Light: Reflection & Refraction - 2 - Class 10 MCQ

For a spherical mirror focal length is one half of its radius of curvature i.e. f = R/2 or R = 2f

The incident ray coming from the object placed at infinity will be parallel to the principal axis. When the parallel beam of light incident on a mirror or lens, irrespective of their nature, after reflection/refraction, will pass or appear to pass through their principal focus. Hence highly diminished and point size image will be formed at their focus.

When a ray of light travelling parallel to the principal axis of a concave mirror is incident on a concave mirror, the reflected beam passes through its principal focus.

When a light ray is incident oblikely on one face of rectangular glass slab, the emergent ray will be parallel to the incident ray and shifted sideward slightly.

Irrespective of the position of an object both convex mirror and plane mirror form virtual and erect images. Of course image formed by a plane mirror is of same size as the object but image formed by convex mirror is always diminished one.

The laws of reflection hold good for light reflected from any smooth surface irrespective of their shapes.

A concave mirror forms a real and inverted image larger than the object size when object is situated between principal focus (F) and centre of curvature (C) of the mirror

When source of light is placed very near to the focus of the reflector which are concave in shape, the reflected light becomes parallel to the principal axis.

When a linear object is placed at a distance equal to focal length of a convex mirror then its virtual image is form ed behind the mirror at a distance f/2 
As per sign convention u = - f and focal length o f convex mirror is + ve, hence from mirror formula we have 
  or   or 

Convex mirror has a wide field of view as it forms virtual, erect and diminished image. Hence, fall length of image of distance tall building can definitely be seen by using it.

As per the new Cartesian sign convention followed focal length of a concave mirror as well as of a concave lens is taken with negative sign.

• Convex mirror is used as rear view mirror and alway forms virtual, erect and diminished image.
• So, magnification produced by a rear view mirror is less than one.

• For a convex mirror irrespective of the position of object the image formed is virtual, erect and diminished one.
• Moreover, the image is always situated between pole and principal focus of the mirror.

Positive sign with power and focal length indicates that the given lens is convex.

Here u = - 15 cm and v = - 30 cm, hence

From figure, it is clear that parallel rays converge at a point and emerges from face B. So convex lens would be possible inside the box.

As the incident light ray is coming parallel to the principal axis of given concave mirror, the reflected ray must pass through the principal focus of mirror.

Figure shows that emergent ray are parallel to the incedent ray and shifted side ward slightly. This can be done by the rectangular glass slab only.

• When an object is placed at infinity, a parallel beam of light is incident on the mirror/lens.
• For all types of mirrors and lenses the beam will get focussed at the principal focus of mirror/lens and a highly diminished, point size image is formed there.

In medium B, light ray bends away from the normal. It indicates that medium B is optically rarer than medium A. Hence speed of light in medium B is more than that in medium A. Now, refractive index
μ_b/μ_a  < 1