A heat engine receives heat from a hot reservoir and exhausts some heat to a cold sink. What happens to the remaining energy?

It is stored as internal energy inside the engine It is converted to mechanical work It is radiated as light It is converted to electrical energy by the hot reservoir

In the correct sequence, what are the four strokes of a four-stroke internal combustion petrol engine?

Compression → Intake → Exhaust → Combustion Intake → Combustion → Compression → Exhaust Intake → Compression → Combustion (power) → Exhaust Combustion → Compression → Intake → Exhaust

How does a diesel engine ignite its fuel, and why does this make it more efficient than a petrol engine?

Diesel uses an electric glow plug that heats the cylinder before each stroke Diesel uses compression ignition — the air is compressed so much it becomes hot enough to ignite the fuel, allowing a higher compression ratio and therefore higher efficiency Diesel has a higher octane rating than petrol, so it burns at a lower temperature Diesel engines use spark plugs but fire them at higher voltage than petrol engines

In a steam turbine power station (Rankine cycle), what is the correct sequence of the working fluid (water/steam)?

Steam is compressed → heated in a furnace → expanded through a nozzle → reheated Water is pumped → heated in boiler → high-pressure steam expands through turbine → condensed back to water Water is heated → drives a piston → exhausted to atmosphere → pumped back in Steam is cooled → compressed by turbine blades → ignited in combustion chamber → exhausted

Coal, natural gas, nuclear fission, and concentrated solar power all generate electricity using the same basic mechanism. What is it?

They all use chemical reactions to produce electrons directly They all use compressed air expanded through a turbine They all produce heat that boils water to drive a steam turbine connected to a generator They all use photovoltaic cells energised by different radiation sources

A jet engine operates on the Brayton cycle. What is the correct sequence of processes in a jet engine?

Air is heated → compressed → exhausted → intake Fuel is burned → air is cooled → thrust is generated → compressor runs Intake air is compressed → fuel is burned → hot gases expand through turbine → remaining energy exhausted as thrust Air enters at high pressure → is cooled by fuel → expands → compresses again

A coal power station burns coal with a chemical energy content of 10,000 MJ per tonne and operates at 38% efficiency. How much electrical energy does it generate from one tonne of coal?

380 MJ 3,800 MJ 6,200 MJ 10,000 MJ

Why can a combined-cycle gas turbine (CCGT) plant achieve ~60% efficiency when a simple gas turbine plant achieves only ~35-40%?

CCGT uses a better fuel (hydrogen) instead of natural gas, which releases more energy CCGT compresses the gas twice before combustion, extracting more energy The hot exhaust from the gas turbine, which would otherwise be wasted, drives a second steam turbine, recovering additional energy from the same fuel CCGT eliminates the cold sink entirely, allowing 100% of heat to become work

In an internal combustion engine, what is the purpose of the compression stroke?

To cool the air-fuel mixture so it burns more slowly and smoothly To compress the air-fuel mixture so that combustion releases more energy and the engine achieves higher efficiency To remove exhaust gases left over from the previous combustion event To draw fresh fuel from the fuel tank into the cylinder

Cooling towers at a power station reject heat to the atmosphere. From a thermodynamics perspective, this waste heat is:

A design flaw that better engineers could eliminate entirely Unavoidable — the Second law requires that some heat be rejected to a cold sink for any heat engine to produce work Caused only by friction in the turbine bearings Primarily a consequence of using water as the working fluid instead of a more efficient refrigerant

A turbocharger on a car engine takes exhaust gas energy and uses it to compress the intake air. What performance benefit does this provide?

Cooler intake air reduces the risk of engine knock at high speed Denser intake air allows more fuel to be burned per stroke, increasing power output without increasing engine displacement The turbocharger converts exhaust heat directly into electrical energy to charge a battery It recirculates unburnt fuel back into the cylinder for a second combustion event

Why do nuclear power plants operate at lower thermal efficiency (~33%) than modern gas turbines (~40%+), even though nuclear fuel releases far more energy per kilogram?

Uranium fuel releases energy too slowly for high-temperature operation Nuclear plants use heavy water instead of steam, which has a lower specific heat capacity Nuclear reactors are limited to lower steam temperatures due to material constraints, so Tc/Th is less favourable than in gas turbines Nuclear fission releases 33% of its energy as neutrinos that cannot be captured