physics - thermal energy

Question 1

What is a system?

Answer 1

A system is an object or group of objects

Question 2

What are the various ways in which energy can be stored in a system?

Answer 2

-thermal store
- elastic store
- kinetic store
- gravitational store
- chemical store
- electrostatic store
- nuclear store
- magnetic store

Question 3

How can energy transfers take place?

Answer 3

Energy transfers happen because of: forces doing work,
- a flow of an electrical current, heating, light, radiation, and sound waves

Question 4

What is internal energy?

Answer 4

the total kinetic and potential energy of all the particles that
make up a system.
The molecules’ kinetic store is related to how fast they are moving, and the molecules’ potential store is related to how far apart they are (their bonds).

Question 5

When an object is heated what
happens to its internal energy?

Answer 5

When a substance is heated the energy transferred to it increases the internal energy of the system. This either raises the temperature of the system (increases the kinetic energy of the particles) or causes a
change of state (increases the potential energy of the particles)

Question 6

How is the temperature of a gas
related to the average kinetic energy of its molecules?

Answer 6

The molecules of a gas are in constant random motion. As the temperature of a gas increases the average kinetic energy of the molecules also increases,

Question 7

What do we mean by specific heat capacity?

Answer 7

the energy (in J) needed to increase the temperature of 1 kg
of a substance by 1 0C

Question 8

How can we measure the specific heat capacity of a substance accurately?

Answer 8

The mass of the metal block is measured using a balance.
The immersion heater is connected to a power supply and transfers energy to the block, this energy is
measured using a joulemeter.
The insulation reduces the amount of energy that is transferred to the surroundings, this reduces uncertainty in the value for the specific heat capacity. The specific heat capacity is calculated by:

Specific heat capacity =

energy transferred/
mass x change in temperature

Question 9

What is accurate data?

Answer 9

Accurate data is data which is close to the true value

Question 10

What is precise data?

Answer 10

Precise data is data in which repeated measurements show very little spread about the mean value.

Question 11

What is reproducible data?

Answer 11

If another person can get the same result with the same, or different method/equipment, then the data is reproducible

Question 12

What is repeatable data?

Answer 12

If the same person can get the same result with the same equipment and method then the data is repeatable.

Question 13

What is random uncertainty?

Answer 13

Random uncertainty causes measurements to be spread around a mean value.

Question 14

What is systematic uncertainty?

Answer 14

when measurement is always too high or too low for each repeat.

Question 15

What is a zero error?

Answer 15

when a measuring instrument reads a value when it should say zero.

Question 16

How do you reduce unwanted thermal energy transfers?

Answer 16

e.g. by lubrication (when parts move) and thermal insulation

Question 17

What does the thermal conductivity of a
material tell us?

Answer 17

tells us the rate at which energy is transferred through the
material when there is a temperature difference either side of it.

Question 18

What do we mean by rate of cooling?

Answer 18

the temperature decrease per second.

Question 19

What factors affect the rate of cooling of a building?

Answer 19

thickness of the building’s walls and the thermal conductivity of its insulation

Question 20

What do we mean by specific latent heat?
(substance, fusion and vaporisation)

Answer 20

• specific latent heat of a substance is the amount of energy (in J) required to change the state of 1 kg of the substance with no change in temperature.
• The specific latent heat of fusion is the amount of energy required to change the state of 1 kg of a substance from solid to liquid with no change of temperature.
• The specific latent heat of vaporisation is the amount of energy required to change the state of 1 kg of a substance from liquid to gas with no change of temperature.