Hip – Hip – Huzzah!!

1. What happened on August 14th, 2003 at 4:11? 50 million people in Ontario and the northeastern US

were plunged into the largest electrical blackout in North American history.

2. What were you doing then and how were you affected?

Various answers3. What is an “energy grid”?

It is a huge, interconnected system of electricity networks (which includes electrical generating stations, transmission lines, and distribution stations).

4. Why does an energy grid have to balance supply with the demand for electricity?

It must maintain a balance of supply and demand because electricity cannot be stored for long after it is generated. If it isn’t and a generator is overloaded, that part of the energy grid is disconnected and electricity will be sent along alternative paths.

A SHOCKING EXPERIENCE1.What is an electric shock?

It is caused by electric charges that gather or accumulate, then are released very quickly.

2.How are lightning and an electric spark similar?They are the same thing, just different in

size – they are caused by electric charges, which are charged particles that exert an electric force on each other.

ELECTRICALLY CHARGED PARTICLES1. What is the charge of a proton?

Positive

2. What is the charge of an electron? Negative

3. What is the charge of a neutron? No charge or neutral

4. Can an atom lose protons? No, they are bound to the neutrons in the

nucleus.

5. Can an atom lose electrons? Yes, they orbit around the outside of the nucleus

and can move from one object to another.

FRICTION AND THE MOVEMENT OF ELECTRONS1. What has happened when an object creates a static

charge? Electrons have moved from one object to another

through some method, and that electric charge builds up on the surface of the object.

2. What is the difference between an object that has a negative charge and the same object when it has a positive charge? A negatively-charged object has more electrons than

protons, whereas a positively-charged object has more protons than electrons.

3. How does rubbing two objects together sometimes result in the building of a static electric charge? The force of friction can remove electrons from one

object and cause them to transfer to the other object.4. Where does the word, “electricity” come from?

It comes from the Greek word electron, meaning amber, which is fossilized tree resin. It has been used for thousands of years to study static electricity.

ELECTRON AFFINITY

1. What does “electron affinity” mean? It is the tendency of a substance to hold on to the electrons.

2. If you rub nylon and steel together which one becomes negative and why? Steel becomes negative because steel is lower on the triboelectric

series.

3. If you rub amber and silk together which one becomes negative and why? Amber becomes negative because amber is lower on the triboelectric

series.

4. If you rub Teflon and human hair together which one becomes negative and why? Teflon becomes negative because Teflon is lower on the triboelectric

series.

5. If you rub ebonite and cat fur together which one becomes negative and why? Ebonite becomes negative because ebonite is lower on the triboelectric

series.

LAWS OF ATTRACTION AND REPULSION

1. What do unlike (or opposite or dissimiliar) charges do? They attract.

2. What do like charges do? They repel.

3. What happens between a neutral object and a positive object? The neutral object is attracted to the positive

object.4. What happens between a neutral object

and a negative object? The neutral object is attracted to the negative

object.

1. Copy the following in your notebook and write if they would attract or repel each other in the blank in the middle.

positive attracts negativepositive repels positive

positive attracts neutralNegative repels negative

negative attracts positivenegative attracts neutral

1. Memorize and understand the laws of attraction and repulsion.

Opposite charges attract; Like charges repel; Charged objects attract neutral objects.

2. What is Charles-Augustine de Coulomb famous for? He made several important discoveries; he showed that

when two charged objects are placed closer together, the attraction or repulsion increases. When the charged objects are moved farther apart, the attraction or repulsion decreases. The metric unit for electric charge is named the coulomb (C).

3. How many electrons are in 1 coulomb? You will need to remember this number.

There are 6.24 x 1018 electrons in one coulomb.

ELECTRICAL INSULATORS AND CONDUCTORS

1. What is conductivity? It is the ability of materials to allow electrons to move

freely in them.2. What does an insulator do?

It is a solid, liquid, or gas that resists or blocks the movement of electrons.

3. If you wanted electricity to move from one location to another location, would you use a conductor or an insulator? I would use a conductor, because those materials allow

electrons to change positions.4. If you had electricity traveling through a wire

and wanted to protect yourself from electric shock what would you cover the wire in, aluminum or rubber? I would cover the wire in rubber because it would not

allow the electrons (the electric shock) move freely.

