Science 9: Electricity

How does a DC generator work?

DC generator = structurally same as a DC motor (Figure 3.10 pg 325)

steady flow of charged particles

Electrical current

-fuel formed from dead plants and animals -eg. coal, oil, and natural gas

Fossil fuels

primary cell that generates electricity directly from a chemical reaction with a fuel

Fuel cells

thin piece of metal that melts to break an electrical circuit when excess current flow occurs

Fuse

energy derived from the internal heat of Earth

Geothermal energy

What are the 2 classifications of energy?

Kinetic or Potential

device in a circuit that converts electrical energy to another form of energy

Load

circuit in which the current can flow in two or more paths

Parallel circuit

-perfect conductor -substance with no resistance to electron flow

Superconductors

How does an object acquire a charge?

Through friction and induction

What is Ohm's Law?

V=IR

-electrochemical primary cell having a liquid electrolyte

Wet cells

What did Faraday prove that electricity could do?

electricity could *produce continuous motion* by using *electromagnetic forces* to move an object

coil of insulated wire (usually wrapped around a soft iron core) that becomes a magnet when current flows through it

electromagnet

ability to do work

energy

What happens to the potential energy of each particle when voltage *rises*?

higher the voltage = greater the potential energy of each particle

Energy our *eyes can detect*

light energy

-1/1000 of a volt -e.g., 30 mV is 0.030 V)

millivolt

When an anode loses electrons

oxidation

What happens to energy as resistance increases? Give 2 examples. GIVE EXAMPLESSS????

-*more resistance = more energy (from each electron passing through) for susbtance = energy gained is dissipated* -Eg. Pg 300 Figure 2.5 The tungsten filament in an incandescent bulb and the element in a heater both radiate heat and light because of resistance.

What will happen to you with 0.10A?

-Electric chair: fatal

What 2 factors make it more likely that you'll get electrocuted?

-High moisture: water = conductor = bridge for you and electrical object = complete circuit -Not standing on an insulator: they absorb the charge and break the circuit, these provide a ground

What is the average watt of a small home appliance?

-Most small appliances in home have power rating of 1500 W or less -electric stove has power rating of 7000 W -calculator could be only 0.4 mW.

How does wave energy work?

-Waves also generate electricity. -eg. up-and-down movement of the water drives piston connected to a generator

How can you make an electromagnet's current stronger?

-add more coils

Who made the first practical battery? BETTER MAKE THIS

Alessandro Volta

What is the average current for home electrical devices?

*-less than 15 A* -ordinary 60-W light bulb is 0.5 A. -Microwave ovens usually use between 5 and 8 A

Name 2 examples of chemical energy being transformed.

-Body -Battery

What are the 3 types of rapid discharges that create lightning?

-Intracloud (most common) -Cloud to ground (second) -Ground to cloud (rarest)

Where are large and small fuel cells used?

-Larger fuel cells used to *power electric cars. * -Smaller ones developed for use with *portable devices*

What are the 5 factors affecting resistance of wires?

-Length: shorter = more res. -Diameter: bigger = less res. -Material: conductor = less res. -Temperature: hotter = -Current: more =

How does *length* affect resistance?

-Resistance increases as the length increases -If the length doubles, the resistance doubles

How does *material* affect resistance?

-Some metals allow electrons to move more freely than others. -conductor vs insulator

What are 10 types of energy? (including the 4 most common and excluding kinetic/potential energy)

-Thermal -Mechanical -Electrical -Magnetic -Sound -Light -Chemical -Elastic -Nuclear -Gravitational

Why are static charges not useful for operating electrical devices?

-They build up and discharge, but they do not flow continuously WHY IS THIS BAD THO

How does induction create a static charge?

-creation of electrical current -causes charge separation -Between objects, *no* direct contact: a charged object is brought close to a neutral object. -Results: one side of neutral object to be positive, and the other side, negative (charge separation)

What are the uses of knowing the conductivity of a solution?

-eg. you could use a simple conductivity measurement to *check the purity of a batch of distilled water.* -In a factory, a technician may use conductivity to check whether a *solution for an industrial process has been mixed properly*

How does a dry/voltaic/galvanic cell work?

-electrolyte reacts with two electrodes. -As a result, one electrode becomes positive and the other, negative. -electrodes are connected to cell's terminals. -In a dry cell, electrons leave from negative electrode, and return to positive electrode. -Chemical energy comes from REDOX reaction between 2 metals: -Oxidation: when anode(-) loses electrons -Reduction: process where ions in solution gains electrons (in saltwater, reduction also creates hydrogen gas) -Transfer of electrons = electrical current

What two conditions does an electrical current need to flow continuously?

