1. A converging lens of focal length 0.236 m forms a virtual image of an object.

Question

1. A converging lens of focal length 0.236 m
forms a virtual image of an object. The image
appears to be 0.924 m from the lens on the
same side as the object.
What is the distance between the object
and the lens?
Answer in units of m




2. Light of wavelength 546 nm from a mercury
arc falls on a di?raction grating ruled with
20400 lines/in.
What is the angular separation between the
?rst-order images on either side of the central
maximum? (Caution: do not use small angle
approximation here.)
Answer in units of ?

Explanation / Answer

(1)
1/f = 1/s + 1/s'
f= 0.236m
s'= -0.924m
s= 0.188m

(2) dsin=n
d=1in/20400 = 0.0254m / 20400 = 1.245e-06 m
=5.46e-07 m

n=1 (first orderimage)

sin=0.4385

=26o

Angular seperation between first order images (n=1 and n=-1) = 2 = 52o

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