2, Friction is the force resisting the relative motion of two surfaces in

contact. When two neutral objects, like glass and cotton, are rubbed

together, electrons are transferred by the rubbing from the glass to the cotton. This happens because glass tends to lose electrons more so than cotton, because glass is higher on the triboelectric series. Glass ends up with a positive charge, while cotton ends up with a negative charge.

3, A neutral object is NOT charged, but contains and EQUAL AMOUNT

of positive and negative charges (protons and electrons). 4 (but change the word “opposite” to “unlike”),

Opposite charges attract; like charges repel. 6,

It could have an equal amount of protons to balance the charge. 7,

A conductor allows electrons to move freely, whereas an insulator resists their movement.

Any metal. Wood, plastic, rubber.

8, A fair conductor only allows SOME movement

of electrons.The human body, soil, impure water.

9Electric charges will spread through the water

and cause you injury. 10,

They do not because neither one is higher or lower on the triboelectric series, so neither one has a larger tendency to gain or lose electrons.

11,

13 You are sitting in a conductor, which makes it easily

for lightning to flow through. The water’s not pure either, so it’ll make it easier for the charges in the lightning to flow through that. Both are potentially dangerous/fatal.

Yes it would partially because you wouldn’t have to worry about the lake killing you, as it is now an insulator.

Pairs Becomes More Positively Charged

Becomes More Negatively Charged

cotton, steel cotton steelcotton, silk silk cottonhuman hair, human hands (dry)

human hands human hair

Teflon, wood wood Teflonglass, plastic glass plastic

1. What is an electroscope used for? It can detect static charge.

2. What are the thin metal flaps in an electroscope called?

They are called leaves.

3. Which law of charges explains why the leaves of an electroscope separate when a charged object is brought near it?

Like charges repel.

4. What is electrostatics? It is the study of static electric charges.

Draw the following three electroscopes, making sure that the number of electrons illustrates what is happening. A closed neutral electroscope. An electroscope that is separated with a

negative charge. An electroscope that is separated with a

positive charge.

CHARGING BY CONTACT When you charge a neutral object by

contact, what charge does the neutral object get? The same charge as the charged object.

1. What is induction? It is the movement of electrons within a substance caused by

a nearby charged object, without direct contact between the substance and the object.

2. Why does rubbing a balloon on your hair make both the balloon and the hair charged?

Electrons transfer from your hair to the balloon, meaning your hair has more protons than electrons and is now positive, while the balloon has more electrons than protons and is now negative charging by friction.

3. What type of material do you need to build up a static electric charge, a conductor or an insulator?

An insulator.4. If you bring a negatively-charged balloon near a wall but

don’t touch it, what charge does part of the wall get? It gets a positive charge.

5. If you bring a negatively-charged balloon near a wall where do the electrons in the wall go?

Further back into the wall because they are repelled by the negative charges in the balloon.

1. What does “grounding” mean? It is the process of connecting a charged

object to Earth’s surface.2. When you induce an electroscope with

a negatively-charged object, what charge does the electroscope get?

It gets a positive charge.3. What do you need to do to make an

induced-charge permanent? You need to ground the electroscope while

holding the charged object near it to provide a path for electrons to escape from the negatively-charged object, or a path for electrons to get from the ground closer to the positively-charged object.

ELECTRICAL DISCHARGE1.When you get an electrical spark, does

the electricity discharge by contact, friction or induction? Induction.

LIGHTNING1.What charge does a storm cloud

normally have, positive or negative? It has a negative charge.

2.What charge does a storm cloud normally induce in the ground? It induces a positive charge.

1. If a Van de Graaff generator has a lower pully made of nylon and a belt made of rubber, which part get negatively-charged, the pully or the belt (look at the Triboelectric series).

Belt gets negatively charged.

2. If a Van de Graaff generator has a upper pully made of Teflon and a belt made of rubber, which part get negatively-charged, the pully or the belt (look at the Triboelectric series).

Teflon gets negatively charged.

1, They are the same, electrical discharges.

2, A negatively-charged object touches a neutral object. A positively-charged object touches a neutral object.

