Listen to part of a lecture in an environmental science class.
Okay, so we've been talking about renewable energy sources, and today I want to focus on solar power. Now, many of you might think of solar panels as a relatively modern invention, but the photovoltaic effect—the process that converts sunlight into electricity—was actually discovered back in 1839 by a French physicist named Edmond Becquerel. However, it wasn't until the 1950s that the first practical solar cell was developed, and even then, it was extremely inefficient, converting less than 2% of sunlight into electricity. Fast forward to today, and commercial solar panels typically have efficiencies of around 15 to 20 percent. But here's an interesting twist: some researchers are now exploring organic solar cells, which use carbon-based materials instead of silicon. These are cheaper and more flexible, but they degrade faster, and their efficiency is still lower, around 10 to 12 percent. So the question becomes, is the trade-off worth it for large-scale use? We'll discuss this further, but keep in mind that cost and durability are just as important as efficiency when choosing a technology.
❓ Pregunta According to the professor, what is a major disadvantage of organic solar cells compared to traditional silicon-based cells?
A. They are more expensive to produce.
B. They convert sunlight less efficiently and degrade faster.
C. They were discovered earlier but not developed until recently.
D. They are not flexible enough for many applications.
✅ Respuesta correcta
They convert sunlight less efficiently and degrade faster.
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word