Physics

Physics

1. Static electricity

   • Caused by an electrostatic charge building up on an insulating material
   • All atoms contain electrically charged particles called electrons and protons
     • Protons have positive charge, and are found in the nucleus
     • Electrons move around the nucleus
     • Noramlly atoms have no positive charge because the the +protons are balanced by the -electrons
     • Neutrons have no charge
   • If you rub 2 insulating materials together, electrons maybe transferred, but protons cannot be transferred
     • Like magnets <+ +> <- -> >+ -<
   • rubbing a balloon on your head is called charging by induction
     • The charge is called induced charge

2. Uses and Dangers of Static Electricity

   • You can build up an electrostatic charge from chairs or carpets, then you get a shock when you touch metal
     • You get this shock when electrons flow between you and the object
       • Electrons move fromyou to the earth, this process is called earthing, and means you have been discharged
   • Static electricity can build can build up in clouds, then it makes huge sparks between the cloud and the ground
     • We can see lightening because there are charged particles flowing through the air
     • We can alos hear it because lightening makes sound waves called thunder
     • Lightening can kill people and damge buildings
   • Static electricity can also build up when fuel flows througha pipe
     • To prevent a spark they have a bonding line (metal wires), this discharges without any sparks
     • Static electricity can also be used in insecticide/spray paint. it spreads more evenly.

3. Current and Voltage

   • The size of the current is measured with an ammeter
     • Ammeter placed in series
   • Potential difference is measured with a voltmeter
     • Voltmeter placed parallel with the component
     • In order to change the size of current in a circuit, you change the potential difference (voltage)
       • The higher the potential difference the bigger the current
     • It measures the difference between the electrons going into the component and those coming out
   • Energy is measured in Joules Charge is measured in Coulombs
     • 1 Volt= 1 Joule per Coulombs

4. Electric Currents

   • Insulating material can be given a charge of static electricity, because any charge transferred to the material cannot be conducted away.
   • All materials contain electrons
     • Electrons in an insulating material cannot move around
       • But in some metals, electrons are free to move around.
         • If the electrons in a metal flow, there is an electric current
   • Batteries supply a direct current
     • Generators produce an alternating current, this means electrons may change directions many times every second
   • Units of charge=coulombs (c)
     • 1 amp is a flow of 1 coulomb of charge per second
       • Q= I X T Charge=Current X Time
   • Units of current=Amperes (a)

5. Changing Resistances

   • The current flowing in a circuit depends on the potential difference of the supply, and on the resistance of the circuit
   • Resistance is a way of measuring how hard it is for electricity to flow
     • Resistance is measured in ohms
     • The resistance in the circuit depends on the resistance of the components in the circuit
   • The higher the total resistance, the smaller the current
   • Potential Difference= Current X Resistance V= I X R
   • Thermistors ()() Detect Heat
     • LDR ** Light Dependent
     • Diodes >> Conduct electricity in one direction

6. Velocity and Vectors

   • Quantities like displacement, velocity and force are all called vector quantities
   • Velocity tells you how quickly an object is moving and the direction it is going, it's is measured in m/s
   • Distance Time Graphs
     • Horizontal line= Stationary
     • Straight sloping line= Constant Speed
     • The steeper the line= The faster it is
     • Speed is calculated from the gradient of the line
       • Choose 2 points on the line, join to make a triangle
         • Minus the first distance from the second distance eg. 240m- 80m= 160m
           • Divide eg. 160m/80s=2m/s
         • minus the original time from the second time eg. 280s- 200s= 80s

7. Transferring Energy

   • When current flows through a resistor, energy is transferred and the resistor becomes warm
     • This is useful in kitchen appliances eg. electric fires, kettles
     • A similar thing happen with all components, eg. motor- electrical energy, turned into kinetic energy
     • Fuses are fitted into plugs to prevent fires, from all the friction of energy being transferred through small wires.
   • Power = The Energy Transferred Every Second
   • Electrical Power= Current X Potential Difference W= I X V
   • Energy Transferred= Current X Potential Difference X Time J= I X V X S