3, It becomes temporarily charged because when the

charged object is brought near, the like charges are repelled by this charged object, into the leaves, inducing an opposite temporary charge (from the charged object) on the electroscope.

4  While holding a charged object near the electroscope,

use your finger to ground the electroscope. Take your finger away while still holding the charged object near. Then take the charged object away, and your electroscope is now permanently charged through induction.

6, Electrons are being transferred in an electrical

discharge from you to the metal to the ground or vice versa. It will make you neutrally charged. The shopping cart is providing a path to or from the ground for the electrons to use.

Again, the air is providing a path for electrons to travel to the ground, neutralizing the cloud more.

7, Charges would have no path to travel down the

metal rod into the leaves. 8,

This happens because like charges repel. This happens because opposite charges attract.

9 The metal rod would receive the shock.

1. Why are large buildings fairly safe during a lightning storm?

They are safe because they will be properly grounded if there is a strike.

2. What should you do during a lightning storm in order to be safe in a car?

Roll up the windows and don’t touch metal parts of the car.

3. Why is it that men during the summer are more often stuck by lightning than women during the fall?

Men are generally taller, making a shorter path for the lighting to travel and more likely to be struck.

LIGHTNING RODS1. What part of the tree conducts the static discharge when a

lightning bolt strikes a tree? The sap inside the tree conducts the electricity down to the ground.

GROUNDING STATIC CHARGES ON VEHICLES1. The textbook doesn’t say it, but when a moving car builds up a

static charge what are the two different types of materials that are rubbing together? Air and particles in it, and metal from the car. OR Rubber from the tires and

asphalt/cement/dirt/gravel from the ground

2. What device can you put on a car that “grounds” the car and prevents a static charge from forming? A grounding strap grounds the car.

3. The textbook doesn’t say it, but when a moving plane builds up a static charge what are the two different types of materials that are rubbing together? Air and particles in it, and the metal on the plane are rubbing together.

4. What device can you put on a plane that “grounds” and prevents a static charge from forming? Dissipaters are needle-like rods that disperse static charges into the air.

5. What type of material (insulator or conductor) do you use to prevent static electric charges from forming? Conductors are used.

STATIC CHARGES AND FLAMMABLE MATERIALS1. Why is a car with a static electric buildup dangerous around gas

stations? Gas is flammable and one static spark can ignite it.

REDUCING STATIC CHARGES IN THE HOME1. What would build up a larger amount of static cling, a load of dirty silk

clothes or a load of dirty silk and wool clothes? A load of dirty silk and wool clothes because they are made of

different material, so when they are rubbed together they will be charged by friction.

2. When do clothes in a drier build up a static charge – when the laundry is wet or dry? More charges build up in dry air like during winter, because dry air

acts as an insulator.3. How do drier sheets reduce static cling?

It adds a thin layer of waxy chemicals to the surface of clothes so there is less friction between the surfaces and therefore fewer unlike charges to attract each other.

4. What are the four different methods for reducing charge build-up in a computer room with a carpet? Use an antistatic mat for your feet; increase the moisture in the air

with a humidifier; spray the carpet with antistatic spray; wear an antistatic wrist strap.

Why do industrial spray painters charge their spray paint with a negative charge? There is less waste due to bounce and overspray and the finish is smooth

and uniform. Why don’t industrial spray painters get spray paint on the floor and walls

behind the object they are painting? The paint is attracted to the surface it is painting, because it is the opposite

charge of the paint. That attraction is so strong that it will be more attracted to the object instead of neutral things around it.

In step 1, what is the charge on the selenium drum? It is positively charged.

When the selenium drum is in the dark does it behave as a conductor or an insulator? Insulator.

When the selenium drum is in the light does it behave as a conductor or an insulator? A type of conductor called a photoconductor.

What happens to the charge on the selenium drum when light is projected on it? The area on the drum becomes conductive and loses its charge, becoming

neutral. What doesn’t happen to the areas of the selenium drum that is still dark when

light is projected on it? They do not become neutral and remain positively charged.

What charge is on the toner (ink)? It is charged negatively.

