1. Introduction to Current Electricity, Part 1
Grade 9 Academic Science
R.H. King Academy

2. Recall Static electricity is the build up of charges on surfaces
An object becomes positively charged by losing electrons
An object becomes negatively charged by gaining electrons

3. Current Electricity Current electricity is the flow of electrons
This type of electricity is used to power all of your electrical devices
How does current electricity work?
Watch this video (only up to 5:20)

4. Video Questions
How does current electricity differ from static electricity?
Identify the two terminals of a battery.
How does electricity flow from one terminal to the other?
What will happen if you connect a short wire between the two terminals of a battery?
The power (potential difference) in a battery or the socket in the wall is measured in __________. An AA battery is ________, and the wall socket is ___________.

5. Circuits
Current electricity is the steady flow of electrons from a negative terminal to a positive terminal in a circuit
A circuit includes:
An energy source (e.g. battery)
A conductor (e.g. wire)
A load (e.g. light bulb)
A circuit may include:
A switch to turn the circuit on and off

6. Optional Accessory: Switches
The electricity does not come from the switch!
A switch simply opens and closes a circuit.
When you open the circuit, electrons stop flowing. Electrical devices turn off.
When you close the circuit, electrons can flow. Electrical devices turn on.

7. Symbols Wire battery / cell light bulb / lamp Resistor Switch Ammeter
voltmeter

8. How to measure current electricity
Three factors are measured in current electricity:
Potential difference: measured in volts (V)
Current: measured in amperes (A)
Resistance: measured in ohms (Ω)

9. Current When electrons flow in a circuit, this is called current
There are two types of current:
Direct Current (DC): All the electrons flow in one direction. Batteries produce this type of current.
Alternating Current (AC). The electrons flow back and forth at regular intervals and cycles. This is the current that is produced by generators and is delivered to our electrical sockets
See the difference here:
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10. Current
To measure current, you measure the number of electrons that are flowing through a circuit
This measurement is in amperes (A), also called amps
1 ampere = 1 coloumb of electrons passing by every second
Therefore, 1 ampere = 6.24 x 1018 electrons passing by a point in the circuit every second!

11. Ammeter
An ammeter measures current in a circuit
What does 0.5 A mean?

12. Equations to know! Q = Charge [C] I = Current [A] t = Time [s]
Q = I x t
I = Q/t
t = Q/I
Note: time is always measured in seconds

13. Current Problems Use GRASP to solve the following problems.
G: Given R: Required A: Analysis (formula) S: Solution P: Paraphrase
Calculate the current of a circuit that has a charge of 960 C flowing through it for a time of 25 min.
A circuit has a current of 2.50 A running through it. Calculate the total charge transferred in the circuit if it runs for a total of 45 s.
Calculate the time required for a circuit with a current of 1.75 A to transfer a total charge of 650 C.
A circuit transfers a total charge of 1450 C in a time of 75 min. What is the current of the circuit?

14. Homework
Pg 436 # 1-3
Handout questions on current