- Dr.Sanjaykumar pawar
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| Units and Measurements Class 11 Physics – Easy NCERT Solutions, Short Notes, Formulas, and NEET Revision Tricks |
Internal Links
Physics Class 11 Chapter 1 Physical World Notes
Measurement Errors Complete Notes
Significant Figures Explained
Vernier Calipers Complete Guide
Screw Gauge Complete Guide
Least Count Formula Explained
Dimensional Analysis Notes
NCERT Class 11 Physics Solutions
NEET Physics Short Notes
NEET Physics Formula Handbook
Class 11 Physics Important Questions
Physics MCQs with Solutions
NCERT Exemplar Physics Solutions
JEE Physics Revision Notes
Measurement Instruments Comparison
UNITS AND MEASUREMENTS
Question (a)
You are given a thread and a metre scale. How will you estimate the diameter of the thread?
Step-by-Step Answer
Step 1: Take a pencil or a cylindrical rod.
Step 2: Wind the thread closely around the pencil without leaving any gap.
Step 3: Make 20–50 turns of the thread.
Step 4: Measure the total length (L) of all turns using the metre scale.
Step 5: Count the total number of turns (N).
Answer: Divide the total length of all turns by the number of turns to obtain the diameter of the thread.
Question (b)
A screw gauge has a pitch of 1.0 mm and 200 divisions on the circular scale. Do you think it is possible to increase the accuracy of the screw gauge arbitrarily by increasing the number of divisions on the circular scale?
Step-by-Step Answer
Step 1: Use the formula
Step 2:
Step 3: Increasing the number of divisions decreases the least count.
Step 4: However, accuracy cannot increase forever because of:
- Human error
- Instrument error
- Manufacturing limitations
- Backlash error
Final Answer:
No. Accuracy cannot be increased arbitrarily by increasing the number of divisions.
Question (c)
The mean diameter of a thin brass rod is to be measured using Vernier Calipers. Why is a set of 100 measurements more reliable than only 5 measurements?
Step-by-Step Answer
Step 1: Every measurement contains small random errors.
Step 2: With only 5 readings, random errors affect the average more.
Step 3: With 100 readings, positive and negative errors cancel each other.
Step 4: Therefore, the mean value becomes closer to the true value.
More Measurements → Less Random Error → Better Mean Value
Short Notes (Quick Revision)
| Topic | Key Point |
|---|---|
| Thread Diameter | Wind the thread around a pencil and use Length ÷ Turns. |
| Screw Gauge | Measures very small thickness like wire diameter. |
| Least Count | Least Count = Pitch ÷ Circular Divisions. |
| Vernier Calipers | Measures external diameter, internal diameter and depth. |
| Repeated Measurements | More readings reduce random errors. |
- More Readings = More Accuracy
- Smaller Least Count = Better Precision
- Screw Gauge is more accurate than Vernier Calipers.
Mnemonics (Easy Memory Tricks)
1. Instrument Order
Mnemonic:
Meter → Vernier → Screw
Sentence:
"My Very Smart Friend"
| Word | Meaning |
|---|---|
| My | Meter Scale |
| Very | Vernier Calipers |
| Smart | Screw Gauge |
2. Accuracy Order
Mnemonic:
Meter < Vernier < Screw
Sentence:
"Accuracy Climbs Up"
| Instrument | Accuracy |
|---|---|
| Meter Scale | Low |
| Vernier Calipers | Medium |
| Screw Gauge | Highest |
3. Formula Memory Trick
L ÷ N = Diameter
Mnemonic:
"Length Needs Number"
| Formula | Meaning |
|---|---|
| L | Total Length |
| N | Number of Turns |
| L ÷ N | Diameter |
4. NEET MCQ Trick
| If Question Says | Remember |
|---|---|
| More Readings | Better Mean Value |
| Increase Circular Divisions | Accuracy improves only up to practical limits. |
| Least Count | Smaller LC → Better Precision |
