PhySci Final Review 3: Thermal and Electrical

PhySci Final Review 3: Thermal and Electrical

By William Lovering

Thermal Energy

Thermal Energy → sum of the kinetic and potential energy of all the particles in an object; thermal energy of an object increases as temperature increases

Heat → thermal energy that flows from something at a higher temperature to something at a lower temperature

Temperature

Average kinetic energy of all the particles in a material; measured by a thermometer in degrees (usually degrees Celsius or degrees Fahrenheit)

Thermal Energy Transfer

Conduction → Transfer of thermal energy by collisions between particles in matter. Occurs in solids, liquids, & gases. Metals are the best conductors.

Convection → Transfer of thermal energy in a fluid by the movement of warmer and cooler fluid from place to place. Occurs in liquids & gases.

Radiation → Transfer of energy by electromagnetic waves. Occurs in gases only.

Heat Transfer

The thermal energy exchange between two objects of different temperatures; energy moves in a predictable pattern from warmer sites to cooler sites until all sites have reached the same temperature

Conduction

Transfer of thermal energy that occurs in solids, liquids, and gases when two substances of different temperatures touch.

Convection

Heat transfer caused by the rising of hotter, less dense fluids and the falling of cooler, more dense fluids.

Radiation

The transfer of energy by the movement of electromagnetic waves or subatomic particles.

Conductor

A substance that allows the flow of electrical charge or transfers thermal energy through matter.

Insulator

A material that does not conduct heat or electric current

Electric Fields

• An electric field is a region around a charged object where the object's electric force is exerted on other charged objects.

• Because positive charges are repelled by positive charges.. and attracted to negative charges..field lines point away from positive charges and towards negative charges

How Does Charge Build Up?

• Most atoms are uncharged, or neutral because the protons equal the electrons.

• Uncharged objects become charged by gaining or losing electrons

• Static electricity is the buildup of charges on an object

• In static electricity, charges build up on an object, but they do not flow in a current

Charging Objects

• Charges are neither created nor destroyed. This is known as the law of conservation of charge.

• If one object loses electrons, another object must pick them up

• There are four methods by which charges can redistribute themselves: Friction, conduction, induction, polarization

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Charging by Friction

• Charging by friction is the transfer of electrons from one uncharged object to another by rubbing objects together

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Charging by Conduction

• When a charged object touches another object, electrons can be transferred

• This is the process of transferring electrons by direct contact

Charging by Induction and by Polarization

• Electrons can react to the electric field of a charged object without touching the object itself. This is induction

• Polarization occurs when electrons move only within their own atoms. In this case, the electrons create charged ends of the atoms

electric currents

What is an electric current?

The flow of electric charges through a conductor.

The difference between static electricity and electric currents.

Electric charges that build up on static electricity do not flow. Instead the charges jump between two objects.

electric currents is a flow of electrons like a stream of water through a conductor like copper or metal.

What is a direct current?

• An electric current in which charges flow in one directly only.

• The current produces by electrochemical cells is direct current. The chemical energy is being changed into electrical energy.

• When the switch is on the electric current produced by the dry cells keeps the light bulb on

Alternating current:

• type of current that does not flow in one direction only.

• constantly changes direction at a regular rate.

• can be transported more easily over long distance

What is a Circuit Made of?

• Objects that use electricity contain circuits

• All electric circuits have these basic features: devices that run on electrical energy, sources of electrical energy, and conducting wires

Circuit Symbols

• Battery

• Bulb

• Switch

• Resistor

Circuit Energy Sources

• Power plants and batteries are examples of energy sources

• These supply the voltage that causes current to flow

• When the energy source is a battery, current flows from the positive end to the negative end

Types of Circuits

• Series Circuits

• Parallel circuits

Series circuits

• All elements in the circuit are in one loop

• Every electron flow through every element

• If one bulb burned out, the rest would also go out

Parallel circuits

• There are several pathways or loops through the circuit

• Electrons flow through just one of those pathways

• If one bulb burned out, the rest of the bulbs would still glow

Ohm's Law

• Georg Ohm found that conductors and most other devices have a constant resistance regardless of the applied voltage

• Ohm's law says that resistance in a circuit is equal to voltage divided by current

• Resistance = voltage / current

• Units for resistance (Ohms); voltage (volts - V), Current is amps (A)

​Volts, Amps, and Resistance

​V = I * R

​Voltage = current multiplied by the resistance

​Series:

​R = R1+R2+R3+R4 ...

