1
Q
When and what did J J Thompson theorise about the atomic structure?
A
- In 1887
- J J Thompson figured out that atoms weren’t solid spheres.
- His measurement of charge and mass showed that an atom must contain smaller negatively charged particles called electrons.
- From his results, he made a model of the atom, known as the ‘plum pudding model.’
- This model shows the electrons spread though the positive ‘pudding’ that made up most of the atom.
2
Q
When and what did Ernest Rutherford theorise about the atomic structure?
A
- In 1909
- Ernest Rutherford, working with Hans Geiger and Ernest Marsden
- conducted the famous gold foil experiment.
- They fired positively charged alpha particles at an extremely thin sheet of gold.
- From the plum pudding model, they expected the particles to pass straight through the gold sheet, only to be slightly deflected.
- Although most particles went straight through the sheet,
- some were deflected more than they expected to
- and a few were deflected straight back the way they came
- the plum pudding model had no evidence to support this.
- Rutherford came up with a new theory of the nuclear atom
- In his model, most of the mass of an atom is concentrated in a tiny, positively charged nucleus at the centre
- surrounded by a ‘cloud of negative electrons
- most of the atom consists of empty space.
- his model was flawed, as scientists recognised that electrons in a ‘cloud’ around the nucleus of an atom like this would be attracted to the nucleus, causing the atom to collapse.
3
Q
When and what did Neils Bohr theorise about the atomic structure?
A
- In 1913
- Niels Bohr proposed a new model where the electrons are in shells.
- He suggested that electrons can only exist in these shells (fixed orbits)
- and not anywhere in between.
- Each shell has a fixed energy.
- His theory was similar to the modern-day model.
4
Q
What does the nucleus contain?
What is the overall charge of the nucleus?
A
- Nucleus contains protons ( + charge) and neutrons ( neutral charge),
- which gives it an overall positive charge.
5
Q
What is the nuclear radius and the whole mass of the atom?
A
- Nuclear radius is 1 x 10^-15m
- whole mass of atom is about 1 x 10^-23, depending on the element.
6
Q
What is the diameter of an atom?
A
1 x 10^-10
7
Q
How small is the nuclear radius compared with the atomic radius?
A
The nuclear radius is around 10 000 times smaller than the atomic radius.
8
Q
What are the relatives masses for a proton, neutron and an electron?
A
Proton = 1 Neutron = 1 Electron = 0.0005
9
Q
What are the relative charges for a proton, neutron and an electron?
A
Proton = +1 Neutron = 0 Electron = -1
10
Q
What is density?
A
-Density is a measure of the mass per unit of volume.
11
Q
What is the formula for calculating density?
A
Density = mass ÷ volume
triangle:
m ----------- p x V
12
Q
What does the density of an object depend on?
A
- What it is made of!
- It DOES NOT vary with size or shape.
13
Q
What determines if an object floats or sinks in water?
A
- The object’s average density of an object- it needs to have a lower average density than the liquid, in order to float.
- If it has a higher average density than the liquid it is submerged in, than it will sink.
14
Q
Describe an experiment used to measure the density of solids and liquids::
A
1) An object submerged in water will displace a volume of water equal to its own volume
2) Use a eureka can (Archimedes)
3) Fill eureka can so that water level is just under the spout.
4) Slightly over-fill the can then let the extra water drain away
5) Place a measuring cylinder under the spout, then gently lower your object in the can, using a thin, strong thread.
6) The displaced water will start to come out of the spout.
7) Wait for the spout to stop dripping, then measure the volume of water collected in the cylinder.
8) This is the volume of water displaced by the object which is equal to the volume of the object.
9) Repeat three times and calculate a mean.
15
Q
How can you work out the volumes of:
- a liquid
- a solid cuboid
- a solid cylinder
A
1) To measure the density of a substance, measure the mass and volume of a substance (use formula)
2) You can measure the mass using a mass balance.
3) To measure the volume of a liquid, pour the liquid into a measuring cylinder
4) 1ml = 1cm3
5) To measure the volume of a solid cuboid, measure its length, width and height than multiply them together.
6) To find the volume of a solid cylinder, measure the diameter of one face of the circle, then halve this to give a radius.
7) Measure the cylinder’s height, and use the formula volume = π x radius^2 x height.
16
Q
Describe what the particle theory says about solids as a state of matter:
A
- Strong forces of attraction hold the particles close together in a fixed, regular arrangement
- The particles don’t have much energy in their kinetic energy stores
- so they only vibrate about their fixed positions.
17
Q
Describe what the particle theory says about liquids as a state of matter:
A
- The forces of attraction between the particles are weaker (than solids)
- The particles are close together,
- but can move past each other
- and from irregular arrangements
- they have more energy in their kinetic energy stores than the particles in a solid
- they move in random directions at low speeds.
