Tuesday, 30 April 2013

6.8 understand that an electric current in a conductor produces a magnetic field round it

If you run an electric current through anything that conducts (e.g. a wire) a magnetic field will be produced around it!

6.7 describe how to use two permanent magnets to produce a uniform magnetic field pattern.

If you put two bar magnets together with their north and south touching, then they will form the same magnetic field as if there were one bar magnet.

'hold two opposite poles close to each other so that they attract as this makes a uniform magnetic field'

6.6 describe experiments to investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnets

To track field lines you can use iron filings, which are magnetic materials, which will line up along the magnetic field. and you can use compasses which will show that the lines go from north to south. The following results will occur:

6.5 understand that magnetism is induced in some materials when they are placed in a magnetic field

Some materials that are not magnetic can become one when they are in a magnetic field. This is because the magnetic field encourages its electrons to align and form poles. This can happen in iron (and steel), cobalt and nickel.

6.4 understand the term ‘magnetic field line’

Magnetic field lines represent the shape and direction of a magnetic field.
Its important to realise that these lines only represent the field and that the spaces in-between the lines are not in fact spaces in the field, a field is also three dimensional, so the lines just give an idea.

6.3 describe the properties of magnetically hard and soft materials

A magnetically hard material retains its magnetic properties for a long period of time/ permanently  They are hard to demagnetise.

A magnetically soft material looses its magnetic properties almost as soon as it leaves a magnetic field.

6.2 understand that magnets repel and attract other magnets and attract magnetic substances

Opposite poles of magnets attract.
Like poles of magnets repel.
Magnetic substances can also be attracted by a magnet.

6.1 use the following units: ampere (A), volt (V), watt (W)

ampere (A)
volt (V)
watts (W)

Thursday, 25 April 2013

5.17 use the relationship between the pressure and volume of a fixed mass of gas at constant temperature

p1V1 = p2V2

5.16 use the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume

The higher the Kelvin the higher the pressure.

If volume and mass are kept the same, then increasing one will increase the other in direct proportion.


5.15 describe the qualitative relationship between pressure and Kelvin temperature for a gas in a sealed container

As Kelvin increase, energy increases. As the energy of something increases, its particles will move faster and with more force. This will mean more force is exerted over a fixed area- increasing pressure.

So if a gas has its kelvin increased, it will exert more force on the container its in, meaning the pressure will go up.

5.14 understand that the Kelvin temperature of the gas is proportional to the average kinetic energy of its molecules

The Kelvin temperature scale is in direct proportion to the energy of particles.

Because it puts 0 where particles have no energy, as the Kelvin go up so does the energy.

5.13 understand that an increase in temperature results in an increase in the average speed of gas molecules

If you increase the temperature of something, you increase the energy levels in it. The molecules of it will then have more kinetic energy- this means they will be travelling faster.

5.12 describe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scales

The kelvin temperature scale uses absolute zero as a starting point.
Absolute zero is 0 Kelvin.

Absolute zero is -273°C

0 kelvin = -273°C

273 Kelvin = 0°C

1 Kelvin = -272°C

274 Kelvin = 1°C

Above are examples of how to convert between the two, as you can see I have just just a solving equations method to work out different values (eg what you do to one side you must add to the other.)

5.11 understand why there is an absolute zero of temperature which is –273°C

Heat is energy, the more energy the more heat. If something were to have no energy it would be 'absolute zero'.

Zero in Celsius is the freezing point of water, 'absolute zero' is -273°C

5.10 understand that molecules in a gas have a random motion and that they exert a force and hence a pressure on the walls of the container

Molecules of gas move randomly about space. When the collide with a surface, they exert pressure on it. For example air particles collide with the surface of a balloon, the pressure the exert keeps the balloon inflated.

5.9 understand the significance of Brownian motion, as supporting evidence for particle theory

Brownian motion is the principle that particles move randomly about a space.
Particle theory says that as particles move about (randomly) they collide, when they collide with a surface the exert a pressure on the surface (like air keeping a balloon inflated.)

