RRB Technician Grade I (Signal) 2024, 2025 PYQs

Concept: In a CRT with electrostatic deflection, the spot on the screen moves in proportion to the voltage applied to the deflecting plates.

1. Deflection sensitivity $s=\frac{D}{E}$, i.e. deflection on the screen per volt of deflecting voltage, measured in mm/V (typically 0.1–1 mm/V).
2. Its reciprocal $\frac{E}{D}$ (V/mm) is called the deflection factor.
3. $s=\frac{L{l}_d}{2d{E}_a}$ shows that $s$ increases with longer plates and distance to screen, and decreases with higher accelerating voltage $E_a$.

Yaad rakhein: Sensitivity = output (deflection) ÷ input (voltage) = $\frac{D}{E}$; deflection factor is its inverse.

Answer: (D) $s=\frac{D}{E}$

Concept: Field inside a long solenoid: $B={\mu }_{0}nI$ (or $\mu nI$ with a core), where $n$ = turns per unit length.

1. $B$ increases with turns per unit length $n$ and current $I$.
2. A soft-iron core raises $\mu$ and hence $B$ many times.
3. The total length of the solenoid does not appear in the formula; only the turn density $n$ matters, so length by itself has no effect.

Yaad rakhein: $B={\mu }_{0}nI$ – only $\mu$, $n$ and $I$; 'length' and 'radius' are absent.

Answer: (B) Length of the solenoid

Concept: $R=\rho \frac{l}{A}$ and for metals $\rho$ rises with temperature.

1. For most metals, higher temperature → more lattice vibration → more collisions → resistance increases. Statement A is true.
2. B is false: $R\propto l$. C is false: $R\propto \rho$ (directly). D is false: $R\propto \frac{1}{A}$.

Yaad rakhein: Long and thin wire = high resistance; hot metal = higher resistance (opposite for semiconductors).

Answer: (A) Resistance increases with an increase in the temperature for most metals.

Concept: Intel 8051 (MCS-51 family, 1980) is an 8-bit microcontroller: its ALU, accumulator and data bus are 8 bits wide.

1. Features: 4 KB on-chip ROM, 128 bytes RAM, 32 I/O lines (4 ports), two 16-bit timers, one serial port.
2. Only the program counter and DPTR are 16-bit (for addressing 64 KB memory); the data width remains 8-bit.

Yaad rakhein: 8051 → 8-bit; 8085 → 8-bit microprocessor; 8086 → 16-bit.

Answer: (D) 8-bit microcontroller

Concept: Accuracy = closeness to the true value; precision = repeatability (closeness of readings to each other).

1. The thermometer always reads exactly $2^{\circ }\text{C}$ high – readings are consistent, so it is precise.
2. Every reading is $2^{\circ }\text{C}$ away from the true value – a systematic error, so it is not accurate.

Yaad rakhein: 'Consistently wrong' = precise but not accurate; random scatter = not precise.

Answer: (A) precise but not accurate

Concept: A conductor of length $l$ moving with speed $v$ perpendicular to a field $B$ develops emf $\epsilon =Blv$.

1. Induced emf $\propto v$ – faster motion cuts more flux per second (Faraday's law $\epsilon =-\frac{d\varphi }{dt}$).
2. Resistance decides the induced current ($I=\epsilon /R$), not the emf; area and temperature do not appear in $Blv$.

Yaad rakhein: $\epsilon =Blv$ – B, length, velocity.

Answer: (C) the speed of the conductor's motion through the magnetic field

Concept: With resistance constant, $P=I^{2}R$.

1. New current $=2I$ → $P^{\prime }=(2I{)}^{2}R=4I^{2}R=4P$.
2. Power becomes four times (quadruples), not double, because current is squared.

Trick: Double $I$ → $4\times$ power; double $V$ (at fixed $R$) → also $4\times$ ($P=V^2/R$).

Answer: (B) Power will quadruple.

Concept: In parallel, all resistors are connected between the same two points, so the voltage across each is the same; the current divides.

1. Same voltage → option D is true; 'same current' (C) is the property of series connection.
2. $\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\dots$ → $R_{eq}$ is smaller than the smallest resistance, so A and B are wrong (B is the series formula).

Yaad rakhein: Series → same current, R adds; Parallel → same voltage, R decreases.

Answer: (D) They have the same voltage.

Concept: For quantities added together, the absolute limiting errors add: $\delta R=\delta R_1+\delta R_2+\delta R_3$.

1. $R=30+60+50=140\Omega$.
2. Absolute errors: $5\%$ of 30 $=1.5$, of 60 $=3$, of 50 $=2.5$; total $=7\Omega$.
3. Result $=140\pm 7\Omega$ (i.e. still $\pm 5\%$).

Trick: When every part has the same percentage error, the sum has the same percentage error: $5\%$ of 140 $=7$.

Answer: (A) $140\pm 7\Omega$

Concept: Energy $E=VIt$ with $t$ in seconds.

1. $t=5\text{ min}=300\text{ s}$.
2. $E=12\times 2\times 300=7200\text{ J}$.

Trick: Power $=VI=24\text{ W}$; $24\times 300=7200$. Forgetting to convert minutes to seconds gives 120 J – not an option, so convert.

Answer: (B) $7200\text{ J}$

Concept: Deflection sensitivity $s$ of a CRT is the spot deflection per volt of deflecting voltage (mm/V); the deflection factor is its reciprocal.

