10.4 Measuring specific heat capacity Flashcards
When using electrical methods to determine specific heat capacity what principle do we have to remember?
electrical energy transferred by heater = increase in internal energy of material
What is the setup for method 1 (working out c of solids)?
A circuit consisting of power supply,ammeter, voltmeter and immersion heater. The immersion heater is in a hole of a lagging outlined material that we’re testing. In the hole we also have cooking oil. There is another hole for the themometer. Under the whole setup we have a heat proof mat and alongside it we have a stopclock.
How is this experiment done?
- the material is weighted using a mass balance
- initial temperature is recorded. The power supply is switched on and stopclock is started. Pd and current are recorded
- At a predetermined time or temperature stop the stopclock and power is switched off. They’re both recorded.
- We use IVt = mc(theta1 - theta2 , according to principle mentioned above
Why do we have cooking oil in the holes?
in order to improve thermal contract and thus heating.
What are the sources of error for this experiment?
- some energy is absorbed by immersion heater, making c greater
- energy is transferred to surroundings despite lagging , making c larger
- a little energy is transferred to lagging and thermometer
- small THETA changes in thermometer so large reading uncertainty
- inaccuracy of meters
Can this setup of method 1 be used to investigate cooling? Given that what
Yes, given that lagging is removed`
What would a heating time graph look like?
A roughly straight line not going through the origin and then becoming less and less steep and then decreasing line
What is the graph initially like?
Fairily steep line, as rate of change of temperature is small due to the time it takes for material and thermometer to conduct energy from immersion heater.
What happens when the line becomes almost linear?
Thermal equilibrium, the rate of transfer of electrical energy in the heater is equal to rate of absorption by material.
Why does the lines suddenly becomes less and less steep?
Rate of rise of temperature becomes gradually smaller. This is due to the fact energy transferred to the surroundings gets greater as temperature of material increases.
Why does the temperature on graph keeps increasing after power has been switched off?
Since it takes a finite time for all energy to be conducted by the material and thermometer.`
When does the temperature start to decrease? shown on the graph?
once all energy has been transferred to material the transfer of energy to surroundings becomes apparent as temperature starts to fall.
in method 1 how can we make allowance for energy transferred to surroundings and components of equipment in practical?
- determine the gradient of temp/time graph at an initial linear point. Due to little change from room temp the energy transferred to surroundings is negligible. This doesn’t take into account the energy to heater and other components
- energy transferred to heater can be limited by assuming heater has equal c and add mass to mass of material. or take a separate experiment.
- thermometer takes little energy and can thus be ignored
What is the thermal equilibrium?
rate of radiating energy is equal to rate of absorbing energy. System will have a constant temperature.
What is the 2nd method setup? (working out c of liquids)
a circuit with a power supply,ammeter,pd and resistor. It is clamped above a beaker of liquid with the resistor in the liquid. There is also a thermometer in the liquid. Alongside the setup we have a stopwatch.
