Physics 5 - Solids, Liquids and Gases

Question 1

What is the unit for density?

Answer 1

Kilogram/metre3 (kg/m3)

Question 2

What is the unit for pressure?

Answer 2

Pascal (Pa)

Question 3

What is the unit for specific heat capacity?

Answer 3

Joules/(Kilogram degree celsius) - (J/kg °C)

Question 4

What is the equation linking density, mass and volume?

Answer 4

Density = Mass/Volume

ρ=m/V

Question 5

Practical: Design an experiment to investigate density using direct measurements of mass and volume for a regular shaped object

Answer 5

Measure the mass using an electric mass balance

Measure the length of the sides using a ruler or digital calliper. If it is a circle or cylinder, use a digital calliper to work out the diameter, measuring at several points.

Work out the volume using an equation: lxwxh or πr^2×l

Use the density equation to calculate the density!

Question 6

5.4 practical: Design an experiment to investigate density using direct measurements of mass and volume for an irregular shaped object

Answer 6

Measure the mass using an electric balance

Fill a measuring cylinder to a known volume (100ml), then place the object in and determine the hight change. This is the volume

Remember, 1ml = 1cm3

Use the density equation to work out density.

If the object is too large, use a eureka can and measure the displaced water to find the volume

Question 7

What is the equation linking pressure, force and area?

Answer 7

Pressure = force/area

P=F/A

Question 8

What direction does the pressure at a point in a gas or liquid act?

Answer 8

At rest it acts equally in all directions.

Question 9

What is the equation linking pressure difference, height, density and gravitational field strength?

Answer 9

Pressure difference = density x height x gravitational field strength

p = h × ρ × g

Question 10

5.8P Explain why heating a system will change the energy stored within the system

Answer 10

By increasing the kinetic energy of the particles, the system’s temperature increases (its energy has increased)

Question 11

5.8P Describe and explain what two things can happen to an object when heated

Answer 11

Raise the temperature of the object - increased kinetic energy of the particles

Changing the state of the object - break the intermolecular bonds

Question 12

5.9P Explain evaporation

Answer 12

It can happen below the boiling point and is caused by a particle escaping the surface of the liquid and becoming a gas - all particles have different energy levels.

Particles near the surface evaporate if:

• They are travelling in the right direction
• They are fast enough to overcome the intermolecular forces

Question 13

5.9P Explain what happens to the temperature of a liquid when particles evaporate from it

Answer 13

The average energy (the temperature) decreases

Question 14

5.11P practical: Design an experiment to obtain a temperature–time graph to show the constant temperature during a change of state

Answer 14

Get a beaker filled with ice, and place a thermometer inside.
Use a Bunsen burner to heat the ice, and measure the change in temperature every 30s (use a stopwatch to time it)
Continue this until the water boils for a minute
Plot the graph.

Question 15

5.11P Sketch a temperature-time graph for ice being heated at a constant rate

Answer 15

SEE ONENOTE

Temperature increases until 0ºC, where it remains constant (the energy is being used to break the bonds and overcome the latent energy)

Temperature increases until 100ºC where it remains constant for a while again.

It then increases

If it is about steam cooling, it simply goes in the other direction

Question 16

5.12P Define specific heat capacity, and what is its unit?

Answer 16

The energy required to increase the temperature of one kilogram of a substance by one degrees Celsius.
(J/kg ºC)

Question 17

5.13P Write down the equation for change in thermal energy in terms of specific heat capacity

Answer 17

Change in thermal energy = mass x specific heat capacity x temperature change

ΔQ= m × c × ΔT

Question 18

5.14P practical: Design an experiment to investigate the specific heat capacity of water

Answer 18

Find the mass of water (measure the container beforehand, using a mass balance)
Get the initial temperature of the water (thermometer)
Place an electric emersion heater into the water and connect an ammeter in series and voltmeter in parallel. Calculate the power by P = IV
Turn it on and measure the time that it is on (stopwatch)
Switch these two off after a rise of 10 degrees. Continue measuring the temperature and measure the maximum value.
Use this equation:
c=IVt/mΔT
Repeat and find the average

Question 19

5.14P practical: Design an experiment to investigate the specific heat capacity of a metal cylinder

Answer 19

Do the same process as water but with a metal cylinder which has holes in it for the heater and thermometer.

Question 20

5.15 Explain the motion of gas molecules

Answer 20

Random motion and speed - random collisions with the side of the container and other gas molecules

Question 21

5.15 Explain pressure at a microscopic level

Answer 21

Molecules exert a force on the walls of the container (they change momentum when they collide and change direction)
This happens over area - P=F/A

Question 22

5.16 Define absolute zero of temperature and give its value in ℃ and K

Answer 22

This is the lowest temperature possible, because particles have the smallest possible kinetic energy and no work can be extracted from the system. This happens at 0K=−273℃

Question 23

5.17 Write down the relationship between the Kelvin scale and Celsius scales of temperature and give the significance of the Kelvin temperature scale

Answer 23

T(K)=T(℃)+273
or
T(℃)=T(K)−273

It is an absolute temperature scale as absolute zero is 0K. It goes up in the same increments as Celsius

Question 24

5.19 Describe how the Kelvin temperature is related to the properties of gas molecules

Answer 24

It is proportional to the average KE of the molecules.

Celsius has a linear relationship but isn’t proportional.

Question 25

5. 20 explain, for a fixed amount of gas, the qualitative relationship between:
   a. pressure and volume at constant temperature

Answer 25

Pressure is inversely proportional to volume.

The larger the container, the less dense the molecules are so they collide less often with the walls - lower pressure.

Question 26

5. 20 explain, for a fixed amount of gas, the qualitative relationship between:
   b. pressure and Kelvin temperature at constant volume.

Answer 26

Pressure is proportional to Kelvin.

Higher temperature leads to higher KE, so there are more collisions with the walls and with more force - higher pressure

Question 27

5.21 Write down the relationship between the pressure, Kelvin temperature and volume of a fixed mass of gas

Answer 27

P1V1/T1 = P2V2/T2