Đề ôn thi Đề thi vào lớp 10 Trường THPT Chuyên KHXH môn Tiếng Anh - Mã đề KHXH-167

A battery is a common device we use every day to power everything from remote controls to smartphones. But how does this small object store energy? The basic principle is quite simple: a battery doesn't store electrical energy directly. Instead, it holds chemical energy and converts it into electrical energy on demand. (35) __________ a standard battery, there are several key components that work together to make this amazing process happen.

The main parts of a battery are its two terminals, one marked positive (+) and the other negative (-). Separating these terminals is a chemical substance called an electrolyte. When the terminals are connected to a device, like a lightbulb, a chemical (36) __________ takes place inside the battery. This reaction causes tiny particles called electrons to build up at the negative terminal, creating a difference in electrical potential between the two sides.

This difference in potential makes the electrons want to move from the negative terminal to the positive terminal. They travel through the external device in order to get there. This flow of electrons is exactly what we call an electrical current. The battery's internal chemical process is designed specifically to (37) __________ this movement of electrons. The flow creates a complete circuit, (38) __________ allows the battery to power the device.

(39) __________, this process cannot continue forever. The chemical reaction uses up the materials inside the battery. Once the chemicals in the electrolyte are depleted, they can no longer push electrons to the negative terminal. The flow of electrons stops, and we say the battery is 'dead'. This is why the power supply is not (40) __________; it has a limited lifespan determined by its chemical composition.

When you connect a battery to a phone or a toy, you are completing the circuit that allows the electrical (41) __________ to flow and do its work. (42) __________ modern portable electronic device relies on this fundamental principle of converting stored chemical energy into useful electrical energy. Understanding this helps us appreciate the clever science packed into such a small and essential item.

The clock strikes midnight, but for many students across Vietnam, the night is far from over. With a major exam just hours away, the temptation to 'pull an all-nighter' is strong. Textbooks are open, coffee is brewing, and the belief is that more hours studying equals a better grade. But what if this common strategy is not just ineffective, but actually harmful to academic performance? This question is becoming increasingly important as students face growing academic pressure.

The answer lies in the science of sleep. While we are unconscious, our brains are hard at work. This process, known as memory consolidation, is when the brain sorts, processes, and stores the information we learned during the day. During different sleep stages, especially REM (Rapid Eye Movement) sleep, neural connections are strengthened, turning short-term memories into long-term knowledge. Without adequate sleep, this crucial transfer cannot happen effectively. It's like gathering ingredients for a meal but never actually cooking it; the information is there, but it isn't ready to be used.

The consequences of skipping sleep extend beyond poor memory. Sleep deprivation directly impairs cognitive functions. A tired brain struggles with focus, making it difficult to concentrate during an exam. Problem-solving abilities are reduced, and creative thinking becomes nearly impossible. Furthermore, a lack of sleep increases the production of stress hormones, leading to anxiety and a negative mood. So, even if you manage to read every page of your textbook, your exhausted brain may not be able to recall or apply the information when it matters most. These effects can also impact physical health and emotional well-being.

This issue has gained significant attention in Vietnam. Health experts have raised concerns that students are not getting the recommended 8 to 10 hours of sleep per night due to heavy homework loads and early school start times. In response, city authorities, such as those in Ho Chi Minh City, have begun discussing and implementing regulations to adjust school schedules. These new policies aim to provide students with a better opportunity to get sufficient rest. They are a clear recognition from officials that quality sleep is a vital component of a student's education and overall health.

Ultimately, the evidence is clear: sacrificing sleep for extra study time is a counterproductive strategy. A more effective approach involves smart time management. Creating a consistent study schedule, breaking down material into smaller chunks, and reviewing regularly are far more beneficial than a single, frantic, overnight session. To improve sleep quality, students should also avoid caffeine late in the evening and create a relaxing bedtime routine. Prioritizing sleep is not a sign of weakness; it is one of the smartest decisions a student can make for academic success.