Which of the following statements for persons suffering from presbyopia is/are correct? 1. They cannot distinguish colours. 2. It usually develops with ageing. 3. They wear either bi-focal lenses consisting of both concave and convex lenses or progressive lenses. Select the answer using the code given below :
- A.1 only
- B.2 only
- C.1 and 3
- D.2 and 3
Correct answer
Explanation
The correct answer is D, 2 and 3. Presbyopia is an age-related loss of near focusing, and it is corrected with bifocal or progressive lenses.
With age the ciliary muscles weaken and the eye lens loses its flexibility, so the power of accommodation falls and the near point moves away. A person usually notices it after about forty, when small print has to be held farther away. Many such people also have myopia or hypermetropia, so they need bifocal lenses: the upper part is a concave lens for distant vision and the lower part a convex lens for reading. Progressive lenses do the same job with a smooth change of power.
A is wrong because statement 1 is false; inability to tell colours apart is colour blindness, a defect of the cone cells of the retina.
B is wrong because it leaves out statement 3, which is also correct.
C is wrong because it includes the false statement 1.
Exam tip: myopia, concave lens; hypermetropia, convex lens; presbyopia, bifocal; astigmatism, cylindrical lens.
Practice Questions
View allConsider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
Show answer
An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.
Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Show answer
Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
Read the full explanation →Which one of the following cell organelles contains DNA?
- A.Golgi apparatus
- B.Mitochondrion
- C.Lysosome
- D.Endoplasmic reticulum
Show answer
Mitochondria carry their own small, circular DNA and their own ribosomes. Mitochondria are the powerhouses of the cell, where aerobic respiration makes ATP.
Read the full explanation →Which set of vegetables is underground stem or modified stem of a plant?
- A.Potato, artichoke, round gourd
- B.Onion, garlic, carrot
- C.Potato, onion, garlic
- D.Potato, garlic, turnip
Show answer
All three are underground modified stems: the potato is a stem tuber, and onion and garlic are bulbs. A stem can be told from a root by its nodes and buds.
Read the full explanation →A sound wave having frequency of 300 Hz is travelling in an unknown medium. Its wavelength is not known. It travels a distance equal to 150 times its wavelength in time t. The value of t is :
- A.0.5 s
- B.1 s
- C.1.5 s
- D.2 s
Show answer
A wave moves forward by one wavelength in each cycle, so 150 wavelengths take 150 cycles, and 150 cycles at 300 per second take half a second.
Read the full explanation →