1. What does an electrostatic precipitator do?

Through the use of static electric charges, it cleans gas by removing tiny pollutant particles and sends clean gas out into the air. The particles in the gas are charged when it is sent through pipes, charging the particulate matter negatively. The gas moves through an area with positively charged plates, which attract the negative pollutant matter and remove them from the gas.

1 (you could get struck by lightning is not enough of an answer – why is a tree more dangerous than a shrub?), Trees may be the highest point in the area, which makes

it more likely that it will be struck by lightning. 3,

Vehicles build up static charge through friction between the vehicles outer surface and the air.

4, It grounds the truck, allowing excess static charge to be

transferred to the ground so that the flammable liquid inside the truck does not get ignited by an electric spark.

5, The paper may still be charged when it comes out of the

photocopier. 6

Antistatic dryer sheets, antistatic spray, electrostatic precipitators, and photocopiers are four applications that use electrostatic principles.

7, It is so large with so many positive and negative charges, that

overall it is not affected by any electron transfers and is considered neutral.

8, When they are brought through pipes, the particulate matter

becomes negatively charged and so is attracted to the positively charged plate.

9 (how does the insulation protect the electronics?), This is so your body does not transfer its charge into the metal

tool, and then into the electronic equipment, damaging it. 10,

Through the third law, charged objects attract neutral objects. 11,

Water can be pure and therefore an insulator and not conduct electricity; water is also only a fair conductor, and so it is not great at conducting electricity at the best of times.

12 You could get rid of your carpet, use antistatic spray and

antistatic dryer sheets to reduce or eliminate these problems.

1. Why isn’t static electricity useful for operating electrical devices?

They build up and discharge, but they do not flow continuously.

2. How do you want electrons to flow when you operate an electrical device?

You need a steady flow of electrons.

3. What are the two things that this section says you need for a circuit?

The flow of electrons requires an energy source and the path the electrons follow must be complete.

4. What is current electricity? It is the continuous flow of electrons in a

circuit.

1. What is an electrical load? It is a device that converts electrical energy to another

form of energy.

2. What does an electrical load do to electrical energy? It converts it to another form of energy.

3. List the four things you need to make an electrical circuit. I have scrambled the letters of each one to help you remember them. (reengy reoucs, ploceemt thap, chwist, alod)

Energy source, complete path (connector/conductor/wires), switch, load

4. What is an open switch? It means that there is a break in the path, so the electrons

cannot flow through the circuit.

5. What is a closed switch? This means the circuit is complete and electrons can

flow.

1. What is an electrochemical cell? It is a package of chemicals that converts chemical

energy into electrical energy that is store in charged particles.

2. What is a battery? It is a combination of electrochemical cells.

3. What is the difference between an electrochemical cell and a battery?

Battery contains many electrochemical cells.4. Note: Usually an “electrochemical cell” is simply

called a “cell”.5. A cell is made of two different electrodes. What

happens at each of the electrodes? Electrons collect on one of the electrodes, making it

negatively charged. The other electrode has lost electrons, so it is positively charged.

6. What does the electrolyte do in a cell? It reacts with the electrodes and conducts electricity.

What is the difference between a wet cell and a dry cell?Wet cells use a liquid electrolyte, while dry

cells use a paste electrolyte. Where do you commonly find wet

cells?You find them in cars and other vehicles.

Where do you commonly find dry cells?You find them in flashlights, hand-held

video games devices, cameras, and watches.

RECYCLING AND RECHARGING DRY CELLS What do dry cells (common batteries)

commonly have in them that makes them bad for the environment to simply throw away? They contain toxic materials like heavy

metals, including nickel, cadmium, and lead.

FUEL CELLS What makes a fuel cell more reusable than

reusable batteries? The cell is not used up like ordinary cells

would be because as the electricity is produced, more fuel is added.

1. What has more potential energy, an apple on a tree or an apple that has fallen from a tree?

The apple on the tree has more potential energy.2. What is another term for potential difference?

Another term for potential difference is voltage.3. Explain what is meant by the term potential

difference? (this is very important to understand) The difference in electric potential energy between two

points in a circuit is termed potential difference or voltage. This difference causes current to flow in a closed circuit. The greater the potential difference in a circuit, the greater the potential energy of each electron.

