Sports & Games — National & International Events

Why This Chapter Matters

RRB Group D papers pull 2 to 4 questions straight out of this one chapter, every single attempt, without fail. Ask any student who has cleared the exam and they will tell you the same thing: unit and instrument questions are the easiest marks on the paper, because there is nothing to understand, only to remember correctly. No numerical, no long passage, no tricky diagram. Just a name and a fact, sitting there waiting to be recalled in four seconds flat.

Here is the shape of what is coming. First you get a full working list of SI units for every physical quantity that RRB has ever asked about, then a complete instruments table with what each one measures, then the metric prefix ladder that trips up more students than it should, and finally a table of scientific discoveries paired with the scientists who made them. The single biggest mistake aspirants make in this chapter is mixing up the unit of work/energy with the unit of power, or confusing an instrument's name with what it actually measures because two names sound alike (barometer vs barograph, ammeter vs voltmeter). We will flag every one of these traps as we go, so read the exam trap boxes carefully, do not skim past them.

1. What Is the SI System, and Why Does RRB Love It

SI stands for Système International d'Unités, the International System of Units. It was adopted in 1960 so that scientists across the world, whether in Delhi or Berlin, could report a measurement and mean exactly the same thing. Before SI, different countries used different base units for the same quantity, and comparing results was a mess. Think of it like a common currency for measurement. Just as the rupee lets a vendor in Chennai and a vendor in Patna agree on a price without converting anything, SI lets a physicist in Mumbai and one in Tokyo agree on a mass or a length without translation.

SI rests on seven base units. Every other unit in physics, no matter how complicated, is built by combining these seven. RRB frequently asks you to simply name the base unit of a given quantity, so learn this table cold.

Table 1: The Seven SI Base Units

Physical Quantity	SI Unit	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

Memory hook: picture a tailor's shop. He measures cloth length in metres, weighs thread on a scale for mass in kilograms, watches the wall clock for time in seconds, checks the shop's electric meter for current in amperes, feels the room's temperature in kelvin, counts sacks of dye by the mole, and switches on a bulb rated in candela. Seven jobs, seven units, one small shop. If you can walk through that shop in your head during the exam, the seven base units come back to you in order.

Exam trap: the SI unit of mass is the kilogram, not the gram, even though kilogram itself contains the prefix "kilo." It is the only base unit that carries a prefix in its own name. RRB has repeated this one for years because it looks wrong at first glance.

2. Derived Units — Built From the Base Seven

A derived unit is simply a combination of base units. Once you know force is mass times acceleration, and acceleration is metres per second squared, the unit of force falls out automatically: kilogram-metre per second squared, which we simply rename newton. RRB rarely asks you to derive these; it asks you to recall the final name. So memorise the final answer, not the derivation, though understanding the derivation helps the memory stick.

Table 2: Complete SI Units Reference for RRB Group D

Physical Quantity	SI Unit	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Temperature	kelvin	K
Electric current	ampere	A
Amount of substance	mole	mol
Luminous intensity	candela	cd
Area	square metre	m²
Volume	cubic metre	m³
Density	kilogram per cubic metre	kg/m³
Speed / velocity	metre per second	m/s
Acceleration	metre per second squared	m/s²
Force	newton	N
Pressure	pascal	Pa
Energy / work / heat	joule	J
Power	watt	W
Electric charge	coulomb	C
Electric potential / voltage	volt	V
Electric resistance	ohm	Ω
Electric capacitance	farad	F
Frequency	hertz	Hz
Magnetic flux	weber	Wb
Magnetic flux density	tesla	T
Inductance	henry	H
Luminous flux	lumen	lm
Illuminance	lux	lx
Radioactivity (activity)	becquerel	Bq
Absorbed dose of radiation	gray	Gy
Amount of heat	joule	J
Plane angle	radian	rad
Solid angle	steradian	sr
Sound intensity level	decibel	dB
Atmospheric pressure	pascal (also bar, atm)	Pa

Exam trap: energy, work, and heat all share the same SI unit, the joule. Students often assume heat must have its own separate unit because it "feels different" from mechanical work. It does not. Whether you lift a bag of rice or boil a kettle of water, the energy transferred is measured in joules.

