Refraction at plane and spherical surfaces, thin lens and lens maker formula
- Two transparent media A and B are separated by a plane boundary. The speed of light in those media are 1.5 × 10^8 m/s and 2.0 × 10^8 m/s, respectively. The critical angle for a ray of light for these two media is : Answer: 3. sin⁻¹(0.750) Refractive index n=c/v : n_A=3×10⁸/1.5×10⁸=2 and n_B=3×10⁸/2×10⁸=1.5 . Total internal reflection is possible when li... 1
- A light ray falls on a glass surface of refractive index √(3), at an angle 60°. The angle between the refracted and reflected rays would be : Answer: 4. 90° Use Snell's law: sin60^°=sqrt3sin r⇒sin r=1/2⇒ r=30^° . The reflected ray makes 60^° with the normal, the refracted ray 30^°... 1
- A point object is placed at a distance of 60 cm from a convex lens of focal length 30 cm. If a plane mirror were put perpendicular to the principal axis of the lens and at a distance of 40 cm from it, the final image would be formed at a distance of… Answer: 4. 20 cm from the plane mirror, it would be a virtual image. Key idea: lens, then mirror, then lens again. Lens: u=-60,\ f=30⇒ v=60... 1
- Pick the wrong answer in the context with rainbow. Answer: 3. An observer can see a rainbow when his front is towards the sun. We pick the wrong statement. Two internal reflections give the s... 1
- An air bubble in a glass slab with refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is Answer: 2. 12 Apparent depth =real depth/μ . The bubble is at a fixed real depth x from one face and t-x from the other. x/1.5=5⇒ x=7.5 cm;... 1