4. What is potential difference measured in (what units is it measured in)?

It’s measure in volts (V).5. What is the name of the equipment that you

measure potential difference with? It is called a voltmeter.

1. When you turn on a circuit, do all the electrons along the wire move towards the negative terminal or do the electrons all have to start from the negative terminal?

The electrons start from the negative terminal.2. What is electric current?

It is a measure of the amount of electric charge that passes by a point in an electrical circuit each second.

3. What is the difference between direct current and alternating current?

Direct current only flows in one direction, while alternating current flows back and forth at regular intervals.

4. What is a common source of DC? A common source of DC is batteries.

5. What is a common source of AC?A common source of AC is wall outlets or sockets.

MEASURING CURRENT What is the name of the equipment that you

measure current with? You measure current with an ammeter.

What is the unit current is measured in? Current (I) is measured in amperes or amps (A).

 CURRENT ELECTRICITY AND STATIC

ELECTRICITY What is the difference between current and

static electricity in relation to current?Current electricity is the flow of electrons in a

circuit through a conductor; static electricity is the electric charge that builds up on the surface of an object. Static electricity discharges when given a path, but does not continue to flow.

What colour is the positive terminal of an ammeter? It is red.

What colour is the negative terminal of an ammeter? It is black.

What terminal do you connect the red terminal of an ammeter to when measuring current in a circuit?You connect it to the positive terminal.

What is resistance? It is the degree to which a substance opposes

the flow of electric current through it. What type of substance has more

resistance, a conductor or an insulator?An insulator has more resistance.

What unit is resistance measured in? It is measured in ohms (Ω).

What does resistance do to the energy in electricity, use it up or push it backwards? It uses it up, converting the electrical

energy into other forms of energy.

What is a resistor? It is a material that can slow current flow.

Why does the filament in a light bulb produce light? It has a high resistance to the electron’s electrical

energy and that causes it to heat up and produce light.

When does a circuit have a higher potential difference, before it enters a resistor or after it enters a resistor? It has a higher potential difference before it enters a

resistor. What happens to a circuit’s potential energy

when the electrons leave a resistor? The potential energy has been converted to

another form of energy, and so it decreases.

List some of the materials that resistors are made out of.Some materials that resistors are made out

of are heat-resistant metal with insulating cores, as well as those materials mixed with carbon.

What would have less resistance, a thick wire or a thin wire?A thin wire would have more resistance

because there is not as much space for the electrons to get through.

1. They are composed of an electrolyte and two electrodes; an electrolyte can be a liquid or a paste that conducts the electricity produced by the ionization of the electrodes, usually zinc and copper.A reaction is produced between the electrolyte and electrodes in a wet cell, which creates electricity.

2. They flow from the negative end of the source to the positive end.

3. Voltmeters measure potential difference.Potential difference it measured in volts (V).

4. Ammeters measure current.Current is measured is amperes or amps (A).

5. Potential difference is the pushing force of electrons, while current is the number of moving electrons.

1. DC flows only in one direction, while AC flows back and forth in intervals.

2. An electric load converts electrical energy into another type of energy (i.e. heat, light, sound, etc).Some examples of electrical loads are lights, motors, and resistors.

3. It is the degree to which a substance opposes the flow of electrons through it.

4. It slows down the movement of electrons and converts the electrical energy into other forms of energy.

5. The four factors affecting resistance in a wire are the following: the material, the cross-sectional area or thickness, the length, and the temperature.

1. What are the two rules you need to follow when drawing a circuit diagram?

Always use a ruler to draw straight lines for the conducting wires.

Make right-angle corners so that your finished diagram is a rectangle.

2. What is wrong with the circuit diagrams shown here? The first rule isn’t obeyed. The second rule isn’t obeyed. No electrical symbols are used.

3. For practice, draw and label each of the symbols for the following components found in a circuit diagram.

wire battery light bulb resister switch voltmeter ammeter

 

1. What is a series circuit? Write down the second sentence, the one that starts, “A series circuit has only one …”

…path along which electrons can flow. 2. Recall that current is the amount of electrons flowing

through a circuit each second. In a series circuit is the current at the end of the circuit less, the same or more than the current at the beginning of the circuit?

The TOTAL current is the same.

