Unit 5 Physics Flashcards
Power, Watt, Kilowatt, Megawatt, Gigawatt
the rate of using energy doing work measure in watt (W) = j/s
kilowatt (kW) = 1000 Watt
megawatt (MW) = 106 Watt
gigawatt (GW) = 109 Watt.
Convert Degrees To Kelvin
oC to Kelvin by adding 273.15 K,
kelvin to 0C by subtracting 273.15
Pressure,
Newton Per Meter Squared
liquid/gas exerts pressure in all directions
measure in pascals {Pa] = newton per meter squared {Nm2}
Work Done As Energy Transferred
Work is the measure of energy transfer when a force (F) moves an object through a distance (d). Energy transferred and work done are both measured in joules (J).
force and displacemt
Work done = Force × Distance Moved In Direction Of Force {∆X }
pressure and volume
work done = pressure x change in volume of gas
Efficiency =
Useful Energy Output / Total Energy Input
Ideal Gas Equation
Pv = Nkt n= number of particles k= 1.38 x 10 ^-23 j/l t= temprature
Law Of Conservation Of Energy
The law of conservation of energy states that energy can neither be created nor destroyed - only converted from one form of energy to another. This means that a system always has the same amount of energy, unless it’s added from the outside.
system
the part of the universe whose properties you
are investigating. It is enclosed by a boundary defined
by you, the experimenter.
surroundings
the rest of the universe, outside the system boundary
Internal Energy (U),
The internal energy is the total amount of kinetic energy and potential energy of all the particles in the system. When energy is given to raise the temperature , particles speed up and gain kinetic energy.
∆U=U2 - U1
First Law Of Thermodynamics
(Q = ∆U + W)
heat in = energy change in the system + work out
Qin - Qout = ∆U + W
Isothermal
two bodies in thermal equilibrium
heat can flow in either direction reversibly
0 temperature difference = no net heat transfer
Adiabatic Processes
work input = internal energy gained
-w = ∆U, no energy wasted compressing gas leads to a corresponding temperature rise
Second Law Of Thermodynamics
A natural process can never be reversed in its entirety.
It is impossible to completely change heat into work.
Heat will not flow from a colder body to a hotter one without an input of work.
You cannot reverse the direction of time
Heat Refrigerators Pumps
refrigrators cool and enclosed space and reject heat from the outside
heat pumps draw heat from the ground or outside air and move that heat at a higher tempreture positioning of the heat exchanges
which space is bung contrilled
Maximum Theoretical Coefficient Of Performance (Cop)
minimise temp gapexpand a liquid bevause the volume is small
cut friction of vicous flow losses
keep compression work low
Idealised Engine Cycles
1–2 adiabatic compression – zero heat transfer.
2–3 isothermal expansion – heat absorbed by the system, Qin
3–4 adiabatic expansion – zero heat transfer
4–1 isothermal compression – heat absorbed by the
system, −Qout
For Heat Engine - Efficienty And Maximum Theoretical Efficiency
real engine can achieve a thermal efficiency higher than that of an ideal reversible engine operating between the same temperatures. (If this were not so it would be possible to create a machine that violated the Second Law and moved heat from a colder to a hotter body without doing work.) In practice, engine efficiency is always lower than this because all real engines have irreversible processes that produce less net work output and instead output more heat at the low temperature.
Transfer Of Energy Producing Temperature Change Or Changes Of State,
heat transfers,q, into the system counts as positive; flows out count as negative.
work done by system counts aas positive
direction of heart transfers depends on the tempratures outside the system,
Thermal Capacity,
the number of heat units needed to raise the temperature of a body by one degree.
