Science Test Review (Unit 3)

4- Unit of Measurements:

Formula Symbol

Unit Short Form

Current (# of electrons per time)

I ampere A

Potential Difference/Voltage

V volt V

Resistance R ohm 0

(omega)

Power P watt W

Energy E joule J

Charge (# of electrons) Q coulomb C

Time T second s

Electrical Energy Resistance wattfkilowatt hour

Wh/KWh

**Efficiency does not have a unit unless you are calculating percentage efficiency. (%)

4- Time Conversions:

Conversion Results

1 minute -I seconds 60 seconds

1 hour 4 minutes 60 minutes

1 hour 4 seconds 3 600 seconds

1 day --) hours 24 hours -->

1 day 4 minutes 1 440 minutes

day 4 seconds 86 400 seconds L 1

Created by Lynda L

Science Test Review (Da- 3)

4- Formulas:

r Q Q Q = It

-I_ current (A) *Q — charge (C) *t - time (s)

1 = t

t = I

E E E = VQ

*v - voltage (V) *Q — charge (C) *E — energy (J)

V = Q Q = V

V V V = IR

*I — current (A) *v- voltage (V) *R — resistance (0)

I = R

R = I

E E E = Pt

*t - time (s) *P — power (W) *E — energy (J)

P = — t

t = ----,-, r

P P V = 7

1 P = IV

*v - voltage (V) *1- current (A) *P — power (W) I = A / V

Electrical Energy = electric power X time interval (E = P x At)

*t — time (h) *P — power (W) *E — electrical energy (W.h/KW.h)

Efficiency — Useful Energy Output Energy Input

Percentage Efficiency — Useful Energy Outputx 100%

Energy Input

4- Series & Parallel Circuit Formulas x

Series Circuit Parallel Circuits

Current I total = = 12... I total == I1Il + 12...

Potntial Difference V total = VI + V2... V total = V1 = V2...

Total Resistance of Circuit

R total = R1 + R2... 1 1 1

– + R total R1 R2.•

Created by Lyna

Science Test Review ('Unit 3)

4- Parts of an Electric Circuit

.7. Source — something that produces electrical energy > E.g. cells, batteries, generators, wall outlets

Electrical Load — a device that converts electrical energy into another from of energy that we use W E.g. light bulbs convert electrical energy into heat & light

.7. Electric Circuit Control Device — also known as a switch, turns "on" and "off" a circuit U "On" is when the switch is closed since the electrons can flow through q.) "Off" is when the switch is open because the current cannot pass through the entire circuit

Connectors — the conducting wires that allow electric currents to flow around a circuit

4- Schematic Circuit Diagrams

Object Function Diagram Symbol

Sources

Cell Produces electrical

energy

I'

3 cell battery I I.

Control Devices

Swich Turns "on" and "off" a circuit

Loads

Bulb Converts energy into light energy

Resistor Impedes the flow of

electrons in conductors NAAA/`---

Motor Conve y into mechanical energy

Connectors Wire Allows the electrical energy to flow

Meters

Ammeter Measures the current in

amperes A 1----

Voltmeter Measures the voltage in volts

,-' ----0.._9

3

Ct6y Lynda L

Science Test Review (Unit 3)

4- Electric Current & Charge

• An electric current is electrical energy carried by an electric charge from one place to another through an electric circuit. The current is a controlled path. CURRENT is the amount of charge passing a point in one second.

• Each cell has a positive terminal and a negative terminal. Current flows from the negative terminal to the positive terminal. A battery is made up of multiple cells connected to one another.

* Charges flow when the circuit is COMPLETE and all switches are CLOSED.

Charges carry electrical energy. Charge is measured by coulombs and made of electrons.

1 Coulomb = 6.25 x 10 19 electrons

4- Potential Difference

• Electrons build-up at one terminal of the battery; therefore, that side is negatively charged.

• The "energized" electrons can be used to do work. W E.g. Like lighting a light bulb, turning a motor, or creating heat.

• Electrical energy stored in a battery is known as chemical energy or potential electrical energy.

• Energy comes in many forms. E.g. heat, light, electrical, chemical, mechanical

When energy is converted from one form to another, energy is often lost in the conversion into heat.

Potential energy is stored energy.

• In electricity, POTENTIAL DIFFERENCE is the amount of energy stored in one unit of charge (electrons) compared to the amount of energy stored in that same unit of charge at another point in the circuit.

4 ➢ The two points can be... Start and end of a circuit

q> Before and after a load • Before and after many loads

* Potential difference is how much energy the electrons can give up.

Potential difference is also the "voltage drop." W Voltage drop: a measure of the energy each electron gives up as it moves through a circuit

+ Each time charges pass through a load, they release energy to the load.

4- Electrical Resistance

• In good conductors, electrons move easily and lose little potential energy.

* In resistors, electrons give up potential energy.

RESISTANCE is when the flow of the electrons is impeded (slowed). Devices that do this are resistors.

