1. Ohm’s law
Part 2

2. resistors
A device that slows down current and transforms electrical energy into other forms of energy
Resistors are used to provide the correct voltage and current to other components of the circuit
The circuit symbol for resistors is:
Resistance in a circuit can be measured using an ohmmeter

3. V = IR
Ohm’s Law
If voltage increases, what will happen to the current and resistance?
Current and resistance will increase
If current increases and resistance remains constant, what will happen to the voltage?
Voltage will increase
If resistance increases and voltage remains constant, what will happen to the current?
Current will decrease

4. Prefixes Prefixes are used to indicate the magnitude of a value
Example 1:
1km = ?m
Since k = kilo = 1000
1 km = 1000m
Example 2:
1 cm = ?m
Since c = centi = 0.1 = one-tenth
1 cm = 0.1m

5. Prefixes milli (m) = one-thousandths 25 mA = ? A
kilo (k) = one thousand
5.0 kΩ = ? Ω
= 5.0 (1000) Ω= 5000 Ω
mega (M) = one million
12 MV = ? V
= 12 ( ) V = V

6. e. g. : A light bulb filament has a resistance of 96 Ω
e.g.: A light bulb filament has a resistance of 96 Ω. It needs a current of 1250 mA to operate. What voltage is required?
V = I x R
= 1.25 A x 96 Ω
= 120 V

7. PRACTICE
A 15 mA current flows through a 400 Ω lamp. What is the voltage across the lamp?
6.0V
A 12 kΩ load is connected to a 90 V power supply. What is the current through the load in milliamperes?
7.5mA
A device draws a current of 1.2 mA when connected to 120 V. What is the resistance of this device? Give your answer in both ohms and kilo-ohms
100,000 Ω; 100 kΩ
(From textbook page 294)

8. To do now 8.3 Workbook (skip page 124 – do page 125-127)
Due next class!