Is Ray Optics and Optical Instruments part of the EAPCET Physics syllabus?

Yes. Ray Optics and Optical Instruments is taught in Intermediate second year Physics, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.

How many Physics questions are there in EAPCET?

40 of the 160 questions in the Engineering paper are Physics, spread across 30 chapters.

What mistakes do students make in Ray Optics and Optical Instruments?

Using the mirror formula’s plus sign for a lens — the lens formula is 1/v − 1/u = 1/f. Calculating power with f in centimetres — P (in dioptres) = 1/f with f in metres, or 100/f with f in cm. Applying total internal reflection when light goes from a rarer to a denser medium — it happens only from denser to rarer, beyond the critical angle. Dropping the sign of u, so a real image appears virtual — keep every distance signed throughout the calculation.

EAPCET Physics · Intermediate second year

Ray Optics and Optical Instruments

Ray Optics covers reflection and refraction, mirrors, lenses, prisms, total internal reflection and optical instruments.

Subject: Physics
Taught in: Intermediate second year
Physics in the paper: 40 of 160 questions

Key formulas and results

Mirror: $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$ , with $f = R/2$
Lens: $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$
Lens maker’s formula: $\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_{1}} - \frac{1}{R_{2}}\right)$
Snell’s law $\mu_{1}\sin i = \mu_{2}\sin r$ ; critical angle $\sin C = 1/\mu$
Prism: $\mu = \dfrac{\sin\left[(A + \delta_{m})/2\right]}{\sin(A/2)}$
Power $P = 1/f$ (in metres); lenses in contact: $P = P_{1} + P_{2}$
Lateral shift through a glass slab of thickness $t$ : $d = \frac{t\sin(i - r)}{\cos r}$
Normal shift through a slab: $x = t\left(1 - \frac{1}{\mu}\right)$ ; through several slabs: $x = \sum t_{i}\left(1 - \frac{1}{\mu_{i}}\right)$
Plane mirror: deviation $\delta = 180^\circ - 2i$ ; images between two mirrors inclined at $\theta$ : $n = \frac{360^\circ}{\theta} - 1$
Refraction at a spherical surface: $\frac{\mu_{2}}{v} - \frac{\mu_{1}}{u} = \frac{\mu_{2} - \mu_{1}}{R}$
Lens in a medium: $\frac{1}{f} = \left(\frac{\mu_{\text{lens}}}{\mu_{\text{medium}}} - 1\right)\left(\frac{1}{R_{1}} - \frac{1}{R_{2}}\right)$
Prism relations: $r_{1} + r_{2} = A$ and $\delta = i_{1} + i_{2} - A$ ; thin prism $\delta = (\mu - 1)A$
Simple microscope: $M = D/f$ for the image at infinity, $M = 1 + D/f$ for the image at the near point $D$
Compound microscope $M = \frac{v_{0}}{u_{0}}\cdot\frac{D}{u_{e}}$ with length $v_{0} + u_{e}$ ; astronomical telescope $M = f_{0}/f_{e}$ with length $f_{0} + f_{e}$ in normal adjustment

What this chapter covers

Reflection by spherical mirrors
Refraction and total internal reflection
Refraction at spherical surfaces and lenses
Prisms and dispersion
Microscopes and telescopes

How it is usually asked

Image position and magnification
Prism deviation
Total internal reflection
Magnifying power of instruments

Understanding Ray Optics and Optical Instruments

Ray optics treats light as straight-line rays. With the Cartesian sign convention, all distances are measured from the pole of a mirror or the optical centre of a lens, positive in the direction of the incident light and negative against it. Using this convention consistently, the mirror formula 1/v + 1/u = 1/f and the lens formula 1/v − 1/u = 1/f cover every case, and the signs of v and magnification tell you whether an image is real or virtual, erect or inverted.

Refraction follows Snell’s law. Going from a denser to a rarer medium beyond the critical angle, light is totally internally reflected, which is how optical fibres work. A prism deviates light, with minimum deviation linked to its refractive index. Lens power is 1/f in dioptres when f is in metres, and powers of lenses in contact add.

