1. Current, Volts and Resistance (Ohm’s Law)

2. Coulomb Recall that one Coulomb has 6.25 X 1018 electrons.
If the current coming out of the outlet on the wall has 600 C, how many electrons are coming out of the outlet?
1C = X 1018 electrons C #e-
Cross multiply and you get 3.75 X 1021 electrons

3. Symbol: I
Units: Amperes, A
Current Intensity
Current Intensity - the amount of electrons that flow past a given point in a circuit every second (i.e through a wire)
Example: 0.7 amperes is shown by I = 0.7 A
An ammeter is the instrument used to measure current intensity A

4. I = q/t Current Intensity
The current intensity in a circuit can be determined using the formula:
I = q/t
I is the current intensity in amps (A)
q is the charge in coulombs (C)
t is time in seconds (s)
NOTE: 1 Amp (A) = 1 Coulombs (C)/1 second (s) A=C/s

5. Example #1
What is the current flowing through a car headlight if there are 900 C of charge used in 1 minute? I = q/t I = 900 /60 I = 15A

6. Example #2
How much charge does it take to operate an MP3 player for 15 minutes if the current is 2A? I = q/t 2 = q/900 q = 1800C

7. Potential Difference (Voltage)
Symbol: V
Units: Volts, V
Potential Difference (Voltage)
Potential Difference is the amount of energy transferred between two points in an electrical circuit. It is the voltage that is measured at a load.
Example: Energy that is provided by a battery or power supply. It could be a 12 volts battery (also know as 12V)
A voltmeter is used to measure potential difference V

8. Potential Difference (Voltage)
The potential difference can be determined using the formula:
V=E/q
V is potential difference in volts (V)
E is the energy in joules (J)
q is the electric charge in coulombs (C)
Note: 1 Volts = 1 Joule / 1 Coulombs V=J/C

9. Example #3
In a house, how much energy is provided by 120V service providing 200C of charge?
V=E/q
120 = E/200
E = J

10. Resistance Resistance is how difficult it is for current to flow
Symbol: R
Units: Ohms, Ω
Resistance
Resistance is how difficult it is for current to flow
Resistance analogy: imagine a river flowing. If you put a large boulder in the river, the current on the other side of the boulder will slow down. If you put a small boulder in the river, the current on the other side of the boulder will still be quick. Now replace river flow with flow of electrons, and a boulder with a resistor.
A resistor is used to slow current down and convert electrical energy into heat energy (e.g. light bulb, stove element).
Resistor–
high resistance &
low current flow
Conductor (wire) -
low resistance &
high current flow

11. Ohm’s Law
Ohm’s Law states – that for a given resistance, the potential difference in an electrical circuit is directly proportional to the current intensity.

12. Formula to Solve Circuits
Resistance, current intensity and potential difference are all related R = V/I
R is the resistance in Ohm’s (Ω)
V is the potential difference (Volts)
I is the current intensity (Ampere)
Note: 1 Ohms= 1 Volts / 1 Amper
1 (Ω) = 1 V / 1 A

13. Example #4
An stove element 30 Amperes going through it, and carries 120 volts of electricity, how much resistance is in this circuit?
R = V/I
R = 120 V/30 A
R = 4 V/A = 4 Ω

14. Example #5
A circuit has a potential energy difference of 240 V and offers a resistance of 6Ω, what is the intensity of the current flow?
R=V/I
6 = 240 /I
I = 240 /6
I = 40 A

15. Example #6
A circuit has a resistance of 10Ω & a current intensity of 5A. What is the potential difference?
R=V/I
10 = V/ 5
10 X 5 = 50V

16. Causes electrons to flow
Summary Table
Resistance
Current
Potential Difference
Definition
Slows current down
The flow of electrons
Causes electrons to flow
Symbol R I V
Units
Ohms (Ω)
Amps (A)
Volts (V)
Formula
(if applicable)
R=V/I Ω=V/I
I=q/t A=C/s
V=E/q V=J/C
How measured
Circuit Formula
Ammeter or formula
Voltmeter or formula

17. Assignment
Page 319 – Questions 1 – 11
Handout