Day 69 – Current Electricity & Its Applications (ECET 2026 Physics)

Concept Notes (Deep Explanation + Examples)

🔹 Basics of Current Electricity

When charges move through a conductor, electric current is said to flow.
If a potential difference (voltage) is applied across a wire, free electrons drift towards the positive terminal — this movement constitutes electric current.

👉 Definition:
Electric current (I) is the rate of flow of electric charge.

• Unit: Ampere (A)
• 1 A = 1 coulomb per second

🔹 Types of Current

1. Direct Current (DC): Flows in one direction (used in batteries, mobile circuits).
2. Alternating Current (AC): Changes direction periodically (used in household supply).

🔹 Drift Velocity

When an electric field is applied, electrons acquire a small average velocity opposite to the field direction — called drift velocity (vₐ).

• e → charge of electron
• E → electric field
• τ → relaxation time
• m → mass of electron

👉 Example: In a copper wire, even though drift velocity is very small (~10⁻⁴ m/s), current is large because of a huge number of free electrons.

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🔹 Ohm’s Law

According to Ohm’s Law, at constant temperature, current through a conductor is directly proportional to potential difference applied.

Where:

• V = Potential difference
• I = Current
• R = Resistance

Real-life Example:
When you use a mobile charger, the internal resistance controls how much current flows to your phone’s battery — governed by Ohm’s Law.

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🔹 Resistance and Resistivity

Resistance depends on the conductor’s length, area, and material.

Where:

• ρ = resistivity
• l = length
• A = area of cross-section

Resistivity (ρ) is the material property — for example:

• Copper: very low ρ → good conductor
• Nichrome: high ρ → used in heaters

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🔹 Series and Parallel Connections

Series:

• Current is same through all resistors.
• Voltage divides.

Parallel:

• Voltage is same.
• Current divides.

Example: In home wiring, circuits are connected in parallel — so if one bulb fails, others glow.

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🔹 Electric Power and Energy

Power (P) = Rate of doing electrical work.

Example:
A 100 W bulb consumes more power than a 60 W bulb → brighter and uses more current.

Electrical Energy:

Used to calculate electricity bills (in kWh).

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🔹 Applications of Current Electricity

1. Electric Heater / Iron: Uses Joule Heating Effect ()
2. Electric Fuse: Melts when current exceeds safe limit.
3. Electric Motor: Converts electrical energy → mechanical energy.
4. Electroplating: Uses current to coat metals (e.g., gold-plated jewelry).
5. Kirchhoff’s Laws Applications: Used in analyzing complex electrical networks.

Diagram (in words):
Imagine a rectangular circuit: battery connected to a resistor → ammeter in series → voltmeter across resistor — shows Ohm’s Law practically.

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⚙️ Formulas

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🔟 10 MCQs (ECET + GATE Hybrid)

1. The SI unit of electric current is:
   A) Volt
   B) Ampere
   C) Coulomb
   D) Ohm
2. The drift velocity of electrons is proportional to:
   A) Current
   B) Voltage
   C) Electric field
   D) Resistance
3. In Ohm’s Law, if resistance doubles, current becomes:
   A) Double
   B) Half
   C) Same
   D) Zero
4. Resistance of a wire depends on:
   A) Temperature only
   B) Material, length, area
   C) Voltage
   D) Current
5. Two resistors 4Ω and 6Ω connected in series. Their equivalent resistance is:
   A) 10Ω
   B) 2.4Ω
   C) 1.67Ω
   D) 24Ω
6. Two resistors 4Ω and 6Ω connected in parallel. Equivalent resistance is:
   A) 2.4Ω
   B) 10Ω
   C) 1.67Ω
   D) 5Ω
7. Power consumed by a 2Ω resistor with 4A current is:
   A) 4W
   B) 8W
   C) 16W
   D) 32W
8. A 100W bulb connected to 200V supply, current = ?
   A) 0.25A
   B) 0.5A
   C) 2A
   D) 1A
9. In household wiring, bulbs are connected in:
   A) Series
   B) Parallel
   C) Mixed
   D) None
10. The heating effect of current is given by:
    A) V=IR
    B) I=V/R
    C) H=I²Rt
    D) P=VI

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✅ Answer Key

Q No | Answer
1 | B
2 | C
3 | B
4 | B
5 | A
6 | A
7 | C
8 | B
9 | B
10 | C

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🧠 MCQ Explanations

1️⃣ Ampere is the SI unit of current → 1 coulomb/second.
2️⃣ Drift velocity increases with electric field strength → directly proportional.
3️⃣ → if R doubles, I becomes half.
4️⃣ Resistance depends on material (ρ), length (l), and area (A).
5️⃣ Series: .
6️⃣ Parallel: .
7️⃣ .
8️⃣ .
9️⃣ Household wiring uses parallel connection for independent operation.
10️⃣ Heating effect → .

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🎯 Motivation (ECET 2026 Specific)

This topic — Current Electricity — repeats every single year in ECET Physics because it connects concept + formula + application.
Mastering it boosts your rank since numerical questions come directly from Ohm’s Law, power, and resistors.
Solve one topic daily, revise formulas weekly — that’s how toppers maintain 100+ marks pace! ⚡

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📲 CTA (Fixed)

Join our ECET 2026 CSE WhatsApp Group for daily quizzes & study notes:
👉 https://chat.whatsapp.com/GniYuv3CYVDKjPWEN086X9

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