Riya's father, Professor Samiran Sen, was driving the family car. After enjoying Delhi's famous pav bhaji at Nehru Place Market, Arka was in an especially cheerful mood. He had bought several electronic gadgets at bargain prices and packed them into his bag. On their way home, Professor Sen stopped at Chittaranjan Park and bought a huge hilsa fish.
Seeing it, Minu masi remarked, "Hilsa isn't worth eating unless it's really good. It's already almost eight o'clock. If you keep it in the fridge and cook it later, it won't taste the same. Besides, can you even get fish in Delhi that's as good as what we get in Kolkata?"
The professor defended himself. "Maybe not exactly like Kolkata, Minu di, but you do get excellent hilsa in Delhi. You saw how huge the market is! And there's no need to refrigerate it. Your sister had the day off today, and she's crazy about hilsa. You'll see, she'll start cooking it right away."
"Start cooking now? Have you thought about how late we'll end up having dinner?" Minu masi protested.
Riya came to her mother's defence. "Masi, my mum cooks ilish bhapa in the microwave oven. You'll see how delicious it turns out! It'll be ready in just twenty minutes."
Minu masi wrinkled her nose. "That machine is the bane of my life. It ruins every dish. These days everyone's obsessed with cooking in microwave ovens. The advertisements are endless. I have one at home too, but it just sits there gathering dust."
Riya's father objected. "Why should it gather dust? It's extremely useful. These days life feels incomplete without a microwave. You're from Kolkata why do you have such old-fashioned ideas?"
"Have you gone mad? My husband had a pacemaker fitted about five years ago. He's retired and spends all day pottering around the kitchen. What if using one of those microwave contraptions causes his pacemaker to malfunction?"
Arka immediately protested. "What? Why would a pacemaker malfunction? Modern microwave ovens have high-quality shielding that prevents the microwaves from escaping the oven. Even if a tiny amount did leak out, it would travel no more than a few inches. And surely none of us hugs the microwave while it's running!"
The sarcasm in Arka's remark left Minu masi momentarily speechless. But she wasn't one to back down easily.
"All right," she said. "Let's see how this hilsa turns out. But I'm certainly not going anywhere near that microwave oven."
Riya loved hilsa. She exclaimed excitedly, "I'll help Mum! It'll be a good chance to learn."
As soon as they got home, Riya and her mother became busy preparing steamed hilsa in the microwave oven. Meanwhile, Arka settled onto the sofa in the living room and began transferring files after connecting the computer hard drive he had just bought. Riya's father picked up an old newspaper and, while casually leafing through it, began explaining to Minu masi.
"You see, Didi, microwaves have become a part of everyday life. In urban areas, you'd be hard-pressed to find a home without one. Has your tea gone cold? Just put the cup in the microwave, press a button, and in a minute it's piping hot again. The tea gets hot, but the cup itself doesn't. Among the many important inventions of the last century, the microwave is certainly one of the most significant. And it's not just microwave ovens. Even the mobile phone, which has become indispensable in both cities and villages, owes much of its existence to microwave technology."
Hearing this, Arka quipped, "In that case, Minu masi, you shouldn't let Uncle use a mobile phone either. It might interfere with his pacemaker."
Just then Riya returned from the kitchen and announced, "It smells wonderful, Arka! The steamed hilsa is ready. We'll be sitting down for dinner in just a little while."
Ignoring her interruption, Riya's father continued addressing Minu masi.
"The invention of the microwave actually has its roots in warfare. After the Second World War, military strategists realised that faster communication systems were essential. If an enemy warship or helicopter suddenly crossed the border, its presence had to be detected instantly; otherwise, there would be no way to defend against a surprise attack or bombing raid. So scientists were instructed to develop a device that could detect the presence of enemy aircraft or ships immediately. And, as ordered, they did."
Picking up where he left off, Arka added, "Back in the mid-nineteenth century, Sir James Clerk Maxwell showed mathematically that electromagnetic waves could be used for communication over long distances. At that stage, however, it was only a theoretical prediction expressed through equations. Later, the German physicist Heinrich Hertz generated electromagnetic waves using a high-frequency induction coil and detected them with another coil placed some distance away, proving that electromagnetic waves could travel without any physical medium. That discovery paved the way for the invention of radio. Over the next sixty or seventy years, radio technology gradually evolved."
The professor smiled approvingly. "Excellent! Now let me tell you how the microwave oven itself was invented.
"After the Second World War, in 1945, electrical engineer Percy Spencer was working with radar equipment. Incidentally, RADAR is an acronym for Radio Detection and Ranging. Spencer was employed by the Raytheon Company, then America's largest manufacturer of military equipment.
