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Solved 2024: FYUG Even Semester Exam, 2024 PHYSICS (2nd Semester) Electrical Circuits and Safety (PHYSEC-151T)

Subject: PHYSICS
Paper Code: PHYSEC-151T
Semester: 2nd Semester (FYUG)
Full Marks: 50 (Pass Marks: 20)
Time Duration: 2 Hours

SECTION-A (1 Mark Each)

Answer any fifteen questions. All questions solved below.

Question 1

1

State Ohm's law.

Ohm's law states that the current passing through a conductor between two points is directly proportional to the voltage across the two points, provided physical conditions remain constant

.

Question 2

1

What is the unit of power?

The SI unit of power is the Watt (W)

.

Question 3

1

Average e.m.f. during positive half cycle of peak value E0?

E_avg = 2 * E0 / pi

Question 4

1

State KCL first law.

Kirchhoff's Current Law (KCL) states that the total current entering a junction or node is exactly equal to the total current leaving that junction

.

Question 5

1

Materials used for wiring?

Common materials include copper or aluminum for conductors, and PVC or rubber for insulation

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Question 6

1

What is delta wiring?

Delta wiring is a type of three-phase electrical wiring configuration where the three components are connected in a closed loop, forming a triangle shape

.

Question 7

1

Define conduit wiring.

A wiring system where electrical wires are run through tubes or pipes (conduits) made of metal or plastic to protect them from damage

.

Question 8

1

What is electrical conductor?

An electrical conductor is a material that allows the flow of electric current through it with minimal resistance

.

Question 9

1

Define power factor.

Power factor is the ratio of real power flowing to the load to the apparent power in the circuit

.

Question 10

1

Is transformer an active or passive component?

A transformer is a passive component because it does not require an external power source to function and does not provide power gain

.

Question 11

1

Which transformer has Np < Ns?

(a) Step-up transformer

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Question 12

1

Define an electric generator.

An electric generator is a device that converts mechanical energy into electrical energy

.

Question 13

1

What are rectifiers?

Rectifiers are electrical devices that convert Alternating Current (AC) to Direct Current (DC)

.

Question 14

1

Symbol for capacitor and inductor.

Capacitor: Two parallel lines ( | | ). Inductor: A series of loops/coils.

Question 15

1

Units of inductance and capacitance?

Inductance: Henry (H). Capacitance: Farad (F).

Question 16

1

Draw circuit diagram of a half-wave rectifier.

Question 17

1

What is electrical safety?

Electrical safety is a set of practices and procedures followed to prevent electrical hazards and injuries like shocks, fires, and explosions

.

Question 18

1

Effects of electric current on human body?

Effects range from minor tingling sensations to muscle contractions, respiratory paralysis, and cardiac arrest

.

Question 19

1

Define 'short circuit'.

A short circuit occurs when a low-resistance path is accidentally established between two points in an electrical circuit, causing excessive current flow

.

Question 20

1

Full forms of MCB and RCCP?

MCB: Miniature Circuit Breaker. RCCP: Residual Current Circuit Protector (often referred to as RCCB).

SECTION-B (2 Marks Each)

Question 21

2

Series and parallel combination of resistances.

  • Series: Resistances are connected end-to-end. Equivalent R = R1 + R2 + ...
  • Parallel: Resistances are connected across the same two nodes. Equivalent 1/R = 1/R1 + 1/R2 + ...

Question 22

2

Differences between AC and DC.

AC ElectricityDC Electricity Magnitude and direction change periodically.Magnitude and direction remain constant. Can be easily stepped up/down using transformers.Difficult to change voltage levels.

Question 25

2

Step-down and step-up transformers?

  • Step-up: Increases output voltage (Secondary turns > Primary turns).
  • Step-down: Decreases output voltage (Primary turns > Secondary turns).

    • Question 30

    2

    Two steps to prevent short circuit.

  • Using circuit protection devices like fuses or MCBs.
  • Ensuring proper insulation of wires and regular maintenance.

    • SECTION-C (Long Answers)

    Question 31

    3+4=7

    (a) Kirchhoff's Voltage Law (KVL).

    KVL states that the algebraic sum of all electrical potential differences around any closed loop or network is zero

    . Sum(V) = 0.

    (b) Find the unknown resistance.

    In the given circuit: 12V source, resistances 3 ohms, 1 ohm, 4 ohms in series with unknown resistance B

    . Total voltage = 12V. Current = 1A.
    V = I * R_total => 12 = 1 * (3 + 1 + 4 + B).
    12 = 8 + B => B = 4 ohms.

    Question 32

    4+1=5

    (a) Define Time period, Frequency, Phase, and Phase difference.

  • Time Period: Time taken to complete one full cycle.
  • Frequency: Number of cycles completed in one second.
  • Phase: The position of a point in time on a waveform cycle.
  • Phase Difference: The angular displacement between two waveforms of the same frequency.

    • (b) Oscilloscope calculation.

    10 cycles in 1 ms (0.001 s)

    . Frequency = 10 / 0.001 = 10,000 Hz.
    Time Period = 1 / f = 0.001 / 10 = 0.1 ms.

    Question 38

    4+1+2=7

    (a) Working of full-wave rectifier and advantage.

    A full-wave rectifier uses both half cycles of the AC input to produce DC. This is typically done using a center-tapped transformer with two diodes or a bridge rectifier with four diodes.
    Advantage: Higher efficiency and lower ripple factor compared to half-wave rectifiers.

    (b) Efficiency of full-wave rectifier?

    The maximum theoretical efficiency of a full-wave rectifier is approximately 81.2%

    .

    Question 40

    3+2+2=7

    (a) Short-circuit prevention.

    Prevention includes using high-quality insulated cables, circuit breakers (MCB), and fuses that trip the circuit when excessive current flows

    .

    (b) DP isolator and MCB vs Fuse.

    A DP (Double Pole) isolator completely disconnects both the live and neutral wires from the supply for safety during maintenance

    .
    Difference: An MCB is a reusable switch that trips on overcurrent, whereas a fuse contains a wire that melts and must be replaced after a single fault.

    Exam Focus Enhancements

  • Exam Tips: In Circuit diagrams, clearly mark the polarity (+/-) of the source and the direction of current flow.
  • Common Mistakes: Confusing Step-up and Step-down transformer turn ratios. Remember: Ns/Np = Vs/Vp.
    • Important Formulas:
  • P = V * I
  • f = 1 / T
  • V = I * R (Ohm's Law)

    • Prepared by Knowlet

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