Unit notes and practice questions
Everything here is for unit 6 of the Grade 10 Physics textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.
The cards filed under this chapter on the Grade 10 Physics page. Open one at a time.
| Primary Color 1 | Primary Color 2 | Resulting Secondary Color |
|---|---|---|
| Red | Green | Yellow |
| Red | Blue | Magenta |
| Blue | Green | Cyan |
When you use it
Use to determine the secondary color produced by mixing primary colors of light.
Watch out
Color addition applies to light beams, not to mixing physical paint pigments.
Drafted from Grade 10 Physics, page 156 onwards, then checked twice before it went up
When you use it
Use to find object distance, image distance, or focal length for thin spherical lenses.
Watch out
The lens formula has a minus sign before the 1/u term, unlike the mirror formula.
Drafted from Grade 10 Physics, page 156 onwards, then checked twice before it went up
When you use it
Use to calculate image position, object position, or focal length for spherical mirrors.
Watch out
Focal length is positive for concave mirrors and negative for convex mirrors.
Drafted from Grade 10 Physics, page 156 onwards, then checked twice before it went up
When you use it
Use to calculate lens power from focal length or determine corrective lenses for vision defects.
Watch out
Focal length must be converted to metres before calculating power in diopters.
Drafted from Grade 10 Physics, page 156 onwards, then checked twice before it went up
When you use it
Use when finding angles or refractive indices as light passes between two optical media.
Watch out
Angles must be measured relative to the normal line, not relative to the boundary surface.
Drafted from Grade 10 Physics, page 156 onwards, then checked twice before it went up
10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.
Question 1
According to the textbook, which three colors are the primary colors of light?
Answer: C Red, green, and blue
Why
Red, green, and blue are the three primary colors of light.
Question 2
What is the speed of light in a vacuum, represented by c?
Answer: A 3.00 × 10<sup>8</sup> m/s
Why
Light travels with a speed of 3.00 × 108 m/s in a vacuum.
Question 3
Which light-sensing photoreceptor cells in the human retina are sensitive to colors?
Answer: B Cones
Why
Rods and cones are the two photoreceptors in the retina, and cones are specifically sensitive to colors.
Question 4
Why is a convex mirror preferred as a rear-view mirror in vehicles?
Answer: D It gives a wider field of view and forms erect, diminished images
Why
A convex mirror is used as a rear-view mirror because it gives a wider field of view and always forms a virtual, erect, and diminished image.
Question 5
Which of the following correctly lists electromagnetic radiations in order of increasing frequency?
Answer: B Infrared, visible light, ultraviolet, X-rays, gamma rays
Why
In order of increasing frequency, the electromagnetic radiation sequence is infrared, visible light, ultraviolet, X-rays, and gamma rays.
Question 6
In the addition of colored light, what color is produced when red light is mixed with green light?
Answer: A Yellow
Why
Combining red light and green light gives yellow light (Red + Green = Yellow).
Question 7
In a school laboratory in Hawassa, a student places an object between two plane mirrors inclined at an angle of 30°. How many images are formed?
Answer: C 11
Why
The formula for the number of images formed by two inclined mirrors is (360° / θ) - 1. Here, (360° / 30°) - 1 = 12 - 1 = 11.
Question 8
What are the near point and far point of vision for a young adult with normal vision?
Answer: B Near point is about 25 cm, and far point is infinity
Why
For a young adult with normal vision, the near point is about 25 cm, and the far point is at infinity.
Question 9
Which two conditions must be satisfied for total internal reflection to occur?
Answer: D Light must travel from an optically denser medium to a less dense medium, and the angle of incidence must be greater than the critical angle.
Why
Total internal reflection requires light to travel from an optically denser medium (higher refractive index) to an optically less dense medium (lower refractive index) and the angle of incidence to exceed the critical angle.
Question 10
An optometrist in Addis Ababa prescribes a lens with a power of -5.5 D to correct a person's distant vision defect. What is the focal length of this lens?
Answer: C -0.181 m
Why
The relationship between focal length and power is f = 1 / P. Therefore, f = 1 / (-5.5) = -0.181 m.
The app holds 12 questions on this unit, marked as you go. These are the first 10.
The whole Grade 10 Physics textbook, free as a PDF.
Ministry of Education edition, English, 212 pages
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