Leaving cert. Physics - Heat

What is meant by the temperature of a body?

The Temperature of an object is a measure of the hotness or coldness of that object.

What does a thermometer measure?

Temperature.

What is the unit of temperature?

The SI unit of temperature is the Kelvin (K)

What is heat?

Heat is a form of energy

What is the difference between heat and temperature?

Heat is a form of energy.Temperature is a measure of the hotness of an object.

To calibrate a thermometer, a thermometric property and two fixed points are needed.What are the two fixed points on the Celsius scale?

The melting point ( 0 ) and boiling point (100 ) of water.

Name two scales that are used to measure temperature

Celsius and Kelvin.

Give the equation that defines temperature on the Celsius scale.

T(C) = T(K) - 273

What is the boiling point of water on the Celsius scale?

100 °C

The SI unit is named in honour of Lord Kelvin. What is the temperature of the boiling point of water in kelvin?

273.15 + 100 = 373.15 K

Explain the term thermometric property.

A thermometric property is a property which changes measurably with temperature.

Name the thermometric property used in a mercury thermometer.

Length (or volume) of the liquid.

What is the thermometric property of a thermocouple?

Its emf

Name a thermometric property other than emf.

Length, pressure, volume, resistance, colour.

Name one other type of thermometer and state its thermometric property.

Thermistor - resistance, Thermocouple - emf, Liquid crystal - colour

Why is it necessary to have a standard thermometer?

Different thermometers have different thermometric properties at the same temperature.

Will every thermometer agree at the same temperature?

No, because different thermometric properties vary differently with changing temperature

What is a thermocouple?

If two different metals are joined together to form a complete circuit and the two junctions are maintained at different temperatures a small emf (voltage) appears in the circuit. The emf can be measured using a voltmeter. The size of the emf varies with the temperature difference between the junctions.

Name four everyday practical thermometers

Clinical thermometers, oven thermometers, boiler thermometers , the temperature gauge in a car

Define specific heat capacity.

Specific heat capacity is the heat energy required to raise the temperature of 1 kg of a substance by 1 K

Define specific latent heat .

Specific latent heat is the heat energy required to change the state of 1 kg of a substance without a change in temperature.

What is heat?

Heat is a form of energy

Name three methods by which heat can be transferred.

Conduction, convection and radiation.

What is meant by conduction?

Conduction is the movement of heat energy through a substance by the passing on of molecular vibration from molecule to molecule, without any overall movement of the substance.

Why are the pipes in the solar panel usually made from copper?

It is a good heat conductor.

What is meant by the U-value of a structure?

The U-value of a structure is the amount of heat energy conducted per second through 1 metre squared of that structure when a temperature difference of 1 kelvin is maintained between its ends

What is the effect of increasing the U-value of a structure?

It means that the heat conductivity of the structure is increased

What is the SI unit of U-value?

The watt per metre squared per kelvin (W/M-2/K-1)

Give two ways in which the U-value of a house can be reduced.

Fibreglass in attic, insulation in cavity wall, double glazing, carpets

What is radiation of heat?

This is the transfer of heat energy from one place to another in the form of electromagnetic waves.

Why is insulation used to surround the bricks?

To prevent heat-loss.

Name a material that could be used as insulation in a storage heater.

Fibre glass / rock wool / cotton wool.

What is convection?

Convection is the transfer of heat through a fluid by means of circulating currents of fluid caused by the heat.

Why is the heating element of an electric kettle near the bottom?

Because hot water rises.

Explain how the storage heater heats the air in a room.

The heater heats the air which is beside it. This hot air then rises and is replaced by cold air. This process then gets repeated.

Why does warm water rise to the top of the solar panel?

The water expands when heated and therefore has a lower density and gets replaced by water which has a higher density (cold water). This is convection.

How does and electric toaster heat bread?

An electric toaster heats bread by convection and radiation.

What is the solar constant?

This is the average amount of the Sun's energy falling per second perpendicularly on 1 metre squared of the Earth's atmosphere.

What is the difference between convection and radiation as a means of heat transfer?

Convection requires a medium, radiation does not.

Why are the pipes in the solar panel usually painted black?

Black is a good absorber of radiation.

Storage heaters have a large heat capacity. Explain why.

They are heated only at night but must release energy slowly during the day.

Why does the temperature of an athlete reduce when she perspires?

As the water evaporates it takes heat energy from the body.

Define heat capacity

The heat capacity of an object is the amount of heat energy needed to change its temperature by 1 kelvin

Define specific heat capacity

The specific heat capacity of a substance is the amount of heat energy needed to change the temperature of one kilogram of that substance by one kelvin.

What is a storage heater?

A storage heater consists of an electric heater surrounded by bricks of high specific heat capacity

Define latent heat

The latent heat of a substance is the heat energy needed to change its state without a change in temperature

What is the SI unit of latent heat?

The joule per kilogram

What is a heat pump?

A heat pump is a device that transfers heat from a cooler region to a warmer one