Physics Optics

A combination of two thin lenses in contact behave as converging lens of focal length 80 cm if one of the lense is convrging lens of focal length 20 cm,  the power of other lens will be

Explanation.
f= focul length of combination of two lenses
f1= focul length of ist lens
f2= focul length of 2nd lens
As 1/f =1/f1  + 1/f2
1/80 = 1/20 + 1/f2
1/f2 = 1/80 - 1/20
f2 = -26.66cm
 = -0.266 m

As Power of lens P= 1/f (where f will be in meters)

So
P=1/-0.266
= -3.75D

ECAT MCQs Part 1

1. Converse of pair production is
   a)compton effect
   b)annihilation of matter
   c)photoelectric effect
   d)none of them
2. de broglies hypothesis was experimentally verified by
   a)maxwell
   b)compton
   c)einstien
   d)davion and germar
3. What is the unit of absorbed dose?
   a)gray
   b)severt
   c)curie
   d)roentgen
4. The decay of neutron results into the formation of
   a)proton,positron
   b)proton,electron
   c)electron,anti neutrino
   d)proton,helium
5. The unit of concentration is
   a)mol. ml
   b)mol dm^-3
   c)gm equivalent lit^-1
   d)g. lit^-1
6. If there are weak intermolecular forces in a liquid, it will be
   a)more volatile
   b)more dense
   c)less volatile
   d)heavy dense
7. In the definition of conic the constant ratio is called
   a)directrix
   b)focus
   c)vertex
   d)eccentricity
8. Which sentence is correct?
   A. How beautiful moon is!
   B. How beautiful the moon is!
   C. How beautiful that moon is!
   D. How beautiful the moon is.
9. sugar crystals belong to the
   a)cubic
   b)monoclinic
   c)triclinic
   d)orthrorhombic
10. weber is a unit of
    a)magnetic flux
    b)magnetic flux density
    c)magnetic induction
    d)none of these