Determining the specific heat of water using a heater of known power

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Wyznaczanie ciepła właściwego wody przy użyciu grzałki o znanej mocy

You will learn

analyze the water heating process with an electric heater: calculate the values of water and heat energy supplied by the heater,
arrange the energy balance for the water heating process with an electric heater,
determine the specific heatspecific heatspecific heat of water,
analyze the causes of measurement uncertaintymeasurement uncertaintymeasurement uncertainty in the process of determining the specific heatspecific heatspecific heat of water,
choose the right equipment and materials to conduct the experiment in English

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nagranie abstraktu

Research hypothesisresearch hypothesisResearch hypothesis

Using an electric kettle, you can estimate the specific heatspecific heatspecific heat of water.

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Theoretical introduction to the experiment

The amount of energy needed to rise the temperature of water of a mass m is determined by the following formula:

Q = m c_{w} Δ t

If the electric current flows through the electric kettle with the rated power P (for the time t), then the following work is done:

W = P t

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Assuming 100% efficiency of work exchange done by the current flowing through the kettle to warm water, we get the following relation:

Q = W

m c_{w} Δ t = P t

Thus, the following formula can be derived:

c_{w} = \frac{P t}{m Δ t}

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MeasurementmeasurementMeasurement set

What is necessary to determine the specific heatspecific heatspecific heat?

The measurementmeasurementmeasurement set includes a kettle with known power rating, a container to determine the mass of water and a thermometer with which we measure the initial temperatureinitial temperatureinitial temperature of water. The stopwatch is also necessary.

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Instructions for running the experiment

1. Measure the volume of water, e.g. 300 cmIndeks górny 3.

2. Using the information that 1 cmIndeks górny 3 of water weighs 1 g, complete the table with the mass of water.

3. Measure the initial temperature of water.

4. Pour water into the kettle.

5. Measure the time needed to boil water in the kettle.

6. Repeat steps 1 to 5 several times.

7. Write the results in the measurementmeasurementmeasurement table.

Measurement table
No.	Water volume [cmIndeks górny 3]	Water mass [g]	Initial temperatureinitial temperatureInitial temperature [°C]	Heating time t [s]	Comments
1
2
3

Development of measurementmeasurementmeasurement results

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nagranie abstraktu

- Determine the value of the specific heatspecific heatspecific heat for each of the measurements.

- Determine the average valueaverage valueaverage value of the specific heatspecific heatspecific heat of water on the basis of the results.

- Find the smallest and the greatest value of the specific heatspecific heatspecific heat of water you have determined.

- Determine the accuracy of determining the average specific heat value of water from the formula:

Δ c_{w} = \frac{c_{max} - c_{min}}{2}

- Record the result obtained with the accuracy of its designation $(c_{w} \pm Δ c_{w})$ . Compare the result obtained with the value read from the physical tables.

- Explain why the result obtained in the experiment differs from the specific heat value given in the physical tables.

Summary

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The method described above for determining the specific heatspecific heatspecific heat of water is very simple but it is burdened with high inaccuracyinaccuracyinaccuracy. Nevertheless, it can be used to estimate the specific heatspecific heatspecific heat of water.

Exercises

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Exercise 1

The statements below are related to the process of conducting the experiment. Determine which sentences are true.

Repeating measurements during the experiment is not necessary. One measurement is enough to obtain the correct result.
If an open vessel with a heater is used in the experiment, the result of the experiment will be greater than the table value of the specific heat.
The inaccuracy of the time measurement has the greatest influence on the final result in the experiment.
The most likely result of the experiment will be lower than the table value of the specific heat.

zadanie

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Exercise 2

In the conducted experiment, the following values of the specific heat were obtained, the units is $[\frac{J}{k g \cdot K}]$ :

4280 4000 4100 4300 4200

Calculate the average value and the inaccuracy of this value. (Look at Development of measurement results, point 4)

4176 $\frac{J}{k g \cdot K}$ , 150 $\frac{J}{k g \cdot K}$

Exercise 3

Modify the experiment in such a way to make it possible to determine the specific heat of the metal of which the cube is made. What other equipment will you need?

Write a short manual instruction in English.

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Exercise 4

Indicate which pairs of expressions or words are translated correctly.

ciepło właściwe - specific heat
hipoteza badawcza - research hypothesis
niedokładność - inaccuracy
pomiar - measurement
wartość średnia - initial temperature
temperatura początkowa - average value

zadanie

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Match Polish terms with their English equivalents.

research hypothesis
hipoteza badawcza
niedokładność
ciepło właściwe
specific heat
inaccuracy
pomiar
measurement

Source: Zespół autorski Politechniki Łódzkiej, licencja: CC BY 3.0.

Glossary

average value

wartość średnia

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wymowa w języku angielskim: average value

inaccuracy

niedokładność

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wymowa w języku angielskim: inaccuracy

initial temperature

temperatura początkowa

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wymowa w języku angielskim: initial temperature

measurement

pomiar

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wymowa w języku angielskim: measurement

measurement uncertainty

niepewność pomiarowa

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wymowa w języku angielskim: measurement uncertainty

research hypothesis

hipoteza badawcza

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wymowa w języku angielskim: research hypothesis

specific heat

ciepło właściwe

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wymowa w języku angielskim: specific heat

Keywords

specific heatspecific heatspecific heat

research hypothesisresearch hypothesisresearch hypothesis

inaccuracyinaccuracyinaccuracy

measurementmeasurementmeasurement

Scenariusz

Research hypothesisresearch hypothesisResearch hypothesis

Theoretical introduction to the experiment

MeasurementmeasurementMeasurement set

Instructions for running the experiment

Development of measurementmeasurementmeasurement results

Summary

Exercises

Glossary

Keywords