P7.1 Energy

Question 1

What is law of conservation f energy

What is a closed system..

Answer 1

Energy can not be created or destroyed. Only transferred between different energy stores.

In a closed system energy does not change not effected by anythint

If you in a closed system, this will be true , there is no net change. No external forces act on, nothing goes in or nothing goes out

Question 2

Remember kWh is just

Answer 2

Energy transferred

So when they say power if 2 kHz used 2 hours

Just power = word down / time

Question 3

What are the different energy stores

Answer 3

Chemical - coal
- thermal- anything hot
- kinetic - anything moving
Elastic- spring
- gravational- anything held up
- nuclear hydrogen in sun ?, ATOMIC RADII THAT RELEASE ENERGY IN REACTIONS

• electrostatic : twomoppsote charges held apart
  Magnetic - magnet

Question 4

In energy analysis what must you consider and assume?

Answer 4

You must consider that some of the energy when changing stores actually can get transferred to thermal stiess of surroundings because of FRICTION, SOUND, or AIR RESITSNCE / DRAG

Therefore your final answer may be higher then expected because you assumed no energy was dissipated, but this it was closed.

Question 5

How to do energy analysis

Like light fillamenr example?

Answer 5

Say you stationary car in race. Your chemical high but kinetic store low

As you start, the Chicago gets lower as kinetic gets higher. By the end the kinetic high and chemical low.

If you add them up, it should be the same in energy is conserved…

2)here chemical energy form battery transferred to thermal energy of light

Question 6

Another situation?

Car is moving , surroundings relatively cool. Car comes to stop quickly, what happens

Why can’t you calculate the temp of the surroundings when car stops

Answer 6

Kinetic energy high, thermal energy of surroundings low

Then kinetic STORE (NOT ENERGY)zero, but due to friction thermal STORE high. Not completely, because some would have escaped as sound, etc

You can’t calculate the temperature of the surroundings because it changes so quickly?

Question 7

How to do calculations with different energies? IMPORTSNT AND

Just remember about real situations?

Answer 7

Just put two equations next to each other, cancel out anything on both sides (like mass) or give them a random value, and then re arrange for one thing. Pretty cool . EQUATIONS RELATE TO EACH ORHER

Real situations are not closed systems… thus energy transfer won’t be the same

Question 8

More realistic

For example

Answer 8

Include other energy stores and what probably is going on, like thermal. And also sound

Sun glasses are falling, kinetic energy is high, and due to resistance thermal store is meh

Then it hits ground and kinetic iz zero but thermal is high

Question 9

How do you pay for abill

What is KWH anyways

Here what unit of time?

Answer 9

Money= kWh x rate per kWh

Basically they given electrical power rating which tells you how much energy they transfer between stores in a certain time

Power= word done /time so thus 1000=x/3600
And x=360000000 joules

HOURS NOW

Question 10

What happens to the surroundings of a wire as you heat it up

Also what is light represented by?

Answer 10

Current to wire increases the heat of it, thermal store increase and this energy is wastedi

This always happens In an electrical circuit

2) thermal energy like filament lamp

Question 11

How do energy get transferred in temp

Answer 11

When a temperature difference happens, a transfer of energy is produced which happens from hot to cold until its equilibrium

Question 12

What does energy being dissipated mean

IMPORTSNT

Answer 12

Basically once energy is used it transferred to surroundings

Thus

When energy is transferred to the surrounding such that it is not easily accessible again and not in a store that is useful

Question 13

How to reduce energ dissipated due to friection by and heating by

Answer 13

Lubrication for friction (oil just common sense)

Insulation for heating (like foam)

Question 14

How do conditions affect ways in which heating is lost in houses

Thickness and thermal conductivity

What is thermal conductivity of a material?

Answer 14

1) thicker wall, lower rate of temp to drop
2) this is TELLS you the rate at which means energy is transferred through a. Wall with 1m2 area, 1m thickness and a temperature difference of 1 °.

