2.0- Transfer and Controlling Electrical Energy

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

Parallel vs. Series Circuit explained

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