IELTS Academic Reading Practice Test 173

Boiling water in the home once meant setting a kettle on a coal fire and waiting. The electric kettle appeared in the 1890s, once power supplies had reached some houses and public buildings, and it was among the first appliances to use electricity for heating rather than light. The early models were heavy, expensive and slow, and they cost far more than a kettle for the fire. Water, it turned out, is an awkward substance to heat with current: it conducts electricity well enough to be dangerous, and the arrangements needed to heat it safely took decades to perfect.

The first designs avoided putting anything electrical into the water. The heating element, a wire that grows hot when current passes through it, sat in a separate chamber beneath the body of the kettle, and its heat travelled through a metal wall. This was safe and easy to clean. It was also inefficient, because much of the heat went into the surrounding air rather than into the water. The obvious improvement was to immerse the element directly, so that heat passed straight into the liquid. Immersed elements became common in the 1920s, and they made kettles noticeably quicker.

Making an element that could survive being boiled proved difficult. The wire had to become red-hot while remaining insulated from the water. The answer, developed during the 1920s, was a tube of metal containing a coil of resistance wire, with the space between them packed with a powder that conducts heat but not electricity. The wire itself was made from alloys of nickel and chromium, which resist oxidation at high temperatures and do not soften when they glow.

Safety was a more serious problem. A kettle is a metal object full of water, handled by people with wet hands, and early models often had no connection to earth, so a fault inside the element could make the whole body live. Plugs and sockets were not standardised until well into the twentieth century, and flexes frayed. Successive regulations gradually made the appliance safer, through earthed connections, double insulation and, eventually, bodies made of plastic, which does not conduct at all.

The convenience of a kettle that switches itself off arrived in the 1950s. The mechanism depends on a bimetallic strip: two thin strips of different metals bonded together, which expand at different rates when heated and so bend. In 1955 a small British firm, Russell Hobbs, sold a kettle in which steam from the boiling water was directed onto such a strip, which bent, released a catch and broke the circuit. A second strip, warmed by the element itself, protected against the kettle being switched on with too little water inside. Versions of this arrangement gradually became standard.

The next change concerned the flex. A kettle with a cable attached must be carried to the tap and back with the cable trailing behind it. In the 1980s manufacturers introduced models that stood on a separate base, permanently connected to the mains, so that the kettle itself could be lifted off and set down again with one hand. The base also carries the electrical contacts, which are arranged so that they cannot be touched while the kettle is in use.

Compared with heating water in a pan on a hob, an electric kettle is efficient, because the element is surrounded by the water it heats and almost all the energy ends up in the liquid. The British electricity grid has long had to allow for this. When a popular television programme ends, millions of kettles are switched on within a few minutes and demand rises sharply. Operators keep reserve generating capacity ready for these surges, although the spread of streaming has made them smaller and harder to predict.

In much of Britain and parts of Europe the water is hard, meaning that it contains dissolved calcium and magnesium salts. When it is boiled, these salts come out of solution and form limescale, which coats the element. Scale conducts heat poorly, so a scaled element must run hotter to do the same work, wasting energy and eventually failing. Descaling with a mild acid, such as citric acid or vinegar, dissolves the deposit and restores performance.

From the late 1980s manufacturers began to seal the element beneath a flat metal plate forming the floor of the kettle, so that nothing protruded into the water. A concealed element is easier to wipe clean and leaves no gap in which scale can collect, and it is now the usual arrangement in Europe.

Today the electric kettle is an unassuming object, yet it has acquired features that would once have seemed extravagant: variable temperature settings for different kinds of tea, keep-warm functions, filters, and windows showing how much water remains. Designers have worked on speed, and on quietness, since the noise of a boiling kettle is unwelcome in an office or an open-plan kitchen. In countries where tea is drunk several times a day the kettle may be used a dozen times before lunch; elsewhere it may sit idle for weeks. Even so, the basic principle has barely changed in a century.