1. $G=\frac{1}{s}$, expressed in V/mm – the voltage needed for 1 mm deflection.
2. Typical values: $s\approx 0.1$–$1$ mm/V, so $G\approx 1$–$10$ V/mm.

Yaad rakhein: Sensitivity high ⇔ factor low; $G=1/s$.

Answer: (B) $G=\frac{1}{s}$

Concept: Eddy currents are circulating currents induced in a bulk conductor when the magnetic flux through it changes (Faraday's law).

1. A changing (time-varying) field or relative motion between conductor and field → changing flux → eddy currents.
2. A uniform/constant field with no motion produces no change of flux, hence no induced current; an electrostatic field does not induce currents in this way.

Yaad rakhein: No change in flux → no induction. Laminated cores are used to reduce eddy-current loss.

Answer: (A) a changing magnetic field

Concept: Astronomical distances are expressed in light-years: the distance light travels in one year, $\approx 9.46\times {10}^{15}\text{ m}$.

1. 1 astronomical unit (AU) = mean Earth–Sun distance $\approx 1.5\times {10}^{11}\text{ m}$ – used within the solar system, far too small for stars and galaxies.
2. Metre and kilometre are everyday units; the nearest star is about 4.2 light-years ($\approx 4\times {10}^{13}\text{ km}$) away, so the light-year is the practical unit.

Yaad rakhein: AU → solar system; light-year / parsec → stars and galaxies ($1\text{ pc}\approx 3.26$ ly).

Answer: (D) light-year

Concept: The standard Intel 8051 has 128 bytes of internal data RAM (addresses 00H–7FH).

1. This RAM holds 4 register banks (32 bytes), a bit-addressable area (16 bytes) and general-purpose scratch pad (80 bytes).
2. The 8052 variant has 256 bytes; 4 KB is the on-chip program ROM, not RAM.

Yaad rakhein: 8051 → 128 B RAM, 4 KB ROM; 8052 → 256 B RAM, 8 KB ROM.

Answer: (B) 128-byte

Concept: From rest, $s=\frac{1}{2}a{t}^2$, so distance $\propto t^2$.

1. Distance in first $t$: $s_1=\frac{1}{2}a{t}^2$.
2. Distance in total time $3t$: $s=\frac{1}{2}a(3t{)}^2=\frac{9}{2}a{t}^2$.
3. Distance in the next $2t$: $s_2=\frac{9}{2}a{t}^2-\frac{1}{2}a{t}^2=4a{t}^2$.
4. $s_1:s_2=\frac{1}{2}:4=1:8$.

Trick: Distances in intervals $t,2t$ from rest are $1^2:(3^2-1^2)=1:8$.

Answer: (A) $1:8$

Concept: Principle of homogeneity: every term added, subtracted or equated in a physical equation must have the same dimensions.

1. Dimensional consistency means the equation obeys this principle – option B.
2. It is a necessary but not sufficient test: a dimensionally consistent equation may still be wrong (numerical constants, $\sin \theta$ etc. are dimensionless), so A and C overstate it.

Yaad rakhein: Consistent ≠ correct; inconsistent = definitely wrong.

Answer: (B) the equation respects the principles of homogeneity of dimensions

Concept: Resistivity $\rho$ is the reciprocal of electrical conductivity: $\rho =\frac{1}{\sigma }$. It is a material property set by how freely charge carriers move.

1. High conductivity (copper, silver) → low resistivity; insulators have very low conductivity → high resistivity.
2. Temperature coefficient only tells how $\rho$ changes with temperature; density and melting point do not fix $\rho$ (silver is denser than copper yet a better conductor).

Yaad rakhein: $\rho =1/\sigma$; unit $\Omega \text{m}$ and $\text{S/m}$.

Answer: (B) Electrical conductivity

Concept: When force changes with position, work is the integral (area under the F–x graph): $W=\int Fdx$.

1. $W=Fd$ and $W=Fd\cos \theta$ apply only to a constant force.
2. $W=\frac{1}{2}m{v}^2$ is kinetic energy (work-energy theorem result), not the definition of work by a variable force.

Yaad rakhein: Variable → integrate; constant → multiply.

Answer: (C) $W=\int Fdx$

Concept: LED brightness depends on the forward current through it; a series resistor sets $I=\frac{V_s-V_D}{R}$.

1. When the source voltage $V_s$ is much greater than the diode drop $V_D$ ($\approx 2$ V), $I\approx \frac{V_s}{R}$ and small changes in $V_D$ hardly alter the current, so brightness stays nearly constant.
2. Temperature affects LED output only slightly; it is not the controlling variable.

Yaad rakhein: LED = current-driven device; $V_s\gg V_D$ → constant current.

Answer: (C) current; greater

Concept: A load cell or proving ring is an elastic member; the applied force produces a strain, and bonded strain gauges convert that strain (change in resistance) into an electrical signal, thereby measuring the force.

1. Sequence: force → strain in the elastic element → strain gauge → force reading, i.e. 'force by the strain'.
2. LVDT measures displacement, piezoelectric transducers suit dynamic forces, capacitive transducers measure displacement/pressure – not the standard load-cell element.

Yaad rakhein: Load cell = strain gauges in a Wheatstone bridge.

Answer: (B) Strain gauges; force by the strain