EAPCET mainly asks for image position and nature, prism and critical-angle calculations, the combined power of lenses and the magnifying power of microscopes and telescopes. For instruments, remember that an astronomical telescope in normal adjustment has magnifying power fₒ/fₑ and tube length fₒ + fₑ, while a compound microscope magnifies in two stages, so its magnifying power is the product of the two magnifications.

Worked example

EAPCET-style question

An object is placed 0.30 m in front of a convex lens of focal length 0.20 m. Where is the image formed, and what is the magnification?

(1)0.60 m on the other side of the lens, magnification −2
(2)0.12 m on the other side of the lens, magnification −0.4
(3)0.60 m on the same side as the object, magnification +2
(4)0.12 m on the same side as the object, magnification +0.4

Solution

Sign convention: $u = -0.30\ \text{m}$ and $f = +0.20\ \text{m}$ for a convex lens.
Lens formula: $\frac{1}{v} = \frac{1}{f} + \frac{1}{u} = \frac{1}{0.20} - \frac{1}{0.30} = 5 - 3.33 = 1.67\ \text{m}^{-1}$ .
$v = +0.60\ \text{m}$ , so the image is real and on the other side of the lens.
Magnification $m = \frac{v}{u} = \frac{0.60}{-0.30} = -2$ , so the image is inverted and twice the size.

Answer: 0.60 m on the other side of the lens, magnification −2

Shortcuts and results to remember

A glass lens ( $\mu = 1.5$ ) placed in water ( $\mu = 4/3$ ) has four times its focal length in air, while a mirror’s focal length does not change in water.
Rotating a mirror by $\theta$ rotates the reflected ray by $2\theta$ .
A ray passing through any stack of parallel slabs emerges parallel to the incident ray if the first and last media are the same.
To see your full image in a plane mirror, the mirror needs only half your height.
Cutting a lens along its axis gives two lenses of the same focal length; cutting it perpendicular to the axis gives two lenses of focal length $2f$ each.

Common mistakes to avoid

Using the mirror formula’s plus sign for a lens — the lens formula is 1/v − 1/u = 1/f.
Calculating power with f in centimetres — P (in dioptres) = 1/f with f in metres, or 100/f with f in cm.
Applying total internal reflection when light goes from a rarer to a denser medium — it happens only from denser to rarer, beyond the critical angle.
Dropping the sign of u, so a real image appears virtual — keep every distance signed throughout the calculation.

How to prepare it

Choose one sign convention and apply it to every distance — this chapter punishes inconsistency more than any other.

Once the formulas feel familiar, test them the way the exam does: practise Ray Optics and Optical Instruments questions chapter-wise, then attempt a full previous year paper to see whether it holds up under a 3-hour timer.

Related Physics chapters

See every chapter in the EAPCET Physics syllabus.

Practise Ray Optics and Optical Instruments chapter-wise

Chapter-wise quizzes show exactly which topics in this chapter you still get wrong — before a full paper does.

Frequently asked questions

Is Ray Optics and Optical Instruments part of the EAPCET Physics syllabus?: Yes. Ray Optics and Optical Instruments is taught in Intermediate second year Physics, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.
How should I prepare Ray Optics and Optical Instruments for EAPCET?: Choose one sign convention and apply it to every distance — this chapter punishes inconsistency more than any other.
How many Physics questions are there in EAPCET?: 40 of the 160 questions in the Engineering paper are Physics, spread across 30 chapters.
What mistakes do students make in Ray Optics and Optical Instruments?: Using the mirror formula’s plus sign for a lens — the lens formula is 1/v − 1/u = 1/f. Calculating power with f in centimetres — P (in dioptres) = 1/f with f in metres, or 100/f with f in cm. Applying total internal reflection when light goes from a rarer to a denser medium — it happens only from denser to rarer, beyond the critical angle. Dropping the sign of u, so a real image appears virtual — keep every distance signed throughout the calculation.