RRB Radiographer cheat sheet

X-ray production: thermionic emission from a tungsten filament; less than 1% of electron kinetic energy becomes X-rays and the rest becomes heat, so rotating anodes are used for high-output work.

mAs governs photon quantity and receptor exposure; kVp governs photon energy, penetration and subject contrast. Raising kVp by 15% roughly doubles density, so halve mAs to keep exposure constant.

Inverse square law: intensity is inversely proportional to the square of distance from the source; doubling FFD cuts intensity to one quarter and requires four times the mAs.

Grid ratio = height of lead strips / interspace width. Higher ratios remove more scatter but need more mAs and raise patient dose; grids suit thick parts and high-kVp techniques.

Photoelectric absorption dominates at low kVp and high atomic number and gives high contrast (bone, barium Z=56, iodine Z=53); Compton scattering dominates at higher kVp and produces scatter fog.

Dose limits (ICRP): occupational effective dose 20 mSv/year averaged over five years, never above 50 mSv in one year; public limit 1 mSv/year; ALARA applies to every exposure.

Typical FFD/SID: 180 cm for chest radiography and 100 cm for most other projections; greater distance reduces magnification and geometric unsharpness but needs more mAs.

Automatic processing: developer near 35 degrees C with a 90-second cycle; exhausted developer causes low density and fog, while exhausted fixer leaves yellow-brown staining.

Positive contrast: barium sulfate for gastrointestinal studies (avoid if perforation is suspected); iodinated water-soluble media for intravenous, urinary and many fluoroscopic procedures.

Indian Railways' first passenger train ran from Bori Bunder (Mumbai) to Thane on 16 April 1853, covering about 34 km.

Railway Board is the apex policy body, chaired by the Chairman and CEO; zones are headed by General Managers and divisional units by Divisional Railway Managers.

RDSO (Research Designs and Standards Organisation) is at Lucknow and acts as technical adviser and standards body for Indian Railways.

Vande Bharat Express is an indigenously built semi-high-speed train set designed for 180 km/h; the first service ran Delhi-Varanasi in 2019.

Bharat Ratna is the highest civilian award, instituted in 1954; Padma Vibhushan is the second-highest civilian award.

Right to Constitutional Remedies is Article 32; Dr. Ambedkar called it the heart and soul of the Constitution.

National Emergency is Article 352, President's Rule is Article 356 and Financial Emergency is Article 360.

Tropic of Cancer passes through eight states: Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura and Mizoram.

RBI was established in 1935 and nationalised in 1949; it issues currency under the RBI Act, 1934, and is headquartered in Mumbai.

Percentage change = (new - old)/old x 100; successive changes of a% and b% give a net change of a + b + ab/100 percent.

Profit% = (SP - CP)/CP x 100; loss% = (CP - SP)/CP x 100; discount% is calculated on marked price, not cost price.

SI = PRT/100; CI = P(1 + r/100)^t - P; for two years, CI exceeds SI by P(r/100)^2.

Average = sum of observations / number of observations; weighted average = sum(value x weight) / sum(weights).

1 km/h = 5/18 m/s; distance = speed x time; a train crossing a platform uses total length (train + platform) and relative speed.

If A does 1/a work per day and B does 1/b, together they take ab/(a + b) days; filling pipes are positive rates and leaks negative.

Boats: downstream speed = boat + stream, upstream = boat - stream; time = distance / effective speed.

Alligation: quantity ratio = (mean price - cheaper price) : (dearer price - mean price), used for mixtures and weighted averages.

Mensuration: circle area = pi r^2, circumference = 2 pi r; cylinder volume = pi r^2 h; sphere volume = (4/3) pi r^3.

Letter positions: A=1 to Z=26; reverse position = 27 - forward position; EJOTY gives 5,10,15,20,25 and CFILORUX gives 3,6,9,12,15,18,21,24.

Number series: test differences, ratios, squares/cubes, primes and alternating patterns before assuming one rule.

'All A are B' is not reversible; 'Some A are B' is reversible; 'No A is B' is reversible; accept only conclusions true in every possible Venn diagram.

Blood relations: draw a tree by generation; vertical lines show parent-child, horizontal lines marriage or siblings; never infer gender from a name.

Direction sense: draw the compass path; net displacement uses Pythagoras; left and right turns are relative to the current facing direction.

Clock: angle = |30H - 5.5M| degrees; if the result exceeds 180 degrees, subtract it from 360; hands coincide 11 times in 12 hours.

Calendar: an ordinary year has 1 odd day and a leap year 2; 100 years have 5 odd days, 200 have 3, 300 have 1 and 400 have 0.

Standard dice: opposite faces sum to 7; two faces visible together cannot be opposite, so eliminate such options.

Circular arrangement: facing the centre, left is clockwise and right anticlockwise; facing outward, reverse these directions.