Thermal Physics

Question 1

What is conduction

Answer 1

Vibrating molecules (solids)

Question 2

What is convection

Answer 2

Vibrating molecules (liquid or gas)

Question 3

What is radiation

Answer 3

Waves from the electromagnetic spectrum, especially involving IR

Question 4

What reduces conduction

Answer 4

An insulator

Question 5

What reduces convection

Answer 5

Trapping the liquid or gas in small pockets

Question 6

What reduces radiation (2)

Answer 6

1. Shiny, light coloured surfaces
2. Low surface temperature

Question 7

What stops conduction (2)

Answer 7

1. A vacuum
2. A layer of gas

Question 8

What stops convection

Answer 8

A vacuum

Question 9

What stops radiation

Answer 9

Nothing

Question 10

Are gases very good insulators or conductors and why

Answer 10

Poor conductors, very good insulators, because the molecules are far apart

Question 11

What is the definition of specific heat capacity

Answer 11

The amount of energy required to heat a substance by 1ºC per unit mass

Question 12

What are the units for specific heat capacity

Answer 12

Joules per kilogram per ºC (J/KG/ºC)

Question 13

What is the equation for specific heat capacity energy

Answer 13

Energy = mass x specific heat capacity x change in temperature

q = mc∆T

Question 14

Why do we get different results for the SHC of water when we do an experiment compared to the actual value

Answer 14

The experiment is unreliable - not 100% efficient, some heat lost to surroundings

Question 15

What is the specific heat capacity of water

Answer 15

4200 J/KG/ºC

Question 16

What is internal energy

Answer 16

The sum of all the kinetic and potential energies of the particles in a substance

Question 17

What happens to the energy of an object if the temperature increases/decreases

Answer 17

Increases = more energy
Decreases = less energy

Question 18

What increases when kinetic energy increases

Answer 18

Velocity

Question 19

What is the link between the average kinetic energy of particles in a substance and the temperature of the particles

Answer 19

Directly proportional

Question 20

Define temperature using energy

Answer 20

Temperature is a measure of the average kinetic energy of molecules in a substance.

Question 21

Describe the solid state (3)

Answer 21

Solids are very compact and vibrate back and forth. Held in place by stronger intermolecular forces than in liquids.

Question 22

Describe the liquid state (3)

Shape/volume as a hint

Answer 22

Liquids move to fill a container but they slide over each other. Takes the shape of a container but not the volume.

Question 23

Describe the gas state

Shape and volume as a hint

Answer 23

Gases are very spaced out and are free to move. They take the shape and volume of the container that they are in.

Question 24

What is a fluid

Answer 24

A liquid or a gas

Question 25

What is the change of state from gas to solid or solid to gas called

Answer 25

Sublimation

Question 26

Name a substance that can sublimate

Answer 26

Dry ice (CO2)

Question 27

Do these have a set volume or changeable Gas Liquid Solid

Answer 27

Gas = changeable Liquid = fixed Solid = fixed

Question 28

Do these have fixed or changeable shape Gas Liquid Solid

Answer 28

Gas = changeable Liquid = changeable Solid = fixed

Question 29

How do particles move as a gas

Answer 29

Freely and quickly

Question 30

How do particles move as a liquid

Answer 30

Fluid motion

Question 31

How do particles move in solids

Answer 31

Particles vibrate around fixed positions

Question 32

What is the change of state from gas to liquid called

Answer 32

Condensation

Question 33

Are feathers and fur good or bad insulators

Answer 33

Good

Question 34

Why are cooling units at the top of a freezer, but the heating element in a water tank is at the bottom

Answer 34

Heat rises

Question 35

Why is it more comfortable to wear white than black in summer

Answer 35

Bright colours reflect energy from the sun, but black absorbs it

Question 36

Why do people with hypothermia get wrapped in a plastic sheet coated with shiny aluminum

Answer 36

Plastic insulates, foil is shiny so keeps heat in and keeps cold out

Question 37

Why are several layers of thin clothes better at keeping you warm than one thick layer

Answer 37

Air is a good insulator and there are layers of air between the thin clothes layers

Question 38

Why is newspaper used to keep fish and chips hot but ice cream cold

Answer 38

It is a bad conductor/a good insualtor

Question 39

Why is a fire fighting suit bright and shiny

Answer 39

To reflect the heat of the fire away from the person

Question 40

Why is the inside of a greenhouse warmer than the outside

Answer 40

Glass allows heat in but then traps it inside

Question 41

Why does food in a chest freezer stay frozen for long when the door is open but in an upright freezer it will being to defrost quickly

Answer 41

Heat rises

Question 42

Why does your face go vividly red during exercise

Answer 42

The body tries to lose heat by sending the blood closer to the skin to lose some heat to the surroundings

Question 43

How do you calculate specific heat capacity from a graph of Energy transferred (x) and temperature (y)

Answer 43

C = 1/gradient x mass

Question 44

How do you calculate specific heat capacity

Answer 44

ΔE = mc Δ ϴ Change in energy = mass x specific heat capacity x change in temperature This reaction is also known as Q = mc ΔT

Question 45

Describe an experiment a student can carry out to measure the specific heat capacity of a metal block. (6 marks)

Answer 45

To determine the specific heat capacity of a metal block, the following equipment would be required: a power supply, wires, a metal block, a thermometer, an ammeter, a heating rod, a voltmeter and an insulating layer of wool to surround the metal block. 1. Set up the circuit, with the heating rod and thermometer in separate holes in the metal block, but with the power off. 2. Record the initial temperature of the block. 3. Turn the power on and read the ammeter and voltmeter to get the readings for voltage and current. 4. Every 30 seconds, measure the current, voltage and temperature of the metal block and record in a table. Repeat for 10 minutes. 5. Use voltage x current to work out the power, then multiply by the time to work out the total output of energy from the system, working this out for every 30 second interval. 6. Plot a graph of energy transferred on the X-axis and temperature on the Y-axis. 7. Find the gradient. 8. Calculate the specific heat capacity using the equation c = 1/(mass x gradient). 9. Repeat the experiment 2 more times. 10. Calculate the average results from these repeats.