2.0- Transfer and Controlling Electrical Energy
A. Controlling Current
Review:1) What is the difference between
current, voltage and resistance?
2) What are each measured in?
Voltage – the energy of each electronCurrent – how fast the electrons are flowingResistance – how much energy is stripped from the
electrons; is how hard it is for electrons to flow
A. Controlling Current
3. What is the difference between an insulator and conductor?
Insulators - Resist or prevents the flow of electrons; tightly hold onto electrons
Conductors –Allow the flow of e-; Electrons are not as tightly bound to the nucleus and are free to move
A. Controlling Current
4. What is the difference between:
a) Wet cell vs. dry cell?b) Primary vs. secondary cell?c) cell vs. batteryd) electrorefining and electrolysis?e) Galvanizing and electroplating
A. Controlling Circuit
Review:
Insulators - Resists or prevents the flow of electrons Electrons are tightly bound to the
positive nucleus of the atoms
A. Controlling CurrentII. Conductors - Allow the flow of
electrons Electrons are not as tightly bound
to the nucleus and are free to move
A. Controlling Current
I. Resistors Are conductors which provide SOME
resistance (slowing) to the flow of electrons, in order to reduce current
Resistors will gain energy from each electron that passes through as light or heat
Ex. Tungsten light bulbs and space heaters are both resistors (light and heat are produced)
A. Controlling Current
1) Resistors Every conductor resists the flow of
electrons slightly so….. The longer and thinner the wire, the
higher the resistance is The larger in diameter (thickness)
the lower the resistance is
Draw a quick diagram to remember this by!
A. Controlling Current
2. Switches Open and close a circuit to control
current
3. Rheostat / Variable Resistor Increase or decrease the current in a
circuit by adjusting the resistance Ex. Volume control, Dimmer
switches, thermostats
A .Controlling Current Microelectronic circuits are tiny
circuits found in microchips, iPod’s etc.
These use transistors, instead of
switches to control the current.
B. Safety with Current
B. Safety with Current
I. Current vs. Voltage What should you be more concerned
about…..current or voltage?? Why?Current – since it is how many electrons will be flowing through your body! A small current has a dramatic effect!
B. Safety with Current
II. Safety Features Circuit breakers – flip a
switch if the current drawn from an appliance is too high
Fuses- melt causing an open circuit when current drawn is too high
Brainstorm……
How does an outlet work?
Why are there 3 holes?
Hint: Consider what a circuit needs in order for electricity to flow…
B. Safety with Current
What is the purpose of a 3-pronged plug?
Third prong supplies a ground wire to the building as a safety against a
short circuit
C. Measuring Electricity
I. Ohm’s Law Relates current, voltage and
resistance As long as temperature is constant:
Resistance stays constant Voltage and current are directly
proportional ( V increases = I increases)
C. Measuring Electricity
I. Ohm’s Law R = VI
V- voltage (V) I – current (A) R – resistance ()
Required Steps to Solving Problems 1. Write down what you know 2. Write down unknown 3. Choose formula 4. Substitute with units 5. Solve – make sure there are units!
C. Measuring Electricity
Ex. What is the current of a circuit with a 9.0V battery and a 5 resistor?
C. Measuring Electricity
Ex. What is the resistance of a circuit with a 1.5 V battery which outputs 0.70A?
C. Measuring Electricity
Ex. What is the voltage of a circuit which has a resistance of 24 and current of 4.0A?
What is the resistance of this circuit?
Hyperlink to practice qs.
C. Measuring Electricity
II. Using Test Meters Voltmeters – measure voltage drop
across a circuit (connected in parallel )
Ammeter – measures current by being connected in series Galvonometers – test very small currents
Multimeter – tests multiple measurements such as voltage, current and resistance
Connected in the same path as the circuit
Connected as an additional path in the circuit
D. Building/Analyzing Circuits Types of Circuits1) Series – where only 1 path is present for
electricity to flowKey Ideas: 1. If interrupted, the circuit will not work 2. Adding more loads causes: -an increase in total resistance -a decrease in current (but current is the same
through each load) -Total voltage is the same, but drops over loads*Used in older Christmas lights - all lights go out
when one goes out
Ex. Draw a series circuit with two lightbulbs that are controlled by the same switch.
What happens to the brightness of the lights as you add more lightbulbs to the circuit?
2) Parallel – where a separate path is present for each load/switch
Key Ideas: 1. Circuit WILL work if interrupted (multiple
paths) 2. Adding loads will not effect resistance 3. Adding loads draws higher current from
the source (current is split between pathways)
*House wiring is in parallel
D. Building/Analyzing Circuits
Ex. Draw a picture of a circuit with two light bulbs that can be turned off and on separately from each other.
Ex. If both of the previous circuits have 100V sources, which would have the most resistance?
The most current?
ACTIVITY: Connect a circuit with one source where two light bulbs (lamps) can be shut off independently of each other.
Build a circuit where a light switch can be turned on/off by either two switches (such in a room with two entry doors or a hallway).
Draw a schematic diagram to represent this.
A. Controlling CurrentTry: Set up the following circuit.
What occurs when both, one or no switches
are closed?
http://www.youtube.com/watch?v=20Vb6hlLQSg creation of electrica lenergy