1. Science 9
Ohm’s Law

2. Unit Conversions
1 Km = 1000 m 1 m = 100 cm 1 cm = 10 mm 1 KA = 1000 A 1 A = 1000 mA 1 V = 1000 mV

3. Resistance & Ohm’s Law
Resistance is the property of any material that slows down the flow of electrons and converts electrical energy into other forms of energy.

4. Lights…just a resistor
The filament of the light bulb resists the flow of electrons
The filaments high resistance causes the electrons electrical energy to be converted into light and heat energy

5. Ohm’s Law
Georg Ohm, a German physicist, learned how to calculate the electrical resistance of a circuit.
Electrical resistance has units of Ohm (Ω) Ω = omega (Greek letter)
JOIN THE RESISTANCE!

6. Volts = Current x Resistance
Ohm’s Law
The mathematical relationship describing the relationship between current, voltage, and resistance is called Ohm’s law:
V = IR
Volts = Current x Resistance
Volts = (Amps)(Ohms)

7. Ohm’s Law V = IR

8. Word Problem Practice
What is the resistance of a flashlight bulb if there is a current of 0.75 amps through the bulb when connected to a 3.0V battery?

9. Word Problem Practice
The current through a load in a circuit is 1.5 A. If a potential difference across the load is 12 Volts, what is the resistance of the load?

10. Word Problem Practice
The resistance of a car headlight is 15 Ω. If there is a current of 0.80 amps through the headlight, what is the voltage across the headlight?

11. Word Problem Practice
If the potential difference across a load is 12 V and the resistance is 18 Ω, what is the current through the load?

12. Word Problem Practice with conversions
You may also come across metric prefixes when you do your calculations.
For example:
Milli (m) = one thousandth So, 25 mA = 25/1000 A = A
Kilo (k) = one thousand So, 5.0 kΩ = 5000 Ω
Mega (M) = one million So, 12 MV = V
Always change the prefixes to the base unit before doing your calculation.

13. Word Problem Practice
What is the voltage across a 12 kΩ load that allows a current of a 6.0 mA?

14. Word Problem Practice
A 15 mA current flows through a 400 Ω lamp. What is the voltage across the lamp?

15. An ohmmeter is a device that can be used to measure the resistance of a device or resistor. The other way to find out resistance is to know the voltage and amperes in a circuit, and then use Ohm’s law to calculate the resistance.

16. The Resistor
A resistor is an electrical component that has a specific resistance. Resistors can be used to control current or voltage in a circuit, so that the correct number of volts or amps is delivered to another component of the system.
The circuit symbol for a resistor is:

17. Resistors
Resistors slow down electrons and make it more “work” for the electrons to get through the circuit. When this happens, energy is “lost”. The electrical energy is transformed into other types of energy (often heat).
Resistors have coloured bands to help identify the amount of resistance they provide.

18. Reading Resistors

19. Worksheet Practice Complete problems on worksheets
Use calculator, but show ALL your steps