-energy *source* -*complete circuit*for the charged particles to flow through

What is the average volts for major electrical devices?

-industrial machinery operates at 600 V -major electrical transmission lines can have over 100 kV

How do rechargeable batteries work?

-the *chemical reactions *in a rechargeable cell can be *reversed by using *an external *electrical source* to* run electricity back *through the cell. -The *reversed flow* of electrons *restores the reactants that are used up *when the cell produces electricity. We can say that the chemicals in a rechargeable cell store electricity supplied by the external source.

What devices use secondary cells?

-used to start cars -operate portable electronic devices (notebook computers and cellular phones)

meter used to measure electrical current in amperes

Ammeters

An electric stove is connected to a 240-V outlet. If the current flowing through the stove is 20 A, what is the resistance of the heating element?

An electric stove is connected to a 240-V outlet. If the current flowing through the stove is 20 A, what is the resistance of the heating element? Answer on pg 306 (R = 12 Ω)

a material that electric charge can move through easily

Conductors

-cell that has its electrolyte in the form of a paste, usually in a sealed case -the type of cell commonly used in portable devices such as flashlights

Dry cells

How do you converts watts to kW? FIXXXX THISSSS

E = 0.8 kW 0.5 h = 0.4 kW x h.

How do you calculate the amount of energy a device uses?

E = Pt

study of chemical reactions involving electricity

Electrochemistry

substance that strongly resists the flow of electricity

Insulators

-atom that has become electrically charged because it has lost or gained electrons -a positive ___ is an atom that has lost one or more electrons -a negative ___ is an atom that has gained one or more electrons

Ion

circuit made up of miniaturized components, especially an integrated circuit

Microcircuits/integrated circuits

instrument used to measure small voltages

Millivoltmeters

-law stating that as long as the *temperature constant = resistance of conductor constant*, and the *current is proportional to voltage *applied - V = IR

Ohm's law

the unit of resistance

Ohms

What is the relationship between power, current, and voltage? IS THIS RIGHT

P=IV

A hair dryer has a power rating of 1000 W. It is plugged into a 120-V outlet. What is the current flowing through the hair dryer?

Pg 332

circuit in which there is only a single pathway for the current so the same current passes through all the components

Series circuit

device with two joined wires (different heating metals), so voltage is produced between the ends, proportionate to the difference of their temperatures

Thermocouple

How do rechargeable batteries die? SEE HANDOUTS

This process does not reform the electrodes perfectly, however, so even rechargeable cells wear out in time.

device usually with three layers arranged such that a small voltage through the middle layer controls a current between the outer layers, allowing the device to act as a switch or amplifier

Transistors

-machine that uses the flow of a fluid (steam, water, air) to rotate a shaft -a long shaft with many fan blades

Turbine

If a halogen light bulb is 18% efficient, this means that most of the input electrical energy... a) is transformed into waste heat b) is transformed into light c) passes right through the bulb without being changed d) is grounded to prevent electrical shocks

a

several modules put together

arrays

A current of 16A passes through a hair dryer when it is connected to a 110V wall outlet. What is the power of the hair dryer? a) 6.9W b) 1.8 x 10 (to the power of 3)W c) 145W d) 0.145W

b

Consider the following functions of the wiring in a house. 1) supply high-energy electricity to appliances 2) return low-energy electricity from appliances 3) protect against electric shock Which sequence below correctly identifies the function of each color-coded wire in a wiring cable? a) white 1, black 2, green 3 b) white 2, black 1, green 3 c) white 3, balck 1, green 2 d) red 3, black 2, green 1

b

Which combination of characteristics describes a wire that carries the most current without overheating? a) large diameter, as long as possible b) large diameter, as short as possible c) short diameter, as long as possible d) short diameter, as short as possible

b

Which factor does NOT affect the strength of an electromagnet? a) amount of current b) direction of current c) number of coils of wire d) type of material in the core

b

Which of the following fossil fuels often used in thermoelectric plants? 1. coal 2. uranium 3. natural gas 4. crop wastes 5. municipal wastes 6. fuel oil a) 2, 4 and 5 b) 1, 3, and 6 c) 1, 2, 3, and 5 d) 1 and 6

b

Which of the following is NOT a requirement for an electric circuit? a) a continuous pathway b) a grounder c) a conductor d) a source

b

Which of the following statements are true? 1. light emitting diodes are brighter than incandescent bulbs 2. light emitting diodes last longer than incandescent bulbs 3. light emitting diodes use less power than incandescent bulbs a) all are true b) 2 and 3 c) 1 and 3 d) 1 and 2

b

Why are alkaline cells the most common type of dry cell?