The HIGHER THE thermal conductivity, the more energy lost, so greater rate drop of temperature. Therefore lower thermal conductivity Ed are used in house

Question 15

Efficiency equation

Answer 15

= useful energy/ total energy

Efficiency of 0.5 but 50% efficient

Never fully efficient energy always dissipated

Question 16

How to draw SANKEY diagram like what to make sure

What does arrow represent

Answer 16

Sanity diagram show where energy goes, width of arrow = AMOUNT IF ENERGY TRANSFERRED

Question 17

How to increase efficiency

3 ways

Why cant you just say use dissapted energy

Answer 17

• easy
  1) insulation
  2) lubrications
  3) make devices that reduce unwanted energy waste
• Develop new technology like LEDs that are just better

More efficient = less power.

You can’t say find something useful with wasted energy because it gets dissapated there is. I thing useful with it as it’s hard to transfer back

Question 18

When estimating what number do you pick

dismtee of a wheel?

Answer 18

Magnitude ofn10s

remember diameter then need to do circumeference

Question 19

Remmeber some key speeds

Answer 19

A

Question 20

Thinking distance, braking and stopping distance

What affects thinks and braking.

What about speed makes it 20mph in areas with house

Answer 20

Thinking distance = time x speed
= reaction time x speed (so like 0.2 but it depends)
- what affects this is your reaction time so sleepy, caffeine , intoxicated, distractions, drugs
- and speed of car

Braking distance = v2 - u2 = 2AD, solve for d
@ affected by mass in car
- brake grip strength
- condition of roads so slippery or what

Because braking distance is very dependent on speed , then built up areas are 20 but not is 30

Stopping = thinking and braking

Question 21

Reaction time test?

Answer 21

Rule drop test
@) Hand Open, get someone else to drop a ruler. Make sure Finger in line with zero
2) drop ruler, calculate distance
3) find the final velocity using equation of motion
4) Find AVERAGE SPEED, which is final + inital velocity /2,
then do next step

You know s = d/t
And if speed = final velocity and distance = distance dropped, then done

Question 22

What does 3G mean

Answer 22

If you experience a 3G force, you experience a force that’s 3 x gave its x your mass, or 3 x your weight

Question 23

Okay so how do you explain why when you multiply speed by 2, the braking distance increases by
4

Also what about relationship between thinking distance and speed

Answer 23

For a car to stop, work must be done by the brakes that is = to all of the energy in the car therefore

0.5 x Mx V2 = FxD

As you can see, if you multiply msss by 2, the braking distance is mutliokied by 2, but if you multiply v byb2, the braking happens by 4

2) since distance = speed x time, multiply speed by 2, distance by 2 they are proportional

Question 24

Renewable vs non renewable

Answer 24

Non renewable take millions of years to form, renewable fast

Renewable= biofuels, solar, hydro, wind, geothermal

Non renewable, nuclear (diesn’t contributes to global), hyrdocarbins etc

Problem with non renewable affect climate
Problem with renewable expensive ti set up, things like wind turbines ruin the view, and only work when certain conditions met such as solar and windy etc.

Building these require a lot of energy too

Question 25

Why energy sources change dived time?

Problem of energy supply
like what happen to renwable prices
what governemnt consider when picking renwable

also for renwable

Answer 25

Population expand from 1 billion to 7 billion today so more energy

More devices using fuels used

Non renewable finite and run out , and as basic rule of supply and demand as supply lower deman increase and expense too

Burning fossil fuels produce co2 contribute to climate change , leading to more sea level rising and weather pattern and food disruption

Govemnemt tryha. Increase renewable as a streust but consider price, effect in environment to set them up (energy used), contribution to climate change and how worth it is it compared to the effect it brings
also like geothermal cant bare be used everywhere

Question 26

Ac / a v uk

Frequency and voltage

Answer 26

230 v with 50 hz = mains

DC comes from batteries and the marinas, AC comes when alternating of happens creating ac, but in the national grid

Question 27

National grid thing

Transformers

Answer 27

National grid is just grid of wires network from everywhere

higher currents means p= i2r somire power is lost, meaning more fuels needed and energy overall- eneegu transferred to surroundings and wires heat up.
- wasted energy costs more, much cheaper to step up and thus NATIONAL GRIDE EFFICIENT WAY TO TRASNPORT CURRENT

thus step UP used from geberator to grid network so the plwer lost is minimal ans xosn step down to homes, from like 400000 to 230

this is possible using ratios of cables and idea that power= power2

Transformers change the old of wires to reduce the heating effect and therefore MORE EFFICENT way to distribute electricity .

