ENB 130 H9 – Heat Production and
3rd of May 2012 10-12am Session Group Members: Daniel, Henry and Luke
S c i e n c e a n d E n g i n e e r i n g Q U T Aim
Part A: To measure the heat output generated by an electrical current.
Part B: To rank various materials in decreasing order of thermal conductivity
so as to appreciate which materials are good and which are poor
Part C: To examine the rate of cooling of a hot object.
Energy is defined as an objects ability or capacity to do work . Energy exsists
as many different forms throughout the universe such as heat, sounds, kinetic,
potential, chemical and many more. The law of Conservation of Energy states
that energy cannot be created nor destroyed but instead only transformed from
one energy type to another .
Heat is one form of energy related to the movement of atoms and molecules
within an object. It is capable of being transferred through liquids, gases and
solids by conduction, convection or radiation. Heat is transferred between
objects as a result of temperature differences among them . In part A of the
experiment, the conversion of electrical energy into heat is observed through a
convection transfer from a heating element in water.
Electricity is a form of energy created by the flow of electrical charge or electrons
through a conductor. Electrical power (P) is measured in Watts (W) and can be
calculated for a circuit with the following formula:
This formula only requires two knows to calculate an unknown in a conductor or
circuit. If the voltage (V) and the current (I) are known, then the Electrical power
can be calculated. Current, measured in coulombs per second, or ampere (A), is
the rate that electrons pass through an electrical conductor or circuit. Voltage is
an electrical difference between two points of a circuit. It measures the force
required to pass one ampere through a resistance (R) of one ohm (Ω). Every
electrical circuit and conductor has a resistance for electrons to pass through.
This resistance is a quantity measured in ohms, describing a materials opposing
flow of electricity . The relation between voltage, current and resistance can
be measured using Ohm’s Law:
The second part of the experiment looks at the thermal conductivity of different
substances. The thermal conductivity of an object is its ability to transfer and
conduct heat. Materials with higher thermal conductivity are better substances
at absorbing and radiating heat energy. The conductivity of four different metals,
copper, brass, steel and aluminium, will be analysed by observing the time taken for each material to melt wax off their tips from a Bunsen flame held at a
common centre. The time taken for each metal to melt the wax will be relevant to
their thermal conductivity. The faster the wax melts, the higher the thermal
conductivity will be for that substance.
The final part of the experiment looked at the radiation of a cooling substance in
relation to Newton’s Law of cooling. This law suggests that if the temperature of
an object is doubled, the rate of cooling of that object will also be doubled. While
Newton’s Law of Cooling mostly explains the cooling of heated water, it is
important to realise that the cooling fins on hot sections of equipment are
painted black which also assists the cooling process. This is due to the fact that of
all colours, black absorbs and radiates the most heat.
There were three different experiments that were performed to investigate heat
production and transition. The first experiment measured the heat output
generated by an electrical current. The equipment used for this experiment
- 30 Volt AC power unit with stand
- Digital Multimeter
- Wire heating element
The procedure for the experiment (Part A)
went as follows:
1. Measure the resistance of the
heating element and the output
voltage of the power unit using the
digital multimeter and record. Figure 1: Apparatus for Part A
2. Fill 200ml of water into the beaker
3. Set up the circuit as Figure 2.
4. Record the initial temperature of the
5. Switch the power unit on and record the
temperature of the water at one minute
intervals for 10 minutes.
6. Draw a graph of temperature verse time
and record its gradient.
7. Calculate the electrical power input and
the heat power and record
Figure 2: Electrical Circuit for Part A
The second experiment (Part B) compared the
heat conductivity of four different substances. The time it took for wax to fall off the tips of Copper, Brass, Steel and Aluminium
rods was used to determine the thermal conductivity of the four metals. The
process was as follows:
1. 1. The 5 different rods were each heated over a small bunsen flame at
their common centre and the approximate time for the wax to melt on
each different rod was recorded.
2. The order of melting was noted.
The last experiment (Part C) looked at radiation and Newton’s law of cooling.
This part of the experiment looks at the cooling rate of water from 50° above
room temperature. Using the same heated water as the first experiment (Part A)
the method for Part C was as follows:
1. The room temperature (T sC) was recorded.
2. The temperature (T 0 of the water was recorded, the power unit was
switched off and timing commenced.
3. The temperature of the water was recorded at two-minute intervals.
4. t, T, θ(=T – Ts) and lnθ was tabulated.
5. A graph of lnθ against t was drawn and found to be a straight line of
Resistance of heating element (R 1 35.4 Ω
Output Voltage of Power Unit (V1) 32.5 A
Heater Current (I) 0.893 A
Table 1. Resistance, Current and Voltage associated with Power Unit
Time (min) Temperature (°C)
Table 2. Time (min) vs Temperature (°C) 60
50 y = 2.2182x + 28
0 2 4 6 8 10
Chart 1. Time (min) vs Temperature (°C)
Ordering of Material Approx. Melting Thermal
Melting Time (min) Conductivity
1 Copper 2:01 400
2 Aluminium 2:38 250
3 Brass 3:37 109
4 Steel 45:00 18
Table 3. Thermal Conductivity of Different Substances
Elapsed Time Temperature, T θ= T- TS (Ts=25°C) ln (θ)
0 TO= 50 θO= 25 3.21
2 47 22 3.10
4 45 20 2.99
6 43 18 2.89
8 41 16 2.77
10 40 15 2.71
12 38 13 2.56
14 37 12 2.48