PRELIMINARY STAGE 2024
Contest 40
Chemu SHS: 43 points (Winner)
Our Lady of Mt. Carmel Girls’ SHS: 33 points
Manya Krobo SHS: 28 points
Contest 41
Adiembra SHS: 34 points (Winner)
St. Paul’s Senior High & Minor Seminary: 24 points
Biakoye Community SHS: 07 points
Contest 42
Swedru Secondary School: 49 points (Winner)
Edinaman SHS: 29 points
Techiman SHS: 23 points
ROUND 5 - RIDDLE
RIDDLE
I characterize a thermal state.
I occur in systems in thermal contact with each other.
I'm the state of a collection of systems in which each subsystem has the same temperature as any other subsystem.
I obtain in the situation where no net heat flows between systems in thermal contact.
Who am I?
ANSWER:
THERMAL EQUILIBRIUM
EXPLANATION:
Systems in thermal contact are in thermal equilibrium when they are all at the same temperature.
No net heat then flows between them.
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PRACTICE QUESTIONS
1. RIDDLE:
I am a law of thermodynamics.
I was named after the first and second laws, but put before them.
I say two bodies each in equilibrium with a third are in equilibrium with each other.
I make thermometers meaningful.
I allow temperature to be defined.
My number comes before one.
Who am I?
ANSWER: ZEROTH LAW
EXPLANATION:
If A and C, and B and C, are in thermal equilibrium, then A and B are too.
2. RIDDLE:
I am a physical quantity.
I am equal for bodies in thermal equilibrium.
Heat flows from a body with more of me to one with less of me.
My SI unit is the kelvin.
A thermometer measures me.
I measure the average kinetic energy of molecules.
Who am I?
ANSWER: TEMPERATURE
EXPLANATION:
Temperature decides the direction of heat flow; bodies at the same temperature are in thermal equilibrium.
3. RIDDLE:
I am energy in transit.
I flow because of a temperature difference.
I stop flowing at thermal equilibrium.
I flow by conduction, convection and radiation.
My SI unit is the joule.
I always flow from hot to cold on my own.
Who am I?
ANSWER: HEAT
EXPLANATION:
Heat is energy transferred because of a temperature difference.
4. RIDDLE:
I am a partition between two systems.
I let heat pass through me.
Two systems separated by me reach thermal equilibrium.
A thin metal sheet is a good example of me.
I am the opposite of an insulating partition.
My name comes from the Greek for 'through heat'.
Who am I?
ANSWER: DIATHERMIC WALL
EXPLANATION:
A diathermic wall allows heat exchange, so the systems on each side come to the same temperature.
5. RIDDLE:
I am a partition between two systems.
I allow no heat to pass through me.
Systems separated by me can stay at different temperatures.
A vacuum flask tries to be me.
Processes behind me exchange no heat.
My name comes from the Greek for 'not passable'.
Who am I?
ANSWER: ADIABATIC WALL
EXPLANATION:
An adiabatic (insulating) wall prevents heat exchange.
6. RIDDLE:
I am a device.
I come into thermal equilibrium with the body I touch.
My reading is then the body's temperature.
The zeroth law makes me trustworthy.
I may use mercury, alcohol or a thermistor.
My name means 'heat measurer'.
Who am I?
ANSWER: THERMOMETER
EXPLANATION:
A thermometer reaches thermal equilibrium with an object and so shows its temperature.
7. RIDDLE:
I am the sum of the kinetic and potential energies of all the molecules of a body.
My SI unit is the joule.
Two bodies in thermal equilibrium need not have equal amounts of me.
A bath of warm water has more of me than a cup of hot water.
For an ideal gas I depend only on temperature.
In the first law, my change is ΔU.
Who am I?
ANSWER: INTERNAL ENERGY
EXPLANATION:
Internal energy depends on the amount of matter as well as its temperature, so it need not be equal at equilibrium.
8. RIDDLE:
I am a quantity of a body.
I tell you how much energy raises its temperature by one kelvin.
My SI unit is the joule per kelvin.
A large body of water has a lot of me.
I decide how much a body's temperature changes as it approaches equilibrium.
I equal mass times c, the value per kilogram.
Who am I?
ANSWER: HEAT CAPACITY
EXPLANATION:
Heat capacity $C = mc$; a body with large $C$ changes temperature little.
9. RIDDLE:
I am an experimental technique of calorimetry.
A hot body and a cold one are put together until they reach equilibrium.
I use 'energy lost equals energy gained'.
I need a well-insulated calorimeter.
I measure specific heat capacities.
My name says things are combined.
Who am I?
ANSWER: METHOD OF MIXTURES
EXPLANATION:
At equilibrium the heat lost by the hot body equals the heat gained by the cold one.