Physics

• when measuring the pendulum, make sure to measure from the clamp to the middle of the bob

  A) Length

  B) full swing

  C) right to the left

  D) left to the right

  
• measuring 20 oscillations rather than one oscillation helps students have a more reliable value is because it allows you to reduce errors and averaging your results
• when doing experimental design questions, make sure to mention plotting a graph and then repeating the experiment to take the average
• this is the symbol for a thermistor

  
• to make a negatively charged object that is attracted to a positively charged object to lose mass, you can transfer more electrons to the negatively charged object from the positively charged object so that the difference is bigger which leads to further attraction
• Remember that resistance increases as cross-sectional area decreases
• Remember to explain that when a magnet is nearby a magnetic material, it becomes an induced magnet and is attracted to eachother because opposite poles attract
• When talking about energy changes, remember to mention that it can also be dissipated into the environment
• Insulating Material Method:

  • Suspend one of the insulating materials using a cradle and a length of string so that the material can rotate freely
  • Rub one end of the material using a cloth (in order to give it a charge)
  • Now take a second piece of insulating material and charge that by rubbing with a cloth
  • Hold the charged end of the second piece close to the charged end of the first piece:
  • If the first piece rotates away (is repelled) from the second piece then the materials have the same charge
  • If the first piece moved towards (is attracted to) the second piece then they have opposite charges
• Testing Electrical Conductors and insulators with GLE

  • Charge the plate of the GLE so that the gold leaf stands clear of the rod
  • Carefully touch the plate of the GLE with the items being tested e.g. metals, non-metals, plastics, comparision of two objects
  • Record the observations each time
  • Leaf falls - material is a good conductor
  • Leaf remains in place - object is a poor conductor (good insulator)
  • Leaf falls slowly - material is a poor conductor
• In insulators, all of the electrons are strongly bound to each atom and aren't free to move around from atom to atom. In conductors, some of the electrons are loosely bound to each atom so they can easily move around, allowing charge to flow and redistribute throughout the conductor
• Electric field - a region in which an electric charge experiences a force
• The direction of an electric field at a point is the direction of the force on a positive charge at that point
• The direction of the field lines in an electric field is the direction of the force on a positive charge at that point

  • Fields lines always point away from positive charges and towards negative charges
  • The definition of the force direction refers to a positive charge, in demonstrations, it is always electrons (negative charges) which are free to move according to that force
• The field lines around a charge conducting sphere are also radial - like a point charge

  • the charges on the surface of the sphere will be evenly distributed
  • the charges are the same, so they repel
  • the surface is conducting, allowing the charges to move
• The electric field between two parallel plates is a uniform electric field

  • field patterns are uniform
  • Uniform electric field lines:
  • Directed from the positive to the negative plate
  • Parallel
  • Straight lines
• Ammeters can be either

  • Digital (with an electronic read out)
  • Analogue (with a needle and scale)
• Analogue ammeters - typical ranges are 0.1-1.0 A and 1.0-5.0 A

  • Always double check exactly where the marker is before an experiment, if not at zero, you will need to subtract this from all your measurements
  • Always read the meter from a position directly perpendicular to the scale
• Zero errors - when a measuring system gives a false reading when the true value fo the measured quantity is 0
• Parallax error - an error in a reading caused by not reading at eye level
• Digital ammeters - measure very small currents, in mA or µA

  • Shows the measured values as digits and are more accurate than analogue displays
  • Easy to use because they give a specific value and are capable of displaying more precise values
• Digital displays may 'flicker' back and forth between values and a judgement must be made as to which to write down

  • should be checked for zero error
  • Make sure the reading is zero before starting an experiment, or subtract the “zero” value from the end results
• Direct current (D.C) - produced when using dry cells and batteries (and sometimes generators, although these are usually ac)

  • The electrons flow in one direction only, from the negative terminal to the positive terminal
• Alternating current - typically comes from mains electricity and generators

  • The direction of electron flow changes direction regularly
  • A typical frequency for the reversal of AC current in mains electricity is 50 Hz
• If asked to explain the difference between alternating and direct current, sketch the graphs
• EMF - the work done by a source in moving a unit charge around a complete circuit
• Potential different - the work done by a unit charge passing through a component
• EMF equation: E = W/Q

  • E = electromotive force (e.m.f.) (V)
  • W = energy supplied to the charges from the power source (J)
  • Q = charge on each charge carrier and these are electrons in circuits (C)
• Analogue voltmeters are subject to parallax error

  • Always read the meter from a position directly perpendicular to the scale
• Typical ranges are 0.1-1.0 V and 0-5.0 V for analogue voltmeters although they can vary

  • Always double check exactly where the marker is before an experiment, if not at zero, you will need to subtract this from all your measurements
  • They should be checked for zero errors before using
• Digital voltmeters can measure very small potential differences, in mV or µV
• Digital displays show the measured values as digits and are more accurate than analogue displays

  • easy to use because they give a specific value and are capable of displaying more precise values
  • digital displays may 'flicker' back and forth between values and a judgement must be made as to which to write down
• Digital voltmeters should be checked for zero error

  • Make sure the reading is zero before starting an experiment, or subtract the “zero” value from the end results
• Equation for PD: V = W/Q

  • V = potential difference (p.d.) (V)
  • W = energy transferred to the components from the charge carriers (J)
  • Q = charge on each charge carrier and in circuits these are electrons(C)
• 4 factors affecting resistance

  • length - when the length increases, the resistance increases
  • cross sectional area - it is easier for electrons to move through a wider space than a smaller one which is why thin wires have more resistance while thicker wires have less resistance
  • material - the type of material affects its conductivitiy which influences resistance
  • temperature - resistance increases with temperatures because more particles are moving around inside the material so it’s more difficult to move acorss
  • semiconductors decrease in resistance when temperature increases
• Label

  A) resistor

  B) current

  C) potential difference

  D) filament lamp

  E) curent

  F) potential difference

  
• Label

  A) semiconductor diode

  B) current

  C) potential difference

  
• Power = IV
• Energy = IVt
• The kilowatt hour - A unit of energy equivalent to one kilowatt of power expended for one hour