RRB ALP (Assistant Loco Pilot) Trade-Specific / Relevant Trade (CBT Stage 2 Part B - Qualifying) Syllabus

State the basic working principle of a DC motor.

When a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force (Fleming's left-hand rule); this force produces rotation of the armature in a DC motor.

State the basic working principle of a DC generator and the rule used to find current direction.

A DC generator works on electromagnetic induction (Faraday's law): an EMF is induced when a conductor cuts magnetic flux. The direction of induced current is found by Fleming's right-hand rule.

What is the main constructional difference between an AC motor (induction) and a DC motor?

A DC motor has a commutator and brushes to reverse armature current; a 3-phase induction (AC) motor has no commutator—it uses a rotating magnetic field in the stator and a squirrel-cage or wound rotor without electrical connection to the rotor.

What is the EMF equation of a transformer?

E = 4.44 × f × N × Φm, where E = induced EMF (volts), f = frequency (Hz), N = number of turns, and Φm = maximum flux (Wb).

State the transformer turns ratio relationship between voltage and current.

V1/V2 = N1/N2 = I2/I1. The voltage ratio equals the turns ratio; current ratio is inverse to the turns ratio (a step-up transformer increases voltage and decreases current).

Why is a moving-iron instrument suitable for both AC and DC measurement?

In a moving-iron instrument the deflection depends on the square of the current (or on magnetic attraction/repulsion), which is independent of current direction, so it reads correctly on both AC and DC.

How is the range of an ammeter and a voltmeter extended?

An ammeter range is extended by connecting a low-resistance shunt in parallel with the meter; a voltmeter range is extended by connecting a high-resistance multiplier in series with the meter.

What is a wattmeter and what does it measure?

A wattmeter is an instrument (usually dynamometer type) that measures electrical power in watts; it has a current coil in series with the load and a pressure (voltage) coil in parallel with the load.

What determines the current-carrying capacity (ampacity) of a cable?

Conductor cross-sectional area, conductor material (copper/aluminium), type of insulation and its temperature rating, ambient temperature, and method of installation (grouping, ventilation).

What is the difference between a fuse and an MCB?

A fuse is a one-time protective element—its wire melts on overcurrent and must be replaced. An MCB (Miniature Circuit Breaker) is a reusable switch that trips on overcurrent/short circuit and can be reset by hand.

Name the three colours of the IEC/Indian wiring code for live, neutral, and earth conductors.

Live (phase) = brown (old red), Neutral = light blue (old black), Earth = green/yellow striped (old green).

List the two main classes of electronic components and give examples of each.

Active components—supply or amplify energy/control current (diodes, transistors, ICs, SCRs). Passive components—store or dissipate energy without gain (resistors, capacitors, inductors).

What do the colour bands on a resistor represent, and what does a gold 4th band indicate?

The first two bands are significant digits, the third is the multiplier (number of zeros), and the fourth is tolerance. A gold tolerance band = ±5%.

What is the function of a capacitor and how does it behave with DC vs AC?

A capacitor stores energy in an electric field. It blocks DC (after charging) but allows AC to pass; its opposition to AC is capacitive reactance Xc = 1/(2πfC).

What is the function of a diode, and name a common rectifier use?

A diode allows current to flow in only one direction (forward biased) and blocks reverse current. It is commonly used as a rectifier to convert AC to DC (half-wave or full-wave/bridge rectifier).

What is the key difference between analog and digital signals?

An analog signal is continuous and can take any value within a range; a digital signal is discrete, represented by only two levels (0 and 1 / LOW and HIGH).

What is the output of an AND gate and an OR gate for inputs A and B?

AND gate output = A·B (HIGH only when all inputs are HIGH). OR gate output = A+B (HIGH when any input is HIGH).

State the truth-table behaviour of a NAND gate.

A NAND gate output is LOW (0) only when all inputs are HIGH; for all other input combinations the output is HIGH (1). It is the inverse of AND and is a universal gate.

Convert binary 1011 to decimal.

1011₂ = (1×8)+(0×4)+(1×2)+(1×1) = 8+0+2+1 = 11 in decimal.

What is the purpose of a cathode-ray oscilloscope (CRO)?

A CRO displays the waveform of an electrical signal on a screen, allowing measurement of voltage (amplitude), frequency/time period, and phase, and visual analysis of signal shape.

What is a multimeter and what quantities can it measure?

A multimeter is a multi-function test instrument that measures voltage (AC/DC), current (AC/DC), and resistance; many also test continuity, diodes, and capacitance.

What composition of solder is commonly used for electronic soldering, and what is the role of flux?

A common solder is 60/40 tin-lead (60% tin, 40% lead) with a low melting point (~188°C). Flux cleans the metal surfaces, removes oxides, and helps the molten solder flow and wet the joint.

What is the ideal characteristic of a good soldered joint?

A good joint is shiny/bright, smooth, concave (well-wetted) and mechanically strong with low electrical resistance; a dull, grainy, or blobby joint indicates a 'dry' (cold) joint.

What are the four strokes of a four-stroke petrol (SI) engine in order?

Suction (intake), Compression, Power (expansion/combustion), and Exhaust. The cycle is the Otto cycle and takes two crankshaft revolutions.

What is the main difference between a petrol (SI) engine and a diesel (CI) engine in terms of ignition?

A petrol/SI engine uses a spark plug to ignite an air-fuel mixture (spark ignition, Otto cycle). A diesel/CI engine has no spark plug—fuel injected into hot compressed air self-ignites (compression ignition, Diesel cycle), with a much higher compression ratio.

What is the function of the fuel injector and the fuel pump in a diesel engine?

The fuel-injection (FIP) pump pressurizes diesel and delivers a metered quantity at the right time; the injector atomizes and sprays the high-pressure fuel into the combustion chamber for efficient burning.

Name the two main types of engine cooling systems and the key part of a liquid cooling system.

Air cooling and liquid (water) cooling. The radiator is the key part of a liquid cooling system—it dissipates heat from the circulating coolant, aided by a water pump, thermostat, and fan.

What is the function of a clutch and a gearbox in a vehicle transmission?

The clutch engages/disengages the engine from the gearbox to allow smooth starting and gear changing. The gearbox (transmission) provides different gear (speed/torque) ratios between engine and wheels.

What is the basic difference between drum brakes and disc brakes?

Drum brakes use brake shoes that press outward against the inner surface of a rotating drum. Disc brakes use pads that clamp onto a rotating disc/rotor; disc brakes dissipate heat better and resist fade.

In automobile maintenance, why is regular engine-oil change important, and what does the oil do?

Engine oil lubricates moving parts (reduces friction/wear), cools, cleans (carries away contaminants), and seals. Over time it degrades and accumulates contaminants, so periodic changing maintains lubrication and prevents engine damage.