A student obtained a blurred image of an object on a screen using a concave mirror. In order to obtain a sharp image on the screen, he will have to shift the mirror -

Four students $A\mathit{,}\mathit{ }B\mathit{,}\mathit{ }C\mathit{ }$and $D$ carried out measurements of focal length of a concave mirror as shown in the four diagrams.

the best result will be obtained by students:-

Parallel rays, from the top of a distant object, incident on a concave mirror, form an image on the screen.

The diagram correctly showing the image of the object on the screen is-

The focal length of the concave mirror in the experimental set-up, shown below, equals

Image formed by a concave mirror-

To determine the focal length of a convex lens by obtaining a sharp image of a distant object we generally follow the following steps which are not in proper sequence

$\left(i\right)$ Hold the lens between the object and the screen.

$\left(ii\right)$ Measure the distance between the lens and the screen.

$\left(iii\right)$ Select a well lit distant object.

$\left(iv\right)$ Place a screen opposite to the object on the lab table.

$\left(v\right)$ Adjust the position of the lens to form a sharp image.

The correct sequence of these steps is

To determine focal length of a concave mirror a student obtains the image of a well lit distant object on a screen. To determine the focal length of the given concave mirror he needs to measure the distance between—

Three students $X, Y and Z$ are finding the focal length of the given concave mirror by obtaining the image of the objects elected by them. $X$ obtains the image of the grill of the nearest window of the lab. $Y$ obtains the image of a white painted building near the lab and $Z$ obtains a point size image of the sun. The most correct value of the focal length is obtained by