thermodynamics

Question 1

when is work done positive

Answer 1

when it is work done by the gas

Question 2

W=PV, what is the condition for this equation

Answer 2

pressure is constant

Question 3

isobaric meaning

Answer 3

constant pressure
Q=U+PV

Question 4

isothermal

Answer 4

constant tempereture
Q=U

Question 5

adiabatic

Answer 5

no heat transfer therefore any work done directly effects internal energy
-W=U

Question 6

difference between isothermal and adiabatic graphs

Answer 6

adiabatic is a steeper curve

Question 7

what are the fazes of a four stroke engine

Answer 7

induction
compression
power
exhauset

Question 8

induction faze

Answer 8

piston moves down the cylinder drawing air petrol mixture into the cylinder as the volume increases. The pressure remains at atmospheric

Question 9

compression faze

Answer 9

the inlet valve is closed and the piston moves back up doing work on the gas. This is an adiabatic process.
almost at the end of the stroke the spark plug fires causing temperature and pressure of gas to rise rapidly at constant volume

Question 10

Power

Answer 10

high pressure forces the piston back down the cylinder so work is done by expanding gas
- exhaust valve opens and pressure reduces to atmospheric

Question 11

exhaust

Answer 11

piston moves up the cylinder forcing burnt gases through open exhaust value whilst the pressure remains constant

Question 12

assumptions of a theoretical PV diagram

Answer 12

-pressure and temperature change instantaneously
- expansion and compression happens adiabatically
- no friction

Question 13

induction vase in diesel

Answer 13

same as petrol however only air is drawn in

Question 14

compression for a diesel

Answer 14

air is compressed with no fuel inside, this causes large temperature increase which ignites diesel without spark plug, diesel is injected as a fine spray by a fuel injector

Question 15

expansion and exhaust fases for a diesel

Answer 15

same as petrol