The specific thermal capacity of lead
Practical Activity for 14-16
Transferring energy mechanically to lead shot and measuring its temperature rise.
Apparatus and Materials
For each group of students
- Lever-arm or top pan balance (+/- 10g is sufficiently accurate)
- Cardboard tube (approx 50 - 100 cm long)
- Lead shot, 500 g
- Plastic or cardboard cups
- Metre rule
- Corks or bungs to fit tube, 2
Health & Safety and Technical Notes
There is no need to handle the lead shot. However, if it is spilt and is collected by hand (for example), the hands must be washed thoroughly before eating.
- Measure out about 500 g of lead shot in one of the plastic or cardboard cups.
- Put a thermometer into the lead shot to find the temperature.
- Seal one end of the cardboard tube with a cork or bung. Put the lead shot into the tube and seal the open end.
- Measure the length of the tube, Δh.
- Turn the tube over 20, 40 or 50 times, counting the number. Quickly pour the shot into the cup and measure the maximum temperature again.
- When the lead is falling take care that it falls vertically rather than sliding along the tube, when friction will come into play. Also a hand should not cushion the bottom of the tube when the shot hits the bottom, otherwise
transferredinto the hand.
- Turning the tube over more times in order to achieve higher temperature rises is not advisable. The longer time and higher temperature differences will allow more thermal transfer to the surroundings.
- The energy transferred is equal to the number of falls (n) x mgΔh and therefore n x mg x Δh = m x specific thermal capacity x temperature rise.
- Note that there is no need to record the mass of the lead, m.
- Lead is used because its specific thermal capacity is about 1/30 that of water. It is the thermal capacity per unit mass which is important. (Most metals have approximately the same thermal capacity per unit volume.) It is also an inelastic metal so that the energy of the shot stored gravitationally is then stored thermally. The temperature rises.
- When Joule was investigating energy conservation he is said to have measured the temperature at the top and bottom of a waterfall on his honeymoon in Switzerland. This is a useful model of his experiment.
This experiment was safety-tested in January 2006