Question 1 :
The nature of image of a candle flame located $40$cm from a concave spherical mirror is real, inverted and magnified four times. Then the radius of curvature of the mirror is:

Question 2 :
Assertion: Although the surface of goggles' lens is curved, it does not have any optical power. Reason:  In case of goggles, both the curved surfaces have equal radii of curvature and have centre of curvature on the same side.

Question 3 :
The image of a square hole in a screen illuminated by light is obtained on another screen with the help of a converging lens. The distance of the hole from the lens is $40\ cm$. If the area of the image is nine times that of the hole, the focal length of the lens is :

Question 4 :
An electric bulb illuminates a plane surface. The intensity of illumination on the surface at a point 2 m away from the bulb is $5\times10^{-4}$ phot $(lumen/cm^2)$. The line joining the bulb to the point makes an angle of $60^o$ with the normal to the surface. The luminous intensity of the bulb in candela (candle power ) is

Question 5 :
An object is placed $1\ m$ in front of the curved surface of a plano-convex lens whose plane surface is silvered. A real image is formed in front of the lens at a distance of $120\ cm$. Then, the focal length of the lens is:<br>

Question 6 :
A thin lens has a focal length of $-50 cm$. What kind of lens is it?