Thermal Physics

Question 1

Thermal Energy

Answer 1

• transfer + store of energy
• transferred via conduction, convection, radiation
• increase in temperature = increase in thermal energy

Question 2

States of matter

Answer 2

• solid
• liquid
• gas
• plasma

Question 3

Plasma

Answer 3

• 4th state of matter
• formed when a gas becomes so hot the electrons leave the atom → form ions

Question 4

Solid

Answer 4

• regular lattic structure
• particles vibrate around a fixed position
• closely packed

Question 5

Liquid

Answer 5

• particles can move past each other
• still touching
• move randomly

Question 6

Gas

Answer 6

• particles are spread out
• arranged randomly
• in a constant state of random motion

Question 7

Bonds

Answer 7

Forces acting between particles. Forces in solids are stronger than in liquids + gases

Question 8

Change of State

Answer 8

• solid → liquid = melting
• solid → gas = sublimation
• liquid → solid = freezing
• liquid → gas = evaporation / vaporisation
• gas → solid = deposition
• gas → liquid = condensation

Question 9

Vaporisation + Evaporation

Answer 9

vaporisation → takes place above/at the boiling point
evaporation → takes place below the boiling point

Question 10

Temperature stays the same during a change of state

Answer 10

energy is used to break bonds

Question 11

Pressure unit

Answer 11

measured in Pascals (Pa)

1Pa = 1N/m2

Question 12

Fluid Pressure Equation

Answer 12

Pressure = density x depth x gravity

P = ρ g h

Question 13

General Pressure Equation

Answer 13

Pressure = Force / Area

P = F / A

Question 14

Fluid Pressure

Answer 14

• exerted on the walls of a container at 90°
• acts in all directions

Question 15

Why is pressure exerted by a gas on the walls of its container?

Answer 15

• gases are in a constant state of random motion
• the particles collide with the walls
• collisions cause a change in direction + a change in momentum
• force is exerted on the molecule → F = (mv-mu) / t
• force is exerted on the wall (Newton’s 3rd Law)
• P = F/A → pressure is exerted on the wall

Question 16

Specific Heat Capacity

J/kg/°C

Answer 16

The energy required to increase 1kg of a substance by 1°C

ΔQ = mcΔθ

Question 17

Specific Latent Heat

J/kg

Answer 17

Energy required to change the state of 1kg of a substance without changing its temperature

Q = mL

Question 18

Breaking Bonds

Answer 18

Endothermic → absorbs energy

Question 19

Forming Bonds

Answer 19

Exothermic → releases energy to the surroundings

Question 20

Pressure + Temperature

Answer 20

If the volume of a gas is kept constant and the temperature increases:
* thermal energy increases kinetic energy of particles
* particles move more with increased velocity
* rate of collisions increases
* change in momentum per second increases
* force exerted on wall increases
* pressure increases

Question 21

Absolute Zero

Answer 21

0K = -273°C
* particles have no kinetic energy
* no pressure is exerted
* the substance has no volume

Question 22

Pressure Law

Answer 22

For a fixed mass of gas at a constant volume, pressure is proportional to temperature in Kelvin

Question 23

Pressure + Volume

Answer 23

If the temperature of a gas is kept constant and the volume of gas in increased:
* rate of collisions increases
* increases change in momentum per second
* exerts a greate force on the walls
* pressure increases

Question 24

Boyle’s Law

Answer 24

For a fixed mass of gas at a constant temperature, pressure is inversely proportional to volume

P = kV

Question 25

As volume increases, pressure decreases

Answer 25

Plot Pressure over 1/vol to get straight lune graph