Real and virtual images

Question 1

What do the images produced by a lens depend on?

Answer 1

the type of lens being used and the position of the object with respect to the lens and focal point

Question 2

When can an object be said to be ‘at infinity’?

Answer 2

when the distance from the lens is much greater than the focal length of the lens

Question 3

What does moving the image closer to a converging lens do?

Answer 3

magnifies it

it remains real and upside down

Question 4

When are the object and image of a converging lens the same size?

Answer 4

when at twice the focal length (2F)

Question 5

When is a virtual image formed by a converging lens?

Answer 5

when the object is between the focal point and the lens

Question 6

What three properties are used to describe an image?

Answer 6

upright or inverted

reduced/diminished or magnified

real or virtual

Question 7

upright or inverted

Answer 7

whether the image is the same way up, or upside down

Question 8

reduced/diminished or magnified

Answer 8

bigger or smaller than the object

Question 9

real image

Answer 9

An image that is formed where the rays of light are focused

it is formed on the other side of the lens and can be projected onto a screen

Question 10

virtual image

Answer 10

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

it is formed on the same side of the lens

Question 11

How do you draw a virtual image?

Answer 11

trace the refracted rays back to the point they intersect on the other side of the lens

Question 12

Where are convex lenses used and why?

Answer 12

cameras and eyes

projectors contain convex lenses
an object between one and two focal lengths has an image that is:
-inverted 
-magnified
-real

film is loaded upside down to fix this

Question 13

What type of lense does a magnifying glass use?

Answer 13

convex lens

when the object is before the focal point the image is:

• upright
• magnified
• virtual

Question 14

Where are concave lenses used and why?

Answer 14

peep holes in doors

the lens forms an image that is upright, virtual, and diminished

Question 15

State what type of image is formed by:

a) the human eye [1]
b) a magnifying glass [1]

Answer 15

a) a real image
reduced and inverted

b) a virtual image
magnified and upright

Question 16

State what type of image is produced on a screen at the cinema [1]

Answer 16

real image

inverted and magnified

Question 17

Explain why real images cannot be produced by converging lenses when the object being viewed is closer to the lens than a distance equal to the focal length of the lens [3]

Answer 17

light rays need to pass through the lens and be brought to a focus on the other side of the lens to form a real image

when the object is closer to the lens than the focal point, the rays are refracted so that they are non-parallel and diverge

they cannot be brought to a focus at a point so a real image cannot be formed

Question 18

What is the focal length of a lens?

Answer 18

distance between focal point and the middle of the lens