Measurement of the specific heat capacity of a metal by an electrical method
Apparatus
Joulemeter, block of metal, heating coil to match, beaker, lagging, thermometer accurate to 0.1 °C, glycerol, electronic balance and a low voltage a.c. supply.
Procedure
- Find the mass of the metal block m .
- Set up the apparatus as shown in the diagram.
- Record the initial temperature q1 of the metal block.
- Plug in the joulemeter and switch it on.
- Zero the joulemeter and allow current to flow until there is a temperature rise of 10 °C.
- Switch off the power supply, allow time for the heat energy to spread throughout the metal block and record the highest temperature q2.
- The rise in temperature Dq is therefore q2– q1.
- Record the final joulemeter reading Q .
Results
Mass of metal block m =
Initial temperature of the block q1 =
Final temperature of the block q2 =
Rise in temperature Dq = q2 – q1=
Final joulemeter reading Q =
Calculations
The specific heat capacity of the metal c can be calculated from the following equation:
Energy supplied electrically = energy gained by the metal block
Q = mcDq .
Sample readings might be as follows.
Mass of aluminium block = 1 kg
Initial temperature of block = 15 °C
Final temperature of block = 22 °C
Joulemeter reading = 6350 J
Calculations
Electrical energy supplied = energy gained by aluminium block
W = mc Dq
6350 = 1 × c × 7
6350 = 7c
Specific heat capacity of aluminium, c = 9.1 × 102 J kg -1 K-1
Measurement of specific heat capacity of water by an electrical method
Apparatus
Joulemeter, calorimeter, heating coil, beaker, lagging, thermometer reading to 0.1 °C, electronic balance and a low voltage a.c.
Procedure
- Find the mass of the calorimeter m cal.
- Find the mass of the calorimeter plus the water m1. Hence the mass of the water mw is m1 – mcal.
- Set up the apparatus as shown. Record the initial temperature q1.
- Plug in the joulemeter, switch it on and zero it.
- Switch on the power supply and allow current to flow until a temperature rise of 10 °C has been achieved.
- Switch off the power supply, stir the water well and record the highest temperature q2. Hence the rise in temperature Dq is q2 – q1.
- Record the final joulemeter reading Q .
Results
Mass of the calorimeter m cal =
Mass of the calorimeter plus the water m1 =
Mass of the water mw = m1 – mcal =
Initial temperature of water qSUB>1 =
Final temperature q2 =
Rise in temperature Dq = q2 – q1 =
Final joulemeter reading Q =
Calculations
Given that the specific heat capacity of the calorimeter ccal is known, the specific heat capacity of water cw can be calculated from the following equation:
Energy supplied = energy gained by water + energy gained by calorimeter
Q = mwcwDq + mcal ccalDq
A typical set of results might look like this:
Mass of calorimeter = 0.080 kg
Mass of calorimeter + water = 0.150 kg
Mass of water = 0.070 kg
Initial temperature of water + calorimeter = 15 °C
Final temperature of water + calorimeter = 24 °C
Increase in temperature = 9 K
Specific heat capacity of copper = 390 J kg–1 K–1
Energy supplied = 2900 J
Calculations
Q = mwcw Dq+ mcccDq
2900 = 0.07 × cw × 9 + 0.08 × 390 × 9
2900 = 0.63 cw + 280.8
cw = 4157.46
= 4.2 × 103 Jkg–1 K–1
Measurement of the specific heat capacity of a metal or water by a mechanical method
Apparatus
Copper calorimeter, copper rivets, beaker, boiling tube, lagging, thermometer accurate to 0.1 °C, heat source and electronic balance.
Procedure
- Place some copper rivets in a boiling tube. Fill a beaker with water and place the boiling tube in it.
- Heat the beaker until the water boils. Continue boiling for a further five minutes to ensure that the copper pieces are 100 °C.
- Find the mass of the copper calorimeter mcal.
- Add cold water to the calorimeter until it is quarter full. Find the combined mass of the calorimeter and water m1. Hence the mass of the water mw is m1 – mcal.
- Record the initial temperature of the calorimeter plus water q1.
- Quickly add the hot copper rivets to the calorimeter, without splashing.
- Stir the water and record the highest temperature q2. The fall in temperature Dqc of the copper rivets is 100 °C – 02. The rise in temperature Dqw of the calorimeter plus water is q2– q1.
- Find the mass of the calorimeter plus water plus copper rivets m2 and hence find the mass of the rivets mc.
Results
Mass of the calorimeter mcal =
Mass of the calorimeter plus the water m1 =
Mass of the water mw = m1 – mcal =
Initial temperature of water q1 =
Initial temperature of rivets 100 °C
Initial temperature of calorimeter q1 =
Final temperature of water Dq2 =
Rise in temperature of water Dq2 = q2 – q1 =
Fall in temperature of rivets Dq1 = 100 °C – q2
Mass of calorimeter plus water plus rivets m2 =
Mass of rivets mco = m2 – m1
Calculations
Assume that heat losses to the surroundings or heat gains from the surroundings are negligible.
Given that either the specific heat capacity of water cw or the specific heat capacity of copper cc is known, the other specific heat capacity can be calculated from the following equation:
Energy lost by copper rivets = energy gained by copper calorimeter + the energy gained by the water
mcoccDqc = mcalccDqw + mwcwDq2
If cw is known, then cc can be calculated or alternatively if cc is known, cw can be found.
Sample results
Mass of calorimeter 0.082 kg
Mass of calorimeter + water 0.158 kg
Mass of water 0.076 kg
Mass of copper pieces 0.033 kg
Initial temperature of copper pieces 100 °C
Initial temperature of water in calorimeter 16 °C
Final temperature of water in calorimeter 19 °C
Specific heat capacity of water 4180 J kg-1 K-1
mcoccDq1 = mcalccDq2 + mwcwDq2
0.033 × cc × 81 = 0.076 × 4180 × 3 + 0.082 × cc × 3
2.673 cc = 953.0 + 0.246 cc
cc = 3.9 × 102 J kg-1 K-1
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