18
Q
Describe what the particle theory says about gases as a state of matter:
A
- There are almost NO forces of attraction between the particles
- Particles have more energy in their kinetic energy stores than those in liquids.
- and are free to move
- and travel in random directions
- at high speeds.
19
Q
What are the physical changes between solid to liquid and liquid to solid called?
A
Solid to Liquid - melting
Liquid to Solid - freezing
20
Q
What are the physical changes between liquid to gas and gas to liquid called?
A
Liquid to gas - evaporating
Gas to Liquid - condensing
21
Q
What are the physical changes between gas to solid and solid to gas called?
A
Gas to Solid - deposition
Solid to Gas- sublimating
22
Q
Where is the energy in a substance’s thermal energy stored?
A
- Held by its particles in their kinetic energy stores
- …..this is what the thermal energy store actually is!!
23
Q
In terms of energy stores, what happens during the process of boiling?
A
- When you heat a liquid, the extra energy passes into the particles’ kinetic energy stores
- making them move faster
- when enough of the particles have enough energy to overcome their attraction to each other
- bubbles of gas form in the liquid
- this is boiling!
24
Q
In terms of energy stores, what happens during the process of melting?
A
- When you heat a solid, the extra energy makes the particles vibrate faster
- until eventually the forces between them are partly overcome
- and the particles start to move around
- this is melting!
25
How does volume and density change when substances change state?
- When substance changes state its volume does change
- The particles in most substances are closer together when they're a solid than a liquid
- (except ice and water)
- and are closer together when they're a liquid than a gas
- Since density = mass ÷ volume, then density must change too.
- generally, substances are most dense when they're solids and least dense when they're gases.
26
What is temperature a measure of?
-The average internal energy of a substance.
27
What is the specific heat capacity of water?
-4200 J/kgºC
28
What is specific heat capacity?
- The specific heat capacity of a substance is the change in energy
- in the substance's thermal store
- needed to raise the temperature of 1kg of that substance
- by 1ºC
29
What is the equation to calculate the change in thermal energy?
Change in Thermal Energy (J) = mass (kg) x Specific Heat Capacity (J/kgºC) x change in temperature.
30
Describe an experiment used to find the specific heat capacity of a substance?
1) Measure the mass of your substance
2) Make sure the joulemeter reads zero
3) (go on page 15 to find experiment set-up)
4) Measure the temperature of the substance you are investigating, then turn on the power
5) Always keep you eye on the thermometer.
6) When the temperature has increased (e.g. by 10 degrees)...
7) stop the experiment and record energy on the joulemeter
8) and record the increase in temperature
9) Then calculate the SHC of your substance by rearranging the equation.
10) Repeat the whole experiment 3 times (at least), then calculate the mean SHC of your substance.
11) You have to watch out for systematic errors due to energy escaping from your experiment.
12) The insulating container helps by reducing the amount of energy that escapes from the sides and the bottom of the substance you are investigating.
13) You could reduce the energy loss further by adding a lid to the container.
31
On a heating/cooling graph, why are there flat spots in between each gradient?
-When you heat a solid or liquid, you are transferring energy to the kinetic energy stores of the particles
-making the particles in the substance vibrate or move faster
-when a substance is melting or boiling, you are still putting in energy
-but the energy is being used for breaking bonds between particles rather than raising the temperature
-this leaves flat spots on the graph
-when a substance is condensing or freezing, bonds are forming between particles,
which releases energy.
-This means the temperature doesn't go down until all the substance has turned into a liquid (condensing) or a solid (freezing).
32
What is specific latent heat?
- The specific latent heat of a change of state for a substance is the change of energy in its thermal energy store
- when 1kg of the substance changes state without changing its temperature
- Specific latent heat is different for different materials, and for different changes of state.
33
What is specific latent heat of fusion?
-Changing between a solid and a liquid (melting or freezing)
34
What is specific latent heat of vaporisation?
-Changing between a liquid and a gas (boiling or condensing)
35
What is the formula for calculating the thermal energy for change in state (J)?
Thermal Energy
for a Change in = Mass (kg) x Specific Latent Heat
State (J/kg)
36
Using the particle theory, explain how gases create pressure:
- a gas is free to move around in completely random directions.
- as gas particles move about, they randomly bump into each other, other obstacles and the walls of the container
- gas particles have a mass- when they collide with something they exert a force on it
- all of these collisions cause a net force on the inside surface of the container.
- The force acting per unit area is the pressure.
- the more particles there are in a given volume, the more often they'll collide with the walls and each other
- so they higher the pressure will be.
37
How does changing the temperature affect pressure of gases in a closed system?
- The pressure a gas exerts on its container also depends on how fast the particles are going
- and how often they hit walls.
- if you hold a gas in a sealed container (closed system) with a fixed volume and heat it
- energy is transferred to the kinetic energy stores of the gas particles
- and they move faster
- this means the particles hit the container walls harder
- and more often
- creating more pressure
- if a gas is cooled, the particles have less energy and move less quickly
- the particles hit the walls with less force and less often
- so pressure is reduced.