​Parallel:

​R = 1/R1 + 1/R2 + 1/R3 ...

​

Voltage in Series Circuits

• The voltage drops each time it passes through a resistor (like a lightbulb)

• Total voltage equals the sum of all the voltage drops.

• V total = V₁ + V₂ + V₃ + V₄ ...

• Total Voltage also equals the voltages of all batteries placed in series

Voltage in Parallel

• The voltage is the same no matter which branch of the parallel circuit you're on.

• V_Total = V₁ = V₂ = V₃ = ...

• Like a platform with several water slides (paths down), no matter which one you choose, everyone ends back up at the bottom.

Current in Series

• The same current is shared by the whole circuit, since there's only one path for the electrons to go, so all the electrons go that way

• I_Total = I₁ = I₂ = I₃ = I₄ = I₅ = ...

Current in Parallel

• In parallel, the electrons will split and go down different paths, so only some will go down any given path

• This decreases the current through each path.

• Current will be faster where there's less resistance.

• Electrons regroup at the end, though, so... I_T = I₁ + I₂ + I₃ + ...

Resistance in Series

• The more resistors you add, the more resistance overall.

• Adding more lightbulbs to this circuit would make each bulb dimmer and dimmer.

• R_Total = R₁ + R₂ + R₃ + R₄ ...

Resistance in Parallel

• Total resistance decreases the more resistors you add in parallel

• It's like on Black Friday when the checkout line gets long and they add another checkout. There won't be as many people going through each line, but each person won't have the line holding them back as much.

• 1/R_T = 1/R₁ + 1/R₂ + 1/R₃ ...

Multiple Choice

What word means how fast the electrons flow.

• Current
• Voltage
• Resistance
• Power

Multiple Choice

The mathematical relationship among Voltage, Current, and Resistance

• Faraday's Law
• Tesla's Law
• Edison's Law
• Ohm's Law

Multiple Choice

Electricity that flows in a closed path is called a

• path
• current
• circuit
• light

Multiple Choice

What is Resistance?

• The flow of electrons
• Electric potential difference
• A battery
• The ability to reduce the flow of electrons

Multiple Choice

What is current measured in?

• Ω (Ohms)
• V (Volts)
• A (Amps)
• W (Watts)

Multiple Choice

What is resistance measured in?

• Ω (Ohms)

• V (Volts)

• A (Amps)

• W (Watts)

Multiple Choice

If two charges repel each other, the two charges must be

• Positive and neutra
• Positive and negative
• positive and neutral
• negative and negative

Multiple Choice

If you rub a glass rod with a piece of silk, the rod becomes positively charged. This means that

• friction destroyed electrons in the rod.
• the silk has become negatively charged.
• protons have moved to the rod.
• glass attracts more protons.

Multiple Choice

Objects that have opposite charges

• are attracted to each other, and the force between the objects pulls them together.
• are attracted to each other, and the force between the objects pushes them apart.
• are repelled by each other, and the force between the objects pulls them together.
• are repelled by each other, and the force between the objects pushes them apart.  

Multiple Choice

Is it possible to CREATE electrons?

• Yes, that's what static electricity is.
• No, you can move them, but they are never created or distroyed.
• Sometimes, it depends on the voltage.
• Sometimes, it depends on the element.

Multiple Choice

If you added a can of Coke (20^oC) to a fridge (5^oC), at what temperature would heat stop moving?

• when the coke is at 10 degrees and the fridge is at 5 degrees.

• When the coke is at at 6 degrees and the fridge is at 6 degrees

• When the coke is at at 5 degrees and the fridge is at 15 degrees

• When the coke is at at 20 degrees and the fridge is at 5 degrees

Multiple Select

Electricity happens with the flow of

• electrons.