3. Does adding more resistance in a series circuit increase or decrease the current?

Adding more resistance will decrease the TOTAL current. 4. If you add more lights in a series circuit does that

make the light brighter or dimmer or do they stay the same?

Adding more lights will make all the lights dimmer in a series circuit.

What is the full explanation of a parallel circuit? It is an electric circuit in which the parts are arranged so

that electrons can flow along more than one path. If one path in a parallel circuit is cut, will the rest of the

circuit still be able to work? Yes, it will still be able to work.

Does the addition of a new path in a parallel circuit increase, keep the same or decrease the total resistance? It decreases the total resistance of the circuit.

What does most of the current in a parallel circuit go through, the path with the most resistance, all paths equally or the path with the least resistance? Most of the current will pass through the path with the least

resistance. What is the same along each path in a parallel circuit,

the voltage, the current or the resistance? The voltage is the same along each path in a parallel

circuit.

1. Complete the following table:

Series Circuit Parallel CircuitNumber of paths for electrons to

travel

one path more than one path

Current stays the same divides into different paths, with the pathway with less resistance having a greater current

Voltage divides into the different loads stays the same

What is the current at each of the points of the following circuits?

IT= 5 A

I5=5AI23=5A

I1=5AI4=5A

IT= 5A I1= 2A I2=3A

What is the voltage at each of the points of the following circuits?

VT= 5V V1= 5V V2=5V

VT= 10V

V5= 2VV23= 3V

V1= 1V

V4=4V

Draw circuit diagrams for circuits with the following. A series circuit that has:

1x cell 3x lights 1x open switch

A series circuit that has: 1x 2-cell battery 1x motor 1x resister 1x closed switch 

A series circuit that has: 2x 3-cell batteries 3x lights 1x open switch

A parallel circuit that has: 2x 3-cell batteries in series 2x lights (each in parallel) 2x open switches (each switch controls one light)

A parallel circuit that has: 2x 3-cell batteries in parallel 2x resisters in parallel 1x open switch (that controls both lights at the same time)

Why is the letter “I” used for current? (see box “words matter”) The symbol “I” is used for current because it stands

for INTENSITY.  What is the full name of the high school teacher

who first worked out Ohm’s Law? The high school teacher’s name is Georg Simon Ohm.

Ohm’s law is true so long as what stays the same? As long as the temperature stays the same, Ohm’s

law will hold true.  Complete the three equations:

V = IR I = V/R R = V/I

A current of 4.0 A flows through a 40 resister in a circuit. What is the voltage? Given – I = 4.0A, R = 40 Required – V = ? Analysis – V = IR Substitution and Solution V = IR

V = (4.0A)(40)V = 160V

Paraphrase – The voltage in this circuit is 160V.  A 30 V battery generates a current through a 15 resister.

How much current does the battery generate? Given – V = 30V; R = 15 Required – I = ? Analysis – I = V/R Substitution and Solution I = V/R I = (30V)/(15)

I = 2A Paraphrase – The battery generates 2A of current.

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? Given – V = 240V; I = 20A Required – R = ? Analysis – R = V/I Substitution and Solution R = V/I R = (240V)/(20A) R = 12 Paraphrase – The resistance of the heating element is 12. 

A current of 1.5 A flows through a 30 resister that is connected across a battery. What is the battery’s voltage? Given – I = 1.5A; R = 30 Required – V = ? Analysis – V = IR Substitution – V = IR = (1.5A)(30) = 45V Paraphrase – The battery’s voltage is 45V.

If the resistance of a car headlight is 15 and the current through it is 0.60 A, what is the voltage across the headlight? Given – R = 15; I = 0.60ARequired – V = ? Analysis – V = IR Substitution – V = IR = (0.60A)(15) = 9V Paraphrase – The voltage across the headlight is

9V. A firetruck has a searchlight with a resistance of

60 that is placed across a 24 V battery. What is the current in this circuit? Given – R = 60; V = 24V Required – I = ? Analysis – I = V/R Substitution – I = V/R = (24V)/(60) = 0.4A Paraphrase – The current in this circuit is 0.4A.

