Exercise Book: 18 A piece of
radioactive material contains
2000 atoms. If its half life is 20 seconds
the time take for 125 atoms to remain is?

Explain why the aperture of the spherical mirror should be small compared to the radius of curvature of the mirror.

22. the effect of threshold braking is to a cause skids. b. lock wheels. c. prevent locking of wheels. d. increase stopping distance.

Unpolarized light of intensity i_0=750w/m^2 is incident upon two polarizers. after passing through both polarizers the intensity is i_2=280w/m^2. (a) what is the intensity of the light after it passes through the first polarizer in w/m^2? (b) write an equation for the angle between the polarizers in terms of the initial (i_0) and final (i_2) intensities. (c) find the angle between the polarizers in degrees.