Exam trap: power is not the same as energy. Power is the rate at which energy is used or produced, measured in watt, which equals one joule per second. RRB loves to swap "unit of work" and "unit of power" in wrong options. If the question says "rate," the answer is watt. If it just says amount of energy, the answer is joule.

A Second Look at Pressure

Pressure gets its own note because RRB asks about it in three different flavours: SI unit (pascal), a commonly used practical unit (bar), and the old but still-tested unit (atmosphere, atm). One atmosphere is roughly the pressure the air around us exerts at sea level, close to 101325 pascal. A bicycle tyre pump reads pressure in bar because pascal is too small a number to be convenient day to day, the same way you would never measure the distance from Delhi to Mumbai in millimetres.

3. Common Scientific Prefixes — The Ladder Students Keep Falling Off

A prefix multiplies or divides a base unit by a power of ten. This is the part of the chapter where students lose the most marks, purely from confusing "milli" with "micro" or forgetting whether "kilo" makes a unit bigger or smaller. Think of prefixes as floors in a building. Kilo is upstairs, on a higher floor, meaning the value is bigger. Milli and micro are downstairs, in the basement, meaning the value is smaller. The further down you go, the smaller the fraction.

Table 3: Prefixes Frequently Tested by RRB

Prefix	Symbol	Multiplying Factor	Example
tera	T	10¹²	terabyte
giga	G	10⁹	gigahertz
mega	M	10⁶	megawatt
kilo	k	10³	kilogram
hecto	h	10²	hectare
deca	da	10¹	decagram
deci	d	10⁻¹	decilitre
centi	c	10⁻²	centimetre
milli	m	10⁻³	millimetre
micro	µ	10⁻⁶	micrometre
nano	n	10⁻⁹	nanometre
pico	p	10⁻¹²	picofarad

Memory hook: read the prefixes top to bottom in the table as a staircase going down from a terrace to a basement: Terace, Ground-plus-two, Main floor, kitchen level, then you step down through hallway, door, deck steps, cellar stairs, until you reach mud floor, µnderground, narrow tunnel, pit. Silly, but the point is direction: every step down the list is a step down in size.

Exam trap: one micrometre (10⁻⁶ m) is a thousand times smaller than one millimetre (10⁻³ m), not the same thing despite the similar spelling. Also, do not confuse the prefix "micro" with the instrument "micrometer" (a measuring tool for very small lengths) — same root word, different exam context entirely.

A quick example makes this concrete. A red blood cell is roughly 7 to 8 micrometres across. A grain of fine sand might be a millimetre or so. That single order-of-magnitude jump between micro and milli is exactly why doctors, not carpenters, need the microscope.

4. Measuring Instruments — What Each One Actually Does

This is the most exam-productive part of the chapter. RRB frequently gives you the name of an instrument and asks what it measures, or gives you what needs measuring and asks which instrument does the job. Learn both directions.

Table 4: Complete Instruments Reference for RRB Group D

Instrument	What It Measures
Thermometer	Temperature
Barometer	Atmospheric pressure
Altimeter	Altitude (height above sea level), using air pressure
Anemometer	Wind speed
Hygrometer	Humidity (moisture content in air)
Ammeter	Electric current
Voltmeter	Electric potential difference (voltage)
Ohmmeter	Electrical resistance
Galvanometer	Presence and direction of small electric current
Wattmeter	Electric power
Odometer	Distance travelled by a vehicle
Speedometer	Speed of a vehicle
Tachometer	Rotational speed (RPM) of an engine or shaft
Seismograph	Intensity and duration of earthquakes
Seismometer	Ground motion during an earthquake
Sphygmomanometer	Blood pressure
Stethoscope	Sounds from the heart and lungs
Audiometer	Hearing sensitivity / loudness threshold
Lactometer	Purity of milk (density-based)
Hydrometer	Relative density (specific gravity) of liquids
Manometer	Pressure of gases in a closed system
Barograph	Continuous record of atmospheric pressure over time
Thermograph	Continuous record of temperature over time
Pyrometer	Very high temperatures (furnaces, molten metal)
Calorimeter	Heat exchanged in a chemical or physical process
Spectrometer	Wavelengths of light / spectral lines
Photometer	Intensity of light
Micrometer (screw gauge)	Very small lengths / thickness with high precision
Vernier caliper	Small lengths, internal and external diameters
Telescope	Distant objects (astronomical viewing)
Microscope	Very small objects, invisible to the naked eye
Periscope	Objects above the observer's direct line of sight
Endoscope	Internal body organs (medical viewing)
Binoculars	Distant objects, viewed with both eyes
Gyroscope	Orientation and angular velocity
Chronometer	Precise time, especially at sea
Dynamometer	Force or mechanical power (engine output)
Flowmeter	Rate of fluid flow
pH meter	Acidity or alkalinity of a solution
Salinometer	Salt concentration in a solution
Bolometer	Intensity of radiant heat / infrared radiation
Actinometer	Intensity of sunlight (solar radiation)

