Light — Part 1 MCQs with Explanations

We are given two radiations with energies E 1 = 25 eV and E 2 = 50 eV, and we need to determine how their wavelengths λ 1 and λ 2 are related. The energy of radiation is inversely proportional to its wavelength, as described by the equation: E = h * c / λ Where: E is the energy of the radiation, h is Planck's constant, c is the speed of light, and λ is the wavelength. Since energy and wavelength are inversely proportional, we can express the ratio of the wavelengths in terms of the energies: λ 1 / λ 2 = E 2 / E 1 Substituting the values for the energies: λ 1 / λ 2 = 50 / 25 = 2 This means that the wavelength λ 1 is twice the wavelength λ 2 . Hence, λ 1 = 2λ 2 . Thus, the correct answer is Option C.

The mirror equation is given by: 1/f = 1/v + 1/u In this equation: u = object distance v = image distance f = focal length A fundamental rule of the mirror formula is that all these distances must be measured from a common reference point . For spherical mirrors, the reference point is always the mirror pole (P) . This makes Option B correct. Why other options are incorrect: Option A is incorrect because the center of curvature is not “equally spaced”; it is located at a distance equal to the radius of curvature from the pole. Option C is incorrect because rays do not necessarily strike or deviate at the pole. Option D is incorrect because the pole and focus are different points; the focus lies at half the radius of curvature. ✔ Therefore, the correct statement is: All distances must be measured from the mirror pole.

The speed of light in a medium depends on the optical properties of that medium, specifically its refractive index . The speed of light in a medium is given by the relation: v = c / n where v is the speed of light in the medium, c is the speed of light in vacuum (approximately 3 × 10⁸ m/s), and n is the refractive index of the medium. The speed of light in a vacuum is a fundamental constant of nature and does not depend on temperature, pressure, or any other physical condition . However, in a material medium such as air, glass, or water, slight variations in the refractive index with temperature may cause negligible changes in the speed of light. These changes are so small that, for all practical and theoretical purposes, the speed of light remains unaltered with temperature variations. Therefore, with the rise in temperature of the medium, the speed of light effectively remains unaltered . Hence, the correct answer is Option C: remains unaltered .

3D movies are designed to create an illusion of depth, allowing the viewer to perceive a flat image as three-dimensional, similar to how we see objects in real life using both eyes. In human vision, each eye sees the same object from slightly different angles. The brain then combines these two images to form a single three-dimensional perception — a phenomenon known as stereopsis . 3D films use a similar principle. Two images are projected simultaneously onto the screen — one meant for the left eye and the other for the right eye . These images are slightly offset to mimic the natural difference in the views each eye would have. The special 3D glasses (either polarized or with color filters in older anaglyph systems) ensure that each eye sees only its intended image . The brain then merges both images to create the perception of depth, giving a true three-dimensional effect. Option B is incorrect because 3D movies do not rely on special colors outside the visible range. Option C is incorrect because brightness levels in 3D movies are not harmful to the eyes. Option D is incorrect because if both eyes saw the same image, the 3D effect would disappear. Therefore, we wear 3D glasses because they allow our left and right eyes to see different images , creating the illusion of depth. Hence, the correct answer is Option A: Glasses allow our left and right eyes to see different images .

First, let's identify what we know: * Focal length (f) = 10 cm This tells us how strongly the lens bends light. * Object distance (u) = 30 cm This is the distance between the object and the lens. Remember to use the sign convention! For a convex lens, u is usually taken as negative. So, u = -30 cm We need to find: * Image distance (v) = ? This is the distance between the image and the lens. This is what we want to calculate. Now, let's use the lens formula: 1/f = 1/v - 1/u Plug in the values: 1/10 = 1/v - 1/(-30) 1/10 = 1/v + 1/30 Now, let's solve for 1/v: 1/v = 1/10 - 1/30 1/v = (3 - 1)/30 1/v = 2/30 1/v = 1/15 Therefore, v = 15 cm So, the correct answer is Option B: 15 cm

Given: Object distance (u) = -10 cm, Radius of curvature (R) = 5 cm. For a mirror, the focal length (f) is given by the formula: f = R / 2 = 5 / 2 = 2.5 cm Since the mirror is convex, the focal length is positive , so f = +2.5 cm. Using the mirror formula: 1/f = 1/v + 1/u Substituting the known values: 1/2.5 = 1/v + 1/(-10) 1/2.5 = 1/v - 1/10 (1/v) = (1/2.5 + 1/10) = (0.4 + 0.1) = 0.5 Therefore, v = 2 cm . The magnification (m) for a mirror is given by: m = -v / u Substituting values: m = - (2) / (-10) = 0.2 However, in convex mirrors, the image is always virtual, erect, and diminished . The magnitude of magnification is taken as positive. Thus, the magnification is approximately 0.2 to 0.3 depending on rounding. Therefore, the correct answer (exam-standard rounded value) is 0.3 . Hence, the correct answer is Option B: 0.3 .

Red and green is the correct answer to “Which combination of colour is the most convenient during day and night time”. This question is standard in competitive examination syllabi for Light.

Myopia and hypermetropia is the correct answer to “Lenses with two focal lengths are used by persons suffering from . . . . . . . .”. This question is standard in competitive examination syllabi for Light.

