ECAT Physics — Physical Optics
Physical Optics is part of the Physics section of the UET ECAT (30 of the 100 MCQs). It breaks into 4 subtopics, and we hold 32 ECAT-pattern practice MCQs on it, each with a written explanation. Tap a subtopic below to practise just that.
Subtopics (4)
How Physical Optics is tested
Across the 7 ECAT past papers on ParhaiKrlo, Physical Optics accounts for 10 questions. It appears in all 7, about 1.4 questions a paper. The heaviest was ECAT Past Paper 06, with 3 questions, and the most recent is ECAT Past Paper 07, with 1.
| Paper | Questions |
|---|---|
| ECAT Past Paper 07 | 1 |
| ECAT Past Paper 06 | 3 |
| ECAT Past Paper 05 | 1 |
| ECAT Past Paper 04 | 2 |
| ECAT Past Paper 03 | 1 |
| ECAT Past Paper 02 | 1 |
| ECAT Past Paper 01 | 1 |
Physical Optics MCQs from the ECAT past papers
Try each one before opening the answer. Each comes with a short explanation.
- Q1 · ECAT Past Paper 07 · Physical Optics
Young's double-slit experiment is used to study the interference of:
- A.Microwaves
- B.Radio waves
- C.Sound waves
- D.Visible light
Show answer
Answer: D. Visible light — Young's experiment showed the interference of light.
- Q2 · ECAT Past Paper 06 · Physical Optics
The lines of a diffraction grating have a spacing of 1.2 µm. When monochromatic light falls normally on the grating, the first-order maximum makes an angle of 30° with the normal. The wavelength of the light is:
- A.1200 nm
- B.450 nm
- C.600 nm
- D.700 nm
Show answer
Answer: C. 600 nm — d sin θ = nλ: λ = 1.2 µm × sin 30° = 0.6 µm = 600 nm.
- Q3 · ECAT Past Paper 05 · Physical Optics
A wave has a wavelength of 5000 Å. This wave is in the:
- A.UV region
- B.Radio region
- C.Visible region
- D.Infrared region
Show answer
Answer: C. Visible region — 5000 Å = 500 nm, which lies in the visible range (400–700 nm).