Exam trap: barometer measures atmospheric pressure at one instant; barograph produces a continuous, drawn record of that pressure over hours or days. RRB likes to test whether you know the "-graph" ending means a recording device, while the plain "-meter" ending means a single-reading device. This same "-meter versus -graph" pattern repeats with thermometer/thermograph and seismometer/seismograph. Learn the pattern once, and you solve three questions instead of memorising three unrelated facts.

Exam trap: an ammeter measures current, a voltmeter measures potential difference. Both get connected into a circuit, but in opposite ways: an ammeter is placed in series (current must flow through it), a voltmeter is placed in parallel (it measures the "gap" between two points). If the question mentions "connected in series in the circuit," think ammeter. If it says "connected across the component," think voltmeter.

Memory hook for medical instruments: a doctor's basic kit tells a story in order. First the stethoscope listens to your heart, then the sphygmomanometer checks your blood pressure, then if something looks internal, the endoscope goes in to look closer. Three instruments, one visit, in the natural order a checkup actually happens.

A Note on the Barometer's Inventor

The barometer deserves a special mention because RRB sometimes pairs the instrument with its inventor in the same question. It was invented by Evangelista Torricelli, an Italian physicist, in 1643. He filled a glass tube with mercury and inverted it in a mercury dish, discovering that the mercury column's height in the tube changes with atmospheric pressure. That is why atmospheric pressure is still sometimes reported in "mm of mercury" even today, a direct descendant of Torricelli's original tube.

5. Important Scientific Discoveries and Their Discoverers

RRB frequently tests this pairing in a simple match-the-following or single-fact style question. The goal here is not depth, just accurate recall of who is credited with what.

Table 5: Discoveries and Discoverers

Discovery / Invention	Scientist	Nationality
Law of gravitation	Isaac Newton	English
Theory of relativity	Albert Einstein	German-born
Laws of motion	Isaac Newton	English
X-rays	Wilhelm Röntgen	German
Radioactivity	Henri Becquerel	French
Radium and polonium	Marie Curie	Polish-French
Electron	J. J. Thomson	English
Proton	Ernest Rutherford	New Zealand-British
Neutron	James Chadwick	English
Structure of the atom (nuclear model)	Ernest Rutherford	New Zealand-British
Periodic table	Dmitri Mendeleev	Russian
Theory of evolution	Charles Darwin	English
Circulation of blood	William Harvey	English
Vaccination (smallpox)	Edward Jenner	English
Penicillin	Alexander Fleming	Scottish
Germ theory of disease	Louis Pasteur	French
Laws of heredity	Gregor Mendel	Austrian
Telephone	Alexander Graham Bell	Scottish-American
Electric bulb (practical)	Thomas Edison	American
Radio	Guglielmo Marconi	Italian
Steam engine (improved)	James Watt	Scottish
Law of floating bodies	Archimedes	Greek
Telescope (early refracting)	Galileo Galilei	Italian
Pendulum clock	Christiaan Huygens	Dutch
DNA double helix structure	James Watson and Francis Crick	American / English
Polio vaccine	Jonas Salk	American
Barometer	Evangelista Torricelli	Italian
Thermometer (mercury)	Daniel Gabriel Fahrenheit	German-Dutch

Exam trap: do not confuse Isaac Newton (laws of motion, gravitation) with Albert Einstein (relativity). RRB sometimes lists all four together as options and asks who proposed relativity specifically, banking on students picking the "more famous physicist" name out of habit rather than the correct one.