A bulb of 15 resistance is in a circuit powered by a 3 V battery. What is the current in this circuit?Given – R = 15; V = 3VRequired – I = ?Analysis – I = V/RSubstitution – I = V/R = (3V)/(15) = 0.2AParaphrase – The current in this circuit is

0.2A. A current of 0.75 passes through a flashlight

bulb that is connected to a 3.0 V battery. What is the bulb’s resistance?Given – I = 0.75A; V = 3.0V Required – R =

?Analysis – R = V/ISubstitution – R = V/I = (3.0V)/(0.75A) = 4Paraphrase – The bulb’s resistance is 4.

A current of 625 mA runs through a bulb that is connected to a 120 V power supply. What is the resistance of the bulb?Given – I = 625mA = 0.625A; V = 120VRequired – R = ?Analysis – R = V/ISubstitution – R = V/I = (120V)/(0.625A) = 192Paraphrase – The resistance of the bulb is 192.

What would the current be if the resistance was 45 using a 3 V battery?Given – R = 45; V = 3VRequired – I = ?Analysis – I = V/RSubstitution – I = V/R = (3V)/(45) =0.067AParaphrase – The current would be about

0.067A.

A table lamp draws a current of 200 mA when it is connected to a 120 V source. What is the resistance for the table lamp? Given – I = 200mA = 0.200A; V = 120V Required – R = ? Analysis – R = V/I Substitution – R = V/I = (120V)/(0.200A) = 600 Paraphrase – The resistance for the table lamp is

600. The current in a circuit is 0.50 A. The circuit has two

resisters connected in series: one is 110 and the other is 130 . What is the voltage in the circuit? Given – I = 0.50A; R = 110 + 130 = 240 Required – V = ? Analysis – V = IR

Substitution – V = IR = (0.50A)(240) = 120V Paraphrase – The voltage in the circuit is 120V.

How does temperature change the resistance of a material?Resistance is lower when a conductor is

cooler, while when the temperature increases, resistance increases.

Why do incandescent bulbs often burn out within the first millisecond of turning them on?They do this because of the sudden

temperature change and other forces caused by the large initial current.

How does temperature change the resistance of a material?Resistance is lower when a conductor is

cooler, while when the temperature increases, resistance increases.

 Why do incandescent bulbs often burn out within the first millisecond of turning them on?They do this because of the sudden

temperature change and other forces caused by the large initial current.

If you are trapped in a car with a live wire touching the car (as in Figure 11.39 pg 462) why is it safer to remain in the car than to walk out? It is safer to remain in the car than to walk out

because if you come in contact with the wire, the electricity will take a path through your body to the ground and seriously injure or cure you.

If you are trapped in a car with a live wire touching the car (as in Figure 11.39 pg 462) why is it safer to jump out of the car than to walk out? It is safer to jump out rather than walk would

so that he does not provide a path for the electricity to flow through him to the ground.

What happens to a fuse if there is too much current flowing through it? If the current gets too high, the metal in the fuse melts and

the current flow stops, which helps to prevent further problems, such as damage to your electrical components or a possible fire.

Which type of metal would it be better to make a fuse out of if you want the fuse to be sensitive, lead (melts at low temperatures) or iron (melts at high temperatures)? Lead would be better because it has a low melting point.

What does a circuit breaker and a fuse do that is similar? It does the same job as a fuse (turns off the circuit), except

that the wire inside does not melt. A circuit breaker is more modern.

If a circuit breaker does not melt and turn off a circuit, what does it do to turn the circuit off when there is too much current? The wire heats up and bends, which triggers a spring

mechanism that turns off the flow of electricity.

What does the third round prong on a three-prong plug do with unwanted electricity? It connects the device to the ground wire of the building,

sending any unwanted current flow directly to the ground. What do the other two prongs do? (The answer is not in the

textbook – but you can figure it out – Hint: what are the two ends of a battery) One side is negative, releasing electrons and carrying the

current to the load, while the other side is positive, returning the current to the source.

What is the short form for ground fault circuit interrupter? The short form is GFCI.

Why when you go home will you usually only find GFCI’s in your kitchen and bathroom? You usually only find GFCI’s in the kitchen or bathroom

because water is used most often there, allowing current to flow more freely if it comes into contact with the water. The GFCI will notice this and open the circuit so there is less chance of injury to you.