(a)(i) What is an eclipse?
(ii) List the three types of eclipse.
(b) A student in a lecture theatre can read from the board clearly but requires a pair of spectacles to read from a book.
(i) What eye defect has this student?
(ii) What type of lens is needed to correct the eye defect?
(iii) The focal length of the lens used to correct this defect is 10cm. Calculate the power of the lens.
(c) A car B moves towards a stationary car A. If B produces an ultrasonic sound at a point and it takes 5.6 x 10\(^{-3}\)s for a beep to be heard in B, calculate the distance between the two cars at that instant. (Speed. sound in air = 340 ms\(^-\))
(d) The image of an object is located 9 cm behind a convex mirror. If magnification produced is 0.6, calculate the focal length of the mirror.
Explanation
(i) An eclipse is a shadow that results from the obstruction of light from the sun by the moon or the earth.
(ii) Types of eclipse:
-Eclipse of the sun or solar eclipse.
-Annular eclipse
- Eclipse of the moon or lunar eclipse.
(b i) The eye defect is long sight or hypermetropia.
(ii) The type of lens to correct the defect is convex or converging lens.
(iii) Power of lens = \(\frac{1}{f} = \frac{1}{0.1} = dioptre(D)\)
(c) Velocity of an echo = \(\frac{2d}{t}\)
d = \(\frac{vt}{2} = \frac{340 \times 5 \times 10^{-3}}{2} = 0.952 m\)
(d) M = \(\frac{v}{u}\)
U = \(\frac{V}{M} = \frac{9}{0.6} = 15cm\)
\(\frac{1}{f} = \frac{1}{u} + \frac{1}{v} = \frac{1}{15} + \frac{1}{-9}\)
f = -22.5cm