15 Ω. What is the current through this load? I = V/R I = 60 V/ 15 Ω I = 4.0 A The current through this load is 4.0 A. Sample Calculations Using the Ohm’s Formula

  11. Practice Problems • Pg. 293 #1-3

  12. Converting Prefixes • Prefixes are used to indicate the magnitude of a value • Mili (m) represents one-thousandth (eg. 25mA = 25/1000 = 0.025A) • Kilo (k) represents one thousand (eg. 5.0KΩ = 5000Ω • Mega (M) represents one million (example: 12MV = 12 000 000V) • Practice Problems Pg. 294 #1-3 • Pg. 295 – Calculating Resistance

  13. Resistor – an electrical component that has a specific resistance. Used to control the current or voltage in a circuit. When charge encounters resistance, it is transformed into other forms of energy (i.e. heat). The Resistor

  14. Resistor Colour Code Table 8.2 Page 297 (Accuracy) (Accuracy)

  15. Example: Red, blue, brown, gold 260 Ω +/- 5% Example: Green, orange, black, silver 53 Ω +/- 10% Circuit Diagrams Pg. 296 Circuit Diagrams Resistor Colour Code

  16. Resistors • If a resistor has a fourth band, it represents the percentage of accuracy between the indicated value and actual value • Gold 5% • Silver 10% • No Color 20%

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