"One day, while working with a high-powered microwave beam, he noticed that the chocolate bar in his coat pocket had melted even though it was quite cold at the time. Realising that microwaves could generate heat, he scattered some corn kernels near the equipment, and within moments they popped into popcorn. Curious to investigate further, he placed a whole egg near the microwave source. As soon as he switched on the machine, the egg exploded, splattering its contents everywhere. The reason was simple: microwaves agitate water molecules, producing heat. The moisture inside the egg rapidly turned into steam, creating pressure until the shell burst."
"The Raytheon Company quickly patented Spencer's discovery. They built an enormous microwave oven that stood nearly six feet tall and weighed around three hundred and fifty kilograms. It cooked food remarkably quickly and attracted tremendous attention. There was just one problem—how could such a huge machine possibly fit into an ordinary kitchen? Manufacturers therefore began working on making microwave ovens smaller and less expensive. Gradually, they became compact enough for household use. During the past ten to fifteen years, microwave ovens have also become increasingly popular in India.
"That's the story of the invention. Now let's look at the science behind how a microwave oven cooks food.
"A microwave is a type of electromagnetic wave with a frequency ranging from about 300 megahertz to 300 gigahertz. The speed of an electromagnetic wave equals its frequency multiplied by its wavelength. This means wavelength is inversely proportional to frequency—the higher the frequency, the shorter the wavelength. High-frequency microwaves have wavelengths ranging from about one metre to one millimetre. Because of their high frequency and short wavelength, microwaves carry considerable energy and can travel long distances in nearly straight lines. These properties make them extremely useful in telecommunications. Signals for mobile phones and television, for example, are transmitted using microwaves.
"Now let's see how microwaves are generated. They are produced by a device called a magnetron. It consists of a copper cylinder with cavities that acts as the anode, while a cathode is placed at its centre. Inside the cathode is a filament that heats it. The cathode is coated with a layer of barium oxide. When electricity passes through the filament, the cathode becomes hot and emits a stream of electrons. A powerful permanent magnet is positioned so that the electric current and the magnetic field act at right angles to each other. Entering this electromagnetic field, the electrons spiral towards the anode. As these high-energy electrons pass through the narrow cavities in the anode, they produce oscillations known as cavity resonance, which generate microwaves. The microwaves are then directed by a special structure called a waveguide, whose purpose is to channel them along a precise path."
Professor Sen had barely finished his explanation when Riya looked at him in amazement.
"Dad, how do you know so much about microwave ovens? We studied magnetrons in our Class Twelve Physics syllabus."
Smiling, he replied, "Perhaps you never noticed that I've always been interested in how machines work, Riya. It's good to know at least a little about the devices we use every day."
Arka, who had been listening attentively all this while, added, "Inside a microwave oven there's a rotating glass turntable on which the food is placed. The turntable keeps spinning so that the food heats evenly on all sides."
Riya's father continued, "Modern microwave ovens usually have three operating modes—Microwave, Convection and Grill.
"In Microwave mode, you must never use metal utensils because microwaves striking metal can produce sparks through short-circuiting, which is extremely dangerous. Instead, glass or specially designed microwave-safe plastic containers are used. Microwaves cannot excite the molecules in glass or plastic, so they pass through these materials and penetrate the food itself. Water molecules are affected the most by microwaves. Since almost all food contains water, the food heats up within a minute or two, while the glass container itself remains relatively cool.
"In Convection and Grill modes, however, the magnetron remains switched off. Instead, a special electric heating element produces heat inside the oven, while a built-in fan automatically circulates the hot air evenly throughout the cavity. In Grill mode, the high-temperature heating element browns and grills the food. Since the magnetron is inactive in both Convection and Grill modes, no microwaves are produced. Therefore, metal utensils can safely be used in these two modes. Cakes, for example, are baked using Convection mode."
Riya asked, "But Dad, why doesn't food taken straight from the refrigerator heat evenly? Even after running the oven for several minutes, the bottom part often stays cold."
"That's because microwaves lose much of their energy after penetrating only a few inches into the food," he explained. "The best method is to heat the food for two or three minutes, stir or turn it over, and then heat it again. That ensures even heating."
Arka now glanced sideways at Minu masi and remarked, "We often hear people say that the powerful magnetic field inside a microwave oven can harm the human body. That's simply not true. Because of the magnetic shielding surrounding the oven, neither the magnetic field nor the microwaves generated inside can escape. Most manufacturers also provide recipe books and cooking instructions with the oven. If you read those carefully, you can prepare plenty of delicious dishes. And Riya, you mentioned reheating refrigerated leftovers in the microwave. In fact, that's often better than reheating them in a frying pan, where excessive heat can reduce both the nutritional value and the flavour of the food. A microwave reheats the food more gently."
Just then Riya's mother entered the living room and announced, "Dinner is served. Everyone, please come to the table. Minu di isn't used to staying up late. But remember, once you reach Australia, you'll have to make friends with a microwave oven!"
With a weary smile, Minu masi got up and said, "First let me get there. Then we'll see what sort of oven I'll be cooking with."