because they offer a good combination of cost, electricity output, shelf life, reliability, and leak resistance

-concentration of like charges in specific areas of a neutral object -caused by the approach of a charged object

charge separation

Where does electricity produced by electrochemical cells come from?

chemical reactions

How does biomass work?

cities + towns bury *biodegradable waste* in landfills →* decomposes *→ produces *combustible gases* → collected + used as *fuel for steam*-driven *generators.*

Which of the following characteristics do parallel circuits display? 1. the potential difference is the same across each branch 2. the sum of the currents through all branches is equal to the total current through the entire circuit 3. the total resistance of the circuit increases as more loads are added in parallel a) 2 and 3 b) 1 and 3 c) 3 d) 1 and 2

d

Which of the following electrochemical cells would be classified as a "wet" cell? a) a zinc-carbon cell b) a zinc-air cell c) a nickel-cadmium cell d) a lead-acid cell

d

Name the two main types of electrochemical cells.

dry cells and wet cells

-ratio of the useful energy output to the total energy input in a device or system -usually given as a percent

efficiency

Energy stored in *stretched* objects

elastic energy

-It causes static -sudden transfer of electrical charge from one object to another -indicated by a spark

electrical discharge

invisible negatively charged particle that orbits the nucleus of an atom

electron

electricity in animals is produced by this special organ in the tail that contains thousands of modified muscle cells

electroplaques

How does cogeneration work?

industrial processes use very high temperature furnaces to burn fuel= waste heat from the manufacturing process → used to produce steam → used to drive a turbine → generate electricity.

Where the wires are twisted or in contact with one another in a thermocouple

junctions

-commonly used unit of electrical energy -equal to a power consumption of 1000 W for one hour

kilowatt hour

fundamental principle that energy cannot be created or destroyed

law of conservation of energy

Energy causing *push or pull*

magnetic energy

-pH of 7 -a neutral substance is neither an acid nor a base

neutral

-a resource that cannot be replenished -eg. coal, natural gas

nonrenewable resource

Why aren't there many tidal power stations in the world?

not many tidal power stations in world because: Difficulty finding suitable locations

Energy stored in the *centre/nuclei* of particles

nuclear energy

What problems would 0.015 to 0.020 amps?

painful shock and loss of muscle control

Water directed through a channel

penstock

diagram using standardized symbols to show the components and connections in a circuit

schematic/schematic diagram

Determines which object will become negative or positive after it touches another material

triboelectrical force/effect

instrument for measuring potential difference in volts

voltmeter

-the unit of power -equal to one joule per second

watt (W)

Many wind-powered generators connected together, because = larger amounts of electrical energy.

wind farms

A magnet can induce a voltage (potential difference) in a wire... a) when either the magnet or the wire move at an angle b) when either the magnet or the wire move parallel to each other c) only when the wire moves d) only when the magnet moves

b

A voltage is induced in a wire that is... a) held still near a magnet b) moved parallel to a magnet c) moved at an angle to a magnet d) wrapped tightly in a coil around a magnet

b

Electrical circuits that have more than one circuit path are called a) series circuit b) parallel circuits c) short circuits d) complete circuits

b

Five 1.5V cells are connected in parallel. Their total voltage is a) 0.3V b) 1.5V c) 2.5V d) 7.5V

b

The current that flows through a thermocouple can be increased by a) heating both junctions b) heating one junction and cooling the other c) cooling both junctions d) reversing the positions of the hot and cold junctions

b

The function of ground wire in an electrical circuit is to... a) return low energy electricity to the generator b) reduce the risk of electrical shock c) supply high energy electricity to the load d) strengthen the cables and cords in the circuit

b

A home theatre requires 10A to operate. What is the power of the theatre when it is connected to a 120V household circuit? a) 12 W b) 8300W c) 1200W d) 83W

c

Which characteristic is typical of digital electronic devices? a) have no electrical resistance b) are based on electronic switches called transistors c) require AC power d) are seldom used in modern computers

b

-the rotating shaft with the coil wrapped around it -rotating shaft and coil in a motor or generator

Armature

set of cells connected together

Battery

-organic matter used as an energy source -particular type of garbage -eg. food/agricultural waste, yard clippings, dead trees, unused crops, and food-based garbage

