PTE Listening Practice Test 19

"In this lecture I'll outline how people have measured time through history. The earliest methods relied on nature: sundials used the moving shadow of the sun, while water clocks measured time by the steady flow of water from one container to another. Mechanical clocks appeared in European monasteries and towers in the thirteenth and fourteenth centuries, but they were often inaccurate by many minutes each day. A major advance came in the seventeenth century, when the pendulum clock reduced errors to a few seconds a day. Accurate timekeeping at sea was essential for navigation, and in the eighteenth century John Harrison built marine clocks that allowed sailors to calculate their longitude. Today, atomic clocks, which measure the vibrations of atoms, are so precise that they would lose less than a second in millions of years, and they make technologies such as GPS possible."

প্রথমে সূর্যঘড়ি ও জলঘড়ি দিয়ে সময় মাপা হতো। ত্রয়োদশ শতকে যান্ত্রিক ঘড়ি আসে, সতেরো শতকে পেন্ডুলাম ঘড়ি নির্ভুলতা বাড়ায়। হ্যারিসনের সামুদ্রিক ঘড়ি নৌচলাচলে সাহায্য করে, আর আজ পারমাণবিক ঘড়ি জিপিএস সম্ভব করেছে।

"Crowdfunding platforms allow people to raise money for projects by collecting small contributions from large numbers of supporters online. For creative projects and start-up products, this can provide funding without giving up ownership to investors, and it also tests whether there is real demand for an idea. However, studies show that a majority of campaigns fail to reach their targets, and successful ones usually depend on extensive preparation and existing networks of supporters. Backers should also remember that their money is not always protected if a project fails to deliver."

"Cities are often several degrees warmer than the surrounding countryside, a phenomenon known as the urban heat island effect. Dark surfaces such as roads and roofs absorb sunlight during the day and release heat at night, while buildings block cooling winds. The extra heat increases energy use for cooling and can be dangerous during heatwaves, especially for elderly people. Planting trees, creating parks and using light-coloured or reflective materials on roofs and pavements are among the most effective ways to reduce the effect."

"The Arctic fox is superbly adapted to one of the coldest environments on Earth. Its thick winter coat provides such good insulation that the fox does not begin to shiver until the temperature drops to around minus seventy degrees Celsius. It also has short legs, a short muzzle and small rounded ears, all of which reduce the surface area through which heat can escape. In summer, its coat changes from white to brown or grey, helping it to blend in with the rocks and plants of the tundra."

"When you see a flash of lightning and then count the seconds until you hear the thunder, you can estimate how far away the storm is, because light reaches you almost instantly while sound travels much more slowly through the air."