Required Practical: Investigating Specific Heat Capacity

what is the aim of the experiment?

The aim of the experiment is to determine the specific heat capacity of a substance, by linking the amount of energy transferred to the substance with the rise in temperature of the substance

what is the independent variable?

Time, t

what is the dependent variable?

Dependent variable = Temperature, θ

what are the 3 control variables?

• Material of the block

• Current supplied, I

Potential difference supplied, V

how many pieces of equipment is needed?

7

list all the pieces of equipment required

• 1kg block of metal or a beaker containing a known mass of water

• thermometer

• immersion heater

• power supply

• stopwatch

• voltmeter

• ammeter

purpose of the metal/water?

is the substance to calculate the SHC

purpose of the thermometer?

to measure the temperature rise of the substance

purpose of the immersion heater?

to heat the substance

purpose of the power supply?

to supply power to the heater

purpose of the stopwatch?

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

purpose of the voltmeter?

to determine the p.d through the heater

purpose of the ammeter?

to determine the current from the power supply to the heater

what are the 4 pieces of measuring equipment?

• Thermometer

• Stopwatch

• Voltmeter

• Ammeter

what are the different resolutions of the 4 pieces of measuring equipment

• Thermometer = 1 °C

• Stopwatch = 0.01 s

• Voltmeter = 0.1 V

• Ammeter = 0.01 A

how many steps are there to the method?

6

1st step to the method

Start by assembling the apparatus, placing the heater into the top of the block

2nd step to the method

Measure the initial temperature of the aluminium block from the thermometer

3rd step to the method

Turn on the power supply and start the stopwatch

4th step to the method (3)

• Whilst the power supply is on, the heater will heat up the block.

• Take several periodic measurements, eg. every 1 minute of the voltage and current from the voltmeter and ammeter respectively,

• calculating an average for each at the end of the experiment up to 10 minutes

5th step to the method

Switch off the power supply, stop the stopwatch and leave the apparatus for about a minute. The temperature will still rise before it cools

6th step to the method

Monitor the thermometer and record the final temperature reached for the block

list the full method of the experiment

1. Start by assembling the apparatus, placing the heater into the top of the block

2. Measure the initial temperature of the aluminium block from the thermometer

3. Turn on the power supply and start the stopwatch

4. Whilst the power supply is on, the heater will heat up the block. Take several periodic measurements, eg. every 1 minute of the voltage and current from the voltmeter and ammeter respectively, calculating an average for each at the end of the experiment up to 10 minutes

5. Switch off the power supply, stop the stopwatch and leave the apparatus for about a minute. The temperature will still rise before it cools

6. Monitor the thermometer and record the final temperature reached for the block

what variables would be used in the results table

time/s → p.d/v → current/A → average → initial temperature → final temperature

What 2 equations would you use to analyse the results and how?

thermal energy supplied to the block should be calculated using:

• energy = charge x voltage (E = QV)

• charge = current x time (Q = It)

what do the symbols mean in these two equations → energy = charge x voltage (E = QV)

• charge = current x time (Q = It)

• E = thermal energy, in joules (J)

• Q = Charge, in coulombs (C)

• I = current, in amperes (A)

• V = potential difference, in volts (V)

• t = time, in seconds (s)

What steps would you take to combine these two equations: energy = charge x voltage (E = QV)

• charge = current x time (Q = It)

• Rearrange to make Q the subject - E = QV → Q = E/V

• Substitute into the Q = It equation - Q = It → E/V = It

• Rearrange to make E the subject - E = IV

what is the equation to calculate the change in thermal energy?

change in thermal energy = mass x SHC x change in temperature

what would be the equation to work out SHC

how would you calculate the change in temperature

change in temperature = final temp = initial temp

how would you calculate the change in energy?

change in energy = (average current x final temperature) - (average current x initial temperature)

What would be a systematic error of this experiment and how would it be avoided?

• Make sure the voltmeter and ammeter are initially set to zero, to avoid zero error

What would be a random error of the experiment?

Not all the energy transferred from the heater will be transferred to the block, some will be dissipated to the surroundings into the surroundings and some will be transferred to the thermometer (also part of the surroundings) 

• This means the measured value of the specific heat capacity is likely to be higher than what it actually is

Give three ways to avoid the random error

• make sure the block is fully insulated

• A joulemeter could be used to calculate energy directly

  • This would eliminate errors from the voltmeter, ammeter and the stopwatch

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

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

List 3 safety considerations for this practical

Any 3 out of:

• Make sure never to touch the heater whilst it is on, otherwise, it could burn skin or set something on fire

  • Run any burns immediately under cold running water for at least 5 minutes

• Allow time for all the equipment, including the heater, wire and 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