Biomass

-mechanism that makes electrical contact with the moving commutator in a motor -usually bars of carbon pushed against the metal commutator by springs

Brushes

special wire that heats up and turns off switch when excess current flows through an electrical circuit

Circuit breakers

-use of waste energy from a process for another purpose -eg. heating or generating electricity

Cogeneration

split ring in a motor that breaks the flow of electricity for a moment and then reverses the connection of the coil

Commutator

rechargeable cell

Secondary cells

The scale on a certain voltmeter is designed to measure a maximum of 5V and this scale is divided into 25 segments or divisions. Each division on the scale then represents a reading of: a) 0.1V b) 0.2V c) 0.5v d) 1.0V

b

-voltage across a resistor or other device in a circuit

Voltage drop

The voltage of most household appliance is a) 240V b) 120V c) 9V d) 6V

b

What current flows in a 20ohm electric toaster connected to a 120 volt source a) 0.166A b) 6.0A c) 100A d) 2400A

b

A 150W driveway light produces 8.3 x 10 to the power of 4J of light energy over a 4.0h period. What is its efficiency? a) 3.8% b) 4.3% c) 26% d) 43%

a

A negatively charged rod attracts... a) only positively charged objects b) only negatively charged objects c) neutral and positively charged objects d) neutral and negatively charged objects

c

Which of the following devices do NOT use electromagnets? a) maglev trains b) electric motors and generators c) magnetic compasses d) MRI medical imaging machines

c

What creates a magnetic field?

current flowing through a wire nearby a magnet creates a magnetic field around the wire.

How does electroplating/electrolysis work?

The item to be coated and a bar of the coating metal are immersed in an electrolyte, like the electrodes in a wet cell. A source of electricity is connected between the two metals. The flow of electricity through the electrolyte deposits atoms from the positively charged metal onto the negatively charged one.

-a stationary electric charge

static electricity WHAT CAUSES IT THO? ELECTRIC DISCHARGE?

List 2 negatives and 2 positives for series circuits.

- pathway interrupted = whole circuit cannot function. -adding components = increase total resistance = decrease current = dimmer. -possible to turn off all the electricity in the circuit. -uses less electricity because less loops for electron

What are the parts of a *Voltaic/Galvanic* cell?

-*2 electrodes* (solid conductors that undergo chemical reactions and give/take electrons): -*Anode (-): give electrons,* eg. zinc -*Cathode (+): takes electrons,* eg. copper -*2 electrolytes* (solutions that can conduct electricity and must contact ions) -*Salt bridge *(allows the passage of ions without contaminating the two half cells- keeps it neutral)

What causes attractive or repulsive forces between particles?

-*Law of electrical charges:* -*charges* on the particles can cause *attractive (opposites) or repulsive forces (same)* between the particles

What is the average volts for minor electrical devices?

-*Less than 12V *(that's what cars use) Flashlights and portable stereos rarely use more than 6 V -almost all cars have a 12-V electrical system -home and school have 120-V wall sockets

Name 4 examples of where electrolysis is used.

-*chlorine* produced by electrolysis is used to make* drinking water safe.* -also used to produce polyvinyl chloride (*PVC)* products such as pipe and wire insulation. -Electrolysis of *water *produces the *fuel *for the *space shuttle.* -*electroplating*

How does geothermal energy work?

-*hot water + steam* come to* surface *after *heated by hot rock* in Earth's crust (geothermal energy) →* steam channeled *through pipes → used to *drive turbines. * -Sometimes: water is injected back into ground to take full advantage of the geothermal energy source.

How can solutions be used as resistors? Give 2 examples.

-*more charged particles in solution = better it conducts.* -Eg. *Distilled water is not a good conductor *because it contains *only water *molecules. These molecules have *no electrical charge.* -Eg. *Tap water* and water in the environment* are conductors* because of the *many dissolved minerals *they contain.

How does an AC generator work?

-AC generator is slightly different than DC generator -central axle of AC generator has loop of wire attached to 2 slip rings. -Recall: when wire moves in magnetic field, current is generated in wire.

How does lightning form?

-Cloud undergoes *charge separation *(one side turns negative, and the other, positive) -*Lightning: rapid discharge of electrons *(from negative side) to positive side

How does a wet/electrolytic cell work?