38
What is the equation for a fixed amount of gas at a constant temperature?
Pressure (Pa) x volume (m^3) = constant
(you need to rearrange the equation to calculate pressure, e.g.:
pressure x 0.020 = 1000 its like algebra!
pressure = 1000 ÷ 0.020
39
How can a change in pressure cause a change in volume and force?
- A gas exerts a force on its container due to collisions between the particles and the walls of the container
- these collisions happen in random directions
- but add together to produce a net force at right angles to the wall of the container.
- if the pressure of the gas in increased, the force increases.
- if the pressure of a gas is decreased, the force decreases
- if the gas is in a container that can change volume (e.g. balloon) this can change the volume of the container, so the gas.
40
Describe what happens if you increase/decrease the pressure of a balloon:
- Unless it is a vacuum, the outside of a gas container is also under pressure from the air around it (atmospheric pressure)
- If a balloon isn't expanding or contracting, then the pressure (and force) of the gas inside the balloon pushing outwards
- is equal to the pressure (and force) of the air outside the balloon pushing inwards
- if you increase the pressure of the gas inside the balloon
- the force pushing outwards will be higher than the force pushing inwards
- there is a net outwards force on the walls of the balloon
- this causes the balloon to expand.
- As the balloon expands, the gas particles inside come in contact with the walls less frequently.
- This causes the pressure inside the balloon to decrease
- Once the pressure inside the balloon has fallen back to the same level as atmospheric pressure
- the balloon will stop expanding
- The opposite happens if you reduce the pressure inside the balloon.
- the pressure on the outside will be bigger than the pressure on the inside
- so there will be a net inward force and the balloon will shrink
- this causes the pressure inside the container to rise
- as the particles of the gas hit the walls of the container more frequently
- until pressure inside = pressure outside, again.
41
How does 'doing work' on a gas increase its temperature?
1) Doing work on a gas increases its internal energy, which increases its temperature
2) You can do work on a gas mechanically (e.g. bike pump)
3) The gas exerts pressure on the plunger of the pump, so exerts a force on it.
4) Work has to be done against the force to push down the plunger
5) This transfers energy to the kinetic energy stores of the gas particles so increases the internal energy
6) and therefore increases the temperature
7) If the pump is connected to e.g. a tyre, some of this energy is transferred from the gas to the thermal energy store of the tyre
8) this is why sometimes you can feel the tyre getting warmer as you pump it up.
42
How far does the Earth's atmosphere go to? Approxiamately.
-100km roughly.
43
What creates atmospheric pressure?
The weight of the air high in the atmosphere pushes down on the air above us. This pressure acts in all directions.
Because atmospheric pressure is always present, and because it is equal in every direction, we can feel this pressure.
44
What is the atmospheric pressure like closer to sea level?
| What is atmospheric pressure like really high up (mountain range)?
- The lower you are (sea level) the more atmosphere there is above you, so the higher the atmospheric pressure is.
- Atmospheric pressure is over 100 000 Pa at sea level.
- As you gain height, there is less atmosphere above you, so the atmospheric pressure decreases.
- At the top of Mt. Everest the atmospheric pressure is around 33 000 Pa.
45
What is the density of the atmosphere like as you elevate higher?
Sea Level - Mountain Range
- The density of the atmosphere gets higher the closer you are to sea level.
- This is because the weight of the air above pushes down on the air below it, compressing it.
- The density of the atmosphere decreases the closer you are to mountain range (higher in the atmosphere)
46
How does an object submerged in a liquid experience liquid pressure?
- Experiences liquid pressure from all directions due to the particles of the liquid.
- The pressure increases with depth, due to the weight of the 'column' of liquid directly above the object.
47
How can you calculate the pressure at a given depth?
Using the equation:
pressure due to height density
a column of liquid = of column x of liquid x g (N/kg)
(Pa) (m) (kg/m^3)
*g is the gravitational field strength. (equal to about 10N/kg)
48
What is the equation to find the difference in pressure?
difference in pressure = difference in depth x density x g
49
What is upthrust?
- An object that is partly, or completely, submerged experiences a greater pressure on its bottom surface than on its top surface.
- This force is called upthrust .
- An object in a fluid is displacing some of the fluid.
- The upthrust force is equal in size to the weight of the fluid displaced by the object.
50
What determines if an object will float or sink in terms of upthrust?
- The upthrust acting on an object is equal to the weight of fluid
- it has displaced
- if the upthrust is equal to the object's weight
- then the object will float
- if the upthrust is less than the object's weight,
- then it will sink.
- so to make an object float, you need to make it less dense than the liquid you are trying to float it in,
- so it will have displaced a volume of water with a weight equal to its own weight.
GCSE OCR Physics- Triple
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