Light

• (a) An image that cannot be obtained on a screen is called virtual.
• (b) Image formed by a convex mirror is always virtual and smaller in size.
• (c) An image formed by a plane mirror is always of the same size as that of the object.
• (d) An image which can be obtained on a screen is called a real image.
• (e) An image formed by a concave lens cannot be obtained on a screen.

• (a) We can obtain an enlarged and erect image by a convex mirror. (False) (It's always diminished).
• (b) A concave lens always forms a virtual image. (True).
• (c) We can obtain a real, enlarged and inverted image by a concave mirror. (True).
• (d) A real image cannot be obtained on a screen. (False).
• (e) A concave mirror always forms a real image. (False) (It can form virtual too).

1. Image is erect (upright).
2. Image is of the same size as the object.
3. Image is at the same distance behind the mirror as the object is in front.
4. Image is laterally inverted (Left appears right).
5. Image is virtual (cannot be caught on screen).

Letters like A, H, I, M, O, T, U, V, W, X, Y appear same because they are vertically symmetrical.

An image that cannot be obtained on a screen is called a virtual image.

Example: Image formed by our face in a plane mirror.

1. Concave lens is thin in middle and thick at edges. Convex lens is thick in middle and thin at edges.
2. Concave lens diverges light. Convex lens converges light.

• Concave Mirror: Used by dentists to see enlarged image of teeth. (Also in car headlights).
• Convex Mirror: Used as side view (rear view) mirrors in vehicles.

Concave mirror can form a real image.

Concave lens always forms a virtual image.

(i) concave lens
(ii) concave mirror
(iii) convex mirror
(iv) plane mirror

Answer: (ii) concave mirror

Initally: dist(image to mirror) = 4m. So dist(David to mirror) = 4m.
Moves 1m towards: New dist(David to mirror) = 4 - 1 = 3m.
New dist(image to mirror) = 3m.
Total dist(David to image) = 3 + 3 = 6 m.
Answer: (iii) 6 m

In a plane mirror, the relative speed of the image with respect to the object is double the speed of the object (or mirror relative to object/image).
Speed = 2 * 2 m/s = 4 m/s.
Answer: (iii) 4 m/s

• Rectilinear Propagation: Light travels in straight lines.
• Reflection: Bouncing back of light from shiny surfaces (Mirrors).
• Plane Mirror Image: Erect, Virtual, Same Size, Laterally Inverted.

• Concave Mirror (Inner surface reflects): Can form Real or Virtual images. Can be Magnified. Converging mirror. Used by Dentists, Headlights.
• Convex Mirror (Outer surface reflects): Always forms Virtual, Erect and Diminished images. Diverging mirror. Used as Side View Mirrors.

• Convex Lens (Thick middle): Converging. Can form Real/Virtual images. Used as Magnifying Glass.
• Concave Lens (Thin middle): Diverging. Always forms Virtual, Erect and Smaller images. Used in Peep holes.

• Dispersion: Splitting of white light into 7 colours (VIBGYOR).
• Rainbow: Natural phenomenon showing dispersion.
• Newton's Disc: Disc with 7 colours appears white when rotated fast (Mixing colours).

• Real Image: Can be obtained on screen. Formed by actual meeting of light rays.
• Virtual Image: Cannot be obtained on screen. Light rays appear to meet.
• Lateral Inversion: Left side appears right and vice versa (e.g. in Plane Mirror).

• Spoons act as mirrors. Inner side: Concave. Outer side: Convex.
• AMBULANCE is written inverted so that it reads correctly in rear view mirrors of cars ahead.
• Convex lens is also called Converging Lens.
• Concave lens is also called Diverging Lens.