-Each *electrode *in wet cell *reacts differently with electrolyte*. -The acidic* electrolyte *gradually *eats away zinc electrode*. This process *leaves behind electrons* that *give disappearing electrode negative charge.* Eventually the zinc *electrode must be replaced. * -The chemical reaction between the *copper electrode and electrolyte leaves copper with positive charge*, but *does not eat the copper. * -*Electrons travel* along the wire *from the negative *zinc electrode *to the positive *copper electrode. -*connect wires from both electrodes to light bulb = light up.* The electric current flowing from one electrode to the other provides the energy for the light.

What type of devices use DC?

-Eg. small *portable* devices -Plug-in devices using DC come with own power supplies -power supply converts power company's 120-V AC to DC and supplies device's required voltage

What makes the *Electrolytic* cell different from a Voltaic cell?

-Electrolytic: *uses electrochemistry/electrolysis*, is *wet, non-spontaneous (needs energy source)* -Voltaic: uses *REDOX, dry, spontaneous*

How does *temperature* affect resistance?

-If the *temperature of resistor changes = resistance changes*. -Generally, *resistance lowest = cool conductor*. -As the temperature increases, resistance increases. -eg. example, a filament in a light bulb often has 10 times its normal current flowing through it at the instant it is switched on. This current heats the filament white hot in a fraction of a second. The huge rise in temperature greatly increases the filament's resistance, which reduces the current flowing through it. As explained in subsection 2.1, this increase in resistance causes the filament to glow. Light bulbs sometimes "blow" when they are switched on because of the sudden temperature change and other forces caused by the large initial current.

Name 2 positives and 1 negative for parallel circuits.

-In a parallel-wired string of lights, for example, each bulb has its own path to the current source. An interruption or break in one pathway does not affect the rest of the pathways in the circuit. -Similarly, adding a new pathway with more resistors does not affect the resistance in any of the other pathways. In fact, adding extra resistors in parallel decreases the total resistance of the circuit. This might seem strange, but remember that adding more paths for the current to take means less total resistance. Think about how much less resistance there is when you drink through two straws instead of one.

What are ways to avoid getting struck by lightning?

-Lightning tends to seek the* highest point on the horizon* (eg. hills, under trees, things over your head) to discharge. -tall buildings have *lightning rods *connected to the ground with a wire -go near metal so lightning chooses the easier conductor

What determines if an object is negatively/positively charged?

-More electrons = negatively charged (want to lose electrons) -More protons = positively charged (want to gain electrons) -depends on properties of object (triboelectrical effect)

How has wind energy changed over time?

-Old windmills used sails on ends of shafts to get power to grind grain and pump water. -Modern windmills = more efficient designs with propeller shaped blades.

What is the Law of Electrical Charges?

-Opposite charges attract -like charges repel each other.

Why do power companies use AC?

-Power companies generate AC because, with it, they *can use transformers to change amount of voltage with little energy loss. * -Voltage change is necessary because* most efficient way to transmit current over long distances is at high voltage.*

How does *diameter* affect resistance?

-Resistance decreases as the diameter increases. -If the diameter doubles, the resistance is half as great

How does tide energy work?

-Tidal power stations are simple: Moving water from tides → power turbines→ run generators. *-tide comes in* → water *trapped in reservoir *→* let out past turbines.*

What are the 3 most basic units in current electricity?

-Voltage (volts) -Current (amps) -Resistance (ohms)

How is charge separation caused?

-When *charged objects* are brought* close to neutral objects* -They *repel like charges, leaving the opposite charges close = attraction* -Eg. balloon

How does voltage relate to potential energy? FIXXX THISSS

-a cell, battery, or generator "pumps" electrons to a point with a higher electric potential (voltage). Electricity will not flow without a difference in electrical potential, just as water does not flow without a difference in gravitational potential energy. -The water in a garden fountain might be only a metre from the ground, while the water in a town's water tower might be 50 metres from the ground. The water from the water tower has much more gravitational potential energy and flows to the ground with greater force. -Similarly, the high-voltage electrons from a generating station have more electrical potential energy than low-voltage electrons from a flashlight battery.

How do we use coal to turn a generator?

-coal is *powdered* → *blown* into *combustion chamber* → *burned* to release *heat* → heat *boils water* → superheats resulting *steam* to high *temperature + pressure* → high-pressure steam *drives* large *turbine *by hitting blades → turbine shaft *rotates *large *electromagnetic coils in generator* → *electricity*. -Oil or natural gas can be burned in the combustion chamber instead of coal

How does a thermocouple work? pg 323

-converts* thermal to electrical energy* - *2 metals joined together* that create *heat at different speeds.* -When metals are *heated, difference *in heating speed* = electricity flowing *from one metal to other. -*temperature affects amount of electricity* produced = can use *thermocouple as thermometer. *

What are ways to avoid electrocution?

