7.All the following are required as apparatus in refraction using glass block experiment EXCEPT
a.G-Clamp
b.Drawing board
c.Optical pins
d.Thumb tacks
8.The mirror formula relates I- focal length of the mirror II- object distance III- image distance IV- principal focus
a.I, III and IV only
b.II, III and IV only
c.I, II and IV only
d.I, II and III only