Answer: Option A. ->
:

Concept : 1 Mark
Calculation : 3 Marks
Result : 1 Mark
In the case of a plane mirror, the distance between the object and the mirror is same as the distance between the image and the mirror.

Given,

Distance between the mirror and John's image = 4 m

Distance between mirror and john = 4 m

If John moves 1 m towards the mirror, then distance between mirror and john = 4-1 = 3

Since in plane mirror, the distance between object and mirror is same as that of image and mirror = 3 m

Hence, the distance between John and his image = 3+3 = 6 m

Answer: Option A. ->
:

Lens : 1 Mark
Differences : 4 Marks
Lenses are pieces of transparent material bound by curved surfaces. Lenses are of two types:

(i)Concave and (ii)convex lens

Convex lens:

1) It is thick at the centre and thinner at edges.

2) It is called converging lens.
 

Concave lens:

1) It is thin at the centre and thicker at edges.

2) It is called diverging lens.

Answer: Option D. -> NON
:
D
Image formed by a plane mirror is laterally inverted and therefore the letters get inverted about the vertical axis.A word that is horizontally symmetrical about its centre letter would read the same in a mirror.

Answer: Option C. -> Concave
:
C

Concave mirrors are used in torches used at homes or by dentists.

In a torch, the bulb is placed at the focal point of the concave mirror so the light from the bulb is reflected as a parallel beam. This helps users to specifically see the object, upon which the beam falls.

Answer: Option C. -> $15cm$
:
C

For a convex mirror, the radius of curvature $R$, is twice its focal length $f$.
$R=2f$
$30=2f$
$f=15$

Therefore, the focal length $f=15cm$

Answer: Option A. -> True
:
A
Real images are formed on screen due to the actual intersection/meeting of rays. Virtual images, on the other hand, are result of rays appearing to meet at a point. So, we can obtain a real image on a screen. E.g. The image of the sun obtained on a piece of paper using a concave mirror.

Answer: Option C. -> Indigo
:
C

The letter "I” in "VIBGYOR” represents the colour "indigo”. VIBGYOR stand for violet, indigo, blue, green, yellow, orange and red.

Answer: Option B. -> VIBGYOR
:
B

The colours in the rainbow are labelled as VIBGYOR. 

VIBGYOR stands for violet, indigo, blue, green, yellow, orange, and red.  

Answer: Option D. -> (A)-2, (B)-1, (C)-4, (D)-3
:
D
A plane mirror forms a virtual and erect image. The size of an image is the same as the size of the object.
A convex mirror always forms a virtual, erect and diminished image.
A convex lens can form enlarged images and thus are used in magnifying glass and microscope.
Dentists use a concave mirror to see an enlarged image of the teeth. If an object is placed close to a concave mirror it a forms an erect and enlarged image of the object.

Answer: Option A. -> True
:
A

Yes, a convex lens is the one which is thicker in the middle and thinner at the edges.

Convex lenses are thicker at the middle and therefore the rays of light that pass through the lens are brought closer together (they converge). Hence a convex lens is a converging lens.