Two like poles repel each other and two unlike poles attract each other.
Every magnet has two poles: North and South.
Magnetic fields travel from north to south so be careful to label a diagram in this way with an arrow on the line of field pointing towards south.
A compass can be used to detect a magnetic field.
When electricity passes along a wire, it forms a magnetic field.
Using direct current will make the field in circles around the wire. This can be tested by using a compass.
You need to learn the magnetic rules which includes the right hand grip rule.
If a coil of wire is used a stronger magnetic field is produced.
You also need to know about some devices that work by electromagnetism such as an electric bell and relay.
If you are asked to draw the magnetic field around a magnet REMEMBER:
The lines must travel around the magnet.
They must not touch each other.
Label the magnetic field with arrows going from north to south.
-
Each component separately connected.
-
If one of the components is disconnected then it does not effect those it is parallel with.
-
All components get the full source voltage.
-
Voltage the same in all components.
-
The lower the resistance of a component the greater the current.
-
Total current in the circuit is equal to the currents in its separate branches.
- Total current going into a junction is equal to the total current leaving it.
Series circuits
-
Components are connected from end to end.
-
If one component is removed or disconnected the circuit is broken.
-
Total resistance is the sum of all the resistances.
-
Same current in all parts of the circuit.
-
Total voltage of the supply is shared between components.
- The bigger the resistance of a component, the bigger its share of voltage.
Static electricity
-
There are two types of charge: + positive and - negative.
-
An uncharged material has equal numbers of both so the material is balanced out.
-
Friction between materials caused an exchange of charges.
-
The negative charges move but positive stay where they are.
-
Once a material is charged it will attract materials with the opposite charge and repel materials that have the same charge.
-
An example of static electricity in industry is when painting cars. The car body is charged evenly and the paint is prayed on. The paint particles are attracted to the car and spread out because of the charge. This ensures the car is painted evenly.
Forces and motion
-
Forces are usually a push or a pull.
-
Forces are measured using a newtonmeter and the unit of force is Newtons.
-
Forces work in pairs - as you push down on a table the table pushes up with equal force.
-
When there is no change in velocity or shape of an object then the forces are balanced e.g. book on table
-
When there is a change in velocity or shape of an object then the forces are not balanced e.g. person falling through ice.
-
An example of a force is gravitational force. To work out the weight of an object (with gravity working on it) you use the following formula:
-
Weight (N) = mass (kg) x gravitational force (N/kg)
-
The main formula to use to work out forces is:
-
Force (N) = mass (kg) x acceleration (m/s/s)
OR F=ma
Hooke's Law
-
Hooke's law simply states that the extension of a spring (or other stretch object) is directly proportional to the force acting on it.
-
This law is only true if the elastic limit of the object has not been reached.
- If the elastic limit has been reached the object will not return to its original shape and may eventually break.
Pressure
Pressure is the amount of force acting upon a particular area of an object.
-
The formula for calculating the pressure on an object is:
-
Pressure (N/m2) = Force (N) / Area (m2)
-
The unit N/m2 is known as Pascals.
-
This formula shows that by decreasing the area you will increase the pressure e.g. knives need to excert a big pressure so they have a very narrow area.
-
Pressure in solids. The pressure only acts in one direction in solids.
-
Pressure in liquids. The pressure in liquid gets higher as you go down. The pressure of liquids acts in all directions not just down.
-
Pressure in gases. Gas molecules are free to move anywhere therefore pressure of gases acts in all directions. The pressure gets higher as you go down because of the weight of the gas (air).
Momentum
-
Momentum is the measure of how difficult it is to change an objects' velocity.
-
Momentum can be increased by increasing the mass of the object or the velocity of the object.
-
e.g. a lorry going at 80km/h down a hill with a very heavy load would have a big momentum. - It would be very difficulat to stop! (If this was an exam question you would have to convert hours to seconds and km to m)
-
The formula for calculating momentum is:
-
Momentum (kgm/s) = mass (kg) x velocity (m/s)
-
Conservation of momentum just shows that momentum is never lost but just transferred from one object to another e.g. if the big lorry runs into a car then all the momentum will be transferred to the car.
