Physics Form Four Chapter 5 - Light

REFLECTION

•Reflection is the change in direction of a wavefront at an interface so that the wavefront returns into the medium from which it originated

The Law of Reflection

•The law of reflection states that for specular reflection the angle at which the wave is incident on the surface equals to the angle at which it is reflected .

Applications of Reflection of Light

• Periscope

- A mirror periscope is used to view objects in an elevated position from behind an obstruction.

- In its simplest form, it consists of a tube with mirrors at each end set parallel to each other at 45° so that the angle of incidence is 45°.

- More complex periscopes, using prism instead of mirrors, and providing magnification, operate on submarines.

Mirror Periscope

Prism Periscope

• Kaleidoscope

- A kaleidoscope is a tube of mirrors containing loose, coloured objects.

- The viewer looks in one end and light enters the other end, reflecting off the mirrors.

- Kaleidoscopes operate on the principle of multiple reflection, where several mirrors are attached together. Typically there are two rectangular lengthwise mirrors.

- Setting of the mirrors at 45° creates eight duplicate images of the objects, 6 at 60° and 4 at 90°.

- As the tube is rotated, the tumbling of the coloured objects presents the viewer with varying colour and patterns.

- Any arbitrary pattern of objects shows up as a beautiful symmetric pattern because of the reflections in the mirrors.

Kaleidoscope image

Kaleidoscope image

Kaleidoscope image

Applications of Reflection of Light

(Utilising concave & convex mirror)

Concave Mirror

• The images formed by a concave mirror depends on the position of the object.

• For a real object very far away from the mirror, the real image is formed at the focus.

• For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object.

• For a real object at C, the real image is formed at C. The image is inverted and the same size as the object.

• For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object.

• For a real object at f, no image is formed. The reflected rays are parallel and never converge.

• For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object. 

• Reflector

- a reflector is an improvised or specialised reflective surface used to redirect light towards a given subject or scene.

- The light bulb is fixed in position at the focal point of the concave mirror to produce a beam of parallel light rays so that the light rays will maintain a uniform intensity for a greater distance.

How a reflector works

Path of light on a reflector

Reflector

Car headlight

Board reflector

Reflector umbrella used in photography

• Magnifying Mirror

- Concave mirror in magnifying mirror magnifies the images so that a person can have a closer look on something.

- The images produced are upright.

Magnifying Mirror

Convex Mirror

• The image formed by a convex mirror is always behind the mirror, virtual, upright and diminished.

• Rear-view mirror

- A rear-view mirror is designed to give drivers a wide-angle view and allow them to see rearward through the vehicle's rear windscreen.

- Rear view mirrors are made out of a mirror that is a wedge of glass instead of two parallel planes of glass.

- During daytime viewing, the rear view mirror is set so that the reflection is from the back, silvered part of the mirror.

- At night, the mirror is tilted so that the reflection of the headlights behind you only hit the front glass surface of the mirror and reflects from it. Since this surface is only 5% reflective, the glare is significantly reduced. - If you look at the ceiling while someone else is driving using the night setting of the mirror at night, you see a bright reflection from the car behind you.

Rear-view mirror

Side mirror

• Other examples include wide-angle view mirrors in shopping complexes and safety mirrors at sharp corners on the road.

Thank You

Presented By

LU CHI KIAN KISHENDRAN

LIM WEE ZHENG NEHRU