The train’s average speed is 80km/h
Answer:
2.8 cm
Explanation:
= Separation between two first order diffraction minima = 1.4 cm
D = Distance of screen = 1.2 m
m = Order
Fringe width is given by

Fringe width is also given by

For second order

Distance between two second order minima is given by


The distance between the two second order minima is 2.8 cm
Starting making jokes and rapping
Answer
given,
focal length of lens A = 5.77 cm
focal length of lens B= 27.9 cm
flies distance from mirror = 11.3 m
now,
Using lens formula
q =11.79 cm
image of lens A is object of lens B
distance of lens = 59.9 - 11.79 = 48.11
now, Again applying lens formula
q' =66.41 cm
hence, the image distance from the second lens is equal to q' =66.41 cm