Acceleration
-
Acceleration is the rate of change in velocity of an object.
-
The most common unit of acceleration is m/s/s which can also be written as m/s2 or ms-2. This means the rate of change in velocity per second.
-
For example if an object increased its velocity by 2 metres every second then its acceleration would be 2m/s/s.
-
Accelaration = change in velocity / time taken for change.
-
Therefore if an object travels from stationary to 5 m/s in 2.5 seconds then its acceleration = 5/2.5 = 2m/s/s.
- Uniform acceleration is just the name given to a constant acceleration.
Speed and velocity
-
Speed is the change of movement of an object.
-
Velocity is the speed of an object in a certain direction.
-
The most common unit for both speed and velocity is m/s which shows how many metres an object has moved in one second.
-
Average speed = distance moved / time taken.
-
Average velocity = distance moved in a certain direction / time taken.
Formulae
Here are the formulae for speed, velocity and acceleration. You will probably be expected to learn these for your GCSE exam:
-
Average speed = distance moved / time taken
-
Average velocity = distance moved in a certain direction / time taken
-
Acceleration = change in velocity / time taken
-
Remember all of these formulae can be rearanged.
- e.g. distance = average speed x time taken
-
Below are the formulae you can use when calculating problems which have uniform acceleration (constant acceleration). You probably will be only expected to be able to use these and not learn them but make sure you check this with your teacher.
-
v = u + at
- s = (u + v)/2 x t
-
s = ut + ½at2
-
v2 = u2 + 2as
-
What the letters stand for:
-
u = initial velocity
-
t = time
-
v = final velocity
-
s = distance travelled
-
a = acceleration (must be constant)
Waves
Waves
Waves do not carry matter but they transfer energy.
There are two main types of wave: Transverse Waves and Longitudinal Waves. Below is some information and examples of both:
Transverse waves:
A transverse wave moves across the direction in which the wave is travelling.
An example of a transverse wave is the sea - imagine the shape of a wave.
Another good example is a light wave.
Longitudinal waves:
Longitudinal waves look like this: ||| | | || || | |||| | | | ||
They have a series of compressions and rarefractions.
A compression is when the wavelength (distance between each wave) is small.
A rarefraction is when the wavelength is large.
Longitudinal waves pass on energy as a series of vibrations.
These are sound waves.
Wavelength. The wavelength is the length of a wave e.g. the distance between one crest (high part) and the next crest.
Frequency. Measure of how many waves pass in one second.
Amplitude. The distance between the crest of the wave and the centre line.
Formulae. There are two main formulae on the topic of waves:
Velocity (m/s) = frequency (Hz) x wavelength (m)
Speed (m/s) = distance (m) / time (s)
Electromagnetic Spectrum
-
Below is the electromagnetic spectrum; starting with short wavelengths and getting longer. We have also included some common uses which you may need to give in an exam question
-
Gamma rays. Cancer treatment
-
X-rays. Medical uses and security (at airports etc)
-
Ultraviolet. Sun tanning
-
Visable light. Human sight
-
Infrared. Cooking (heat)
-
Microwaves. Cooking
-
Radio waves. Communication
Light
The primary light colours are red blue and green. They can be mixed, as follows, to form secondary light colours:
red + green = yellow
red + blue = magenta
blue + green = cyan
By using a prism, white light can be separated into all the different (dispersion) colours that make up white light. These are (starting with long wavelength):
red, orange, yellow, green, blue, indigo, violet
Reflection:
The angle of incident always equals the angle of reflection. These are measured against the normal which is an imaginary straight line at a right angle to the mirror.
Refraction:
Refraction is the process that occurs when light travels from one material to another, it is either speed up or slowed down. This has an effect on the light and bends it. The denser the material, the slower the speed of light.
Sound
Sound waves are caused by vibrations in the air. They cannot travel through vacuums. The denser the material, the faster sound can travel.
Sound waves are reflected and this is heard by us as an echo. The echo is the sound being reflected - just like light reflected from a mirror.
Ultrasound has a very high frequency and we canv not hear it but bats use it to fly and it is also used to look inside the body.