5.1 Thermal Physics

Question 1

Define thermal equilibrium between two objects

Answer 1

There is no net transfer of thermal energy between the two objects

Question 2

What is absolute 0

Answer 2

0 kelvin

Question 3

How do you convert from degrees celsius to kelvin

Answer 3

+273

Question 4

Describe the structure of particles in a solid

Answer 4

-Particles are arranged in a regular structure and are closely packed together
-Strong electrostatic forces of attraction between them holding them in fixed positions
-They can vibrate so have some kinetic energy

Question 5

Describe the structure of particles in a liquid

Answer 5

-Particles are more free than in solids so can flow past each other but still very close together
-Have more kinetic energy than solids
-Weak electrostatic forces of attraction between particles

Question 6

Describe the structure of particles in a gas

Answer 6

-Have more kinetic energy than liquid and solid and are free to move
-Move with random motion
-Negligible electrostatic forces of attraction between particles unless if they collide with other particles or container wall

Question 7

How can you investigate Brownian motion

Answer 7

Observe smoke particles or pollen grains in water under a microscope

Question 8

Define internal energy

Answer 8

The sum of the random kinetic and potential energy of atoms/molecules in a system

Question 9

What happens to the internal energy when a substance goes from solid to liquid or liquid to gas

Answer 9

-Kinetic energy remains constant
-Temperature remains constant
-Potential energy increases

Question 10

What happens when you increase the temperature of a substance

Answer 10

-Average kinetic energy of particles increases
-Potential energy remains constant

Question 11

What features of water makes it a good coolant

Answer 11

High specific heat capacity
Can absorb large amount of energy without a significant change in temperature

Question 12

Define specific heat capacity

Answer 12

Energy required per unit mass to change the temperature of a substance by 1 kelvin

Question 13

Describe an electric experiment to determine the specific heat capacity of a metal or liquid

Answer 13

-Set up a power supply in series with an ammeter, variable resistor and heater with voltmeter in parallel of heater
-Measure initial and final temperature of substance with thermometer
-Measure time taken with a stopwatch
-Measure current and p.d with ammeter and voltmeter
-Make sure the solid/liquid is insulated
-Liquid must be stirred to ensure it has uniform temperature throughout
-Calculate energy using E = IVt
-Calculate specific heat capacity, E = MCT

Question 14

What does the graph of temperature against time look like

Answer 14

Straight line with positive gradient

Question 15

What is another way of measuring specific heat capacity

Answer 15

-Measure the mass of 2 substances with mass balance and initial temperature of each with a thermometer
-Specific heat capacity of 1 substance will be known
-Mix substances together
-Measure final temperature when at thermal equilibrium
-Calculate specific heat capacity of 1 of the substance using MCT(1) = MCT(2)

Question 16

Define specific latent heat of a substance

Answer 16

Energy required to change the phase per unit mass while at a constant temperature

Question 17

When do we use specific latent heat of fusion and specific latent heat of vaporisation

Answer 17

Solid to liquid
Liquid to gas

Question 18

Describe an electrical experiment to determine the specific latent heat of fusion

Answer 18

-Use a heating circuit to convert ice to water
-Use a thermometer to ensure the ice is at its melting point before the heater is turned on
-Measure p.d across heater, current in heater and time heater is switched on and calculate energy transferred to ice
-Measure the mass of ice that changes state with a mass balance

Question 19

Describe an electrical experiment to determine the specific latent heat of vaporisation

Answer 19

-Use an electrical heater with a condenser to collect and measure the mass of the liquid that changes state
-Measure p.d, current and time
-Calculate energy and then calculate L

Question 20

What are the five assumptions in a kinetic model

Answer 20

1.Large number of particles in random rapid motion
2.Particles have negligible volume compared to the volume of the gas
3.All collisions are perfectly elastic
4.Time of collisions is negligible compared to time between collisions
5.Forces between particles are negligible except during collision

Question 21

Explain how pressure is exerted on a gas

Answer 21

-Particles collide with container wall and the container wall exerts a force on them, changing their momentum
-Total change in momentum is -2mu
-The atom exerts an equal but opposite force on the container wall
-Force = change in momentum/change in time where momentum = -2mu
-Large number of particles collide with wall and therefore a large force is exerted on the wall
-Pressure = Force / cross-sectional area

Question 22

What is Boyles law

Answer 22

Pressure is inversely proportional to volume given constant temperature
PV = Constant

Question 23

Explain why pressure must be changed slowly when investigating Boyles law

Answer 23

To ensure the temperature remains constant

Question 24

What is the relationship between pressure and temperature

Answer 24

Pressure is directly proportional to temperature at constant volume
P/T = Constant

Question 25

Describe how to investigative PV = Constant

Answer 25

-Use a pressure gauge connected to a foot pump and volume scale
-Pump the pressure to maximum
-Open the tap and close to decrease pressure
-Measure volume
-Plot a graph of P against 1/V
-Straight line through origin

Question 26

Describe how to investigate P/T = Constant

Answer 26

-Use a pressure gauge connected to a round bottom flask in a beaker with water and heater underneath
-Measure temperature with thermometer and pressure at time intervals when heating water
-Plot graph of P against T
-Extrapolate graph

Question 27

What does the gradient in PV against T graph show

Answer 27

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