SSC CGL Physics · Units, Measurement and Dimensions
Units, Dimensions and Measuring
The SI units SSC matches to quantities, units that sound like something else (light year, nit, newton), quantities with the same dimensions, and the parts of a vernier calliper.
Why this matters
Seven questions in the bank: two from the 2023 shifts and five from the 2024 shifts, six of them EASY. Each is a unit-to-quantity match, so the table is the whole page.
Concept 1 of 2: Units and what they measure
Definition
Electrical units: current ampere (an SI base unit), voltage volt, capacitance farad, magnetic field tesla.
Units that mislead:
- A light year is a distance (about 9.46 x 10^15 m), not a time.
- The angstrom (10^-10 m) is a length.
- The nit (candela per square metre) measures luminance.
- Joule, kilowatt-hour and calorie measure energy; the newton measures force.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 1 · Units, Measurement and Dimensions · Units, Dimensions and Measuring
| Column-A (Physical Property) | Column-B (Unit) |
|---|---|
| i. Electric current | a. Tesla |
| ii. Voltage | b. Farad |
| iii. Capacitance | c. Ampere |
| iv. Magnetic field | d. Volt |
A light year is not time
Concept 2 of 2: Dimensions and the vernier calliper
Definition
Dimensions:
- Work and torque both have dimensions [ML^2 T^-2].
- Power is [ML^2 T^-3]; moment of inertia [ML^2]; angle has none.
Vernier calliper:
- Internal jaws: the inside diameter of a hollow cylinder or pipe.
- External jaws: the length of a rod or the diameter of a sphere.
- Depth bar: the depth of a beaker.
| Part | Measures |
|---|---|
| Internal jaws | Inside diameter of a pipeQ |
| External jaws | Diameter of a sphere |
| Depth bar | Depth of a beaker |
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 2 · Units, Measurement and Dimensions · Units, Dimensions and Measuring
Power is not work
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
Dimensions and the vernier calliper3 rows
| Part | Measures |
|---|---|
| Internal jaws | Inside diameter of a pipeQ |
| External jaws | Diameter of a sphere |
| Depth bar | Depth of a beaker |
Watch out for (2)
- A light year is not time→ Units and what they measure
- Power is not work→ Dimensions and the vernier calliper
Test yourself on a real paper
Sit a past SSC CGL paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.