Forming Images

In this worksheet, students will describe how lenses work, and also look at focal points and periscopes.

Key stage:  KS 3

Curriculum topic:   Physics: Waves

Curriculum subtopic:   Light Waves

Difficulty level:

QUESTION 1 of 10

Lenses use the principle of refraction of light when it enters a different medium; for example, from air to glass. Magnifying glasses are lenses and they make things look bigger. They are convex lenses.

Convex lenses gather the rays of light at a certain point: the focal point. This way, they make the object look bigger, sharper and brighter. They are useful for long sighted people, who cannot focus on objects close to them. They are also used in cameras and telescopes. The diagram above shows a convex lens.

Concave lenses (see diagram below), on the other hand, scatter the light rays (spread them apart), creating a clearer image of objects that are far. They are good for short sighted people.

Periscopes are made using the principle of double reflection of light. They are used in submarines to look above the surface of water by using two mirrors, off which light is reflected. The picture and diagram below show how this works.

What principle is used to make a lens to correct eyesight?

In the answer box below, write the word which completes this sentence:

Convex lenses are used by ______ sighted people.

In the answer box below, write the word which completes this sentence:

Concave lenses are used by ________ sighted people.

What is the name of the point where all light rays gather after entering a convex lens?

Is the following statement true or false?

A magnifying glass is a concave lens.

true

false

Select the most suitable word from the list below to complete this sentence:

Periscopes are used in __________.

aeroplanes

ships

cars

submarines

Why are persicopes used in these circumstances?

To view above the surface of water.

To see what is beneath them.

To see round corners.

What phenomenon takes place inside a periscope?

dispersion

reflection

refraction

How many mirrors does a persicope have?

1

2

3

What do concave lenses do?

They help short-sighted people to focus better on long distanced objects.

They help long-sighted people focus better on long distanced objects.

They help in submarines to see above the water surface.

• Question 1

What principle is used to make a lens to correct eyesight?

refraction
refraction of light
EDDIE SAYS
Refraction is the phenomenon where light changes direction when it enters a different medium due to varying densities of the mediums. This can be used to make objects look bigger.
• Question 2

In the answer box below, write the word which completes this sentence:

Convex lenses are used by ______ sighted people.

long
EDDIE SAYS
Long-sighted people can see far objects clearly but cannot focus properly on objects near to them.
• Question 3

In the answer box below, write the word which completes this sentence:

Concave lenses are used by ________ sighted people.

short
EDDIE SAYS
Short-sighted people cannot see far objects clearly but can focus properly on objects near to them.
• Question 4

What is the name of the point where all light rays gather after entering a convex lens?

focal
focal point
the focal point
EDDIE SAYS
Light rays are gathered at the focal point by a convex lens.
• Question 5

Is the following statement true or false?

A magnifying glass is a concave lens.

false
EDDIE SAYS
Magnifying glasses make objects appear bigger so they are convex lenses.
• Question 6

Select the most suitable word from the list below to complete this sentence:

Periscopes are used in __________.

submarines
EDDIE SAYS
Periscopes are used in submarines.
• Question 7

Why are persicopes used in these circumstances?

To view above the surface of water.
EDDIE SAYS
Periscopes help the submariners to see above the surface of the water.
• Question 8

What phenomenon takes place inside a periscope?

reflection
EDDIE SAYS
A double reflection of light rays is used to make a persicope.
• Question 9

How many mirrors does a persicope have?

2
EDDIE SAYS
Periscopes use two mirrors, off which light is reflected.
• Question 10

What do concave lenses do?

They help short-sighted people to focus better on long distanced objects.
EDDIE SAYS
Concave lenses are used by short-sighted people to focus better on long-distanced objects.
---- OR ----

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