Questions & explanations
1. What is a patent?
A patent is a government-granted right that stops others from making, using, or selling an invention without permission. It protects the inventor's idea for a limited time, usually 20 years. To get a patent, the invention must be new, useful, and not obvious. Women inventors in the Soviet Union could apply for patents, but they faced extra challenges. The state owned most industries, so patents were often assigned to the government or a state company. This meant inventors got little personal reward. Still, many women like Lidia K. and others patented inventions in fields like medicine and engineering.
2. What is photolithography and why is it used in making integrated circuits?
Photolithography is a process that uses light to transfer a pattern onto a silicon wafer. It is used because it can create very tiny and precise features, like the transistors and wires in a chip. The wafer is coated with a light-sensitive material called photoresist. Then a mask with the desired pattern is placed over it, and ultraviolet light is shone through. The exposed parts of the photoresist change their chemical properties. After development, the pattern is left on the wafer, and then etching or other steps create the actual structures. This allows millions of transistors to be made at once.
3. What are the main differences between a BJT and a FET transistor?
A BJT (bipolar junction transistor) uses both electrons and holes to carry current, and it is controlled by a small input current. A FET (field-effect transistor) uses only one type of charge carrier and is controlled by an electric field from a voltage. FETs generally have very high input resistance, so they draw almost no current from the input. BJTs have lower input resistance and need a continuous input current. MOSFETs are a common type of FET that uses a metal-oxide insulator between the gate and channel. In simple terms, BJTs are current-controlled, while FETs are voltage-controlled.
4. Compare Leonardo's scientific method to that of a modern scientist. What is similar?
Both Leonardo and modern scientists start by observing the world carefully. They ask questions and form ideas (hypotheses). Then they test these ideas through experiments or further observation. Leonardo, like modern scientists, recorded his findings in detail. However, modern scientists also share their results with others for checking and repeating experiments. Leonardo mostly kept his notes to himself, so his work was not known to many. Also, modern science uses advanced tools like microscopes, which Leonardo did not have. Still, his basic approach of learning from nature is the same.
5. What were the ethical issues with the Wright brothers' patent enforcement?
Some people thought the Wright brothers were unfair because they used their patent to stop all other airplane builders. This kept new ideas from being tested. Other inventors had different ways to control airplanes, but the Wrights' patent was so broad that it covered them too. This was seen as blocking progress. Also, the Wright brothers did not share their knowledge, which went against the spirit of invention. Many felt that patents should protect specific inventions, not whole areas of technology. So the ethical issue was whether it was right to hold back aviation for personal gain.
6. Compare a JFET and a MOSFET in terms of gate insulation.
A JFET (junction field-effect transistor) has a gate that forms a p-n junction with the channel, so the gate is not insulated. This means that if you apply a forward voltage to the gate, current can flow into the gate, which is usually not desired. A MOSFET has a gate that is insulated by a thin layer of silicon dioxide, so no current flows into the gate at all in normal operation. This gives the MOSFET an extremely high input resistance, making it easier to drive. However, the thin insulator in a MOSFET can be damaged by static electricity, while JFETs are more robust in that sense.
7. Compare Sushruta's surgical instruments with modern ones.
Sushruta described over 120 surgical instruments, including scalpels, forceps, needles, and catheters. Many of these are similar to modern instruments but made of materials like iron, wood, or bone. For example, his scalpels had different shapes for different cuts, like modern scalpels. His forceps were used to hold tissues, just like today. However, modern instruments are made of stainless steel and are sterilized to prevent infection. Sushruta also emphasized cleanliness, but he did not have antiseptics. So, the basic designs are similar, but materials and hygiene have improved.
8. What did Tesla believe about grounding, and how was it later disproved?
Tesla believed that a good ground connection would let electricity flow through the Earth with almost no loss. He thought the Earth was like a giant wire. Later, scientists found that the Earth has electrical resistance, especially in dry soil. This means that electricity loses energy as it travels through the ground. Also, the Earth's conductivity varies with location. So, Tesla's idea of efficient global power transmission through the ground was wrong. We now use ground connections mainly for safety, not for sending power. The Earth can carry some current, but not without loss.
9. How does the gate voltage control the current in a MOSFET?
In a MOSFET, the gate is separated from the channel by a thin insulating layer. When you apply a voltage to the gate, it creates an electric field that either attracts or repels charge carriers in the channel. For an n-type MOSFET, a positive gate voltage attracts electrons to the channel, forming a conductive path between source and drain. The higher the gate voltage, the more electrons are attracted, and the lower the resistance. If the gate voltage is too low, the channel is not formed, and no current flows. So the gate voltage acts like a switch or a valve for the current.
10. Compare the challenges faced by women inventors in the Soviet Union with those in capitalist countries.
In capitalist countries, women inventors often struggled to get funding and faced bias from investors. In the Soviet Union, the state provided funding, but women had to follow state priorities. Both systems had barriers: in the West, women were often excluded from networks; in the Soviet Union, they were sometimes pushed into 'feminine' fields like textiles. However, Soviet women had more access to education and jobs in science. For example, the Soviet Union had many female engineers, while Western countries had fewer. So the challenges were different but real in both places.
11. Why did Leonardo da Vinci become more famous after his death than during his life?
During his life, Leonardo was known as a talented artist and inventor, but many of his projects were unfinished or not widely seen. After his death, his notebooks were studied and published, revealing his brilliant ideas in science, engineering, and art. This made people realize he was far ahead of his time. Over the centuries, stories and myths grew, like the idea that he could fly or that he had secret knowledge. His most famous painting, the Mona Lisa, became a global icon in the 20th century. So, his reputation grew slowly as people discovered more about his work.
12. Give an example of a circuit where a BJT might be better than a MOSFET.
A BJT is often better in analog circuits that need to handle large currents, such as audio power amplifiers. BJTs can switch high currents with a lower voltage drop than MOSFETs, which means less heat for the same current. BJTs also have a more predictable relationship between input current and output current, which can be useful for linear amplification. For example, in a simple transistor amplifier for a microphone, a BJT might provide better gain and linearity. MOSFETs, however, are still used in many analog circuits because they have less noise at low frequencies.