Question 1: Define the term 'efficiency' in the context of energy transfers.

Answer: Efficiency is a measure of how much useful energy is transferred or converted compared to the total energy supplied, usually expressed as a percentage.

Question 2: Explain why no energy transfer process is 100% efficient.

Answer: Because some energy is always lost to the surroundings as heat, sound, or other forms of energy due to inefficiencies in the transfer or conversion process.

Question 1: A machine transfers 500 J of energy, but only 350 J is useful. Calculate its efficiency as a percentage.

Answer: Efficiency = (350 / 500) × 100% = 70%

Question 2: A motor consumes 1000 J of electrical energy and delivers 800 J of mechanical energy. What is its efficiency?

Answer: Efficiency = (800 / 1000) × 100% = 80%

Question 1: Describe a simple experimental setup to measure the efficiency of an electrical heater.

Answer: Use an electrical heater, a power supply, and a calorimeter or thermometer to measure the electrical energy input and the heat energy transferred to water or surroundings, then calculate efficiency using the energy transferred divided by energy supplied.

Question 2: Identify two variables that must be controlled during the experiment to ensure accurate measurement of efficiency.

Answer: Electrical power supplied (voltage and current) and ambient temperature or water mass for heat transfer measurements.

Question 1: A device consumes 1500 J of electrical energy and produces 1200 J of useful energy. The surrounding environment loses 300 J as heat. Calculate the efficiency of the device.

Answer: Efficiency = (1200 / 1500) × 100% = 80%

Question 2: In a different scenario, a heat pump transfers 2500 J of heat energy but consumes 3000 J of electrical energy. Comment on the efficiency of this system and explain why it may still be considered useful.

Answer: The efficiency, calculated as useful heat transferred divided by electrical energy input, is less than 100%, specifically around 83.3%. Despite this, heat pumps are considered useful because they transfer more heat energy than the electrical energy they consume, effectively moving energy from cooler to warmer areas, which is beneficial in heating applications.

Question 1: Explain how the efficiency of a car engine affects fuel consumption and emissions.

Answer: Higher engine efficiency means more of the fuel's energy is converted into useful motion, reducing fuel consumption and emissions. Lower efficiency results in more fuel being burned for the same movement, increasing pollution and fuel costs.

Question 2: Discuss how improving the efficiency of renewable energy systems, like wind turbines, can benefit society and the environment.

Answer: Improving the efficiency of renewable energy systems increases the amount of useful energy generated from a given resource, reducing waste and the need for additional resource extraction. This leads to lower costs, less environmental impact, and a more sustainable energy supply for society.