Question 1: Define the term 'energy efficiency' in your own words.

Answer: Energy efficiency is the ratio of useful energy output to the total energy input, expressed as a percentage, indicating how well a device converts energy without waste.

Question 2: Explain why higher efficiency in machines is desirable in everyday life.

Answer: Higher efficiency means less energy is wasted as heat or other forms, leading to lower energy costs, less environmental impact, and better performance of devices.

Question 3: A motor consumes 1000 Joules of electrical energy and does 800 Joules of useful work. What is its efficiency?

Answer: Efficiency = (Useful work / Total energy input) x 100 = (800 J / 1000 J) x 100 = 80%

Question 4: Which of the following devices generally has the highest efficiency? A) Incandescent light bulb B) LED light bulb C) Traditional electric heater D) Mechanical clock

Answer: B

Question 5: Fill in the blank: The efficiency of a machine is expressed as a percentage of the  useful energy transferred.

Answer: useful

Question 6: Describe a simple experiment to measure the efficiency of a hand-crank flashlight.

Answer: To measure efficiency, measure the electrical energy supplied to the flashlight (using a multimeter on the battery and current) and the light energy output (by measuring luminous intensity or illuminance). Calculate the ratio of light energy emitted to electrical energy consumed to find efficiency. Consider safety precautions like handling electrical components carefully and ensuring connections are secure.

Question 7: In a heat engine, some energy is always lost as waste heat. How does this affect the efficiency of the engine, and what is the theoretical maximum efficiency called?

Answer: The energy lost as waste heat reduces the engine's efficiency. The theoretical maximum efficiency is called the Carnot efficiency, which depends on the temperature difference between the hot and cold reservoirs.

Question 8: Explain two real-world methods used to improve the energy efficiency of household appliances.

Answer: Methods include using better insulation to reduce heat loss and incorporating energy-efficient components such as LED lighting or inverter motors, which convert energy more effectively and reduce waste. Additionally, implementing smart controls and timers can optimize energy use based on need.

Question 9: Identify a technological advancement that has increased efficiency in renewable energy systems and briefly describe its impact.

Answer: The development of high-efficiency photovoltaic cells has increased the conversion of sunlight to electricity, making solar power more cost-effective and widespread, reducing reliance on fossil fuels.