Heat and Thermodynamics - SS2 Physics Past Questions and Answers - page 2
Explain the concept of conduction and provide real-life examples where conduction is observed.
Conduction is the heat transfer mechanism that occurs through direct contact between particles within a substance. In solids, heat is transferred through the vibration and collision of atoms or molecules. Good conductors, such as metals, have high thermal conductivity, enabling efficient heat transfer. Examples of conduction include touching a hot object and feeling the heat transfer from the object to your hand, or heating a metal spoon in a hot cup of tea.
Describe the process of convection and provide examples of natural and forced convection.
Convection is the heat transfer mechanism that occurs in fluids (liquids or gases) through the movement of particles. It involves the transfer of heat by the bulk movement of the fluid. Natural convection occurs when heat is transferred due to the density differences within the fluid. For example, hot air rising and cool air sinking in a room is an example of natural convection. Forced convection, on the other hand, is when the fluid movement is induced by an external force, such as a fan or a pump. Cooling a computer with a fan or circulating heated water in a radiator are examples of forced convection.
Explain the concept of radiation and discuss its properties and applications.
Radiation is the heat transfer mechanism that occurs through electromagnetic waves without the need for a medium. Unlike conduction and convection, radiation can occur in a vacuum. Heat energy is emitted in the form of electromagnetic waves, typically in the infrared region. Radiation does not require direct contact between objects. It can travel through space and is responsible for the transfer of heat from the Sun to the Earth. Other examples include feeling the warmth of a campfire or the heat emitted by a glowing filament in an incandescent bulb. Radiation also plays a crucial role in applications such as infrared heating, solar panels, and thermal imaging.
Compare and contrast the three heat transfer mechanisms (conduction, convection, radiation) in terms of their characteristics, efficiency, and applications.
Conduction, convection, and radiation are all heat transfer mechanisms, but they differ in how heat is transferred. Conduction occurs through direct contact between particles, primarily in solids. It is efficient in materials with high thermal conductivity and finds applications in cooking, metalworking, and insulation materials.
Convection involves the movement of fluids and is more effective in liquids and gases. Natural convection occurs due to density differences, while forced convection requires external forces. It is used in heating, cooling, and ventilation systems. Radiation is the transfer of heat through electromagnetic waves and is the only mechanism that can occur in a vacuum. It is essential for heat transfer from the Sun, and its applications include heating, cooking, and thermal imaging.
What is the definition of specific heat capacity?
The amount of heat required to raise the temperature of a substance by 1 Kelvin
The amount of heat required to raise the temperature of a substance by 1 degree Celsius
The ratio of the mass of a substance to its volume
The rate at which a substance transfers heat
Which of the following factors affects the specific heat capacity of a substance?
Its mass
Its volume
Its temperature
Its chemical composition
Calorimetry is a technique used to measure:
Temperature changes in a substance
Heat transfer between substances
Mass of a substance
Specific heat capacity of a substance
How much heat energy is required to raise the temperature of 50 grams of aluminium from 20°C to 80°C? The specific heat capacity of aluminium is 0.897 J/g°C.
To calculate the heat energy, we use the formula: Q = m c ΔT
Q = 50 g x 0.897 J/g°C x (80°C - 20°C)
Q = 50 g x 0.897 J/g°C x 60°C
Q = 2691 J
A 100 gram block of copper is heated to 100°C and then placed in a calorimeter containing 200 grams of water at 20°C. The final temperature of the mixture is 25°C. What is the specific heat capacity of copper? The specific heat capacity of water is 4.18 J/g°C.
In this case, we can use the principle of conservation of energy. The heat lost by the copper is equal to the heat gained by the water.
Q(copper) = Q(water)
m(copper) x c(copper) x ΔT(copper) = m(water) x c(water) x ΔT(water)
100 g x c(copper) x (25°C - 100°C) = 200 g x 4.18 J/g°C x (25°C - 20°C)
-75 c(copper) = 200 g x 4.18 J/g°C x 5°C
c(copper) = - (200 g x 4.18 J/g°C x 5°C) / 75
c(copper) ≈ - 55.73 J/g°C
Note: The negative sign indicates that heat was lost by the copper.
A sample of water at 25°C absorbs 4,000 J of heat energy. If the mass of the water is 500 grams, what is the temperature change of the water? The specific heat capacity of water is 4.18 J/g°C.
We can rearrange the formula Q = m c ΔT to solve for ΔT:
ΔT = Q / (m x c)
ΔT = 4,000 J / (500 g x 4.18 J/g°C)
ΔT ≈ 1.91°C