Light: Reflection & Refraction - 1 - Class 10 MCQ

If the lower half (or a part) of a mirror is covered with a black paper then a complete image of the object will be formed as before. However, the image will be less bright now.

Here, ∠i = 60°, ∠r = 45°
Using Snell’s law of refraction, refractive index of medium B with respect to medium A.

A full length image of a distant tall building can definitely be seen by using a convex mirror because a convex mirror always forms a virtual, erect and highly diminished image.

The angle of incidence of any light ray passing through the centre of curvature of a spherical mirror is 0°, because a line joining centre of curvature to any point on the mirror is a normal drawn at that point of the mirror.

Given h₀ = +10 mm - + 0.1 cm 
h₂ = - 5 mm = -0 .5 cm
for real image, v = - 30 cm                       

Now magnification,

∴ f = -20 cm

In optics, a real and inverted image formed by a concave mirror has a negative magnification. This is because:

• Real Images are formed on the same side as the object.
• These images are inverted, indicating a negative value for magnification.

As light rays from sun (u = ∞) converge at a point 15 cm in front of a concave mirror, hence focal length of concave mirror f = - 15 cm.
To form an image of exactly same size as that of an object, the object should be placed at the centre of curvature (u = R = 2f) of mirror. Hence, the object should be placed at 30 cm in front of mirror.

To get the real and magnified image for a convex lens, the object is placed in between F and 2F.

A concave mirror forms a virtual, erect and magnified image when an object is placed between pole and focus point of the mirror. As focal length of given concave mirror, hence object must be placed at a distance less than 12 cm i.e., u < 12 cm. Thus, the object may be placed at a distance of 10 cm from the mirror.

• (a) Always virtual, erect, and diminished: Incorrect (Only true when the object is very close to the mirror).

• (b) Always virtual, inverted, and diminished: Incorrect (Concave mirrors never form virtual AND inverted images).

• (c) Sometimes real, inverted, and diminished: Correct (This happens when the object is placed beyond centre).

• (d) Always real, inverted, and magnified: Incorrect (Only true when the object is between Centre and Focus).

Since the image can be real, inverted, and diminished in some cases (object beyond Centre), option (c) is the most accurate.

Answer: (c) Sometimes real, inverted and diminished