For most of human history the passage of time was measured by the sky. A day was the interval between one noon and the next, and the second was a sixtieth of a sixtieth of that interval. The arrangement served everyday life, but it had a flaw: the Earth is not a reliable clock. Its rotation is slowed slightly by the friction of the tides, and it shifts in response to earthquakes and the movement of air. A unit tied to the turning planet was never quite the same length twice.

Physicists had long known that atoms offer a different kind of standard. An atom can exist only in certain energy states, and when it moves between them it absorbs or emits radiation at a frequency fixed by the size of the gap. That frequency depends on the structure of the atom and on nothing else. Every atom of a given isotope is identical to every other, so a frequency set by the atom is the same in every laboratory on Earth. A clock built on such a frequency would not drift with temperature, wear out, or disagree with its twin.

The most useful transition for timekeeping was found in caesium-133, the only stable isotope of that element. Caesium has a single electron in its outermost shell, and its nucleus has a small magnetic moment; the two can be aligned with each other or against each other, giving two very slightly different energy states. Flipping the electron relative to the nucleus requires microwave radiation with a frequency of 9,192,631,770 cycles per second. In 1967 an international conference on weights and measures redefined the second in terms of that frequency.

A caesium clock of the traditional kind passes atoms through a series of fields. Caesium is heated in an oven until it evaporates, and the atoms escape through a small hole to form a beam. A magnet sorts the beam, allowing through only those atoms that are in one of the two states. The beam then enters a cavity in which microwaves oscillate; if their frequency is close to the atomic value, many atoms change state. A second magnet and a detector count how many have done so, and an electronic circuit adjusts the oscillator to keep the number of changes at a maximum, which locks it to the atoms.

The first practical instrument of this kind was built in 1955 at the National Physical Laboratory in Britain, by Louis Essen and Jack Parry. It could not be left running unattended, but it was far more stable than any clock based on a pendulum or a quartz crystal. Atomic clocks are needed not to tell the time of day but to coordinate networks that must agree to a millionth of a second.

Accuracy improved again with the fountain clock, in which a cloud of caesium atoms cooled by lasers is launched upwards through a cavity. Gravity slows the cloud and brings it back through the same cavity, so that each atom is interrogated twice. The best instruments of this design are wrong by less than a second in many millions of years.

Atomic clocks come in several designs, which trade accuracy against convenience. Rubidium clocks are small, cheap and reasonably stable, which makes them suitable for satellites, mobile phone base stations and other equipment in the field. Hydrogen masers, in which a beam of hydrogen atoms is made to radiate coherently, are extraordinarily stable over periods of hours, though their frequency drifts slowly over months. Caesium clocks remain the primary standards, because their accuracy has been measured with great care and they underlie the international definition of the second.

The frontier now lies in optical clocks, which use transitions at visible frequencies, tens of thousands of times higher than the caesium transition. A clock that oscillates faster can divide time more finely. Such clocks compare a laser with an atomic transition, and a device called a frequency comb converts optical frequencies into microwave counts, linking the result back to ordinary electronics. In some designs, thousands of atoms are held in an optical lattice, a standing wave of laser light, so that their signals can be combined and read more quickly.

All of this rests on an odd feature of physics. General relativity tells us that clocks run at different rates in different gravitational fields: a clock at sea level, closer to the Earth's mass, ticks more slowly than one on a mountain. Each satellite of the Global Positioning System carries atomic clocks, and relativity cannot be ignored there. The satellites are high enough for weaker gravity to speed their clocks by about 45 microseconds a day, while their orbital speed slows them by about seven, leaving a net gain of 38 microseconds. Left uncorrected, that would put the position calculation out by kilometres within a day.

The list of users of precise time is longer than one might expect. Navigation systems rely on it, and telecommunication networks use it to keep data in step. Stock exchanges time-stamp trades to the microsecond, and power grids synchronise their equipment with it. Civil time is itself an average: Coordinated Universal Time is calculated from a comparison of hundreds of clocks in national laboratories, and because the planet's rotation is not steady, a leap second has occasionally been added. The best optical clocks remain laboratory instruments; portable versions could one day measure height, since a clock's rate changes detectably with altitude.

