Transcript Current Electricity

Introduction to Current
Electricity, Part 1
Grade 9 Academic Science
R.H. King Academy
Review
 What is electricity?
 Electricity is the flow of electrons
 What is static electricity?
 Static electricity is the build up of charges on surfaces
 How does an object become positively charged?
 It loses electrons
 How does an object become negatively charged?
 It gains electrons
Current Electricity
 Current electricity is the type of electricity you use to
power all of your electrical devices
 How does current electricity work?
 Watch this video (only up to 5:20)
http://www.youtube.com/watch?v=D2monVkCkX4
Video Questions
1. How does current electricity differ from static
electricity?
2. Identify the two terminals of a battery.
3. How does electricity flow from one terminal to the
other?
4. What will happen if you connect a short wire between
the two terminals of a battery?
5. 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 ___________.
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
Switches
 When you turn on a light switch, 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.
 See the animation here
http://www.rkm.com.au/animations/animation-electricalcircuit.html
Circuits
1)
2)
3)
4)
Identify the energy source.
Indicate the path of the electron flow.
What happens if you were to lift (open) the switch? What happens if you were to close the switch?
What does the electrical load (the light bulb) do with the electrons that flow through it?
Symbols
 Copy the following symbols off the overhead or board:
 Wire, battery / cell, light bulb / lamp, resistor, switch,
ammeter, voltmeter
How to measure current
electricity
 Three factors are measured in current electricity:
1. Potential difference: measured in volts
2. Current: measured in amperes
3. Resistance: measured in ohms
Current
 When electrons flow in a circuit, this is called current
 There are two types of current:
1. Direct Current (DC): All the electrons flow in one direction.
Batteries produce this type of current.
2. 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:
http://kids.britannica.com/lm/animations/oaltern001d4/product.
html
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!
Ammeter
 An ammeter measures current in a circuit
 What does 0.5 A mean?
Go to handout for GRASP
Calculations
Q = Charge [C]
I = Current [A]
T = Time [s]
Q
Q=IXt
I = Q/t
t = Q/I
Note: time is always
measured in seconds
I
t
Current Problems
 Use GRASP to solve the following problems.
 G: Given
R: Required
P: Paraphrase
A: Analysis (formula)
S: Solution
 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?
Homework
 Pg 436 # 1-3
 Handout questions on current