Exam trap: electron, proton, and neutron were discovered by three different scientists, not one. Thomson found the electron in 1897, Rutherford identified the proton, and Chadwick discovered the neutron in 1932, a full 35 years after Thomson's electron. If a question strings these three together and gives a single name as the answer for all three, that option is wrong on its face.

6. Everyday Grounding: Why These Facts Are Not Just Trivia

Every instrument in this chapter exists because someone needed to solve a real, practical problem. A farmer checking whether it will rain relies, indirectly, on barometric pressure trends. A doctor tapping your wrist with a sphygmomanometer cuff is running the same basic pressure-measurement logic Torricelli worked out with mercury centuries ago. A railway engine's speedometer and tachometer are not decoration on the dashboard; they are what keeps a locomotive running within safe limits. When you next see a fever thermometer, a milk vendor's lactometer, or a mechanic's pressure gauge, you are looking at applied physics, not abstract exam trivia. That is exactly why this chapter carries real weight on the RRB paper: it tests whether science, as taught, has actually become useful in the reader's daily observation.

Quick Revision — One-Line Facts

• SI has seven base units: metre, kilogram, second, ampere, kelvin, mole, candela.
• Kilogram is the only base unit whose name itself carries a prefix.
• SI unit of force is the newton; of pressure is the pascal; of energy is the joule.
• Power is measured in watt, one watt equals one joule per second.
• Frequency is measured in hertz, cycles per second.
• Electric charge is measured in coulomb; potential difference in volt; resistance in ohm.
• Kilo means 10³ (bigger), milli means 10⁻³ (smaller), never confuse the direction.
• Micro (10⁻⁶) is a thousand times smaller than milli (10⁻³).
• Nano (10⁻⁹) is the prefix behind "nanotechnology," dealing with atomic-scale sizes.
• Barometer measures atmospheric pressure; it was invented by Torricelli.
• Ammeter measures current and is connected in series; voltmeter measures potential difference and is connected in parallel.
• Hygrometer measures humidity; anemometer measures wind speed.
• Seismograph records earthquake intensity and duration.
• Sphygmomanometer measures blood pressure; stethoscope listens to heart and lung sounds.
• Lactometer checks milk purity; hydrometer checks liquid density in general.
• Odometer measures distance travelled; speedometer measures current speed; tachometer measures engine RPM.
• Instruments ending in -graph usually make a continuous record; those ending in plain -meter usually give a single reading.
• Pyrometer is used for extremely high temperatures, such as inside furnaces.
• Micrometer (screw gauge) and vernier caliper are precision tools for small length measurement.
• Newton's laws of motion and law of gravitation both belong to Isaac Newton.
• Albert Einstein proposed the theory of relativity, not Newton.
• Electron was discovered by J. J. Thomson, proton by Rutherford, neutron by Chadwick.
• Dmitri Mendeleev created the modern periodic table.
• Charles Darwin proposed the theory of evolution.
• Alexander Fleming discovered penicillin; Louis Pasteur proposed germ theory.
• Edward Jenner developed the first smallpox vaccine.
• Marie Curie discovered radium and polonium, and remains one of the most awarded scientists in history.
• James Watson and Francis Crick described the double helix structure of DNA.
• Gray is the SI unit for absorbed radiation dose; becquerel measures radioactivity.
• Atmospheric pressure is roughly 1 atmosphere, close to 101325 pascal, at sea level.
• Decibel measures sound intensity level, not an SI base unit but widely tested.

