Unit 3 - Forensics

• What is the Independent variable

  something you change (give range and statistics for practical)
• What is the dependent variable

  something you measure
• What is the control variable

  what you keep the same
• How do you write a method

  • instructional for others to follow
  • numbered steps in chronological order
  • name apparatus
  • state what needs to be recorded
  • state repeats
• What is a hypothesis

  prediction on what will happen - doesn't have to be correct
• What is a null hypothesis

  doesn't make a difference if variables occur and the result of the practical (no trend or link)
• How to write a risk assessment

  Hazards - why is it dangerous

  Risk - what and when might something go wrong

  Precautions - to stop the risk
• How to organise a results table

  • first column is the independent variable
  • second column is the dependent variable (and repeats)
  • units only present in the headings
  • all to the same decimal place
  • highlight anomalies
• how to draw a graph

  Scale

  Axis (Dependent - up, Independent - across)

  Labels

  Units

  Title

  Equipment

  Data
• How to describe the trend

  'As you change the __independent__ the __dependent__ will ___ (look at results and describe)'
• What is Qualitative data

  If a substance is present or not e.g. starch & iodine test
• What is Quantitive data

  exactly how much of a substance is present e.g. blood glucose monitor
• What is semi-quanitiative data

  roughly how much of a substance is present e.g. pH scale
• What is standard deviation

  Measure of how far data values are from the mean value
• what are error bars

  the highest and lowest values towards the median range
• what factor is the prefix 'mega' (M)

  1,000,000 (million)
• what factor is the prefix 'kilo' (k)

  1,000
• what factor is the prefix 'centi' (c)

  0.01
• what factor is the prefix 'milli' (m)

  0.001
• what factor is the prefix 'micro'

  0.000001
• how to find the percentage error

  Emr / value x 100

  e.g. measured 36mm on a ruler, absolute error = +-0.5, % error = 0.5/36 x 100
• How to analyse results

  look at the relationship between variables & link to the hypothesis, make a conclusion from the investigation

  • describe using 'increase/decrease'
  • include data if suitable

  'My results show that as the __ increases/decreases the __ will __ because __'
• How to evaluate results

  • explain reasons for anomalous results
  • suggest Improvements - more precise equipment, repeats, problem with method, wide range of independent variables
  • e.g. weighing scales used only measured to nearest gram, use scale measured to nearest 0.1g instead
  • comment on quality of data (repeatable - repeats are similar, reproducible - other groups give similar results)
  • give examples
• What do these do

  Cell – push electrons around

  Battery – number of cells joined together

  Ammeter - measures current

  Voltmeter – measures potential difference (voltage)

  Bulb – lights up when a current passes through

  Fixed resistor – limits current that is flowing

  Variable resistor – allows current to be varied

  Diode – allows current to flow in one direction
• How to add a voltmeter to a circuit

  Add in parallel
• What happens when the number of Batteries increase

  The Current increases
• What is resistance

  Blocks the flow of electrons, reducing the current
• What makes up the fire triangle

  Oxygen

  Heat

  Fuel

  remove one and fire can no longer burn
• How to remove oxygen

  Use of a carbon dioxide extinguisher or fire blanket
• How to remove heat

  Fast moving air or water (not for electrical fires)
• How to remove fuel

  Using fire resistant materials for clothes, furniture or building materials or removing unused fuel in the area
• What is a fuel

  Hydrocarbons
• what percent of air is oxygen

  21%
• What is calorimetry

  Energy is released in chemical reactions as light, sound or electrical energy but mostly heat energy (Measuring heat transfers)
• How to keep something a fair test


  • Same volume
  • Same initial temperature
  • Same temperature increase
  • Same distance of the flame from experiment
  • Complete repeats
• What are the hazards associated with fuels

  Flammability

  Toxicity

  Risk of explosion

  Pollution
• What is specific heat capacity

  The amount of heat energy required to increase the temperature of 1 kg of a substance by 1*C.
• What are enzymes

  biological catalysts that speed up chemical reaction in living things
• What are enzymes made up off

  amino acids
• What happens if an enzymes bonds are broken

  it becomes denatured