71) The power of a lens is 2.5D. Its focal length is

A) 10cm
B) 25cm
C) 30cm
D) 40cm

72) Bifocal lenses used to correct the defect of vision are called

A) hypermetropia
B) presbyopia
C) myopia
D) None of these

73) Pick the correct answer from the following two statements :
(A) In VIBGYOR, wavelength increases from violet to red,
(B) In VIBGYOR, refractive index increases from violet to red

A) only A is true
B) only B is true
C) Both A and B are true
D) Both A and B are false

74) The formation of the rainbow is due to the dispersion of sunlight by the

A) dust particles
B) water droplets
C) N₂ molecules
D) inert gas molecules

75) If i₁ and i₂ are the angles of incidence and emergence respectively and A is the angle of prism, then the angle of deviation is given by

A) (i₁+i₂)=2A
B) (i₁+i2₂)= A
C) A(i₁-i₂)
D) A(i₁+i₂)