Concave and Convex Mirrors Quiz

A concave mirror produces a real image 3 times the size of the object. The object is placed:

• Between F and C

• At C

• Beyond C

• At F

Answer explanation

A concave mirror produces a real image larger than the object when the object is placed between the focal point (F) and the center of curvature (C). Since the image is 3 times the size, the object must be between F and C.

If the radius of curvature of a concave mirror is 20 cm, its focal length is:

• 10 cm

• 20 cm

• 30 cm

• 40 cm

Answer explanation

The focal length (f) of a concave mirror is half the radius of curvature (R). Given R = 20 cm, f = R/2 = 20 cm/2 = 10 cm. Therefore, the correct answer is 10 cm.

A virtual image cannot be obtained with a:

• Concave mirror

• Convex mirror

• Plane mirror

• None of the above

Answer explanation

A virtual image can be formed by concave mirrors, convex mirrors, and plane mirrors. Therefore, the correct answer is 'None of the above' as all listed options can produce virtual images.

The magnification of an image is -0.5. This means the image is:

• Real, erect, and half the size of the object

• Virtual, erect, and half the size of the object

• Real, inverted, and half the size of the object

• Virtual, inverted, and half the size of the object

Answer explanation

A magnification of -0.5 indicates the image is real (negative magnification) and inverted (since real images are inverted). The size being half means the image is half the size of the object.

A ray of light parallel to the principal axis of a convex mirror after reflection:

• Passes through the focus

• Appears to diverge from the focus

• Passes through the center of curvature

• Is parallel to the principal axis

Answer explanation

A ray of light parallel to the principal axis of a convex mirror reflects and appears to diverge from the focus. This is due to the nature of convex mirrors, which cause light rays to spread out.

The image formed by a convex mirror is always:

• Real and erect

• Virtual and erect

• Real and inverted

• Virtual and inverted

Answer explanation

The image formed by a convex mirror is always virtual and erect. This is because convex mirrors diverge light rays, causing them to appear to come from a point behind the mirror, resulting in a virtual image that is upright.

When an object is placed at the center of curvature of a concave mirror, the image formed is:

• At infinity

• At the focus

• At the center of curvature

• Between focus and center of curvature

Answer explanation

When an object is placed at the center of curvature of a concave mirror, the rays reflect back through the center, forming an image at the same point. Therefore, the image is formed at the center of curvature.

The mirror formula 1/f = 1/v + 1/u is applicable to:

• Only concave mirrors

• Only convex mirrors

• Both concave and convex mirrors

• Only plane mirrors

Answer explanation

The mirror formula 1/f = 1/v + 1/u applies to both concave and convex mirrors, allowing for the calculation of image distance (v) and object distance (u) for any type of spherical mirror.

A concave mirror of focal length 15 cm forms a real image of the same size as the object. The position of the object is:

• At the focus

• At the center of curvature

• At infinity

• Between focus and center of curvature

Answer explanation

For a concave mirror, when the object is at the center of curvature (twice the focal length), the image formed is real and of the same size as the object. Here, the focal length is 15 cm, so the center of curvature is at 30 cm.

The focal length of a convex mirror is always:

• Positive

• Negative

• Zero

• Infinite

Answer explanation

The focal length of a convex mirror is considered negative because it diverges light rays. In optics, the convention is that focal lengths for convex mirrors are assigned negative values.