Question

A student obtained a sharp image of a burning candle, placed at the farther end of a laboratory table, on a screen using a concave mirror. For getting a better value of focal length of the mirror, the subject teacher suggested that he focus on a well illuminated distant object. What should the student do?

Answer 1

Hint: For finding the better value of focal length of the concave mirror, the image obtained should be close to the mirror near the focus. To obtain an image close to the mirror, objects should be placed at a larger distance from the mirror.

Complete step by step answer:
A concave mirror is the one which is curved inward in the middle. Concave mirror can produce both types of images, real and virtual. The image can be upright, if virtual, and inverted, if real. Also, the image can be behind the mirror, if virtual, and in front of the mirror, if real. The images can also be magnified, diminished or of the same size depending on the position of the object.
When the object is kept at a large distance from the mirror, the rays coming from the object meet near the focus of the mirror, depicting the focal length of the mirror. The image obtained is real, inverted, diminished and well illuminated.

For determining the focal length of a mirror, the screen should be placed in front of the reflecting surface of the mirror. To obtain a clear and sharp image, the screen should be adjusted accordingly. To get a well illuminated image, objects should be placed at a large distance from the mirror.
As the object distance is increased, the image distance would decrease. For an illuminated image, the mirror-screen distance should be decreased and, therefore, the mirror should be moved towards the screen.

Note: When the object is shifted away from the concave mirror, the image moves towards the mirror close to the focus. A well illuminated image is obtained at the focus of the concave mirror.