1. RESISTANCE AND OHM’S LAW

3. RESISTANCE and THE FLOW OF ELECTRONS
RESISTANCE: property of any material that slows down the flow of electrons and converts electrical energy into other forms of energy
EXAMPLE: the filament of a light bulb
highly resistance filament causes the electrons’ electrical energy to be converted into heat and light energy
The wire connecting the battery to the
bulb has little resistance, which means
that the electrons travelling through the
wire lose almost no electrical energy

4. RESISTANCE AND CURRENT
VOLTAGE: the difference in potential energy per unit of charge between 2 points in a circuit
Voltage is directly proportional to current
The greater the voltage, the greater the current

5. Georg ohm Studied the relationship between voltage and current
Discovered that resistance is an important factor that can affect current
Different objects can have the same potential different BUT different currents depending on the amount of resistance
the greater the resistance, the lower the current!

6. Ohm’s law
Ohm was able to use the amount of current that a voltage produces to calculate the circuit’s resistance.
ELECTRICAL RESISTANCE: the ratio of voltage to current
OHM (): the unit of measurement for electrical resistance
OHM’S LAW: the mathematical relationship comparing voltage (V), current (I), and resistance (R)

7. Practice question 1:
What is the resistance of a flashlight bulb if there is a current of 0.75A through the bulb when connected to a 3.0V battery?

9. Ohm’s law (continued)
We add prefixes to indicate the magnitude of value!
Milli (m) = one thousandanth
25mA  25/1000 A  0.025A
Kilo (k) = one thousand
5.0k  5000
Mega (M) = 1 million
12MV  V
HINT: convert the prefixes BEFORE you do your calculations!

10. Practice question 2:
What is the voltage across a 12k load that allows a current of 6.0mA?

11. Determining the resistance
Method 1: Experimentally measure the resistance
Use a voltmeter to measure the voltage across the load and an ammeter to measure the current through the load
Use Ohm’s Law to calculate the resistance
Method 2: Use an ohmmeter to measure resistance
The meter uses its internal battery to provide a voltage across the load
It then measures the current leaving the battery and calculates the resistance

12. The resistor
REVIEW: Any electrical component that has electrical resistance slows down current and transforms electrical energy into other forms of energy!
Resistor: an electrical component that has a specific resistance
Can be used to control current or potential difference in a circuit to provide the correct voltage and current to the other components of the circuit
Symbolized by

13. When a charge encounters resistance, some of the electrical energy that is stored will be transformed into a different type of energy like heat! To be clear, this electrical energy isn’t actually lost. It’s just been turned into a new kind of energy!

14. Resistor colour code
Resistors are marked with coloured bands that indicate the resistance on a scale from 0-9.
First band: 1st digit of the resistance
Second band: 2nd digit of the resistance
Third band: the multiplier OR power of 10 factor of the resistance (the # of 0s that follow the second digit)
Fourth band (optional): the % of accuracy between the indicated value and actual value
Gold = 5%
Silver = 10%
No colour = 20%

15. Practice question 3:
What is the resistance of the
above resistor?