A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen, in which direction should the student move the lens?

$(i)$ Define the principal focus of a concave mirror.
$(ii)$ Why do we prefer a convex mirror as a rear-view mirror in vehicles?
$(iii)$ We wish to obtain an erect image of an object using a convex lens. Draw a ray diagram to show the image formation in this case.

The image shows the path of light as it travels from one medium to another.
$(9)$ What are medium $1$ and medium $2$?

	Medium $1$	Medium $2$
$A$.	Water	Kerosene
$B$.	Kerosene	Diamond
$C$.	Flint glass	Water
$D$.	Kerosene	Flint glass

$(10)$ The power of a lens $(P)$ is calculated by the formula, $P = \frac{1}{f}$, where $f$ is the focal length of the lens in meters. A lens has a focal length of $-0.25 \ m$. Is it a convex lens or a concave lens? Explain your answer.

The image formed by a spherical mirror is virtual. The mirror will be:

The images show four ray diagrams of images formed by concave mirrors. $P$ is the pole of the mirror. $F$ is the focus. $C$ is the centre of curvature. $AB$ is the object and $A'B'$ is the image.
$1$. Which of these can be concluded from diagram $1$?
$A$. Image is formed at the focus.
$B$. Size of the image is equal to the size of the object.
$C$. Distance between pole and centre of curvature is twice the focal length.
$D$. Distance between the image and focus is half the distance between the object and focus.
$2$. Which diagram shows a real, inverted and enlarged image formed by the mirror?
$A$. Diagram $1$
$B$. Diagram $2$
$C$. Diagram $3$
$D$. Diagram $4$
$3$. In which condition does a concave mirror produce a virtual image?
$A$. When object is located within the focal length
$B$. When object is located at the centre of curvature
$C$. When object is located in between infinity and the centre of curvature
$D$. When object is located in between the centre of curvature and the focus
$4$. Solar cookers contain a concave mirror. How does the concave mirror help in heating the food? Indicate 'Yes' or 'No' for each statement.

How does the concave mirror heat the food?	Yes/No
Sun’s rays are absorbed by the mirror.	Yes/No
Sun’s rays reflected by the mirror converge at a point.	Yes/No
Sun’s rays diverge out when reflected by the mirror.	Yes/No

State one practical use each for a convex mirror, a concave mirror, a convex lens, and a concave lens.