Practicals

• What is the first step to investigate specific heat capacities of a solid material?

  Obtain a block of the material with two holes for the heater and thermometer.
• Why should the block be wrapped in an insulating layer?

  To reduce the energy transferred from the block to the surroundings.
• What should be measured after wrapping the block in insulation?

  The mass of the block.
• What is the potential difference set to during the experiment?

  10 V.
• What happens when the power is turned on in the circuit?

  The current does work on the heater, transferring energy from the power supply to the heater.
• How does the energy transfer occur in the experiment?

  Energy is transferred electrically to the heater's thermal energy stores and then to the material's thermal energy store by heating.
• How often should temperature and current readings be taken during the experiment?

  Every minute for 10 minutes.
• What should be observed about the current through the circuit as the block heats up?

  The current through the circuit doesn’t change as the block heats up.
• What can be calculated using the current and potential difference after turning off the power supply?

  The power transferred to the heater using \( P = VI \).
• How can the energy transferred to the heater be calculated at each temperature reading?

  Using the formula \( E = Pt \), where \( t \) is the time in seconds.
• What assumption is made about the energy supplied to the heater?

  All the energy supplied to the heater has been transferred to the block.
• What type of graph is plotted after collecting enough data in the experiment?

  A graph of energy transferred to the thermal energy store of the block against temperature.
• What does the gradient of the straight part of the graph represent?

  It represents \( \Delta E/\Delta \theta \).
• How is the specific heat capacity of the material calculated?

  Using the formula \( c = \Delta E/(m\Delta \theta) \).
• What can be done to compare specific heat capacities of different materials?

  Repeat the experiment with different materials.
• What is the procedure for investigating specific heat capacities of a solid material?

  1. Obtain a block of the material with holes for heater and thermometer.
  2. Measure the mass and wrap in insulation.
  3. Measure initial temperature and set power supply to 10 V.
  4. Turn on power and record temperature and current every minute for 10 minutes.
  5. Calculate power using \( P = VI \) and energy using \( E = Pt \).
  6. Plot energy against temperature and find the gradient.
  7. Calculate specific heat capacity using \( c = \Delta E/(m\Delta \theta) \).
  8. Repeat with different materials.
• What is the specific heat capacity equation and its components?

  • Specific heat capacity equation: \( c = \Delta E/(m\Delta \theta) \)
  • \( \Delta E \): Change in energy
  • \( m \): Mass of the material
  • \( \Delta \theta \): Change in temperature
• How does the resistance of a filament lamp change with temperature?

  As the current increases, the filament lamp heats up more and the resistance increases.
• What is the behavior of diodes regarding current flow?

  Diodes allow current to flow in one direction but have high resistance if reversed.
• What does the term 'I-V characteristic' refer to?

  • A graph showing how current (I) changes as potential difference (V) increases.
  • Linear components have a straight line characteristic.
  • Non-linear components have a curved characteristic.
• What type of circuit is used to measure I-V characteristics?

  A direct current (d.c.) series circuit is used.
• What is the I-V characteristic of a fixed resistor?

  It is a straight line on the graph.
• What is the I-V characteristic of a filament lamp?

  It has a curved I-V characteristic.
• What is the I-V characteristic of a diode?

  It has a non-linear, curved I-V characteristic.
• What are the steps to find a component's I-V characteristic?

  1. Set up the test circuit.
  2. Vary the variable resistor to change current and potential difference.
  3. Take readings from the ammeter and voltmeter.
  4. Reverse the current direction by swapping battery wires.
  5. Plot a graph of current against voltage.
• What happens to the resistance of a thermistor in hot conditions?

  The resistance decreases in hot conditions.
• What happens to the resistance of a thermistor in cool conditions?

  The resistance increases in cool conditions.
• What are the applications of thermistors?

  • Used in car engines.
  • Used in electronic circuits.
  • Used in sensing circuits to measure temperature.
• How does adding resistors in series affect total resistance?

  1. Total resistance increases with each added resistor.
  2. Measure current and potential difference to calculate resistance.
  3. Plot a graph of the number of resistors against total resistance.
• How does adding resistors in parallel affect total resistance?

  1. Total resistance decreases with each added resistor.
  2. Measure total current and potential difference to calculate resistance.
  3. Plot a graph of the number of resistors against total resistance.
• What type of electricity is supplied by mains supply?

  Mains supply is alternating current (a.c.).
• How does alternating current (a.c.) behave?

  The current constantly changes direction due to alternating voltages.
• What is the frequency of the UK mains supply?

  The frequency is 50 Hz.
• What type of current do cells and batteries supply?

  Cells and batteries supply direct current (d.c.).
• What is direct current (d.c.)?

  Direct current flows in one direction only.
• What are the three wires in most electrical appliances?

  • Live wire (brown)
  • Neutral wire (blue)
  • Earth wire (green/yellow)
• What is the function of the neutral wire?

  The neutral wire completes the circuit and is around 0 V.
• What is the significance of the colour code for wires?

  The colour code helps to identify wires for safety reasons.
• What is the general density comparison between gases and liquids?

  Gases are generally less dense than liquids.
• What are the steps to find the density of a solid object?

  1. Measure mass using a balance.
  2. For regular solids, measure dimensions and calculate volume.
  3. For irregular solids, submerge in a eureka can to find volume.
  4. Use the formula density = mass/volume.