Physics: units, constants and everyday phenomena
| Quantity | SI unit | Quantity | SI unit |
|---|---|---|---|
| Force | newton (N) | Pressure | pascal (Pa) |
| Energy / work | joule (J) | Frequency | hertz (Hz) |
| Power | watt (W) | Electric current | ampere (A) |
| Electric charge | coulomb (C) | Resistance | ohm (Ω) |
| Potential difference | volt (V) | Temperature | kelvin (K) |
| Magnetic flux density | tesla (T) | Radioactivity | becquerel (Bq) |
What is the approximate speed of light in a vacuum?
About 3 × 10⁸ metres per second, or roughly 300,000 kilometres per second. Light from the Sun takes about eight minutes and twenty seconds to reach Earth.
Can sound travel through a vacuum?
No. Sound is a mechanical wave and needs a medium to propagate, which is why space is silent. Light, being electromagnetic, travels through a vacuum without difficulty.
Why does the sky appear blue and the setting sun red?
Because air scatters shorter wavelengths far more strongly than longer ones, so scattered blue light reaches us from all directions. Near the horizon, sunlight travels a longer path and most of the blue is scattered away, leaving the reds.
What is the difference between mass and weight?
Mass is the amount of matter in a body, measured in kilograms, and is the same everywhere. Weight is the gravitational force on that mass, measured in newtons, and changes with location - which is why an object weighs less on the Moon but has the same mass.
Which instrument measures atmospheric pressure, and which measures humidity?
A barometer measures atmospheric pressure; a hygrometer measures humidity. Instrument-to-quantity matching is a standard question, so learn the set including seismograph for earthquakes, ammeter for current and lactometer for milk purity.
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Chemistry: symbols, compounds and properties
Give the chemical symbols for gold, silver, iron, sodium, potassium, lead, tin and mercury.
Au, Ag, Fe, Na, K, Pb, Sn and Hg. These come from Latin names - aurum, argentum, ferrum, natrium, kalium, plumbum, stannum and hydrargyrum - which is exactly why they are the symbols most often missed.
Which metal is liquid at room temperature, and which non-metal?
Mercury is the only metal that is liquid at room temperature; bromine is the only non-metal that is. Both halves of that pair get asked.
What is the hardest naturally occurring substance?
Diamond, which is pure carbon in a tetrahedral covalent network. Graphite is also pure carbon but soft and slippery, because its layers slide over one another - a classic allotrope comparison.
Give the chemical formulas for common salt, baking soda, washing soda and quicklime.
Common salt is NaCl, baking soda is NaHCO₃, washing soda is Na₂CO₃·10H₂O, and quicklime is CaO. Plaster of Paris, CaSO₄·½H₂O, belongs in the same list.
What is the pH of pure water, and what does a pH below 7 indicate?
Pure water has a pH of 7 at 25 °C, which is neutral. Below 7 is acidic and above 7 is basic. The scale is logarithmic, so a change of one pH unit is a tenfold change in hydrogen ion concentration.
Why are noble gases unreactive?
Because their outermost electron shells are completely filled, so they have almost no tendency to gain, lose or share electrons. This is why helium is used in balloons and argon in light bulbs.
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Biology: the human body
How many bones are there in an adult human body?
206. A newborn has around 270, and the number decreases as bones fuse during growth - which is a favourite follow-up question.
What is the largest organ in the human body, and the largest internal organ?
The skin is the largest organ overall; the liver is the largest internal organ. The femur is the longest bone and the stapes in the ear the smallest.
Which blood group is the universal donor, and which the universal recipient?
O negative is the universal donor for red cells and AB positive the universal recipient. The distinction rests on which antigens are present on the red cells.
Which gland secretes insulin, and what happens without it?
The pancreas, specifically the beta cells of the islets of Langerhans. Without sufficient insulin, glucose cannot be taken up properly by cells and blood sugar rises, which is diabetes mellitus.
How many chambers does the human heart have, and what does each side carry?
Four - two atria and two ventricles. The right side handles deoxygenated blood going to the lungs, and the left side oxygenated blood going to the body. The left ventricle has the thickest wall because it pumps furthest.
What is the function of red blood cells, white blood cells and platelets?
Red cells carry oxygen using haemoglobin, white cells defend against infection, and platelets enable clotting. Red cells are the most numerous, and haemoglobin is what makes blood red.
Which part of the cell is called the powerhouse, and why?
The mitochondrion, because it is where most ATP is produced through aerobic respiration. Chloroplasts, found only in plant cells, are where photosynthesis occurs.
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Vitamins, deficiencies and nutrition
| Nutrient | Deficiency disease | Nutrient | Deficiency disease |
|---|---|---|---|
| Vitamin A | Night blindness | Vitamin B1 (thiamine) | Beriberi |
| Vitamin B3 (niacin) | Pellagra | Vitamin B12 | Pernicious anaemia |
| Vitamin C | Scurvy | Vitamin D | Rickets in children, osteomalacia in adults |
| Vitamin K | Poor blood clotting | Iodine | Goitre |
| Iron | Anaemia | Calcium | Weak bones and teeth |
- ✓Fat-soluble vitamins are A, D, E and K; the B-complex vitamins and vitamin C are water-soluble. That grouping itself is often asked.
- ✓Vitamin D is synthesised in the skin on exposure to sunlight, which is why it is sometimes called the sunshine vitamin.
- ✓Vitamin C is destroyed by prolonged heating, which is why it is largely lost in overcooked vegetables.
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Discoveries and the people behind them
Who discovered penicillin, and who pioneered vaccination?
Alexander Fleming discovered penicillin in 1928. Edward Jenner pioneered vaccination, using cowpox material to protect against smallpox.
Who proposed the structure of DNA, and in which year?
James Watson and Francis Crick, in 1953, building on X-ray diffraction work by Rosalind Franklin and Maurice Wilkins. The structure is a right-handed double helix with complementary base pairing.
Who developed the periodic table, and on what basis?
Dmitri Mendeleev arranged the elements by increasing atomic mass and left gaps for undiscovered elements, which is what made his table predictive. The modern table is arranged by atomic number.
Who gave the laws of motion, and who the law of gravitation?
Isaac Newton gave both. His three laws of motion and the universal law of gravitation appear in the Principia, published in 1687.
Who is known as the father of the Indian space programme, and who founded ISRO's predecessor?
Vikram Sarabhai is regarded as the father of the Indian space programme, and was instrumental in establishing the organisation that became ISRO in 1969.
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How to revise general science efficiently
- ✓Learn in pairs and tables. Unit and quantity, symbol and element, vitamin and deficiency, discovery and discoverer - these are matching questions, so revise them as matches.
- ✓Focus on the Latin-derived chemical symbols, since those are where marks are actually lost.
- ✓Learn 'why' answers as one-sentence causes: why the sky is blue, why noble gases are inert, why the left ventricle is thickest. Reason-based questions are increasingly common.
- ✓This section is finite. Unlike history or current affairs, general science can genuinely be finished - which makes it the highest-return part of a GK paper.
- ✓Test yourself in mixed sets, since exams do not tell you whether a question is physics, chemistry or biology.