-electrocution is greater when current can flow easily. -so use insulators (wood, rubber, air) -mud and damp soil conduct electricity somewhat. -Eg. wearing shoes + dry day + touch electric fence = tingle -Bare feet + rain+ touch electric fence = shock

Why are amps more important that volts when it comes to electrical fatality?

-low voltage = can kill if it has high current (amps) -because 1 amp = millions of electrons -and voltage is just the energy in 1 electron

How much of global energy is produced by burning fossil fuels (oil, coal, natural gas)?

65% of all electric power is generated by burning oil, coal, or natural gas.

How much of the world's electricity is from hydro-electric power plants?

About 20% of the world's electricity is generated by hydro-electric power plants.

-the unit of [electrical] current -1 ____ = 1 coulomb (624, 100, 000, 000, 000, 000 electrons) per second

Amperes (amps)

-energy stored in chemicals and released when chemicals react -a form of potential or stored energy

Chemical energy

-pathway that controls the flow of electricity -complete path that charged particles flow through

Circuit

A microwave oven has a power rating of 800 W. If you cook a roast in this oven for 30 min at high, how many joules of electrical energy are converted into heat by the microwave?

E = 1 440 000 J = 1.4 MJ

energy of charged particles; transferred when electrons travel from place to place

Electrical energy

-package of chemicals designed to produce small amounts of electricity -produces electricity from chemical reactions

Electrochemical cell

-conductor through which electric current enters or leaves a device or material

Electrodes

decomposition of a substance by an electric current

Electrolysis

-liquid or paste that conducts electricity because it has ions

Electrolyte

What is a use of electroplating?

Electroplating is often used to protect metals from corrosion. For example, a plating of chromium or nickel can protect iron or steel from rusting

How do simple motors work?

Figure 3.10(a) *Current* flowing through the wire coil *creates a magnetic field around the wire.* This *interacts with the permanent magnets*, making the *coil spin.* Figure 3.10(b) As the *coil spins*, the *commutator changes position* so that its *other half contacts the other brush*. This *reverses the current flow* at just the right time. The *magnetic force* is *directed on the coil* to *keep it spinning.*

The process where the nucleus of an atom is split

Nuclear fission

How do variable resistors/rheostats work?

Rheostats can increase or decrease the amount of current in a circuit* by adjusting which part of the resistor has to current travel through.*

What does Ohm's law state about temperature?

Ohm's law states that as long as *temperature stays the same*: -the* resistance of a conductor stays constant*, and -the *current* is directly* proportional to the voltage *applied. -In other words, if you* increase the voltage = current increases*.

rate at which a device converts energy

Power

-cell that produces electricity by means of a chemical reaction that cannot be reversed

Primary cells

-cell that produces electricity by means of a chemical reaction that can be reversed by using an external source to run electricity back through the cell

Rechargeable cells

-measure of how difficult it is for electrons to flow through a substance -unit of measure is the ohm

Resistance

-device having resistance to the passage of electrical current -often used to control current in a circuit

Resistor

What happens to electrons in a conductor with voltage?

The electrons *flow toward the positive terminal of* the voltage *source.*

What happens to electrons in a conductor with *no voltage* applied?

The electrons are *not as tightly bound to nuclei*. They can *drift away* from the nuclei but *do not flow *in any one direction.

What happens to electrons in a conductor *with* voltage?

The electrons flow* toward the positive terminal *of the voltage source.

What happens to electrons in an *insulator*?

The electrons* (-) *are *bound tightly to *the nuclei *(+)* so they *resist movement*.

-device that changes electricity at one voltage into electricity at a different voltage -a step-up ______ increases the voltage -a step-down ______ decreases the voltage

Transformers

How do VDGs work?

VDGs are particularly effective at building up static charge. They produce static build-up by using* friction:* -Rubber *belt rubs metal scrubber *and *transfer charges to sphere* -charge *builds on sphere* and *transfers to you * -charges *repel like charges* on you, so *hair stands*

resistor whose resistance can be changed by adjusting the portion of the resistor the current travels through

Variable resistor/rheostat

the unit of voltage

Volt

-a measure of how much electrical energy a charged particle carries -potential difference

Voltage

Why is the output energy of a device usually/always smaller than the input energy?

Why: missing energy is lost or dissipated as heat.

