Module 12: Energy, force and communication

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(higher tier in bold green):

12.01 Units

12.02 describe common materials which are electrical conductors or insulators including metals and plastics
An electrical conductor is a material that does allow and an electric current to pass through it.
An electrical insulator is a material that does not allow an electric current to pass through it.
Conductors include: iron, copper, lead, zinc, all other metals and graphite.
Insulators include: polythene, polystyrene, PVC, all other plastics, glass and wood.

12.03 describe how an insulator can be charged by friction, resulting in the transfer of electrons
Rubbing a polythene rod with cloth makes a charge on the rod (and the cloth).
Rubbing any insulator with a different insulator makes a charge.  Charged insulators create forces.  E.g. a charged rod picks up tiny pieces of paper.
Electrons have a negative charge.
Electrons are gained by one insulator so it becomes negatively charged.  The other insulator loses electrons so becomes positively charged.
Task 12.03

12.04 recall that like charges repel and unlike charges attract
     positive charge          + --> (attraction) <--  -       negative charge  
positive charge    <-- +            (repulsion)             +  -->    positive charge
negative charge    <-- -             (repulsion)             - -->      negative charge
Task 12.04

12.05 describe common electrostatic phenomena in terms of movement of electrons
Static shocks from car doors happen when you touch a car door getting out of the car.  Electrons jump between you and the metal door on their way to or from the Earth.
Static charges build up on synthetic fabrics like nylon in shirts.  Dangerous shirt story
See static safe clothing   
Lightning is the movement of a static charge (electrons) between clouds or between a cloud and the ground.

A lighting conductor can prevent damage.

12.06 describe some of the uses and dangers of electrostatic charges in everyday situations
fuelling aircraft and tankers can result in a static charge creating a spark and igniting the fuel.
The tanker and aircraft are connected by a metal wire and connected to Earth to avoid a charge building up and giving a spark.

Photocopiers use static charges.   (The notes an animation below from V. Ryan http://www.technologystudent.com/designpro/prtpro6.htm )

Inkjet printers also use static charge.  Ink flows down onto a charging electrode.  The charged particles of ink are then deflected by a charged plate onto paper.  The charge on the plate is changed to change the position of the ink drop on the paper.

12.07 explain how earthing removes the excess charge on a body, with reference to the movement of electrons
Any charge will flow to the ground if it can find a path.  This is called earthing.  It involves the movement of electrons which carry the charge.

12.08 understand that current is rate of flow of charge
When charges move we say that a current flows.
The size of the current depends on the size of the charge (in coulombs,C) and how long (in seconds ,s) they take to flow past a point.

12.09 recall and use the equation charge (C) = current (A) * time (s)   Q = I * t
charge = current * time     
Q=I*t  
note 1C/s = 1A
E.g. What is the current flowing if a charge of 5C flows in 20s?
Q=I*t
I=Q/t =5C/20s = 0.25C/s = 0.25A
Task 12.09

12.10 understand that electric current in metals is a flow of negatively charged electrons

12.11 understand that electric current in molten or dissolved electrolytes is a movement of both positive and negative ions

Electrolytes like lead bromide contain ions.  These ions have a charge and they are attracted to the charged electrodes because opposite charges attract.  The charged ions carry the current in an electrolyte.

12.12 recall and use the equation P = I * V
electrical power = current * voltage     or
P = I * V  where
P = electrical power (measured in W)
I  = current (measured in A) and 
V = voltage (measured in V)
Task 12.12

12.13 use the equation for energy transferred, current, voltage and time
energy transferred = current * voltage * time    or
E = I * V * t (will be provided if needed) where
E = energy transferred (measured in J)
I = current (measured in A)
V = voltage (measured in V)
t = time (measured in seconds)
Task 12.13

12.14 understand that voltage is the energy transferred per unit charge passed; the volt as a joule per coulomb
The units are: charge - coulombs C, energy - Joule J, voltage volts V.

12.15 recall that a force is exerted on a current-carrying wire in a magnetic field and understand how this is used in a simple d.c. motor
See force on a current carrying wire in a magnetic field    See a d.c. motor animation
Story 12.15 What a shock.