5.8 describe the arrangement and motion of particles in solids, liquids and gases

Solid: low energy; little movement, vibrating on the spot

Liquid: some energy; some movement; particles collide, bouncing apart and creating space between particles

Gas: lots of energy; lots of movement; particles collide a lot, bouncing apart more creating lots of space between particles 

5.7 understand the changes that occur when a solid melts to form a liquid, and when a liquid evaporates or boils to form a gas

Particles in a solid don't move; but if they are heated they gain energy and move, if they move enough they will become a liquid because the particles will bounce off each other moving them further apart.
Similarly, a liquids particles have some energy, but if they gain more they will bounce off each other more frequently moving them further apart; eventually they are far enough apart that it is a gas.

5.6 know and use the relationship for pressure difference

pressure difference = height × density × g

p = h ×ρ × g

5.4 know and use the relationship between pressure, force and area

Pressure= force/ area

p = F/A

5.3 describe experiments to determine density using direct measurements of mass and volume

Using a set mass of one object (eg 100g of water) change the space its in (eg 200ml cylinder taking ten off the ml each time.) Use the formula mass/volume to find the density, it will go up as the volume decreases.

5.2 know and use the relationship between density, mass and volume

Density= mass/ volume

p= m/V

5.1 use the following units

degrees Celsius (oC)
kelvin (K)
joule (J)
kilogram (kg)
kilogram/metre3 (kg/m3)
metre (m)
metre2 (m2 )
metre3 (m3)
metre/second (m/s)
metre/second2 (m/s2 )
newton (N)
pascal (Pa)

3.25 describe how digital signals can carry more information

  • larger bandwidth

4.16 describe the energy transfers involved in generating electricity using several different methods

  • wind- the kinetic energy from the wind, turns a turbine which turns a generator which produces electrical energy
  • water- Kinetic energy from water, turns a turbine which turns a generator which produces electrical energy
  • geothermal resources- Thermal energy heats water, water turns into steam, the thermal energy of the steam turns a turbine which then has kinetic energy, the turbine turns a generator which produces electrical energy
  • solar heating systems- Light energy from the sun into thermal energy in water
  • solar cells-convert light energy from the sun into electrical energy
  • fossil fuels- Chemical energy is burnt to form heat energy, this turns into heat energy in water, this turns into kinetic energy in a turbine, this turns into electrical energy in a generator.
  • nuclear power- kinetic energy in uranium, heat energy in water, kinetic energy in turbine, electrical energy in generator.

Tuesday, 23 April 2013

4.15 use the relationship between power, work done (energy transferred) and time taken

Power= work/ time

4.14 describe power as the rate of transfer of energy or the rate of doing work

Power is the rate of work,
Power is also the rate of energy transfer.
So power is how quickly these processes are done.

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

The best way to explain this idea is with a swinging pendulum:
At the top of the swing, it will have its highest gravitational potential energy (as its further from the earth); but it will have its lowest kinetic energy (it slows to a stop at the top point).
At the bottom of the swing, it will have its lowest gravitational energy (as it is closer to the earth); but it will have its highest kinetic energy (it goes very quickly past the bottom point).

Between the points work (force x distance) is constantly being done: the pendulum is moving through space.
Remembering that work done is equal to energy transferred, we can see that as work is done that moves the pendulum upwards, kinetic energy is transferred in to gravitational potential energy. When work is done to bring the pendulum downwards, energy is transferred from GPE to KE.

The pendulum demonstrates that energy is conserved, as then energy is constantly changing between different forms. The only reason that energy is lost from the pendulum, and it slows down, is that some energy is transferred into heat or sound.

maximum kinteic energy at lowest point of swing - minimum gravitational potential energy. at the highest point of swing there is no kinetic energy, and maximum gravitational potential energy.

4.12 know and use the relationship between kinetic energy, mass and speed

Kinetic energy = 1/2 x mass x velocity²

KE= 1/2 × m × v²

4.11 know and use the relationship: gravitational potential energy = mass × g × height

gravitational potential energy = mass × g × height
GPE = m × g × h

It may be useful to think that mass, gravity and height are all things that increase GPE.

4.10 understand that work done is equal to energy transferred

Work done and energy transferred are always the same.