A series circuit consists of 2 loads and a 6V power source. Readings are taken to measure the resistance of each load. The 6V power source is then replaced by a 9V power source. How does the resistance of each load change after the change in power supply? a) the resistance of each load remains the same b) the resistance of each load increases by a factor 1.5 c) the resistance of each load decreases by a factor of 1.5 d) the resistance of the first load increases, but the resistance of the second load decreases

a

A very large current has to be transmitted along a conducting wire. What kind of wire would do this most safely? a) short, thick, copper wire b) short, thin, copper wire c) short, thick, tungsten wire d) short, thin, tungsten wire

a

Fuel cells make electricity by... a) a chemical reaction that produces water b) using sunlight to get charges moving c) using two different metal strips in an electrolyte d) using water pressure to move a turbine

a

If the resistance of a conductor is 98 ohms and 2.6 volts are used, what is the current? a) 0.027A b) 37.7A c) 100.6A d) 255A

a

If you comb your hair on a cold dry winter's day, your hair tends to stand on end because: a) each separate hair has a similar charge of electricity b) different hairs have opposite charges of electricity c) hair always sticks to plastic d) hair is a good conductor of electricity

a

In a series circuit the current is.... a) the same at every point b) largest through the load c) largest at the positive terminal of the battery d) largest at the negative terminal of the battery

a

What is the difference between an electrochemical cell and a battery? a) a battery is made up of several cells b) a cell is made up of several batteries c) a cell is rechargeable, but a battery is not d) a battery is rechargeable, but a cell is not

a

Which of the following devices is NOT used to prevent danger from electrostatic discharge? a) a variable resistor b) an ionizer c) antistatic packaging d) a grounding strap

a

Which statement best describes a good conductor of electricity? a) low resistance; easy for charge to move b) low resistance; difficult for charge to move c) high resistance; easy for charge to move d) high resistance; difficult for charge to move

a

Which statement best describes series and parallel circuits? a) series circuits have one current path, but parallel circuits have several b) series circuits have several current paths, but parallel circuits have only one c) both series and parallel circuits have one current path d) both series and parallel circuits have several current paths

a

-called "alternating" because it flows back and forth 60 times per second -this is the current used in homes

alternating current (AC)

Where temperature is low compared to the temperature at the hot junction in a thermocouple

cold junctions

-electricity that flows continuously -describes the speed of electron flow at a certain point and time -measured by counting the number of electrons that pass a point per second (amps)

current

A large household appliance such as a refrigerator, which has a fan likely to be powered by a. a DC generator b. an AC generator c. a DC motor d. an AC motor

d

A light bulb is rated at 100 watts if it..... a) must be operated from a 100 volt supply b) draws a current from 100 amperes c) burns out after using 100 joules of energy d) transforms 100 joules of electrical energy every second

d

A series circuit has three 15 Ω resistors. What is the total resistance of the circuit? a) 0.2Ω b) 5Ω c) 15Ω d) 45Ω

d

A voltmeter connected to an electric bell reads 3.0V and an ammeter in series with the bell reads 0.75A. The resistance of the bell is a) 0.25 ohms b) 0.75 ohms c) 2.25 ohms d) 4.0 ohms

d

Alternative energy sources such as wind and solar energy are becoming more competitive with conventional energy sources because a) supplies of fossil fuels are being depleted b) the cost of fossil fuels is increasing c) new technologies make alternative energy plants more efficient d) all of the above

d

Communications satellites orbiting Earth have a lifetime of approximately 10 years. They receive and send signals on Earth night and day. Which of the following would best power this type of satellite? a) geothermal energy b) storage batteries c) solar collectors d) a combination of storage batteries and solar cells

d

Five 1.5V cells are connected in series. Their total voltage is a) 0.3V b) 1.5V c) 2.5V d) 7.5V

d

Household appliances are connected in parallel so that they.... A) all use the same power b) all carry the same current c) all have the same resistance d) can continue to work even if one fails or is disconnected

d

How much does it cost to run a 2kW freezer for 24 hours, if the cost of energy is 10 cents per kWh? a) $o.48 b) $1.20 c) $2.40 d) $8.40

d

If a balloon develops a positive electric charge, this means that it has... a) gained positive charges b) lost positive charges c) gained negative charges d) lost negative charges

d

Producing energy from fossil fuels is not 100% efficient. The process involves several steps. At which of the following steps is some energy lost? 1. collecting fossil fuel 2. transporting the fossil fuel 3. generating electricity 4. transmitting the electricity 5. converting the electricity to other forms of energy in the home a) 1, 2, and 5 b) 2, 3, and 5 c) 2 and 4 d) all steps lose some energy

