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A block of ice at 0°C is placed in a thermally insulated room. Which of the following correctly describes the energy transfers and transformations as the ice melts and eventually reaches thermal equilibrium with the room?
A block of ice at 0°C is placed in a thermally insulated room. Which of the following correctly describes the energy transfers and transformations as the ice melts and eventually reaches thermal equilibrium with the room?
- Thermal energy is transferred from the room to the ice, increasing the internal energy of the ice and causing a phase change from solid to liquid, followed by an increase in the water's temperature until thermal equilibrium is reached. Throughout the entire process, the total energy of the closed system (room + ice) remains constant. (correct)
- Thermal energy is transferred from the room to the ice, increasing the kinetic energy of the water molecules until all the ice melts, after which the additional energy increases the gravitational potential energy of the water.
- No energy transfer occurs since the room is thermally insulated and the ice remains frozen indefinitely.
- Thermal energy is transferred from the ice to the room, decreasing the entropy of the room while increasing the internal energy of the ice, eventually reaching equilibrium when the ice's temperature equals the room's.
A student uses a catapult to launch a small stone. Analyze the energy transfers in the system, from the initial state of the catapult being loaded to the moment the stone reaches its maximum height. Which of the following best describes the sequence and types of energy transformations involved?
A student uses a catapult to launch a small stone. Analyze the energy transfers in the system, from the initial state of the catapult being loaded to the moment the stone reaches its maximum height. Which of the following best describes the sequence and types of energy transformations involved?
- Chemical energy from the person loading the catapult -> elastic potential energy in the stretched catapult bands -> kinetic energy of the stone -> gravitational potential energy of the stone, with some energy dissipated as heat.
- Gravitational potential energy of the stone at rest -> kinetic energy as the stone is launched -> elastic potential energy as the catapult returns to its original position, indicating a closed energy cycle.
- Elastic potential energy in the stretched catapult bands -> kinetic energy of the catapult arms -> gravitational potential energy of the stone as it rises, with all energy transfers being perfectly efficient.
- Elastic potential energy in the stretched catapult bands -> kinetic energy of the stone -> gravitational potential energy of the stone, with a portion of the elastic potential energy converted to sound and thermal energy due to friction and air resistance. (correct)
Consider a scenario where an electric kettle is used to heat water. The kettle is connected to a power supply with a known potential difference. Assuming that the kettle is not perfectly insulated, what are the primary energy transfers, and how does the non-ideal insulation affect the overall energy efficiency of the system?
Consider a scenario where an electric kettle is used to heat water. The kettle is connected to a power supply with a known potential difference. Assuming that the kettle is not perfectly insulated, what are the primary energy transfers, and how does the non-ideal insulation affect the overall energy efficiency of the system?
- Electrical energy is converted into kinetic energy of the water molecules, causing the water to boil. The kettle's insulation prevents any energy transfer to the surroundings, resulting in 100% efficiency.
- Electrical energy is converted directly into gravitational potential energy of the water as it heats up, with the insulation playing no role in the energy transfer process.
- Electrical energy is converted into internal (thermal) energy of the kettle element, which then transfers energy to the water, increasing its temperature. The non-ideal insulation causes some energy to be transferred to the surroundings, reducing the overall efficiency of the process. (correct)
- Electrical energy is entirely converted into the internal (thermal) energy of the water, with no energy losses to the surroundings due to the kettle's insulation.
Flashcards
Energy
Energy
The capacity for doing work. Energy cannot be created or destroyed, only transferred or stored.
Potential Difference (Voltage)
Potential Difference (Voltage)
A measure of the energy given to charge carriers in a circuit, causing current to flow. Measured in volts (V).
Energy Transfer Diagrams
Energy Transfer Diagrams
Diagrams showing energy stores as boxes and energy transfers with arrows. Sankey diagrams use arrow width to represent energy amounts.
Study Notes
- Energy exists in different 'stores'.
- Energy is always conserved; it cannot be created or destroyed.
- Energy can be transferred, dissipated, or stored in different ways.
- Energy can remain in the same store for varying durations.
Energy Transfers
- Energy transfers occur whenever a system undergoes a change, altering how energy is stored.
- Examples of energy transfers:
- A boat moving through water converts chemical energy into kinetic energy.
- An electric kettle uses electricity to increase the internal energy of its element, which in turn heats the water.
- A swinging pirate ship ride converts kinetic energy into gravitational potential energy and vice versa.
Types of Energy Transfer
- Energy can be transferred through:
- Heating
- Waves
- Electric Current
- A force moving an object (mechanical work)
Potential Difference (Voltage)
- Potential difference, measured in volts (V), indicates the energy supplied to charge carriers in a circuit.
- It drives electric current between two points.
- Energy is released by a material, decreasing its internal energy.
- Infrared radiation emitted from the Sun into space exemplifies this.
Work
- 'Work' is the scientific term for energy transfer.
- Examples of doing work:
- A grazing cow
- A firing catapult
- A boiling kettle
Transfer Diagrams
- Transfer diagrams illustrate energy transfers between stores.
- Boxes represent energy stores.
- Arrows indicate energy transfers.
- Example: A child on a slide converts gravitational potential energy into kinetic and internal energy.
- Mechanical work is done to speed up and to do work against friction.
- The child's temperature and the slide increase.
Sankey Diagrams
- Sankey diagrams illustrate how energy is transferred into different stores.
- The width of the arrows is proportional to energy amount.
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