The behaviour of light

Question 1

what is specular reflection?

Answer 1

Reflection in which light travelling towards a surface in one direction is all reflected in a single direction.

Question 2

where does specular refection occur?

Answer 2

-a flat mirror

Question 3

define what is meant by a ‘virtual image’:

Answer 3

An image from which rays of light appear to come but do not do so in reality

Question 4

define ‘diffuse reflection’

Answer 4

When light is reflected off a surface and is scattered in different directions.

Question 5

where does diffuse reflection occur?

Answer 5

on rough surfaces

Question 6

why does diffuse reflection result in a distorted image? (2)

Answer 6

• each individual reflection still obeys the law of reflection
• the different parts of the rough surface are at different angles.

Question 7

what is refraction?

Answer 7

the change in direction of a wave at a boundary of two materials with different densities

Question 8

what happens when a ray enters a denser materials? (2)

-and vice versa

Answer 8

• slows down
• bends towards the normal

-speeds up and bends away from the normal

Question 9

why would it not be possible for refraction to take place if the refracted ray exceeds 90 degrees? (3)

Answer 9

• a ray leaving a more dense medium would be expected to bend away from the normal as it emerges
• however if this would bring the ray out at more than 90° from the normal, the refraction is not possible.
• the ray is reflected inside the more dense medium, following the law of reflection.

Question 10

define ‘critical angle’

Answer 10

The minimum angle at which total internal reflection takes place.

Question 11

define ‘total internal reflection’

Answer 11

Complete reflection of a light ray reaching a boundary greater than the critical angle.

Question 12

what is the angle of incidence called in the instance of TIR?

Answer 12

-the angle of incidence when the ray changes from just refracting to TIR is called the critical angle.

Question 13

what does TIR allow light to be? (in reference to optical fibres)

Answer 13

contained and guided along very thin fibres.

Question 14

uses of optical fibres: (3)

Answer 14

• fibre broadband internet sends computer information coded as pulses of light along underground optical fibres
• doctors can look at the inside of their patients using an endoscope ( a long tube which guides light into the patient and then guides the reflected light back out to give an image)
• decorations ( like some artificial Christmas trees, carry coloured light to different parts of the decoration and let it shine out in different directions)

Question 15

what do different types of glass have?

-what does this cause?

Answer 15

• slightly different densities.

- slight variations in the speed when light travels through the different types of glass

Question 16

why is making optical fibre’s structures of different types of glass beneficial? (2)

Answer 16

• the light can be made to refract slightly as it travels along the fibre.
• this can control the timing of light pulses in the fibre and improves the quality of signal transmissions.

Question 17

describe the pattern in frequency and wavelength in the visible light spectrum as you go down:

Answer 17

increasing frequency and decreasing wavelength

Question 18

what happens when waves are absorbed at the boundary between two different materials?

-what will this usually result in?

Answer 18

• the energy of the wave is transferred to the particles in the surface.
• an increase in the internal energy of the particles.

Question 19

what happens when white light shines on an opaque object and what can we detect? (2)

Answer 19

• some wavelengths (or colours of light) are absorbed and are not detected by our eyes
• other wavelengths are reflected, and these are detected by our eyes.

Question 20

what happens when waves are transmitted at the boundary of two different materials?

Answer 20

the wave continues through the material

Question 21

do translucent materials transmit light?

Answer 21

they transmit some light but are not completely clear

Question 22

what happens when white light is absorbed through a colour filter?

Answer 22

all colours are absorbed except for the colour of the filter

Question 23

how does an object appear to be black?

Answer 23

if it absorbs all the wavelengths of visible light