4 Created by Lynda L

Science Test Review (Unit 3)

When electrons flow through a conductor (good or poor), resistance causes a loss of voltage (potential difference).

• Ohm's Law (published in 1827) The potential difference (voltage) between 2 points is proportional to the current.

• Ohm's law only applies to "ohmic resistors." Ohmic resistor a type of electrical load that does not change electrical resistance with temperature

• If resistance stays the same; then a rise in voltage results in a rise in current. •

What affects resistance of wires? Length — INCREASE in length -> INCREASE in resistance Cross sectional area — INCREASE in area -> DECREASE Temperature — INCREASE in temperature -> INCREASE in resistance Type of material — change material = change in resistance

4.- Series Circuits

• Adding extra loads to a SERIES CIRCUIT, causes the total resistance of the circuit to increase.

• Adding extra loads to a SERIES CIRCUIT, causes the total current of the circuit to decrease.

• The electric current is the same in all parts of the circuit.

• The potential different across the circuit is the same as the battery source.

• There is only one path for the electrons to flow.

• If one of the filament breaks or the light bulb is removed from its socket, the other lights don't light up.

Parallel Circuits

• The current passes through a separate circuit, called a branch circuit, to each bulb.

• Adding extra loads to a PARALLEL CIRCUIT, causes the total resistance of the circuit to increase.

• Adding extra loads to a PARALLEL CIRCUIT, causes the total current from the battery to increase.

• The total current flowing from the battery source equals the sum of branch circuit current.

• The potential different across each branch is the same as the battery source.

• There are multiple paths for the electrons to flow.

• If one of the filament breaks or the tight bulb is removed from its socket, the other lights stay lit.

5 Created. by Lynda L

Science Test Review (Unit 3)

*- Electrical Power

* Rate at which electrical energy is produced or assumed in a given time.

* The higher the POWER, the higher the wattage.

Is greater power always better? (No) • Consider this: • Incandescent tight bulb (60 W) • Compact fluorescent light bulb {CFLs} (15 W) • However, both produce the same amount of light. • All extra energy is converted to thermal energy

* The joule is a realty small unit of energy. So we often measure in watt—hours, kilowatt—hours, or gigawatt—hours.

1 watt hour = 3600 joutes/s

1 kilowatt hour = 1 000 watt hours

1 gigawatt hour = 1 000 000 kilowatt hours = 1 000 000 000 watt hours

4- Forms of Energy Productions/Renewable & Non-renewable Resources

Resources (Non-renewable)

(Renewable)

What is it? How is energy

produced? ADVANTAGES

DISADVANTAGES Or costs

Hydro-electric generation By moving water

Energy of falling water turns turbines, generating energy

-Does not pollute air/water -No smoke stacks -No radioactive materials -High production rate

-Disturbs fish migration -Change of landscape -Destruction of homes -Pricy materials

By fossil fuels Using coal, oil, and natural gases - Coal is easy/cheap to mine

-Burning fossil fuels produces a large amount of energy

-Produces CO 2 into the atmosphere

-Oil spills -Health Problems -Pollutes air/water

By radioactive materials

When a neutron collides with the radioactive form of uranium, a very high energy reaction called nuclear fission takes place

-Produces electricity -Produces steam

-Radioactive materials are dangerous -Cost to process and store waste -Pollution and habitat loss

By biomass (biofuel)

Biomass is any form of plant/animal matter (wood, straw, manure, plant-based oils, and decaying natural materials)

-Can be burned directly, unlike fossil fuel — refined -Can be used right away -Can collect methane gas

-Reduces the &TIC/Lint of land foramount enough energy to be used and fill

people's demands

By wind Two/Three propeller-like blades, mounted on a rotor, run wind turbines

-No CO 2 emissions

-Maintenance fee is inexpensive

-Prod-No wind, noise ,uces no energy -Have to be placed far way from each other, uses a lot of land

By tight A semiconductor cell (usually made from silicon) converts sunlight directly into electricity

-High investment rate

- No CO 2 emissions

-Mostly maintenance free -Independent/Connected to power grid

-Materials are realty expensive -Need more time to produce energy -Cannot be used at night -Geographical/Seasonal variations

6

Created by Lynda L

Science Test Review ( Unit 3)

Other facts/Concepts to know:

Solving Equations: * Given: Write everything that is given to you * Required: What do you need to solve for? * Analysis: How are you going to solve this problem? * Solve: Work through your solution using proper units * Paraphrase: Sum up what you've done with a statement

Renewable energy source: A resource replenished in a short period of time, will never run out.

Non-renewable energy source: A resource that cannot be replaced as quickly as it is consumed.

Efficiency: A measure of how much useful energy an electrical device produces compared with the amount of energy supplied to the device.

Photovoltaic Cell (PV Cell): PV cells create electricity from sunlight. It is a solar cell that produces usable electrical energy. Light strikes the cell, and a certain portion of the light is absorbed by the semiconductor.

7 Created by Lynda L