P14 Light

Question 1

what is diffraction

Answer 1

spreading out of waves in a circular motion when they come to a hole in a boundary

Question 2

what is a virtual image

Answer 2

an image formed at a place where light rays appear to come from after they have been reflected or refracted

Question 3

what is a real image

Answer 3

an image that can be projected onto a screen as it is formed by focusing light rays onto the screen

Question 4

what is specular reflection

Answer 4

reflection from a smooth surface- parallel rays are reflected in a single direction (not scattered)

Question 5

what is diffuse reflection

Answer 5

reflection from a rough surface- light is scattered in different directions

Question 6

what is refraction and why does it happen

Answer 6

the change of direction of light and sound waves- happens because they change speed as they cross the boundary between 2 substances with different densities causing them to change direction

Question 7

when does refraction not occur

Answer 7

when light rays hit the normal straight (90) as all of the wave hits the normal at the same time

Question 8

what happens when a wave crosses a boundary into a substance of a higher density

Answer 8

starts to go slower so it bends towards the normal decreasing the angle of refraction

Question 9

what happens when a wave crosses a boundary into a substance of a lower density

Answer 9

wave travels faster so it bends away from normal

Question 10

how is a critical angle formed

Answer 10

when the angle of incidence gets so big that it refracts at 90 to the normal and angle of i becomes critical angle

Question 11

what is total internal reflection

Answer 11

when the angle of incidence is bigger than the critical angle so the ray is reflected

Question 12

what causes a light wave to be refracted

Answer 12

when they travel across a boundary between air and a transparent medium or between 2 transparent media as speed of light changes

Question 13

what happens in optical fibres

Answer 13

total internal reflection

Question 14

how do colour filters work

Answer 14

by absorbing certain wavelengths and transmitting other wavelenghts eg when white light is directed at a red filter, the filter transmits only red light as it absorbs all other parts of the white light spectrum

Question 15

why does white surface reflect light of any wavelength

Answer 15

has no pigments which are chemicals in the surface materials

Question 16

why can you see clearly through a transparent object

Answer 16

they transmit all the incident light that enters the object that then travels through the object. No light is absorbed at the surface

Question 17

why can you see light but not images through tarnslucent objects

Answer 17

the light is scattered or refracted because the material has lots of internal boundaries that changes the rray direction frequently

Question 18

why can’t you see through an opaque object

Answer 18

it absorbs all the light that reaches it . No light travels all the way through it. It is either; reflected, scattered at the surface or absorbed by the object

Question 19

what is the magnification equation

Answer 19

image height/ object height

Question 20

how does a convex lens (converging lens) work

Answer 20

makes parallel rays converge to a focus ( pricipal focus/ focal point) of the lens. Used as a magnifying glass an in a camera to form a clear image of a distant object

Question 21

how does a concave lens (diverging lens) work

Answer 21

makes parallel rays diverge (spread out ). The rays appear to come from the principal focus of the lens. Used to correct short sight

Question 22

what is the focal length of the lens

Answer 22

the distance from the centre of the lens to the principal focus

Question 23

when is a real image formed by a convex lens

Answer 23

when the object is further away than the principal focus

Question 24

when is a virtual image formed by a convex lens

Answer 24

when the object is nearer than the principal focus

Question 25

what lens is in a camera

Answer 25

convex- forms a real image of an object

Question 26

what lens is in a magnifying glass

Answer 26

convex- forms a virtual image of an object