• water

• sand

Multiple Choice

Which of the following an insulator?

• copper
• wood
• silver
• salt water

Multiple Choice

Lightning is _____.

• a buildup of neutrons
• harmless
• a high-voltage electric current
• a large discharge of static electricity

Multiple Choice

This is an example of a _______ circuit

• open
• series
• parallel
• square

Multiple Choice

What happens to the temperature if I add ice cubes to a glass of soda

• The heat transfers from the coke to the ice

• The heat transfers from the ice to the coke

Multiple Choice

If the Voltage is increased and the resistance stays the same, Current will

• Increase
• Decrease
• Stay the same
• Not enough info

Multiple Choice

In a series circuit, which of the following is the same throughout the circuit?

• Resistance
• Voltage
• Current
• Power

Multiple Choice

What would be the effect on the particles if more heat is supplied to the system?

• They would slow down
• They would stop moving
• They would speed up
• There would be no effect

Multiple Choice

What is current measured in?

• Ω (Ohms)
• V (Volts)
• A (Amps)
• W (Watts)

Multiple Choice

What does power mean?

• Joules transferred per second
• Electron flow per second
• Speed of electrons
• Electron energy

Multiple Choice

Two objects have different temperatures. Object A has a temperature of 42 degrees and Object B is 37 degrees. Which direction should the energy transfer between Objects A and B?

• From Object A to Object B

• From Object B to Object A

• Energy will not transfer

• Energy will transfer both directions

Multiple Choice

What is the unit of power?

• Ohms

• Volts
• Amps
• Watts

Multiple Choice

A circuit with 3 resistors, 20 Ohms, 10 Ohms, and 20 Ohms are in series. What is the total resistance?

• 43 Ohms
• 50 Ohms
• 60 Ohms
• 33 Ohms

Multiple Choice

A high specific heat means...

• It heats up quickly with energy added
• It requires more energy to change temperature

Multiple Choice

Current is...

• moving protons
• moving electrons
• measured in volts
• measured in ohms

Multiple Choice

Resistance is...

• What "slows down" electrons
• What "speeds up" electrons
• Moving electrons
• What "pushes" electrons

Multiple Choice

What characteristics impact resistance of a material?

• Thickness 
• Temperature
• Length
• All of these

Multiple Choice

If the voltage stays the same, but the resistance goes up, the current will....

• increase (speed up)
• decrease (slow down)
• stay the same

Multiple Choice

What size resistor would produce a 3 Amp current flow with a 12 Volt battery

• 1 Ohm
• 3 Ohms
• 4 Ohms
• 12 Ohms

Multiple Choice

Radiation is a method of thermal energy transfer that moves -

• through empty space.
• when objects touch.
• only through solids.
• in the motion of fluids.

Multiple Choice

An example of a situation in which an egg is receiving thermal energy through convection -

• The egg is kept warm by its mother in the nest.
• An egg cracked on a hot sidewalk starts to cook.
• The egg is hard boiled in a pot of water.
• A metal pan on the stove fries the egg.

Multiple Choice

What unit do you use to measure Thermal Energy?

• J/Kg ºC
• Kg
• ºC
• J

Multiple Choice

The accumulation of excess electric charge on an object is called

• Static electricity

• Electric discharge

• Resistance

• Current electricity

Multiple Choice

What was the change in temperature resulting from this heat transfer in degrees Celsius?

• 4.5
• 6.0
• 5.5
• 7

Multiple Choice

This type of thermal energy transfer can take place in fluids (liquids & gases). Rising of warmer fluid and sinking of cooler fluid forms a current.

• conduction

• convection

• radiation

Multiple Choice

If you added ice (0^oC) to a glass of water (15^oC) how would the heat move between the ice & water?

• from the ice to the water

• from the water to the ice

Multiple Choice

An object through which electrons can easily flow is called a(n) ___________.

