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# Light Trivia Quiz

### This quiz is a series of questions on reflection, refraction, lenses and spectrum... basically, on different areas of light.

A multiple-choice quiz by Rossell. Estimated time: 6 mins.

Author
Time
6 mins
Type
Multiple Choice
Quiz #
251,707
Updated
Dec 03 21
# Qns
10
Difficulty
Very Difficult
Avg Score
4 / 10
Plays
2941
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Question 1 of 10
1. A ray of white light strikes a rectangular glass block normally. How many rays of light, and what colour, emerge from the block? Hint

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Question 2 of 10
2. A ray of light strikes a plane mirror and the angle of reflection is noted. The plane mirror is then rotated through an angle of 30 degrees, such that there is an increase in the angle of reflection.

If the initial angle of reflection was 15 degrees, what will be the new angle of reflection, after rotation?
Hint

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Question 3 of 10
3. Which of the following prisms would be suitable for use in a periscope? Hint

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Question 4 of 10
4. A specific mass of pure water is frozen to form completely transparent ice, in the shape of a lens. When forced underwater, the lens diverges light.

What is the shape of the lens?
Hint

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Question 5 of 10
5. Two monochromatic rays of light, one ray violet and the other red, travel from a vacuum into air. Their speeds change as a result.

What is the ratio of the speed of the violet ray to the speed of the red ray?
Hint

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Question 6 of 10
6. Which of the following mirrors is most suitable for using as a reflector in car headlights? Hint

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Question 7 of 10
7. A person suffering from the ophthalmic disorder myopia is wearing spectacles with concave lenses. The transparent concave lenses are yellow in colour. This person looks at a picture of a yellow circle, a green square and a red triangle set against a blue background.

How does the picture appear to the person?
Hint

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Question 8 of 10
8. [1/f= 1/v - 1/u] is the mirror formula, which enables us to evaluate the focal length of a concave mirror.

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Question 9 of 10
9. A camera is focused on a distant object. The distance between the lens and the photographic film is equal to 'f'.

The camera must now focus on a nearby object.

What will be the new distance between the photographic film and the lens?
Hint

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Question 10 of 10
10. An object is placed 10cm away from the lens of a camera. The image formed is the same size as the object.

What is the focal length of the lens of the camera?
Hint

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Quiz Answer Key and Fun Facts
1. A ray of white light strikes a rectangular glass block normally. How many rays of light, and what colour, emerge from the block?

Answer: One ray of white light

Since the ray of white light strikes the glass surface normally and the angle of incidence will be zero, there will be no refraction of light and as a result, no separation of white light into its constituent rays.
2. A ray of light strikes a plane mirror and the angle of reflection is noted. The plane mirror is then rotated through an angle of 30 degrees, such that there is an increase in the angle of reflection. If the initial angle of reflection was 15 degrees, what will be the new angle of reflection, after rotation?

"For a given incident ray, if a plane mirror is rotated through a certain angle, then the angle of reflection increases by twice that angle."

The plane mirror was rotated through 30 degrees, so the reflected ray will increase by (30 multiplied by 2)60 degrees.
3. Which of the following prisms would be suitable for use in a periscope?

Answer: An isosceles right angled prism

A refracting periscope uses isosceles right angled prisms as opposed to mirrors in a reflecting periscope. Refracting periscopes are based on the principle of total internal reflection.
4. A specific mass of pure water is frozen to form completely transparent ice, in the shape of a lens. When forced underwater, the lens diverges light. What is the shape of the lens?

Convex lenses converge light only when placed in a medium less dense than the material they are made of, otherwise they diverge light. The reverse happens with concave lenses. This is why it is inappropriate to designate lenses as 'converging' or 'diverging', as this property is subject to change.

Note: Water is denser than ice. Both are transparent.
5. Two monochromatic rays of light, one ray violet and the other red, travel from a vacuum into air. Their speeds change as a result. What is the ratio of the speed of the violet ray to the speed of the red ray?

All colours of light have the same speed in air and vacuum.
6. Which of the following mirrors is most suitable for using as a reflector in car headlights?

If a source of light is placed at the focal point of a concave mirror, a parallel beam of light is obtained after reflection.

However, a parabolic mirror has a greater aperture, and so if a light source is placed at the focus of a parabolic mirror, a larger beam of light is obtained and a larger area is illuminated.
7. A person suffering from the ophthalmic disorder myopia is wearing spectacles with concave lenses. The transparent concave lenses are yellow in colour. This person looks at a picture of a yellow circle, a green square and a red triangle set against a blue background. How does the picture appear to the person?

Answer: It cannot be stated with certainty from the information given

Just like a light source appearing yellow can emit either monochromatic yellow light or a combination of various other wavelengths, for example red and green, any transparent material that is also yellow in colour, such as a yellow lens, might let not only yellow but also significant amounts of orange, green and red light to pass through while absorbing primarily in the blue spectrum.

Without knowing the absorption characteristics of the lens and the spectral characteristics of the light source, we can thus not conclude just how the picture will look.
8. [1/f= 1/v - 1/u] is the mirror formula, which enables us to evaluate the focal length of a concave mirror.

It is actually the lens formula. The mirror formula is [1/f= 1/v + 1/u].
9. A camera is focused on a distant object. The distance between the lens and the photographic film is equal to 'f'. The camera must now focus on a nearby object. What will be the new distance between the photographic film and the lens?

For distant objects (placed beyond twice the focal length), the image is formed on the other side of the lens at the focus or within the focal length.

However, for nearby objects (placed between twice the focal length and the focal length), the image is formed on the other side of the lens, beyond the focus. As a result, for nearby objects, the distance between the lens and photographic plate will have to greater than that for distant objects.

Note: All camera lenses are convex.
10. An object is placed 10cm away from the lens of a camera. The image formed is the same size as the object. What is the focal length of the lens of the camera?