When current flows, then heat of wire increase- inefficient as resistance increase too,

You transfer a power = vI. High powers must be transferred, so either high I or high V. But high I will increase to high temp and is inefficient . Power dissipated = I2 R that’s why.

• so transformer used to step up / down pd to make it effiecnet.

Question 28

Okay so transformers equations and more understanding

Answer 28

High current used means more power lost, so more power will need to be generated to accumulate- resulting in more fuels being used er. Therefore high voltage used , then low voltage.

Power coil1= power coil 2, where none is lost and temp doesn’t increase
VC= V2C2

Remember when an alternating current is inputted into the primary coil, an alternating magnetic current is formed around it, inducing the iron core with an alternating magnetic field. This carries over to the second coil, and an alternating current is induced in the conductor , base don the coils ratio. More in 1 then 2, step down, more in 2 then 1, step up.

Assume they are almost 100% efficient

Question 29

Wires

What do each do

What colours

What happens in case something bad, how does earth pattern it

what is double insulate

Answer 29

Earth wire = green and yellow
Live wire= BROWN
Natural wire = blue

Live to neutral and earth = 230
Neutral to earth = 0

1) life carries to voltage alternating between - and positive 230. Neutral completes the circuit, out of the wire so 0v. Earth for safety

If live wire becomes loose inside and touches metal casing the casing would become live and is now dangerous, as body is 9v so pd is huge snd current will be big killing you

Therefore earth wire connected to casing so if that happens, current will go to earth wire, and this resistance is low increasing current because v=is, and this melts the fuse. Breaking the circuit, prevent harm. Earth goes to ground connecting circuit there

If it has non conductive casing like plastic don’t need earth wire, as it has casing and non conductive like plastic it’s double insulated

Question 30

What is energy and what is it relation to work done

Answer 30

Energy is the ability of an object to do work

When word is done by an object , energy transfers from the object to something

When work is done by the object energy is transferred to the object

Question 31

How is energy transferred between sources4ways

Answer 31

Mechanically, due to a force acting on it

Electrically with an electric current

Heating with particles where energy go from hot to cold

Heating by radiation , energy transferred by light or sound waves so like sun.

Question 32

How and where is energy lost in house

What about thermal conductivity of ice

Answer 32

Walls floor roof and window

Low so igloos can be warm

Question 33

What is convection
Conduction + how to reduce ? So
Radiation

These are the three ways in which energy is transferred thermal wise

Answer 33

Conduction happens in solids

• hot object has higher kinetic
• this vibrates and collided with other particles adjacent, making them vibrate too. Increase their temp and this happens until temp across object is same

Convection happens in gas and liquid

• idea that particles with more kinetic energy move from hotter to cooler region and take kinetic energy with them
• this means cool air takes its place and circulation of convection currents occur heating evenly
• reduce convection stop movement of air, so like clothes traps air pockets , and so energy conducts slowly and you warm .

3) radiation is where energy is transferred via em wave of infra red which don’t need particles
- hot objects emit more infra cold emit less
- cooler object absorb this infra and temp increase
- black absorb more white less

Question 34

How to reduce nervy loss in house

Answer 34

Loft insulation of FIBREGLASS WOOL

• hot water tank
• double glazing reduces conduction
• thick curtains
• cavity wall insulation- where gaps between wall stops conduction and insulation foam stops convection

THICKER WALLS AND LOWER THERMAL CONDUCTIVITY

• pipes insulate paint white etc

Question 35

Basic energy equations

also force?

Answer 35

P=e/t

GPE= m X G X H

Elastic?= 1/2 spring constant X extension ^2

Kinetic =1/2 mv^2

force = m xa

Question 36

whynis thinking distance bigger in highway code

Answer 36

because used exagerated reaction time

Question 37

now how do engineers reduce firce exerted by crash

what is this force equal to

Answer 37

force = m x a
a revilves time , increase time reduce a and reduce force

the time is collision time. to increase this, you need CRUMPLE ZONES AIR BAGS SEATBELTS TOO, which all deform rsther thsn shatter allowing collison time ti increase.

finally motorway railings also have. the max speed motorway should be 70