Energy Transfers and Efficiency Flashcard

Front

What type of energy transfer occurs in a light bulb when it is switched on?

Back

Electrical to light (and heat)

Answer explanation

When a light bulb is switched on, electrical energy is converted into light and heat energy. This process is why the correct answer is 'Electrical to light (and heat)', as the bulb emits both light and warmth.

Front

Which device is an example of kinetic energy being converted to electrical energy? Options: Solar panel, Wind turbine, Light bulb, Electric heater

Back

Wind turbine

Answer explanation

A wind turbine converts kinetic energy from wind into electrical energy through its rotating blades, making it the correct example. In contrast, solar panels convert sunlight, while light bulbs and electric heaters use electrical energy.

Front

What energy transfer occurs in a solar panel?

Back

Light to electrical

Answer explanation

In a solar panel, light energy from the sun is converted into electrical energy through the photovoltaic effect. This process is why the correct answer is 'Light to electrical'.

Front

Which of the following wastes energy as sound? Electric heater, Light bulb, Car engine, Solar panel

Back

Car engine

Answer explanation

The car engine wastes energy as sound due to the combustion process and moving parts, producing noise. In contrast, electric heaters, light bulbs, and solar panels primarily convert energy without significant sound waste.

Front

Which of the following wastes energy as heat? Electric motor, Wind turbine, Solar panel, Incandescent light bulb

Back

Incandescent light bulb

Answer explanation

The incandescent light bulb wastes energy as heat due to its inefficient design, converting only a small portion of energy into visible light. In contrast, electric motors, wind turbines, and solar panels are designed to minimize heat loss.

Front

If a device has an input energy of 100 J and an output energy of 75 J, what is its efficiency?

Back

75%

Answer explanation

Efficiency is calculated as (output energy / input energy) x 100. Here, (75 J / 100 J) x 100 = 75%. Therefore, the correct answer is 75%.

Front

A machine uses 200 J of energy and produces 150 J of useful work. What is the efficiency of the machine?

Back

75%

Answer explanation

Efficiency is calculated as useful work output divided by total energy input, multiplied by 100. Here, efficiency = (150 J / 200 J) * 100 = 75%. Thus, the correct answer is 75%.

Front

If a light bulb has an efficiency of 20% and an input energy of 50 J, what is the useful output energy?

Back

10 J

Answer explanation

The useful output energy is calculated by multiplying the input energy by the efficiency. Here, 50 J * 20% = 10 J. Thus, the correct answer is 10 J.

Front

A motor has an efficiency of 60% and an input energy of 500 J. How much energy is wasted?

Back

300 J

Answer explanation

The motor's efficiency is 60%, meaning 60% of the input energy is converted to useful work. Thus, useful energy = 0.6 * 500 J = 300 J. The wasted energy is the remaining energy: 500 J - 300 J = 200 J.

Front

Efficiency of a device with input energy of 250 J and output energy of 100 J?

Back

40%

Answer explanation

Efficiency is calculated as (output energy / input energy) x 100. Here, (100 J / 250 J) x 100 = 40%. Thus, the efficiency of the device is 40%.