REQUIRED PRACTICALS

• Determining the specific heat capacity of a material


  1. Place a beaker on a balance and press the zero button

  2. Add oil to the beaker and record the mass

  3. Place thermometer and immersion heater in the oil

  4. Place beaker in insulating foam

  5. Connect joulemeter to immersion heater

  6. Leave set up for 30 minutes

  7. Read total joules of energy passed into immersion heater and final oil temperature
• Specific heat capacity


  The amount of energy required to raise the temperature of one kilogram of a substance by one degree Celsius
• The equation to calculate specific heat capacity is: change in thermal energy = mass x specific heat capacity x temperature change
• Rearranging the equation gives: specific heat capacity = change in thermal energy / (mass x temperature change)
• The experiment calculated the specific heat capacity of vegetable oil as 1670 joules per kilogram per degree Celsius
• Potential sources of inaccuracy in the experiment

  • Thermal energy passing to the beaker and into the air
  • Not all thermal energy from the immersion heater passing into the oil
  • Incorrectly reading the thermometer
  • Thermal energy not spreading evenly through the oil
• Ways to reduce the sources of inaccuracy include using a lower thermal conductivity insulator, ensuring the immersion heater is fully submerged, using an electronic temperature probe, and stirring the oil
• Thermal insulator


  A material that reduces the flow of heat
• Investigating the effectiveness of thermal insulators

  1. Place a small beaker inside a larger beaker

  2. Use a kettle to boil water

  3. Transfer 80 cm^3 of hot water into the small beaker

  4. Use a piece of cardboard as a lid for the large beaker with a hole for a thermometer

  5. Place the thermometer through the hole with the bulb in the hot water

  6. Record the starting temperature and start a stopwatch

  7. Record the temperature every 3 minutes for 15 minutes

  8. Repeat the experiment using an insulating material (e.g. bubble wrap) between the beakers

  9. Test a range of insulating materials (e.g. cotton wool, polystyrene balls)

  10. Use the same mass of insulating material in each case
• Independent variable


  The variable that is changed in the experiment
• Dependent variable


  The variable that is measured for each change in the independent variable
• Control variables


  Variables that are kept constant in the experiment
• The water will cool down most slowly with the most effective insulating material
• Investigating how the thickness of a material affects thermal insulation

  1. Start with a beaker containing 80 cm^3 of hot water

  2. Measure the temperature of the water every 3 minutes for 15 minutes

  3. Repeat the experiment with 2 layers of newspaper around the beaker

  4. Repeat the experiment with 4 layers and 6 layers of newspaper
• Independent variable


  The number of layers of newspaper
• Dependent variable


  The temperature of the water
• The more layers of newspaper, the slower the water cools down, because more layers is a more effective thermal insulator
• Required practical


  At least 15% of the marks in your exam will come from questions relating to required practicals
• Investigating factors affecting resistance of electrical circuits

  1. Use battery, ammeter, voltmeter, and wire

  2. Measure current and potential difference

  3. Calculate resistance using formula: R = V/I

  4. Vary length of wire

  5. Plot graph of resistance vs length
• Graph shows a straight line passing through zero, indicating resistance is directly proportional to length
• Zero error


  A reading on a measuring instrument when the value should be zero, a systematic error
• Zero error is caused by difficulty in positioning crocodile clips at zero on ruler, and resistance from contact between clips and wire
• As temperature of wire increases

  Resistance also increases
• Reducing heating effects


  • Use low potential difference to keep current low
  • Only turn on current when taking readings, turn off between readings
• Variable resistor


  Contains a long piece of wire in a coil, using a slider to change the length of wire the current runs through
• Variable resistors are used to control potential difference across a lamp, increasing resistance dims the lamp
• Investigating the current-voltage characteristics of circuit components

  1. Use a voltmeter to read the potential difference across the component

  2. Use an ammeter to read the current through the component

  3. Record the potential difference and current values in a table

  4. Adjust the variable resistor to get a range of readings

  5. Reverse the direction of the battery and record the new readings
• For a resistor


  Current is directly proportional to potential difference
• The graph of current vs potential difference for a resistor is a straight line passing through the origin
• A resistor is an ohmic conductor
• If the temperature of the resistor increases, the graph will not be a straight line
• For a filament lamp


  Current is not proportional to potential difference
• As current increases, the temperature of the filament lamp increases, causing the resistance to increase
• The graph of current vs potential difference for a filament lamp has the same shape when the direction of the potential difference is reversed
• Investigating the current-voltage characteristics of a diode

  1. Use a milliammeter to measure the low current

  2. Include an extra resistor to protect the diode from high current

  3. Adjust the variable resistor to get a range of readings

  4. Record the potential difference and current values in a table

  5. Reverse the direction of the battery and record the new readings
• For a diode, current only flows when the potential difference is around 0.6-0.7 V
• For a diode, there is no current if the potential difference is reversed
• Diodes have a high resistance in the reverse direction
• You will find plenty of questions on this required practical in the revision workbook
• Density


  The mass per unit volume of a substance or object