• Conductor
• Insulator

Multiple Choice

Specific heat is

• The amount of thermal energy needed to raise the temperature of 1 kg of a substance by 1 degree celsius

• The amount of kinetic energy needed to raise the temperature of 4 kg of a substance by 3 degrees Fahrenheit

• The amount of heat required to raise 10 mg of a substance by 40 degrees celsius

• The amount of temperature to raise 1 kg of a substance by 1 degree Kelvin

Multiple Choice

If a substance needed a lot of energy to raise the temperature by 1 degree Celsius, its specific heat is

• Non-existant

• Low

• Undeterminable

• High

Multiple Choice

The molecules of a liquid vs. a solid....

• Move slower in a liquid.
• Move slower in a solid.

Multiple Choice

An object becomes charged when the atoms in the object gain or lose

• electrons
• protons
• neutrons
• all of the above

Multiple Choice

To turn a liquid into a gas, you _____ energy.

• Add
• Remove

Multiple Choice

There are four cups of hot cocoa. The cup sizes are shown. The temperature of the cocoa in each cup is 25 degrees celsius. Which cup has the MOST thermal energy?

• Large cup (Trenta)
• Small cup (Tall)
• Venti
• All three are the same temperature so they have same thermal energy

Multiple Choice

A region around a charged particle that can exert a force on another charged particle is called an

• electric pulse.
• electric charge.
• electric force.
• electric field.

Multiple Choice

Water has a specific heat of 4184 J/KgºC.  Wood has a specific heat of 1760 J/KgºC.  What material needs more energy to raise the temperature 1ºC

• Wood
• Water
• Both are the same

Multiple Choice

What is resistance measured in?

• Ω (Ohms)
• V (Volts)
• A (Amps)
• W (Watts)

Multiple Choice

A measure of the average kinetic energy of the individual particles in an object is called:

• thermal energy
• conduction
• convection
• temperature

Multiple Choice

What letter is used to represent specific heat capacity?

• H

• P

• C

• T

Multiple Choice

What  is the formula to calculate heat energy required to raise the temperature of any substance?

• Q=mc∆t
• Q=mc
• Q= ½mv
• m=QC

Multiple Choice

The specific heat of platinum is 0.133 J/g°C. How much heat(Q) is released when a 10 g piece of platinum cools from 100°C to 50°C?

• 66.5 J

• 665 J

• 0.0266 J

• 0.665 J

Multiple Choice

A pot of 2400g of water at a temperature of 25˚C is heated on a stove until the water boils (100˚C).  The specific heat of water is 4.18 J/(g˚C).
Determine the heat energy needed to heat the water in the pot to boiling.

• 133.76J
• 43,062.2J
• 752,400J
• 1,003,200J

Multiple Choice

What is resistance measured in?

• Ω (Ohms)
• V (Volts)
• A (Amps)
• W (Watts)

Multiple Choice

Copper, Stainless Steel, Carbon Steel, and Zinc were all heated using the same thermal energy.  What material would be the coolest after being heated?

• Copper
• Carbon Steel
• Zinc
• Stainless Steel

Multiple Choice

The specific heat(c) of copper is 0.39 J/g °C. What is the temperature change(∆t) when 100 Joules of heat(Q) is added to 20 grams?

• 12.82 °C

• 24.12°C

• 1.95 °C

• 5128 °C

Multiple Choice

The condition where two substances in physical contact with each other exchange no heat energy. They are said to be the same temperature.

• Thermal Energy

• Cooler to Warmer

• Energy Transfer

• Thermal Equilibrium

Multiple Choice

This circuit has a 24 volt battery and the resistor is 8 ohms. How many amps are running through the circuit?

• 3 Amps
• 192 Amps
• 2 Amps
• 4 Amps

Multiple Choice

heat always travels from _____ to ______ objects

• hot to cold
• cold to hot
• cold to cold
• hot to hot

Multiple Choice

Conduction can only occur between two objects when –

• one object is less dense than the other.
• both objects are in physical contact with each other.
• one of the objects is made of a metal.
• both objects are exactly the same temperature.