SJVN JFE & FE flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Transformer EMF equation

E = 4.44·f·N·Φ_max volts, where f is supply frequency, N is turns and Φ_max is peak core flux. The 4.44 factor equals 2π/√2 and arises from RMS averaging of the sinusoidal flux.

Synchronous speed formula

N_s = 120f/P revolutions per minute, with f in hertz and P the number of poles. A 50 Hz, 4-pole machine therefore runs at 1500 rpm, and slip is measured relative to this value.

Slip definition

Slip s = (N_s − N_r)/N_s, the fractional difference between synchronous and rotor speed. At standstill s = 1; at no load s is near zero. Rotor frequency equals s times supply frequency.

Per-unit base impedance

Z_base = V_base²/S_base for single-phase quantities, using line-to-neutral voltage and per-phase power. For three-phase systems use line voltage with three-phase MVA and the same formula holds.

Euler buckling load

P_cr = π²EI/(L_e)², where E is Young's modulus, I the minimum area moment of inertia and L_e the effective length. Effective length depends on end conditions: pinned-pinned gives L, fixed-free gives 2L.

Torsion shear stress

τ = T·r/J, where T is applied torque, r the radial distance from the axis and J the polar moment of inertia. Maximum shear occurs at the outer surface; for a solid shaft J = πd⁴/32.

Concrete nominal mixes

Nominal grades: M20 is 1:1.5:3, M25 is 1:1:2 and M15 is 1:2:4 by volume of cement, fine aggregate and coarse aggregate. The number denotes characteristic cube strength in N/mm² at 28 days.

DC machine EMF equation

E = P·Φ·N·Z/(60·A), where P is poles, Φ flux per pole, N speed in rpm, Z total conductors and A parallel paths. Lap winding gives A = 2; wave winding gives A = 2P.

Induction motor torque-slip curve

Torque rises almost linearly with slip near zero, reaches a maximum at the breakdown slip, then falls as slip approaches one. Adding rotor resistance in a wound-rotor machine shifts the maximum towards higher slip.

Steady-state stability limit

For a lossless line delivering power from E to V through reactance X, maximum power is P_max = E·V/X at a load angle of 90 degrees. Real lines reach the limit below 90 degrees because of resistance.

Bending stress formula

σ = M·y/I, where M is bending moment, y the distance from the neutral axis and I the second moment of area. Maximum stress occurs at the extreme fibre, where y equals half the section depth.

Net percentage change

A rise of a percent followed by a fall of b percent changes the original by a − b − (ab/100) percent. Two successive 10 percent increases therefore give 21 percent, not 20 percent.

Compound interest two years

For two years the compound interest exceeds the simple interest by P(r/100)², where P is principal and r the annual rate. The gap grows quickly with rate because interest earns interest.

Work rate formula

If A alone finishes work in x days and B in y days, together they need xy/(x+y) days. Rates add: combined one-day work equals 1/x plus 1/y.

Downstream and upstream speed

Downstream speed equals boat speed in still water plus stream speed; upstream speed equals boat speed minus stream speed. Boat speed is half the sum of the two, stream speed half the difference.

Atbash letter coding

Each letter maps to its mirror position in the alphabet, so position p becomes 27 − p: A to Z, B to Y, C to X. Check constant-shift codes first, then reversal, then positional arithmetic.

Syllogism validity rule

A conclusion is valid only if it holds in every Venn diagram consistent with the premises. Two particular premises yield no universal conclusion, and two negatives yield no affirmative conclusion.

Permutation versus combination

Permutations count ordered arrangements: nPr = n!/(n−r)!. Combinations count unordered selections: nCr = n!/(r!(n−r)!). Use permutations when positions or ranks matter, combinations otherwise.

Relative speed of trains

When two trains move in opposite directions their relative speed is the sum of their speeds; in the same direction it is the difference. Time to cross equals total length divided by relative speed.

Blood relation tree method

Draw generations vertically and siblings or spouses horizontally, marking gender beside each name. Resolve the question by tracing the shortest path between the two named persons on the finished diagram.

Number series strategy

Check successive differences first, then ratios, then alternating or interleaved series, and finally squares and cubes with offsets. Confirm the discovered rule reproduces every given term before applying it.

SJVN Ltd profile

A central public sector enterprise under India's Ministry of Power, incorporated in 1988 and headquartered at Shimla, Himachal Pradesh. It began as a joint venture of the Government of India and Himachal Pradesh.

Nathpa Jhakri Hydro Power Station

SJVN's flagship 1,500 MW run-of-the-river project on the Satluj river in Himachal Pradesh, commissioned in 2004. It was the largest underground hydro station in India at commissioning.

Article 21 of the Constitution

Guarantees the right to life and personal liberty, expanded by judicial interpretation to include privacy, dignity, clean environment and livelihood. It is enforceable against the state through writ petitions.

Fundamental Duties Article 51A

A list of eleven duties of citizens in Part IVA, inserted by the 42nd Amendment Act, 1976 on the Swaran Singh Committee's recommendation. They are non-justiciable and complement Fundamental Rights.

Subject-verb agreement rule

A singular subject takes a singular verb and a plural subject a plural verb. In 'one of the + plural noun', the verb agrees with 'one', so 'one of the boys is' is correct.

Article usage with vowel sounds

Use 'an' before a vowel sound and 'a' before a consonant sound, judged by pronunciation not spelling: an hour, a university, an MP. Use 'the' with superlatives, rivers, and unique entities.

Present perfect tense use

Formed with has or have plus the past participle, it links a past action to the present. Do not combine it with a definite past time marker such as yesterday, which needs the simple past.

Since versus for

Use 'since' with a point of time when an action started, as in since 2010, and 'for' with a duration, as in for five years. Both usually appear with perfect tenses.

Between versus among

Use 'between' for two distinct entities and 'among' for three or more considered as a group. 'Between' can also express relationships involving several parties taken pairwise, as in a treaty between nations.

Passive voice conversion

Make the object the subject, change the verb to the correct form of be plus past participle, and place the original subject after 'by'. The tense of the original sentence must be preserved.

Article 356 President's rule

Allows the President to assume the functions of a state government when constitutional machinery fails there, on the Governor's report. It must be approved by Parliament and remains subject to judicial review.