Science Olympiad Test: Light- 2 - Class 10 MCQ

Step 1: Determine if the focal length is positive or negative.
Step 2: Determine if the image distance is positive or negative.
Step 3: Use the equation 

 to calculate the distance of the object from the lens.

A convex mirror would always produce an erect image, and a concave mirror may produce an inverted or an erect image depending on the position of the object placed.
Thus, independent of the sign convention, the magnification of a convex mirror is always positive, but that of a concave mirror may be both positive or negative.

The plane mirror shows lateral inversion. The left appears right and the right appears left. So if you touch your left ear with your right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with your left hand.

As image of head is bigger, the top portion of magic mirror must be concave. The middle portion appears to be of same size, therefore, middle portion of magic mirror must be plane. As image of his legs appear smaller, the bottom of magic mirror must be convex.

Refractive index for water, mustard oil, glycerine and kerosene are:
μ_w​ = 1.33
μ_m ​= 1.47
μ_g​ = 1.473
μ_k​ = 1.44
Since refractive index of glycerine is highest, ray bends the most in case of glycerine.

When light rays travelling through air enters glass slab, they get refracted and bend towards the normal. Now the direction of refracted ray changes again when it comes out of the glass slab into air. Since the ray of light I know travelling from denser medium to rarer medium, it bends away from the normal.

We know that a convex mirror forms a virtual and smaller image irrespective of position of the object. So, a full length image of a distant tall building can definitely be seen by using a convex mirror.

Convex lens

• A convex lens is a lens with an outward curve.
• The thickness at the centre of a convex lens is more than the thickness at the edges of the lens.
• Convex lenses are converging lenses. They have the ability to converge a parallel beam of light into a point.
• The lens found in the human eye is a prime example of a convex lens.
• Another common example of a convex lens is the magnifying glass that is used to correct Hypermetropia or long-sightedness.

f = – 2 m = – 200 cm

Convex mirrors are used in vehicles for rearview due to their wide field of view. And the convex mirror forms a virtual, erect and diminished image of the object. Therefore, magnification (m) produced by a rearview mirror fitted in vehicles is less than one.

To create a parallel beam of light through which we can see further, the bulb in torches, search lights, and vehicle headlights is placed very close to the focus of the reflector.

The ray of light incident on a concave mirror in a direction parallel to principal axis must pass through focus F on reflection from the mirror.

For a virtual, erect and magnified image, object lie between F and C.
If F = 10 cm, r = F/2 = 5 cm which is OC.