(13) Light Flashcards
(D) DEFINE REFLECTION
Reflection is the bouncing back of a wave that strikes the boundary between two media.
(D) State the Laws of Reflection of Light.
- The angle of incidence i is equal to the angle of reflection r.
- The incident ray, reflected ray and normal at the point of incidence all lie on the same plane.
(D) Name 5 characteristics of the image formed due to reflection in a PLANE MIRROR
- Image is virtual
- Laterally inverted
- Image distance is same distance as the object distance
- Image is UPRIGHT
- It is of the same size as the object
(D) Differentiate between a real image and a virtual image (GIVE BOTH DEFINITIONS)
Take into account: how it is formed and whether it can be captured on screen
➡️A real image can be captured on a screen and is formed by the intersection of light rays from the object at the screen
➡️A virtual image cannot be captured on a screen and is formed by the intersection of light rays which APPEAR to come from the IMAGE
(D) DEFINE REFRACTION
Refraction is the bending of light as it passes from one optical medium to another. This bending is due to the change in the speed of light as it passes between the media.
When an object slows down it
A) bends towards the normal
B) bends away from the normal
When an object speeds up it
A) bends towards the normal
B) bends away from the normal
A
B
Applying the general wave equation v=f入,
Velocity ➡️ depends on medium
Frequency ➡️ depends on source
Wavelength ➡️ changes according to v and or itself
When optical density increases,_________
V increases!!
What if light enters 90 degrees to the normal (from glass to air or air to glass)?
Light ray GO STRAIGHT no deviation. But light ray will be slower in optically denser medium in this case glass
(D) State the principle of reversibility of light.
A ray of light will travel along the Same path even if it’s direction of travel is reversed (applies to both refraction and reflection)
(D) state the laws of refraction of light.
➡️the incident ray, refracted ray and the normal all lie on the same plane
➡️for two given media, the ratio of the sine of the angle of incidence and the sine of the angle of refraction are constant.
n= sin i/sin r
(D) define refractive index
Also state the 2 formulae for refractive index, n.
The ratio of the speed of light in a vacuum to the speed of light in that medium
Formula for refractive index:
n= speed of light jn vacuum ➗speed of light in medium
= c/v
OR
n= sin i ➗sin r
= sin larger angle ➗ sin smaller angle
Air refractive index take it as 1!!
OR
n= real depth ➗ apparent depth
OR
n= 1/sin c where c is the critical angle
(one of the mediums must be air)
When is n= sin i ➗ sin r inapplicable?
When i is not measured in air
Always remember
sin larger angle ➗sin smaller angle !!
For the straw in water question, where to put the dot of the “fake” perceived straw?
Anywhere higher than straw. Need not measure UNLESS question states how much higher it is
(D) Define critical angle
The angle of incidence in an optically denser medium for which the angle of reflection in the optically less dense medium is 90°
(D) define total internal reflection.
The complete reflection of a light ray inside optically denser medium at its boundary with an optically less dense medium
State the conditions of total internal reflection. For it to occur
➡️Light ray should be inside the optically denser medium heading towards the boundary with an optically less dense medium
➡️ angle of incidence, i , in the optically denser medium should be greater than the critical angle, c, of that medium
Structure of optical fiber
Glass of Low refractive index outside with glass of high refractive index inside. This allows for TIR to occur many times
(D) state the advantages of optical fibres
- Can carry much more information than cooler wires due to TIR
- Experience less signal loss
- Lighter than copper wires
- Because Cheaper to manufacture than copper wires
When will images formed in a converging lens be virtual, upright and magnified?
When the object is at F or in front of F
When will images formed in a diverging lens be of the same size?
When object is at 2F
When will objects formed in a converging lens be inverted real and diminished?
When image is distant or slightly beyond 2F
When will the image be the same side as the object with converging lens
When object is at F or in front of F
(D) define principal axis
Horizontal line passing through optical centre C to of the lens
(D) define optical centre
midpoint between the surfaces of the lens on its principal axis
(D) define focal point
Point where all the rays parallel to the principal axis converge after refraction by the lens
(D) Define focal plane
Plane which passes through focal point and perpendicular to the principal axis
(D) define focal length
Distance between the optical centre and focal point/ principal focus of the lens
All light rays drawn from the same point and passed through the converging lens will go back to the same point of the image formed (ie arrow head to arrow head)
YES!!
