Light

Question 1

Why is reflection clear on smooth surfaces

Answer 1

The parallel incident rays are reflected in same direction and reflected rays remain parallel to one another, all rays have same angles of incidence and reflection, laws of reflection apply for each individual ray

Question 2

Why is there diffused reflection on rough surfaces

Answer 2

Parallel incident rays are reflected in different directions as normal at different points on surface are not parallel to one another, angles of _ and _ of one ray different from that of other rays, laws of reflection apply for each individual ray

Question 3

5 characteristics of image formed in plane mirror

Answer 3

Image is same size, upright, virtual, laterally inverted, perpendicular distance of image from mirror is equal to perpendicular distance of object from the mirror

Question 4

What happens to speed and direction of bending of light when light travels into optically denser medium

Answer 4

Speed of light decreases and light bends towards the normal

Question 5

Formula for refractive index

Answer 5

n = c/v, where c is speed of light in vacuum and v is speed of light in medium

Question 6

What is speed of light in a vacuum

Answer 6

3.0 * 10^8 m/s

Question 7

What are laws of reflection

Answer 7

• Incident ray, reflected ray and normal at point of incidence lie in the same plane.
• Angle of incidence is equal to angle of reflection

Question 8

What are laws of refraction

Answer 8

• Incident ray, refracted ray and normal at point of incidence lie in the same plane.
• (Snell’s Law) for two given media, ratio of sine of angle of incidence to sine of angle of refraction is a constant

Question 9

State the equation of Snell’s Law
(Finding refractive index or angle of refraction/incidence)

Answer 9

n1sin x1 = n2 sinx2

Question 10

How to calculate critical angle for light travelling from medium into air

Answer 10

n(medium) = 1/sin c

Question 11

What are conditions for total internal reflection

Answer 11

• Light travels from optically denser to optically less dense medium
• Angle of incidence in optically denser medium is larger than critical angle

Question 12

Why are glass prisms better light reflectors than mirrors

Answer 12

They do not have a silver surface that can wear off and cannot produce multiple reflections

Question 13

Why are optical fibres used over copper wires in telecommunications

Answer 13

Data transfer rate is faster, less signal loss, wires are lighter and cheaper, more information over long distances, immune to electromagnetic interference

Question 14

Advantages of using optical fibres in medicine

Answer 14

Thin and light, kept small for minimally invasive examination.
Flexible

Question 15

Characteristics, location of image and uses of converging lens when object is at infinity

Answer 15

Characteristics: Real, inverted, diminished
Location of I: Image at F, opposite side of object
Uses: Telescope

Question 16

Characteristics, location of image and uses of converging lens when object is slightly further than 2F

Answer 16

Characteristics: Real, inverted, diminished
Location of I: f<v<2f opposite side of lens
Uses: Camera/eye

Question 17

Characteristics, location of image and uses of converging lens when object is at 2F

Answer 17

Characteristics: Real, inverted, same size
Location of I: v = 2F, opposite side of lens
Uses: Photocopier

Question 18

Characteristics, location of image and uses of converging lens when object is between F and 2F

Answer 18

Characteristics: Real, inverted, magnified
Location of I: v >2F, opposite side of lens
Uses: projector, photograph enlarger

Question 19

Characteristics, location of image and uses of converging lens when object is at F

Answer 19

Characteristics: Upright, virtual, magnified
Location of I: image at infinity and same side of lens
Uses: Produce parallel beam of light –> spotlight

Question 20

Characteristics, location of image and uses of converging lens when object is before F

Answer 20

Characteristics: upright, virtual, magnified
Location of I: image behind object on same side of lens
Uses: magnifying glass

Question 21

The refractive index for blue light is greater than that of red light. Explain the effect of this difference in refractive index has on focal length

Answer 21

Blue light has a shorter focal length. For a higher refractive index of blue light, the speed of blue light in light is lower, causing it to bend more towards the normal. This causes blue light to converge over a shorter distance

Question 22

For an object <F, what happens when it is moved closer to the lens

Answer 22

Image produced is closer to the lens and image will decrease in size

Question 23

How to tell if image produced is virtual

Answer 23

Image is on same side of lens as object and is upright