Memory Tables

Table A: Quantity to Unit, Fast Lookup

Quantity	Unit	Symbol
Force	newton	N
Work / Energy	joule	J
Power	watt	W
Pressure	pascal	Pa
Frequency	hertz	Hz
Charge	coulomb	C
Potential difference	volt	V
Resistance	ohm	Ω
Capacitance	farad	F
Magnetic flux	weber	Wb

Table B: Instrument to Quantity, Fast Lookup

Instrument	Measures
Barometer	Atmospheric pressure
Ammeter	Current
Voltmeter	Potential difference
Hygrometer	Humidity
Anemometer	Wind speed
Seismograph	Earthquake intensity
Lactometer	Milk purity
Sphygmomanometer	Blood pressure
Tachometer	Engine RPM
Pyrometer	Very high temperature

Practice MCQs

Q1. What is the SI unit of electric current? (a) volt (b) ampere (c) ohm (d) watt

Q2. Which of the following is the only SI base unit whose name already contains a metric prefix? (a) metre (b) second (c) kilogram (d) candela

Q3. The SI unit of power is the: (a) joule (b) watt (c) newton (d) pascal

Q4. A barometer is used to measure: (a) humidity (b) wind speed (c) atmospheric pressure (d) blood pressure

Q5. Which instrument is used to measure the purity of milk? (a) hydrometer (b) lactometer (c) hygrometer (d) manometer

Q6. An ammeter is connected in a circuit: (a) in parallel with the component (b) in series with the circuit (c) outside the circuit (d) only with a battery removed

Q7. The prefix "milli" represents a multiplying factor of: (a) 10³ (b) 10⁻³ (c) 10⁶ (d) 10⁻⁶

Q8. Who is credited with discovering the electron? (a) Ernest Rutherford (b) James Chadwick (c) J. J. Thomson (d) Niels Bohr

Q9. Which scientist proposed the theory of relativity? (a) Isaac Newton (b) Albert Einstein (c) Galileo Galilei (d) Max Planck

Q10. A seismograph is used to study: (a) rainfall patterns (b) earthquakes (c) ocean currents (d) air pollution

Q11. Which of these instruments gives a continuous recorded trace rather than a single reading? (a) thermometer (b) barometer (c) barograph (d) voltmeter

Q12. The SI unit of energy, work, and heat is the same, and it is called the: (a) watt (b) newton (c) joule (d) pascal

Q13. Which pair correctly matches the scientist with their discovery? (a) Charles Darwin — Periodic table (b) Gregor Mendel — Laws of heredity (c) Alexander Fleming — Radioactivity (d) Marie Curie — Theory of evolution

Q14. A student measures the diameter of a thin wire with high precision using a screw gauge. This instrument is also known as a: (a) vernier caliper (b) micrometer (c) hygrometer (d) dynamometer

Q15. One atmosphere of pressure is approximately equal to: (a) 101325 pascal (b) 1000 pascal (c) 9.8 pascal (d) 1 newton

Answer Key

Q	Answer	Reason
1	(b)	Ampere is the SI base unit for electric current, named after André-Marie Ampère.
2	(c)	Kilogram is the base unit of mass and is the only base unit carrying a built-in prefix, "kilo."
3	(b)	Watt measures the rate of energy transfer, one joule per second, distinct from joule itself.
4	(c)	Barometer measures atmospheric pressure; it does not measure humidity, wind, or blood pressure.
5	(b)	Lactometer specifically checks milk purity by comparing its density to standard milk.
6	(b)	Current must physically pass through the ammeter, so it is always placed in series.
7	(b)	Milli equals 10⁻³, a thousandth of the base unit, smaller not larger.
8	(c)	J. J. Thomson discovered the electron in 1897 through cathode ray experiments.
9	(b)	Albert Einstein proposed both special and general relativity, separate from Newton's laws of motion.
10	(b)	Seismographs record ground motion and are the standard tool for studying earthquakes.
11	(c)	The "-graph" suffix signals a device that produces a continuous recorded trace over time.
12	(c)	Joule is the shared SI unit for all forms of energy, including heat and mechanical work.
13	(b)	Gregor Mendel's pea plant experiments gave us the basic laws of heredity in genetics.
14	(b)	A screw gauge is commonly called a micrometer and measures very small lengths precisely.
15	(a)	Standard atmospheric pressure at sea level is defined as approximately 101325 pascal.