1. A-level Physics
Unit G484:
The Newtonian
World
Specific heat capacity
Thermal physics
2. Internal energy recall LOs
Questions
1. Define internal energy (U).
2. Explain how internal energy can be changed and write an
expression linking U to these mechanisms.
3. Imagine I have two blocks of aluminium and supply 1000 J of
thermal energy to each. The rise in temperature of the two blocks
is different. What is the simplest explanation for this?
4. I have two pieces of metal with the same mass. 1000 J of thermal
energy is supplied to both but, again, the temperature increases
are different. Why?
Thermal physics
3. Lesson focus
• Specific heat capacity
Learning objectives
At the end of the lesson you will be able to:
• define and apply the concept of specific heat capacity;
• select and use the equation E = mcΔθ ;
• describe an electrical experiment to determine the
specific heat capacity of a solid or liquid.
Thermal physics
4. Learning outcomes
All of you should be able to
• give a full definition of the SHC of a substance;
• recall the equation for SHC;
• carry out the practical activity efficiently and safely.
Most of you will be able to
• identify significant sources of experimental error;
• suggest appropriate improvements to the experimental method.
Thermal physics
5. Specific heat capacity LOs
Definition
The amount of energy needed to raise the temperature of
1 kg of a substance by one degree celsius (or one kelvin).
where, c - specific heat capacity
m - mass
ΔE - energy supplied
Δθ - temperature change
i.e. E = mc Δθ
Thermal physics LO 1: define and apply the concept of specific heat capacity
6. Measuring the SHC of water LOs
electrical energy = energy gained
supplied by water
i.e. E = IVt E = mcΔθ
IVt = mcΔθ
E
c =
mΔθ
We need to know
• The energy supplied (E)
• The mass of water (m)
• The temperature change (Δθ)
LO 3: describe an electrical experiment to determine
Thermal physics the specific heat capacity of a solid or liquid.
7. Measuring the SHC of a metal LOs
1. Insert a thermometer and the
immersion heater into their respective
holes in the block. You may wish to drop thermometer
a small amount of oil into the
immersion
thermometer hole to improve the heater
thermal contact between thermometer
and block. lagging
solid
2. Allow the thermometer to reach block
thermal equilibrium and then write
down the temperature.
3. Set up a suitable circuit that will enable
you to measure the energy input to the
heater.
LO 3: describe an electrical experiment to determine
Thermal physics the specific heat capacity of a solid or liquid.
8. Measuring the SHC of a metal LOs
4. Turn on the current, noting the time if you are
measuring energy using an ammeter and a
voltmeter to record power. thermometer
5. Energy = current x potential difference x time. immersion
heater
Monitor and note the meter readings as the
energy is supplied. They may change slightly as
lagging
things warm up. solid
block
6. Allow the block to heat up by about 10 °C, then
turn off the current and note the time again.
7. At this point, keep watching the thermometer.
The temperature at the turn-off time is not the
appropriate final temperature to record. What
do you think is the appropriate final
temperature?
LO 3: describe an electrical experiment to determine
Thermal physics the specific heat capacity of a solid or liquid.
9. Measuring the SHC of a metal LOs
8. Use E = m c Θ to calculate the
specific thermal capacity, c, of your thermometer
block. Compare your answer with a data immersion
book value. heater
9. Was your calculated value of specific lagging
thermal capacity too high or too low? solid
block
Which of the measurements you made
is likely to be the one most in error? In
which direction is it in error, and why
might this be?
LO 3: describe an electrical experiment to determine
Thermal physics the specific heat capacity of a solid or liquid.
10. Measuring the SHC of a metal LOs
Analysis
• Plot a graph to find c.
thermometer
• Plot a second graph of temperature (y-axis)
immersion
vs time (x-axis). Comment on the shape of heater
the graph. What does the graph tell you?
• Compare your experimental value of c with lagging
solid
the published value. Is it too high or too block
low? Explain the reason for the difference.
Evaluation
• Identify possible sources of error. Which of
these errors is the most important?
LO 3: describe an electrical experiment to determine
Thermal physics the specific heat capacity of a solid or liquid.
11. Measuring the SHC of a metal LOs
Time/s Current/A Voltage/V Temperature/ C Total energy Temperature
supplied/J change ( ) / C
If E = m c q what graph should you plot to find c?
LO 3: describe an electrical experiment to determine
Thermal physics the specific heat capacity of a solid or liquid.
12. Measuring the SHC of a metal LOs
Analysis
• Plot a graph to find c. thermometer
• Plot a second graph of temperature (y-axis) immersion
heater
vs time (x-axis). Comment on the shape of
the graph. What does the graph tell you? lagging
solid
block
• Compare your experimental value of c with
the published value. Is it too high or too
low? Explain the reason for the difference.
Evaluation
• Identify possible sources of error. Which of
these errors is the most important?
LO 3: describe an electrical experiment to determine
Thermal physics the specific heat capacity of a solid or liquid.
13. G482 Jan., 2010 Q5 Using ΔE = mcΔΘ LOs
Extension
In measurements of the SHC of a metal, energy losses to the surroundings are
a source of error. Is this a systematic or random error? Justify your answer.
Thermal physics LO2: select and use the equation E = mcΔθ
14. G482 Jan., 2010 Q5 Using ΔE = mcΔΘ LOs
Examiners’ report
Thermal physics LO2: select and use the equation E = mcΔθ
15. Using ΔE = mcΔΘ LOs
Oxford University entrance exam for physics, 2008
Thermal physics LO2: select and use the equation E = mcΔθ
