An image that cannot be obtained on a screen is called a   image.

Draw a ray diagrams of convex lens when the position of the object is between ${\mathrm{F}}_1$ and $2{\mathrm{F}}_1$.

Draw a ray diagrams of convex lens when the position of the object is at $2 {\mathrm{F}}_1$.

Draw ray diagrams of convex lens when the position of the object is at infinity.

Define the terms converging and diverging lenses.