How will you determine the C.G. of an irregular lamina by the method of balance using a plumb line ? 

The diagram shows a ray $\mathrm{AB}$ of a white light incident on a rectangular glass block which is silvered at one surface. This ray undergoes reflection and refraction. Copy and complete the path of ray $\mathrm{AB}$. Which image is the brightest and why? How many images are formed in the above case?

What do you understand by invisible spectrum? How will you investigate the existence of ultraviolet radiation ?  

The diagram alongside represents a wave motion; the wave travels at $12 {\mathrm{ms}}^{-1}$Calculate
(i) Amplitude
(ii) Wavelength
(iii) Frequency of wave. 

Name the factors on which the deviation produced by a prism depends.