For an aeroplane hydraulic supply circuit, the correct statement is :

Kirchhoff’s Current Law (KCL)

Statement:

At any junction (node) in an electrical circuit, the algebraic sum of currents is zero

∑ I=0

Explanation:

• At a junction, current cannot accumulate.

• Therefore, the total current entering must be equal to the total current leaving.

Example:
If currents I1I_1I1​ and I2I_2I2​ enter a node and I3I_3I3​ and I4I_4I4​ leave:     I1​+I2​=I3​+I4​  

2) Kirchhoff’s Voltage Law (KVL)

Statement:

In any closed loop of an electrical circuit, the algebraic sum of all voltages is zero.

∑V=0

Explanation:

• While moving around a closed loop, the sum of voltage rises equals the sum of voltage drops.

• This law is based on the conservation of energy.

Example:
For a loop with a source EEE and voltage drops V1​,V2​:

E−V1​−V2​=0

Similarities and Dissimilarities between Electric and Magnetic Circuits:-

Similarities

1. Closed path required
   Electric current flows only in a closed electric circuit, similarly magnetic flux flows in a closed magnetic circuit.

2. Driving force exists
   In an electric circuit, EMF (E) drives current.
   In a magnetic circuit, MMF (F) drives magnetic flux.

3. Opposition to flow
   Electric circuit offers resistance (R) to current.
   Magnetic circuit offers reluctance (ℛ) to magnetic flux.

4. Ohm’s law analogy
   Electric circuit:I=E/R, Magnetic circuit: Φ= F/R

5. Energy relation
   Both circuits involve energy transfer when the driving force produces flow.

6. Material properties matter
   Resistance depends on resistivity, length, and area.
   Reluctance depends on permeability, length, and area.

7. Network analysis possible
   Both circuits can be analyzed using series and parallel combinations.

   Electric Circuit	Magnetic Circuit
   Flow quantity is electric current (I)	Flow quantity is magnetic flux (Φ)
   Driving force is EMF (Volts)	Driving force is MMF (Ampere-turns)
   Opposition is Resistance (Ω)	Opposition is Reluctance (AT/Wb)
   Current is actual movement of electrons	Flux is not physical flow of particles
   Resistance is nearly constant	Reluctance varies with flux (non-linear)

hili=hglg:- 

Series Magnetic Circuit

A series magnetic circuit consists of two or more magnetic parts connected in series, so that the same magnetic flux (Φ) flows through all parts.

Assumptions (as in notes):

• Flux Φ\PhiΦ is same in all parts

• Magnetic materials may have different lengths and permeabilities

• One part may be iron core, another air gap     

• Magnetic quantities used

  • Magnetic flux: Φ

  • Magnetic field strength: H

  • Length of magnetic path: l

  • Permeability: μ=μ0μr​

  • MMF: F=NI

  MMF=H×l 

• Fi​=Hi​li
• Fg​=Hg​lg​ ​

• Since MMFs add in series:

  Total MMF=Fi​+Fg

• Hence proved:

  Total MMF=Hi​li​+Hg​lg 
• This is the required mathematical expression for a series magnetic circuit. ​​

Rectifier

Definition:
A rectifier is an electronic circuit that converts alternating current (AC) into direct current (DC) using semiconductor diodes.

Bridge Rectifier

A bridge rectifier is a full-wave rectifier that uses four diodes arranged in a bridge form to convert both half cycles of AC input into pulsating DC.

Operating Principle / Working

Consider an AC supply connected to the bridge rectifier with a load resistance RLR_LRL​.

Positive Half Cycle

• Diodes D1 and D3 are forward biased.

• Diodes D2 and D4 are reverse biased.

• Current flows through D1 →RL​ → D3, producing output across RLR_LRL​ in one direction.

Negative Half Cycle

• Diodes D2 and D4 are forward biased.

• Diodes D1 and D3 are reverse biased.

• Current flows through D2 → RL​ → D4.

• Direction of current through the load remains the same.

PN Junction Diode:- Definition:
A PN junction diode is a semiconductor device formed by joining p-type and n-type materials. It conducts electric current in one direction only and blocks it in the opposite direction 

Operation Principle of PN Junction Diode

Formation of PN junction:
When p-type and n-type semiconductors are joined, electrons from the n-side and holes from the p-side diffuse across the junction. This creates a depletion layer with an internal electric field that opposes further charge flow.

Forward bias:
When the p-side is connected to the positive terminal and the n-side to the negative terminal, the depletion layer reduces. Once the applied voltage exceeds the cut-in (knee) voltage (≈0.7 V for silicon, ≈0.3 V for germanium), the diode conducts heavily and current increases rapidly.

Reverse bias:
When the p-side is connected to the negative terminal and the n-side to the positive terminal, the depletion layer widens. Only a very small reverse saturation current flows. At sufficiently high reverse voltage, breakdown occurs and current rises sharply. 

Explanation of V–I curve:
In the forward region, current remains small until the knee voltage, after which it increases steeply.
In the reverse region, current is nearly constant and very small until breakdown, where it increases suddenly. 

Conclusion

A PN junction diode operates by controlling the depletion layer under biasing conditions, allowing current in forward bias and blocking it in reverse bias, which makes it a fundamental component in rectification and electronic circuits.