4.9 know and use the relationship between work, force and distance moved in the direction of the force

work done = force × distance moved
W = F × d

4.1 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s), watt (W).

kilogram (kg),
joule (J),
metre (m),
metre/second (m/s),
metre/second2 (m/s2),
newton (N),
second (s),
watt (W)

Tuesday, 16 April 2013

4.8 explain how insulation is used to reduce energy transfers from buildings and the human body.

An insulator is something that is bad at conducting. If something with heat energy is surrounded by an insulator, it wont lose heat by conduction. This is true in buildings where insulating materials are put in walls and on floors to stop heat being lost from inside. This is the same in humans where we wear clothes to stop heat being lost from conduction. Air is a poor conductor, so materials with many air gaps in are also poor conductors; air trapped between double glazing prevents heat loss through windows.

4.7 explain the role of convection in everyday phenomena

Convection is helpful as it distributes heat energy. This is useful in many situations, for example, a radiator in one place will be able to heat a whole room, as hot air will rise away from it creating a current of cool air to be heated.

4.6 describe how energy transfer may take place by conduction, convection and radiation

Conduction is when energy is passed from one particle to another via contact. For example heat is passed from your skin to a window when they touch.

Convection is when particles with energy rise, the space they leave is filled by other particles. If the source of energy continues these new particles will also gain energy, they will then rise and the process will be repeated.

Radiation is when heat is transferred as infra red waves. These waves can travel through space and be conducted or reflected.

These energy transfers are all for heat energy.

4.5 describe a variety of everyday and scientific devices and situations, explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams

With all devices that aim to use energy for a reason, some of the energy put in to run it comes out as a non useful form of energy. The more energy that comes out as useful, the more efficient the object is. For instance, a light bulb wants to create light energy, but it creates heat at the same time. This is the same for many processes: a fire (for warmth) creates light; a pepper grinder creates sound (even though you just want it to move).
Sankey diagrams use an arrow to represent the energy going in and out of a process:
Here 100j of energy is going in. All 100j must come out. 90j come out as heat, 10j come out as light.

4.4 know and use the relationship between useful energy output, total energy input and efficiency

useful energy output / total energy input= efficiency

4.3 understand that energy is conserved

Energy can never be lost, only transferred. Energy will always carry on, just in a different form.
For example, when you switch on a light, you are not loosing energy from a battery (chemical), you are just converting it to light energy!

4.2 describe energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

Energy can change from one form to another, and frequently does. Some examples include:
Chemical energy in food turns into kinetic energy for movement;
Electrical energy in a circuit turns into heat energy in a resistor;
Kinetic energy in your muscles turns into sound energy from you voice.
Elastic potential energy in a taught rubber band turns into kinetic energy when it sails through the air.

3.32 relate the loudness of a sound to the amplitude of vibration.

The bigger the vibration the higher the amplitude.
The higher the amplitude the louder the sound.

3.31 relate the pitch of a sound to the frequency of vibration of the source

The more something vibrates the higher frequency.
The higher frequency the higher pitch.
So the more vibrations the higher pitch.

This video demonstrates this concept well, but is really quite an odd clip:

3.30 describe an experiment using an oscilloscope to determine the frequency of a sound wave

Have an noise made into a microphone attached to an oscilloscope, for example have someone try to sing a note. See how many oscillations there are per second, this will be your frequency. Try changing the pitch of the note and see it the number of oscillations per second changes.

An oscillation is the completion of one wave i.e from one peak and the next.

3.29 understand how an oscilloscope and microphone can be used to display a sound wave

A microphone detects sound waves, it can feed this information into an oscilloscope which will display it as a wave (or straight line.) Here is an example of what an oscilloscope displays:

3.28 describe an experiment to measure the speed of sound in air

Measure the distance between two places, have a sound made in one place, as soon as you see the sound has been made start a stop watch, as soon as you hear the sound made stop the stopwatch.

distance/time= speed

3.27 understand that the frequency range for human hearing is 20 Hz – 20,000 Hz

The human ear can pick up a limited section of different frequencies of sound: that is between 20 and 20,000 Hertz.