d

The power rating label on a clothes dryer tells you a) how much current the dryer uses per second of operation b) how much energy the dryer uses per second of operation c) how the efficiency of this dryer compares to other kinds of dryers d) how much energy the dryer is likely to use in one year

d

Thermal pollution from generating plants is controlled by... a) returning cooling water directly to lakes and rivers b) returning cooling water to underground storage caverns c) using cooling water in cogeneration systems d) sending cooling water through ponds or towers before releasing it

d

Thermo-electric generating stations produce steam to turn generators by using energy released from... a) sunlight b) splitting atoms c) ocean tides d) burning fuels

d

Two light bulbs are connected in series and attached to a dry cell. One bulb is unscrewed from its socket. What happens to the brightness of the other bulb? a) it remains the same b) it get brighter c) it gets dimmer d) it does not glow

d

What component in an alkaline dry cell serves the same purpose as the sulfuric acid in a wet cell? a. the positive electrode b. the cathode past c. the negative electrode d. the electrolyte paste

d

Which of the following best describes the movement of electrons around a series circuit? a) the electrons take one of several possible paths b) the electrons give up equal amounts of energy as they pass through each branch of the circuit c) the current is higher near the power source than anywhere else in the circuit d) the electrons follow the same path around the circuit

d

-called ___ because the electricity flows in only one direction -Many devices such as mp3 players, computers, cell phones, and calculators also use __

direct current (DC)

-generation of electric current in a conductor by a changing magnetic field HOW DOES IT WORK? using the magnet-motors we made in class

electromagnetic induction

What are the uses of electrolytic cells?

electroplating

use of electricity to coat a thin layer of metal onto an object

electroplating

What is relationship of voltage and the total charge of the electrons?

energy delivered by a flow of charged particles is = voltage x total charge of the electrons

How do you calculate efficiency?

equation on pg 336

-between objects, *direct contact:* one object loses electrons (becomes positive) and one gains (becomes negative)

friction

How do fuel cells work?

fuel cells:* generate electricity* from *chemical reaction* with a* fuel* (eg. hydrogen). The *fuel (hydrogen) comes from sources* (eg. gasoline/alcohol). More *fuel added as electricity is produced*, so *cell is not used up* as ordinary cell would be.

Meters used to measure small currents are sometimes called _____

galvano meter

Energy stored in an object when it's *above the Earth's surface*

gravitational energy

How does nuclear energy work?

happens in nuclear reactor: *atoms of heavy element *(usually uranium) → split (*nuclear fission)* in *chain reaction *→ *releases *an enormous amount of *energy.*

Place where both wires are heated up by a very hot temperature in a thermocouple

hot junctions

Energy we can *hear*

sound energy

meter that can measure voltage, current, or resistance in a circuit

multimeters

When you soak 2 metal plates in an electricity-conducting solution, expose them to sunlight and then detect a small voltage.

photovolataic effect

How does hydro-electricity work?

plants capture *energy of falling water* from: flow of *waterfall/ dam* built across river → store *water in reservoir* → Water directed through a *channel (penstock)* → large paddle-covered* turbine*→ rushing *water spins turbine (connected to a generator *just like steam-driven turbine).

-change in the potential energy of electric charge compared to its potential energy at a reference point (eg. the ground) -voltage

potential difference

positively charged particle in the nucleus of an atom

proton

-means "not moving" or "stationary." -a charge that doesn't flow like electrons in an electrical current

static charge

Process where* ions in a solution gain electrons *(in saltwater, ________ also creates hydrogen gas)

reduction

-resource that is continually replenished and therefore can be used indefinitely -eg. water/wind energy

renewable resource

several solar cells connected together

solar modules

How do you keep an electromagnet spinning in a magnetic field? (using a commutatorm armature, etc.)

switch the direction the current travels through the coil just as it aligns with magnetic field of the permanent magnet. Reversing current = reverses polarity (north and sounds ends) of electromagnet. will then continue turning in order to align the opposite way. Changing polarity of electromagnet every half turn = electromagnet continuously pushed and pulled by the permanent magnet. Many electric motors use commutator and brushes to reverse flow of electricity through the electromagnetic coil. commutator: split ring that breaks flow of electricity for a moment and then reverses connection of the coil (Figure 3.10(a) pg 325). When contact is broken, so is magnetic force. But armature continues to spin because of momentum. result of spinning: commutator reconnects with brushes. magnetic force on coil keeps it spinning continuously (Figure (b)). brushes make electrical contact with moving commutator by "brushing" against it.