Year 9 Physics: Temperature Changes in a System and Specific Heat Capacity

Introduction

Hello Year 9! Today, we’re going to explore a fascinating topic in physics: temperature changes in a system and specific heat capacity. Let’s break this down step by step.

What is Temperature?

Temperature is a measure of how hot or cold something is. When we talk about temperature in physics, we’re often concerned with how it changes when heat is added or removed from a substance.

Key Points about Temperature:

• It is measured in degrees Celsius (°C) or Kelvin (K).
• It helps us understand how energy moves in a system.

What is Specific Heat Capacity?

Specific heat capacity (often just called “specific heat”) is a property of a substance that tells us how much energy is needed to raise the temperature of 1 kilogram of that substance by 1 degree Celsius.

The Formula

The formula to calculate heat energy (Q) is:

$$Q = mc\Delta T$$

Where:

• (Q) = heat energy (in joules, J)
• (m) = mass of the substance (in kilograms, kg)
• (c) = specific heat capacity (in joules per kilogram per degree Celsius, J/kg°C)
• (\Delta T) = change in temperature (in degrees Celsius, °C)

Example

Imagine you have 2 kg of water, and you want to heat it from 20 °C to 30 °C.

1. The specific heat capacity of water is about 4200 J/kg°C.
2. The change in temperature ((\Delta T)) is 30 °C – 20 °C = 10 °C.
3. Using the formula: $$Q = mc\Delta T$$ $$Q = 2 , \text{kg} \times 4200 , \text{J/kg°C} \times 10 , \text{°C}$$ $$Q = 84000 , \text{J}$$

This means you would need 84,000 joules of energy to heat the water.

Why is Specific Heat Capacity Important?

Different materials have different specific heat capacities. This affects how quickly they heat up or cool down. For example:

• Water has a high specific heat capacity, so it heats up and cools down slowly. This is why lakes take longer to warm up in spring.
• Metals, like iron, have low specific heat capacities, so they heat up quickly when you put them on a stove.

Tips for Understanding

1. Visualise: Picture heating water in a kettle vs. a metal pan. Notice how quickly the pan heats up!
2. Practice: Use the formula to solve different problems.
3. Ask Questions: If you don’t understand a part, ask!

Questions

Easy Level Questions

1. What is temperature?
2. How is temperature measured?
3. What does specific heat capacity measure?
4. What is the formula for calculating heat energy?
5. What unit is specific heat capacity measured in?
6. If you heat 1 kg of water by 1 °C, how much energy do you need?
7. Which material has a higher specific heat capacity: water or iron?
8. What does (\Delta T) represent in the formula?
9. If a substance’s temperature increases, what happens to its energy?
10. Is the specific heat capacity of air higher or lower than that of water?

Medium Level Questions

11. What is the specific heat capacity of water?
12. If you have 3 kg of a substance with a specific heat capacity of 850 J/kg°C, how much energy is needed to raise its temperature by 5 °C?
13. How does the specific heat capacity affect the temperature change of a substance?
14. Why do metals heat up faster than water?
15. Calculate the heat energy needed to raise the temperature of 2 kg of water from 15 °C to 25 °C.
16. What happens to the temperature of a substance when heat is removed from it?
17. If a 4 kg metal block has a specific heat capacity of 500 J/kg°C, how much energy is needed to raise its temperature by 10 °C?
18. Describe a real-life example where specific heat capacity is important.
19. How can we measure temperature changes in liquids?
20. Why is it important for some materials to have a high specific heat capacity?

Hard Level Questions

21. A copper pot has a mass of 2 kg and a specific heat capacity of 385 J/kg°C. If it absorbs 1540 J of heat, what will be the change in temperature?
22. How does the specific heat capacity of a substance affect climate?
23. If you have a 1 kg block of material with a specific heat capacity of 2000 J/kg°C, how much energy would be required to raise its temperature from 20 °C to 100 °C?
24. Explain why water is used in radiators in houses.
25. If two substances have the same mass and are heated with the same amount of energy, how would you determine which one has a higher specific heat capacity?
26. Why do you think specific heat capacity is different for gases, liquids, and solids?
27. How does specific heat capacity play a role in weather patterns?
28. If a substance has a very high specific heat capacity, what does this tell you about its temperature change when it absorbs heat?
29. Compare and contrast the specific heat capacities of two different materials.
30. Calculate the amount of energy needed to cool 5 kg of oil (specific heat capacity of 2000 J/kg°C) from 80 °C to 40 °C.

Answers

Easy Level Answers

1. Temperature is a measure of how hot or cold something is.
2. Temperature is measured in degrees Celsius (°C) or Kelvin (K).
3. Specific heat capacity measures how much energy is needed to raise the temperature of a substance.
4. The formula for calculating heat energy is (Q = mc\Delta T).
5. Specific heat capacity is measured in joules per kilogram per degree Celsius (J/kg°C).
6. You would need 4200 joules of energy.
7. Water has a higher specific heat capacity than iron.
8. (\Delta T) represents the change in temperature.
9. When a substance’s temperature increases, its energy increases.
10. The specific heat capacity of air is lower than that of water.

Medium Level Answers

11. The specific heat capacity of water is about 4200 J/kg°C.
12. (Q = mc\Delta T = 3 \times 850 \times 5 = 12750 , \text{J}).
13. Higher specific heat capacity means slower temperature change.
14. Metals heat up faster because they have a lower specific heat capacity.
15. (Q = mc\Delta T = 2 \times 4200 \times 10 = 84000 , \text{J}).
16. The temperature of a substance decreases when heat is removed.
17. (Q = 4 \times 500 \times 10 = 20000 , \text{J}).
18. Boiling water takes time because of its high specific heat capacity.
19. We can measure temperature changes using a thermometer.
20. A high specific heat capacity helps maintain stable temperatures.

Hard Level Answers

21. (\Delta T = \frac{1540}{2 \times 385} = 2 , \text{°C}).
22. Specific heat capacity affects how heat is absorbed and released by bodies of water, influencing climate.
23. (Q = mc\Delta T = 1 \times 2000 \times (100-20) = 160000 , \text{J}).
24. Water absorbs and releases heat slowly, helping to regulate temperature.
25. The substance that experiences a smaller temperature change has a higher specific heat capacity.
26. Gases generally have lower specific heat capacity compared to liquids and solids due to their molecular structure and movement.
27. Specific heat capacity influences how land and sea absorb heat from the sun, affecting weather systems.
28. It indicates that the substance will have a smaller temperature change when it absorbs heat.
29. Water holds heat longer than metals, making it better for temperature regulation.
30. (Q = 5 \times 2000 \times (80-40) = 400000 , \text{J}).

Feel free to ask any questions if you’re unsure about anything! Happy studying!