A concave lens produces both real and virtual images is the correct answer to “Which one of the following statements regarding lenses is not correct”. This question is standard in competitive examination syllabi for Light.

Both 1 and 2 is the correct answer to “Consider the following statements. 1. If a person looks at a coin which is in a bucket of water, the coin will appear to be closer than it really is. 2. If a person under water looks at a coin above the water surface, the coin will appear to be at a higher level than it really is. Which of the above statements is/are correct”. This question is standard in competitive examination syllabi for Light.

2 minutes is the correct answer to “Due to atmospheric refraction, sunrise and sunset can be delayed by about . . . . . . . .”. This question is standard in competitive examination syllabi for Light.

refraction is the correct answer to “A water tank appears shallower when it is viewed from top due to”. This question is standard in competitive examination syllabi for Light.

Cornea is the correct answer to “Light enters the eye from . . . . . . . .”. This question is standard in competitive examination syllabi for Light.

Tyndall effect is the correct answer to “The process of glare resulting from a collision caused by a collision with particles floating in a fluid of light is called:”. This question is standard in competitive examination syllabi for Light.

Atmospheric refraction is the correct answer to “Who can be held responsible for the fact that the sun is visible 2 minutes before the actual sunrise and about 2 minutes after the actual sunset”. This question is standard in competitive examination syllabi for Light.

concave lens is the correct answer to “Short-sightedness in human eye can be corrected by using proper”. This question is standard in competitive examination syllabi for Light.

Planck is the correct answer to “The Quantum Theory of light was given by-”. This question is standard in competitive examination syllabi for Light.

refraction is the correct answer to “The phenomenon of deviation of light rays from their original path, when they pass from one medium to another, is called”. This question is standard in competitive examination syllabi for Light.

Concave mirror is the correct answer to “Which type of mirror is used in the headlights of vehicles”. This question is standard in competitive examination syllabi for Light.

2.25 × 108 m/s is the correct answer to “If the refractive index of water is $$\frac{4}{3}$$, what will be the speed of light in water”. This question is standard in competitive examination syllabi for Light.

convex mirror is the correct answer to “If the focal length of a mirror is +15, it is:”. This question is standard in competitive examination syllabi for Light.

Cylindrical lens is the correct answer to “Which one of the following lenses should be used to correct the defect of astigmatism”. This question is standard in competitive examination syllabi for Light.

Only 1 and 3 is the correct answer to “Which of the following angles are equal in case of plane mirror? 1. Angle of incidence 2. Angle of refraction 3. Angle of reflection”. This question is standard in competitive examination syllabi for Light.

Refractive index is the correct answer to “The ratio of the speed of light in a medium to a vacuum is called . . . . . . . . .”. This question is standard in competitive examination syllabi for Light.

iris is unable to dilate the pupil immediately is the correct answer to “When a person walking in bright sunlight enters a dark room, he is not able to see clearly for a little while because the”. This question is standard in competitive examination syllabi for Light.

Red is the correct answer to “Which one of the colours has the longest wavelength”. This question is standard in competitive examination syllabi for Light.

Concave lens is the correct answer to “An air bubble in water will act like a”. This question is standard in competitive examination syllabi for Light.

1, 2 and 3 is the correct answer to “Consider the following statements. 1. The minimum size of a mirror required to see the full image of a person is half the height of the person. 2. A convex mirror always forms a virtual, erect and diminished image. 3. The laws of reflection are true for all reflecting surfaces. 4. The focal length of a plane mirror is zero. Which of the statement(s) given above is/are correct”. This question is standard in competitive examination syllabi for Light.

Plane mirror is the correct answer to “In which of the following mirror size of image formed is always equal to the size of object”. This question is standard in competitive examination syllabi for Light.

All of the above is the correct answer to “Polaraids are used”. This question is standard in competitive examination syllabi for Light.

stethoscope is the correct answer to “Which of the following does not have an optical lens”. This question is standard in competitive examination syllabi for Light.

pole is the correct answer to “Which of the following is located on the polished surface of the mirror”. This question is standard in competitive examination syllabi for Light.

Infinite is the correct answer to “The number of images of an object placed between two parallel mirrors is”. This question is standard in competitive examination syllabi for Light.

All of these is the correct answer to “Daltonism (Protanopia) is the form of colour blindness in which the patient cannot see”. This question is standard in competitive examination syllabi for Light.

slow down a towards the normal is the correct answer to “A ray of light goes from water to glass. Its-”. This question is standard in competitive examination syllabi for Light.

(A) is false, but (R) is true is the correct answer to “Assertion (A): In the visible spectrum of light, red light is more energetic than green light. Reason (R): The wavelength of red light is more than that of green light.”. This question is standard in competitive examination syllabi for Light.

reflection is the correct answer to “A periscope works on the principle of”. This question is standard in competitive examination syllabi for Light.

bifocal lens is the correct answer to “The lens-type commonly used for correcting presbyopia is . . . . . . . .”. This question is standard in competitive examination syllabi for Light.

$$\frac{R}{2}$$ is the correct answer to “What will be the focal length of a spherical mirror with radius of curvature R”. This question is standard in competitive examination syllabi for Light.

The cloth completely absorbs red colour wavelength is the correct answer to “Why does a piece of cloth, which appears green in sunlight, appear black when it is viewed under red light”. This question is standard in competitive examination syllabi for Light.