2.25 explain some uses of electrostatic charges, eg in photocopiers and inkjet printers.

There are some events in which having two objects of opposite charge is very useful. An example of this is in photocopiers and inkjet printers where the ink is given a charge, and the parts of the paper where its wanted is given the opposite charge, so that the ink is automatically attracted to the right parts of the paper.

2.24 explain the potential dangers of electrostatic charges, eg when fuelling aircraft and tankers

When a large electrostatic charge builds up it can create a spark. When refuelling vehicles the fuel rubbing along the pipe can cause an electrostatic charge, if this sparks if could ignite the fuel causing a fire or explosion. (This can be avoided if the charge is brought to earth by a wire attached to the plain or tanker)

2.23 explain electrostatic phenomena in terms of the movement of electrons

Electrostatic phenomena is an event where static electricity has a specific effect: for example a static shock. Electrons move from one material to another, the material with a negative charge will then look for some way to earth its charge: like clouds through lightening or a car through your hand and body.

Tuesday, 9 April 2013

2.22 understand that there are forces of attraction between unlike charges and forces of repulsion between like charges

Opposite forces attract.
Similar forces repel.

2.21 explain that positive and negative electrostatic charges are produced on materials by the loss and gain of electrons

If two materials are rubbed along each other one will gain electrons from the other.
The one that has gained electrons has a negative charge. The one that has lost electrons will have a positive charge. The charges are electrostatic because they are not flowing.

2.20 describe experiments to investigate how insulating materials can be charged by friction

Get a polyethene rod and rip up some small pieces of paper; the rod will have no effect on the paper.
Rub the polyethene rod with a cloth, now the rod will attract the pieces of paper, this is because it now has a charge they are attracted to.

2.19 identify common materials which are electrical conductors or insulators, including metals and plastics

Electrical conductors are materials that allow a current to pass through them. To do this they need to have 'free' electrons, because current is a flow of electrons. Metals have free electrons because of the way they are bonded (atoms and electrons within a lattice) this means they are good electrical conductors.
Plastics are polymers which are bonded in a way that means electrons aren't free and so can't move. No flow of electrons means no electric current so they are insulators.

2.18 understand that:  voltage is the energy transferred per unit charge passed  the volt is a joule per coulomb.

Often people think of voltage as if it were something pushing current through a circuit, which is helpful, but more accurately its the energy transferred per unit of charge passed.
The unit volt is a joule per coulomb. These are things that simply need to be learnt.

2.17 know that electric current in solid metallic conductors is a flow of negatively charged electrons

Electric current is a flow of electrons, so when there is an electric current in a metal, the electrons in the metal are flowing.

2.16 know and use the relationship between charge, current and time

charge = current × time
Q = I × t

2.15 understand that current is the rate of flow of charge

Current is the rate at which charge is flowing through a circuit.
'It is like the flow of water through a set of pipes'

2.14 know and use the relationship between voltage, current and resistance

voltage = current × resistance
V = I × R

2.13 know that lamps and LEDs can be used to indicate the presence of a current in a circuit

For an LED to light up there must be a current in a circuit. If a LED is in a circuit but not emitting light then there must be no current. If an LED is illuminated then it will have a current flowing through it. By this we know that if the LED in our circuit is shining then there is a current, if it isn't then we don't.

2.12 describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature

An LDR is a light dependent resistor. Its resistance changes with the intensity of light: the brighter it is the less resistance; the less light the more resistance.

Thermistors are temperature dependent resistors. In hot conditions there will be less resistance where as in the cold the resistance is high.

2.11 describe the qualitative effect of changing resistance on the current in a circuit

Increasing the resistance will decrease the current. This can be achieved by adding more components or ones with higher resistance.
Decreasing the resistance will increase the current. This can happen if components are removed or replaced by those with lower resistance.

2.10 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally

If you increase the resistance the current will decrease. resistors, metal filament lamps and diodes all create resistance in a circuit and so will decrease the current.
This can be investigated using an ammeter and measuring the current with and without these components, or with different voltage levels (measured by voltmeter.)