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

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

What is the unit of power?

The SI unit of power is the Watt (W).

Question 3

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

E_avg = 2 * E0 / pi

Question 4

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

Materials used for wiring?

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

Question 6

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

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

What is electrical conductor?

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

Question 9

Define power factor.

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

Question 10

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

Which transformer has Np < Ns?

(a) Step-up transformer.

Question 12

Define an electric generator.

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

Question 13

What are rectifiers?

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

Question 14

Symbol for capacitor and inductor.

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

Question 15

Units of inductance and capacitance?

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

Question 16

Draw circuit diagram of a half-wave rectifier.

Question 17

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

Effects of electric current on human body?

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

Question 19

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

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

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

Differences between AC and DC.

AC Electricity	DC 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

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

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.

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