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Q.18 Physics ⭐ 360° Option Elimination Active
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NEET 2023 Physics Question 18 Solution

Topic: Current Electricity · Official NTA Booklet Code G5
NEET 2023 Physics Question 18: Carbon Resistor Colour Code Determination

Question

Resistance of a carbon resistor determined from colour codes is (22000 ± 5%) Ω. The colour of third band must be:

✓
Verified Against NTA Final Answer Key
Option (4) : Orange
📚 Current Electricity Easy
📋 Given Parameters & Problem Setup
Resistance Value (22000 ± 5%) Ω
Target Band Colour of third band (multiplier band)
⚡

The 30-Second Exam Hall Shortcut: ⚡ BB ROY Great Britain Multiplier Decoder

⏱️ Save ~30 seconds

22000 Ω is 22 × 10³ Ω; the 3rd band represents the power of 10 (10³); in B-B-R-O-Y, 3 corresponds to Orange!

1 Express the resistance in scientific format: 22000 Ω = 22 × 10³ Ω.
2 Identify band roles: 1st digit = 2 (Red), 2nd digit = 2 (Red), 3rd band = multiplier 10ⁿ.
3 The exponent n = 3.
4 Recall the BB ROY mnemonic sequence: Black (0), Brown (1), Red (2), Orange (3), Yellow (4)...
5 Exponent 3 corresponds to Orange.
6 Lock Option (4) Orange in 5 seconds!
🛡️
Why You Can 100% Trust This Shortcut: NCERT Physics · Current Electricity (Resistor colour code standard: R = (AB × 10^C ± D%) Ω where C is multiplier colour).
📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Scientific Notation Decomposition of Resistance Value

Standard 4-band carbon resistors encode resistance as R = (AB × 10^C ± D%) Ω, where A and B are the first two significant figures, C is the decimal multiplier, and D is the tolerance percentage:

R=22000 Ω=22×103 Ω±5%R = 22000\ \Omega = 22 \times 10^3\ \Omega \pm 5\%
Step 2

Identification of Significant Figures and Multiplier

Comparing with the standard colour-code format:

A=2 (First band: Red),B=2 (Second band: Red),C=3 (Third band: Multiplier 103)A = 2\text{ (First band: Red)}, \quad B = 2\text{ (Second band: Red)}, \quad C = 3\text{ (Third band: Multiplier } 10^3)
Step 3

Mnemonic Code Verification for Multiplier Digit 3

Using the canonical mnemonic "B B R O Y of Great Britain has Very Good Wife":

Black(0), Brown(1), Red(2), Orange(3), Yellow(4)  ⟹  Third Band=Orange\text{Black}(0), \, \text{Brown}(1), \, \text{Red}(2), \, \mathbf{Orange}(3), \, \text{Yellow}(4) \implies \text{Third Band} = \mathbf{Orange}
⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan
1 (1)
✗ Incorrect
Verdict & Scientific Reason:

Yellow corresponds to digit 4 (multiplier 10⁴ = 220,000 Ω).

⚠️
Student Fallacy (Why candidates pick this trap): Candidate miscounted the number of trailing zeroes or counted 2200 as 4 digits.
2 (2)
✗ Incorrect
Verdict & Scientific Reason:

Red corresponds to digit 2 (multiplier 10² = 2200 Ω).

⚠️
Student Fallacy (Why candidates pick this trap): Candidate looked at the first two digits (2, 2) and repeated Red for the third band.
3 (3)
✗ Incorrect
Verdict & Scientific Reason:

Green corresponds to digit 5 (multiplier 10⁵).

⚠️
Student Fallacy (Why candidates pick this trap): Candidate confused the 5% tolerance (gold) with green.
4 (4)
✓ 100% Correct
Verdict & Scientific Reason:

Accurate colour: exponent 3 corresponds to Orange in the BB ROY colour code.

💡
Why this is airtight: None. Candidate correctly factored 22 × 10³.
⚠️

NTA Trap Alert: Counting Total Zeroes vs Multiplier Exponent

The number 22000 has 3 zeroes, meaning the multiplier is 10³, which is Orange. Students who count all zeroes plus the significant digits get confused and pick Yellow.

🛡️ How to avoid the -1 mark: Always rewrite in form: Digit1 Digit2 × 10^(exponent). The exponent directly gives the colour!
📖

Core NEET Syllabus Standard

National Eligibility cum Entrance Test (NEET UG) · Current Electricity Standard Benchmark
Core Scientific Principle Tested:

"First two bands give significant digits, third band gives power of ten multiplier, fourth band gives tolerance."

Syllabus Focus: Resistivity and Colour Code for Carbon Resistors
Historical NEET Benchmark Syllabus & Academic Standards ↗

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⚖️ Legal & Fair Dealing Notice: Sourced from publicly released NEET 2023 question papers and NEET answer keys for private study, research, and non-commercial educational practice under Fair Dealing (Section 52(1)(a) of the Indian Copyright Act, 1957). Not affiliated with or endorsed by NTA or NMC.

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