Energy and the Environment Exam

relationship between energy and power

Energy is the capacity to do work, while power is the rate at which that energy is transferred or work is performed.

Power= energy/time

per capitia gdp and energy consumption

More gdp= more money used

But other factors such as geography, size, culture, and lifestyle effect energy usage

energy intensity

Measure of how much energy a society uses relative to its economic scale 

Equation: energy expended/money spent 

Exponential growth 

Stat term that a value doubles over a period of time: U.S energy production has grown exponentially since the 1800s

Goal of energy intensity

To overall reduce it but this is hard since changes to the nations GDP would have to take place 

Population and energy usage

Population is expected to increase although slower than anticipated but this is hard to combat if reduce energy consumption 

Energy

The capacity to do work: makes stuff happen

Units are in joules 

work

transfer of energy

W=F(N)xD(m)

power

Rate of energy use in a given amount of time

power=j/s or energy/time

Watts

joules/seconds

What are kWh

Power(kilowatts)xtime(hours)

Power of a human

roughly around 100 watts(lab #2)

1 kWh= 3,600,000 joules

1000 watt oven running for 2 hours= 2kWh

per capita energy consumption in the US

It’s a lot higher than average compared to most countries 

kenetic energy

energy in motion

Equation: ½ MxV2

gravitational potential energy

MxGxH
force=mass times acceleration

Gravity=10 m/s 

chemical potential energy

Energy content of fuels

Pec= M(fuel) x energy constant

potential energy

stored energy

• Something that pushes or pulls an object

• Eletromagnetic force: creates magnetic PE

thermal energy

Energy associated with changes in tempature of an object  

Q = mcΔT

m=mass

c= specific heat

T= t2-t1

what does 1 newton=

kg m/s2

heat capacity

Property that relates energy input to tempature change in material. How much energy is required to heat up? temperature

first law of thermodynamics

energy is neither created or destroyed. Just transfered. All based on accounting

Equation e=q-w

Q=heat

-w=work done by system 

ex. Kicking a ball is doing some work(W)

electricity

electrons moving through a conductor

Ex. Battery having positive and negative charges meeting up

current

rate of flow of charge

electrical power

current x voltage

ex. 1 amp x 12 volts= 12av or 12 watts

ΔE

a change in internal system energy

tempature

measure of the average thermal molecule

ΔE: Measured in units of kelvin or celcouis

heat

energy that is flowing as a result of a temperature difference

Ex. Always flows from hot to cold

conduction

moving heat from one atom to another

Heat transfer depends on thermal conductivity of the surface

Ex. Aluminum is more conductive than air

Convection

Heat transfer by moving(hot or cold) fluid from one place to another 

Radiation

Transfer of heat through electromagnetic waves. Longer wavelengh=colder temp 

Ex. Sun is hotter therefore emits more radiation at a shorter wave lengh 

radiation equation

P=AεσT4

σ: (sigma) is the Stefan-Boltzmann constant

2nd law of thermodynamics

In any spontaneous process in a system, the total entropy (a measure of disorder or energy dispersal) will always increase or stay the same, never decrease

entropy

measure of how disordered a system is. This principal can be applied to how heat engines work

heat engine

a device that converts less ordered thermal heat into ordered mechanical energy

efficiency

You can go from a less ordered to a more ordered state but that is not 100% efficient

thermodynamic cycle

why we have two resivours in cycle

Because for the cycle to reset a cold tempature needs to offset the hot

General efficiency equation

e= useful energy out / energy in

Maximum thermodynamic efficiency

emax = (Th-Tc)/Th)

refrigerators

Transfers heat from inside to outside through coils

heat pump

Same as refrigeration but can do the opposite cycle: taking 

carnot e for heat pump

emax=th/th-tc

emax=tc/th-tc

Max e for heating(COP)

Same as regular efficiency equation but in kelvin