practical - SHC

• Measuring the specific heat capacity of a metal block:

  Use the MASS BALANCE to measure the mass of the metal block.

  • Record the value.

  SETTING UP THE EXPERIMENT:

  • Place the metal block into insulation and insert both the immersion heater & thermometer into the appropriate holes in the block.
  • Connect the IMMERSION HEATER to the BATTERY PACK & the JOULEMETER.

  
• Measuring the specific heat capacity of a metal block:

  HEATING & MEASURING:

  • Turn on the IMMERSION HEATER to start heating the metal block.
  • Record the initial temperature from the THERMOMETER and the initial energy from the JOULEMETER.

  CALCULATING SPECIFIC HEAT CAPACITY:

  • Once you have finished heating, turn OFF the heater.
  • Record the final temperature and energy readings.
  • Use the SPECIFIC HEAT CAPACITY equation.

  
• Equipment needed to measure the SPECIFIC HEAT CAPACITY of a substance like aluminium:

  • METAL BLOCK
  • IMMERSION HEATER
  • THERMOMETER
  • INSULATION
  • JOULEMETER
  • MASS BALANCE
  • BATTERY PACK
  • heat proof mat
  • ammeter
  • voltmeter
  • stopwatch

  
• METAL BLOCK:

  • Made of the material you are testing, like aluminium, with holes for the heater & thermometer.

  IMMERSION HEATER:

  • To provide heat to the metal block.

  THERMOMETER:

  • To measure the temperature of the metal block.

  
• INSULATION:

  • To minimise heat loss from the metal block.

  JOULEMETER:

  • To measure the amount of energy used.

  MASS BALANCE:

  • To measure the mass of the metal block.

  BATTERY PACK:

  • To supply power to the immersion heater.

  
• ΔΕ = mcΔθ

  • ΔΕ = 37315 J
  • Mass = 1.3 Kg
  • Δθ = 57℃ - 25℃ = 32℃

  c = ΔΕ / mΔθ = 37315 J / (1.3Kg x 32℃) = 897 J/Kg℃ (3 s.f.)

  
• To find out the specific heat capacity of a liquid:

  • Use the procedure to measure the specific heat capacity of a metal block.
  • But instead Use a polystyrene cup with a lid to minimise heat lost to the surroundings, to make calculations more ACCURATE.

  
• Control variables:

  • Material of the block
  • Current supplied, I
  • Potential difference supplied, V

  Independent variable:

  • Time

  Dependent variable:

  • Temperature
• Stopwatch:

  • To measure the time taken for the substance to heat up by a certain temperature.

  Voltmeter:

  • To determine the potential difference through the heater.

  Ammeter:

  • To determine the current from the power supply to the heater.
• Resolution of measuring equipment:

  • Thermometer = 1 °C
  • Stopwatch = 0.01 s
  • Voltmeter = 0.1 V
  • Ammeter = 0.01 A
• The thermal energy supplied to the block can be calculated using the equations:

  • Thermal energy (Joules) = charge (coulombs) x potential difference (volts)
  • E = QV
  • Charge (coulombs) = Current (amperes) x time (seconds)
  • Q = IT
• To calculate ΔE, Change in energy (joules):

  • average current (amperes) x average potential difference (V) x final time (seconds)

  Minus

  • average current (amperes) x average potential difference (V) x initial time (seconds)

  ΔE = IV$\theta_f^{ }$ - IV$\theta_i^{ }$
• Systematic Errors in experiment:

  Make sure the voltmeter & ammeter are initially set to zero, to avoid zero error.
• Random Errors in experiment:

  Not all the energy transferred from the heater will be transferred to the block.

  • Some will go to the surroundings or thermometer.
  • Meaning the measured value of the specific heat capacity is likely to be higher than what it actually is.
  • To reduce this effect, make sure the block is fully insulated.
• Random Errors in experiment:

  A joulemeter could be used to calculate energy directly.

  • To eliminate errors from the voltmeter, ammeter & the stopwatch.

  Make sure the temperature value is read at eye level from the thermometer, to avoid parallax error.

  The experiment can be repeated with a beaker of water of equal mass, the water should heat up slower than the aluminium block.
• Safety Considerations:

  Don't touch the heater when it's on, or it could burn skin / set something on fire.

  • Run any burns under cold running water for at least 5 mins.

  Allow time for all the equipment, including the heater, wire & block to cool before packing away the equipment.

  • Keep water away from all electrical equipment
  • Wear eye protection if using a beaker of hot water
• When making the graph:

  • put the temperature on the y-axis
  • time on the x-axis.

  
• To find the specific heat capacity:

  • draw a right angle triangle with the line of best fit for the linear part of the graph.
  • Take the width of the triangle, that's the change in time
  • divide it by the height of the triangle, that's the change in temperature.
  • Times it by the power
  • Divide by the mass

  
• • measure mass of oil using the top pan balance.
  • measure start temp. of oil using the thermometer.
  • place beaker of oil on heater
  • measure final temp. of oil using the thermometer.
  • measure energy transferred using joulemeter
  • calculate increase in temp.
  • use the equation E = mcΔθ to determine c

  
• Ways to reduce energy transfer from the apparatus to the surroundings:

  • insulate the beaker
  • add a lid

  
• The mass of water decreases during the test, because some evaporated.

  
• Because the heating element in the kettle take time to heat up.

  
• Improvement to the method:

  • repeat the experiment and calculate the mean temperature rise.
  • heat the oil for a longer period of time, to get a wider range of temperatures.