In a handful of restaurants, diners are offered a discount if they hand over their phones for the evening. At some concerts, phones are sealed into locked pouches at the door and released only at the end. Several railway operators set aside quiet carriages, and a few galleries now ask visitors to look at the pictures rather than at their screens. Some of these experiments are faintly absurd, but they are worth taking seriously. Each sets out to create a space in which a screen is not welcome, and each raises the question of whether such spaces should be created deliberately.

The smartphone has become the default companion of the waking day, and the habit of checking it has been built into the design of the device. Notifications arrive at unpredictable intervals and are engineered to be hard to ignore. The consequences for conversation have been widely studied. An influential set of experiments found that the mere presence of a phone on a table changed how people talked to one another, although later attempts to repeat the work produced much smaller effects. Even so, the designers of these systems, and not only their users, bear some of the responsibility for the difficulty of putting a phone away.

The strongest argument for a technology-free space is not that phones are harmful in themselves, but that a place can hold only one purpose at a time. A room in which half the people are talking and half are scrolling is not simply a room with phones in it; it is a different kind of room. Attention, in this sense, is a shared resource. One person filming a performance alters the evening for those around them, and being recorded by strangers is a matter of privacy as well as of mood. None of this requires a belief that screens damage health.

The obvious objection is that adults are capable of deciding for themselves how to spend an evening, and that a rule forbidding a device treats customers like children. Bans are also awkward to enforce, and the friction they create may drive people away rather than draw them in. More seriously, a strict rule can exclude those who need their phones: a parent waiting for news of a sick child, or someone on call for work. Any restriction that survives these objections will need a visible and easy route to an exception.

There is a commercial dimension too. A no-phone policy can be a marketing device, a way for a business to signal that it is thoughtful and exclusive. The venues that adopt such rules are usually the expensive ones, and the customers most able to enjoy a digital detox are those whose working lives allow it. Meanwhile, people whose employers expect them to answer messages at all hours cannot opt out of the technology by choosing a different cafe. If the real problem lies in the design of the software and in the expectations of employers, then a phone-free restaurant addresses a symptom and leaves the cause untouched.

It is worth being honest about the evidence. Most research on screen use and wellbeing is correlational, and the associations it finds are small. Some studies of short periods without a phone report improvements in mood, but it is hard to separate the absence of the device from the walk, the meal or the conversation that replaced it. The case for a quiet space should therefore rest on modest claims about attention and courtesy rather than on promises of health.

Where such rules work, they tend to share a feature: the purpose of the place is obvious and the boundary is clear. Nobody is surprised to switch a phone off in a theatre, a concert hall, a place of worship or a library reading room. In each case the restriction is understood as part of what the visitor came for. Voluntary arrangements are more fragile. A quiet carriage stays quiet only while almost everyone in it complies, and one loud call can ruin the atmosphere for a whole coach, which is why some venues prefer lockable pouches to trust.

Schools are a special case, and not only because children are less able to judge the consequences of a device. Attendance is compulsory, so a rule imposed there applies to everyone, and pupils have had little part in making it. France restricted phone use in schools by law in 2018, and in 2023 a report from UNESCO recommended that smartphones be kept out of classrooms unless a lesson requires them. The evidence on attainment is mixed, though several studies report modest gains where phones are removed, along with less bullying. What can be said with more confidence is that children cannot be expected to establish norms for themselves when the adults around them have not.

My own view is that the deliberate, well-signposted quiet space is a genuine public good, and that the case for it is strongest where attention is the whole point of the visit. I am much less comfortable with compulsory bans in ordinary places, which tend to be either unenforceable or illiberal. What works is a combination of design and persuasion: a room whose purpose is obvious, staff who put their own phones away, and an invitation that is easy to accept and easy to refuse. A city that offers nowhere to put the phone down is the poorer for it; a city that forbade it everywhere would be poorer still.