practicals

• shc:

  independent variable - materials of blocks

  dependent variable - temperature

  control variables - time, starting temperature, mass of blocks
• specific heat capacity (why?):

  1. to reduce energy dissipated
  2. the current transfers energy electrically from the power supply to the heater's thermal energy store, then transferred to the material's thermal store by heating causing the temp to increase.
  3. power by multiplying voltage by current and then energy transferred by multiplying the power by time in seconds, then shc by dividing the change in energy by the change in temp and mass
• 1. get different blocks of material with two holes. measure the mass of a block and *wrap in insulating material and add thermometer and heater in into the holes
  2. attach the heater to an ammeter and power supply and the ammeter to the power supply
  3. measure initial temp of the block and set the potential difference to 10v on the power supply. *turn the power supply on and start a stop watch
  4. every 10mins, take readings of temp and current 10 times and record in a table *
  5. repeat with different materials to compare
• affecters of resistance:

  • length of wire, thickness of wire, temperature
  • as length increases, resistance increases -> electrons have to travel further so will collide with particles more often
  • as thickness increases, resistance decreases -> more room for electrons to flow and collide with particles less often
  • as temperature increases, resistance increases ->particles vibrate more so electrons collide with particles more often
• affecters of resistance :

  independent variable - length of wire/thickness of wire/temperature (3 different practicls)

  dependent variable - resistance

  control variables - length of wire, thickness of wire, temperature

  if testing one of the independent variables, the other two must be controlled, e.g. if length of wire is tested, the thickness and temperature must be the same for the different lengths
• fixed resistor:

  directly proportional, resistance is constant

  
• filament lamp:

  resitance increases and potential difference increases

  
• diode:

  current only flows in one direction, there is high resistance in the reverse direction

  
• density - regular object:

  1. find volume of object with a ruler
  2. length $\times$ width $\times$ height
  3. find mass
  4. put object on mass balance
  5. put into equation density = mass $\div$ volume
• density - irregular object:

  1. find mass
  2. put on mass balance, record results
  3. find volume
  4. fill a measuring cylinder with water to a fixed amount
  5. add object
  6. measure the displacement of the water, the difference between the final and initial volume
  7. put into equation -> density = mass $\div$volume