12.16 understand that when a wire carrying a current is perpendicular to a magnetic field, the resulting force is perpendicular to both
Use Flemming's left hand rule to find directions of current, magnetic field and force.

12.17 recall the structure of a transformer and understand that a transformer changes the size of an alternating voltage by having different numbers of turns on the input and output sides

12.18 recall and use the quantitative relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer
voltage (primary) / voltage(secondary) = turns(primary) / turns(secondary
V_p/V_s = n_p/n_s
Task12.18 

12.19 explain the use of step-up and step-down transformers in transmitting electricity

12.20 understand that transmitting electrical power at high voltages reduces the current required, and this reduces power losses caused by heating
low voltage, high current, high power loss
high voltage, low current, low power loss.

Waves and communication
12.21 recall that waves transfer energy and information without transferring matter
Water waves carry energy forward but water only goes up and down.
Sound waves carry energy and information (e.g. music) forward but air only move backwards and forwards.

12.22 recall and use the equation for all waves:
- wave speed (m/s) = frequency (Hz) * wavelength (m)
v = f *l
Where v = wave speed, f = frequency and  l = wavelength

12.23 understand the condition for total internal reflection to take place and how this is used in optical fibres and in reflecting prisms

Light hits boundary at small angle.  Light is refracted out of the glass but some is reflected back into it.



Light hits the boundary at a larger angle.  This is the critical angle.  Some light is refracted along the glass air boundary but the rest is reflected back into the glass.





Light hits the boundary at a big angle.  This is bigger than the critical angle.  All of the light is reflected back into the glass.  This is total internal reflection.





 
Light enters the prism and total internal reflection happens off of the back surface.  A second total internal reflection happens to send the light back out of the glass in the same direction that it entered.  A cycle relector acts in this way.





12.24 understand that digital signals can carry more information than analogue signals
The TV programmes through an arial show the difference in the amount of information that can be delivered by the two systems.

12.25 recall that waves spread out when they pass through a narrow gap or past an edge and that this is called diffraction
diffraction of radio waves past the edge of a mountain
http://www.learnpremium.co.uk/Whiteboardactiv/Science/Keystage4/
http://micro.magnet.fsu.edu/primer/java/diffraction/basicdiffraction/index.html

12.26 understand that sound and light show diffraction effects
 

12.27 describe and interpret some examples of diffraction, eg
Diffraction of sound by large building/doorways
Diffraction occurs when an obstacle's dimensions are of the same order or less than the wavelength of the sound. In this case the edge of the obstacle acts like a source of sound itself and the sound ray appears to bend around the edge. This limits the effectiveness of barriers.


Diffraction of water waves by harbours


Diffraction of light by a single narrow slit
  Thin bubble film acts like a narrow slit.
Laser light through a narrow opening.

12.28 understand how reflection and diffraction affect the quality of received radio signals
Factors Affecting Radio Signals

1. In a similar way to light, radio waves travel in straight lines and are affected by obstructions which can alter the radio signal. The main factors that affect radio signals are illustrated in the following diagrams:

                        

Signal strength reduced by attenuation when passing through a building.

   Signal loss due to shadowing from terrain.

     Signals can 'bend' round obstructions to some extent (diffraction). 

 

Signal strength reduced by reflection from walls and other objects.

 

Forces and shape
12.29 understand that the upward forces on a light beam supported at its ends vary with the position of a heavy object placed on the beam

5N| ____________________O_______________________|_5N
    ||                                          |   10N                                      ||  

7.5N| _________O_________________________________|_2.5N
       ||                    |   10N                                                         ||  

2.5N| ________________________________O__________|_7.5N
       ||                                                                  |   10N           ||  

12.30 describe how extension varies with applied force for a range of materials including springs and rubber bands
See a demonstration of Hookes law here KHS ID and password needed.

12.31 recall that particles in a gas have random motion and that they exert a force on the walls of the container


12.32 understand the relationship between the pressure and volume of a fixed mass of gas at constant temperature and use the quantitative relationship
 P1 * V1 = P2 * V2 for a fixed mass of gas at constant temperature
This is called Boyle's Law
where P1 = starting pressure of a gas
V1 = starting volume of a gas
P2 = is the new pressure of a gas
V2 = is the new volume of a gas