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In an experiment to verify Joule's law, a constant current $I$ was passed through a heating coil immersed in water and the rise in temperature $\Delta \theta$ was recorded - Leaving Cert Physics - Question 5 - 2022
Question 5
In an experiment to verify Joule's law, a constant current $I$ was passed through a heating coil immersed in water and the rise in temperature $\Delta \theta$ was re... show full transcript
Worked Solution & Example Answer:In an experiment to verify Joule's law, a constant current $I$ was passed through a heating coil immersed in water and the rise in temperature $\Delta \theta$ was recorded - Leaving Cert Physics - Question 5 - 2022
Step 1
Draw a labelled diagram of the apparatus used in this experiment.
Answer
The labelled diagram should include:
- Container: A beaker or similar vessel to hold the water.
- Water: Indicate the water being heated.
- Heating Coil: The coil should be shown submerged in the water.
- Ammeter: Include an ammeter in series to measure the current .
- Voltmeter: If required, place a voltmeter in parallel to measure voltage across the coil.
- Thermometer: Show the thermometer used to measure the temperature rise.
- Additional details like a stopwatch for timing, and a stirrer for mixing, can also be included.
Step 2
Why were the mass and the time kept constant?
Answer
The mass of the water is kept constant to ensure that any changes in temperature are solely due to the electrical energy converted into heat by the current, rather than varying amounts of water affecting the results. The time is kept constant to ensure a fair comparison between trials; if the time varies, it could lead to different amounts of heat being absorbed, which would skew the relationship being measured.
Step 3
In your answerbook, copy and complete the table above.
Answer
The completed table should display calculated power values based on the given current values according to the formula for each current . The completed table is as follows:
| (A) | 1 | 1.5 | 2 | 2.5 | 3 | 3.5 |
|---|---|---|---|---|---|---|
| (A) | 1 | 2.25 | 4 | 6.25 | 9 | 12.25 |
| (°C) | 1.2 | 2.7 | 4.8 | 7.5 | 10.8 | 14.7 |
Step 4
Use all of the data to plot a graph of $P$ against $I$.
Answer
- The graph should have the current on the x-axis and power on the y-axis.
- Plot the points based on the completed data table: (1, 1), (1.5, 2.25), (2, 4), (2.5, 6.25), (3, 9), and (3.5, 12.25).
- Use a ruler to draw a line of best fit through the plotted points.
Step 5
Use your graph to find the current that caused a change in temperature of 6 °C.
Answer
- From the graph, locate the point where °C on the y-axis.
- Draw a horizontal line across from this point to intersect the line of best fit.
- Drop a vertical line down to the x-axis to find the corresponding current . This reading should approximate to about A.
Step 6
Explain how your graph verifies Joule’s law.
Answer
Joule's law states that the heat produced in a resistor is proportional to the square of the current flowing through it, under constant resistance. The graph of against shows a quadratic relationship where the power increases with the square of the current . This consistent linearity with the squared values signifies that as the current increases, the power increases proportionally, thereby verifying Joule’s law.