2c) Energy and potential difference in circuits

Circuits:

Parallel-

• each component separates and is connected separately
• If you disconnect one component it doesn't really effect the others 
• Used for most things like domestic lighting 

Series-

• the different components are connected in a line, end to end 
• can't control current flow 
• circuit gets broken when you disconnect one component 
• not handy so is not widely used 
• example; fairy lights

Currents:

The size of a current ids determined by the total voltage of cell(s) and the total resistance of circuit 

more components= more resistance 

Light-Emitting diodes ----> indicate the presence of a current in a circuit (so can lamps). Used in applicantions to show they are in e.g. a remote control 

Some components can change resistance:

• Light dependent Resistor (LDR)- changes it's resistance depending on how much light falls on it ----> for example a burglar detector 
• From dark to light 
• Thermistor- temperature dependent resistor ----> fro example car engine temperature sensors 
• From cold to hot 

Voltage= current x resistance 

V= I x R 

Current is the rate of flow of electrical charge (in amperes, A) around a circuit 

Charge= Current x Time 

Q= I x t 

electric current in a solid metallic conductor (e.g. copper wire) is charged by negatively charged electrons 

Voltage is the energy transferred per unit charge passed 

                 one volt = one joule per coulomb 

Information in bold, italics are only for paper two

2b) Mains electricity

Safety hazards of plugs:

• If damaged -----> live parts could be exposed and you could get a shock
• Frayed -----> live parts may not be covered 
• Too long -----> trip hazard 
• No water near electrical objects -----> very good conductors 
• Metal conducts electricity -----> shock   

Earthing and fuses:

1. If a fault develops -----> case is earthed down to earth wire 
2. Surge in current -----> blows (melts) the fuse which cuts of live supply 
3. Isolates the whole appliance -----> impossible to get an electric shock -----> prevents fires   

Resistors:

• electric current -----> energy transfer 
• heating effect -----> increases resistance 
• can cause components to melt -----> circuits stop melting 
• Fuses use the effect to protect circuits 
• Advantages: good for toasters and old style light bulbs -----> due to heat 

Electrical Power -----> rate at which an appliance transfer energy 

• high power rated appliances transfer a lot of energy in a short time; energy comes from current 
• fuses are rated 
• Power is measured in watts 

Electrical Power = Current x Voltage 

P = I x V 

Circuit breakers > Fuses:

• electrical safety devices -----> (like fuse) protect circuit from damage 
• detect a surge and break the circuit opening a switch 
• can be easily reset -----> more convenient than fuses (they melt and have to be replaced) 

When a current flows through a component, energy is transferred

Energy Transferred = Current x Voltage x Time 

E = I x V x T 

Alternating Current:

Direct Current: 

2a) Units

Use the following units:

• ampere (A)
• coulomb (C)
• joule (J) 
• ohm (Ω)
• seconds (s)
• volt (V)
• watt (W) 

1d) Astronomy

Gravitational field strength changes in different planets. The gravitational field strength on the Earth is 10.

Gravitational force:

• Causes moons to orbit planets 
• The Earth's moon rotates on own axis every 27.5 days and from Earth we always see the same side of the moon 
• Causes the planets to orbit the Suns 
• Mercury 
• Venus 
• Earth 
• Mars 
• asteroid belt 
• Jupiter 
• Saturn 
• Uranus 
• Neptune 
• Causes artificial satellites to orbit the Earth 
• Causes comets to orbit the sun 
• Balls of ice and dust 
• orbits the sun 
• tail formed when near the sun which points away from the sun called solar wind 
• speed INCREASES when close to the sun due to gravitational pull 
• elliptical (egg-shaped) orbit 

Orbits are objects that travel in a circle and is the balance between a forward motion of object and force pulling inwards 

Orbital speed= (2 x π x orbital radius) / Time period 

V= (2 x π x r) / T 

The universe is a large collection of billions of galaxies, which is a large collection of a billion stars. Our solar system is called the Milky Way 

1c) Forces, movement, shape and momentum

Force= Mass x Acceleration 
F= m x a 

Types of Forces:

1. Gravity or weight always acting straight down
2. Reaction force from a surface acting straight up 
3. Electrostatic force between 2 charged objects direction depends on type of charge 
4. Thrust or Push or Pull speeding something up 
5. drag or Air resistance or Friction slow things down 
6. Lift aeroplane wing 
7. Tension rope or cable 

Scalar quantity: only magnitude. an example is speed 

Vector quantity: has a magnitude (size) and direction. An example is velocity 

Friction is a force that opposes motion

Mass, Weight and Gravity

Weight = Mass x Gravitational Field Strength 

W=m x g

Terminal velocity is the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is failing prevents further acceleration 

               Sycamore Seeds are an example of terminal velocity 

             

Factors that affect vehicles:

Thinking distance 

Stopping distance 

Braking distance 

Road conditions 

Reaction time 

Alcohol and drugs 

Speed 

Mass 

Momentum= Mass x Velocity 

p= m x v 

Momentum and safety:

Seat belts, air bags and crumble zones increase the time taken for the change in the occupants' bodies (during a car crash) which then reduces the forces and chance of injury. 

Seat belts- stretch slightly, increasing the time taken and reducing the forces 

Air bags- slow you down gradually 

Crumble zones- crumble on impact and increasing the time of it to stop 

Force acting (N)= Change in momentum (kg m/s) / time taken for change to happen(s) 

Moment (Nm) = Force (N) x perpendicular Distance (m) between line of action and pivot  

If an object is balanced:

Total clockwise moments = Total anti-clockwise moment 

Newton's Third Law 

The harder you push, the faster the object will speed up 

Paper Two in Bold Italics 

1b) Movement and position

Investigating motion of everyday objects 
You plot the time it takes for a toy car to travel and then plot a distance time graph. Then repeat at different speeds and compare the different graphs.

Alternatively you could use a ticker tape; this makes a mark every second on the tape, If you attach the car to the end of the tape, its speed will be recorded: distance/dots= speed. 



Relationship between Acceleration, Velocity and Time

Speed and velocity are measured in m/s (km/h or mph) and say fast you are going 
Speed: how fast without regard to the direction
Velocity: how fast and the direction specified 

Average Speed= Distance moved/time taken 

Acceleration: how quickly velocity is changing

Acceleration= change in velocity/ time taken 
a=(v-u)/t 

Velocity Time-graphs