Optics

Question 1

What does a convex/converging lens do

Answer 1

It focuses parallel light. The focal length of a convex lens is the distance from the middle of the lens to the point where the light is focused

Question 2

What is a concave/diverging lens

Answer 2

It spreads out parallel light. The light appears to come from a point. The focal length is from the middle of the lens to where the light appears to come from

Question 3

How to find the focal length of a concave lens:

Answer 3

1. get the lens and a flat white surface
2. Find a distant light source and focus an image on the screen
3. Move the screen and lens until the image is in focus
4. Measure the distance from the lens to the screen to give the focal length

Question 4

If the focal length is negative what lens is it

Answer 4

Concave / diverging

Question 5

In a camera what lens is used to produce an image on a film

Answer 5

Converging

Question 6

When an object is 5 m away, the image is:

Answer 6

• smaller
• inverted
• real

Question 7

When the object is 25cm, the image is

Answer 7

• larger
• upright
• virtual

Question 8

When the object is 75cm away the image is

Answer 8

• real
• inverted
• smaller

Question 9

What does real mean

Answer 9

The image can be projected onto a screen. The image distance will be positive and the opposite side to the object

Question 10

What does virtual mean

Answer 10

The image cannot be projected onto a screen. The image appears to be where the Ray is coming from. The image distance will be negative and the same side as the object

Question 11

What do refracting telescopes do

Answer 11

Combine lenses to form an image of a distant object

Question 12

How does a telescope work

Answer 12

1. The telescope is aimed at an object and light is reflected off the object
2. The light is refracted by the objective lens. The lens is convex so it focuses the light. The lens is large so a lot of light can enter it
3. The light is refracted and magnified by the eye piece lens which is used by an observer to view the image

Question 13

What are issues with making a telescope

Answer 13

• making a good lens smooth and clear
• making them large
• weight

Question 14

A simple refracting telescope uses

Answer 14

• an objective lens that is convex

* a lens as an eyepiece that is convex

Question 15

What does the image look like through a refracting telescope

Answer 15

• vertically and horizontally inverted (upside down)
• real
• larger

Question 16

How does the image look through a reflecting telescope

Answer 16

• real
• larger
• vertically and horizontally inverted

Question 17

What do reflecting telescopes do

Answer 17

Combine lenses and mirrors to form an image of a distant object

Question 18

What does a simple reflecting telescope use

Answer 18

• primary concave mirror that reflects and focuses the light
• secondary plane mirror that changes the direction of the light by 90 degrees
• eyepiece is always a convex lens to magnify the image

Question 19

Issues with making a reflecting telescope

Answer 19

• making a smooth mirror
• making a good lens, smooth and clear
• making them large

Question 20

Benefits and disadvantages of reflecting and refracting telescopes

Answer 20

• refracting combine lenses to form an image of a distant object
• reflecting combine mirrors and lenses to form an image of a distant object
• refracting telescopes have a convex lens that is large to focus the light, making a lot of light enter
• disadvantages of refractive include it is hard to make the lens large, and they are heavy
• reflective telescopes have brighter images.
• it is easier to make larger mirrors
• refracting are easy to build, but have a dimmer light as light reflects of the lens

Question 21

How does the eye work

Answer 21

1. Light passes through the cornea
2. The pupil controls the amount of light let in
3. The lens refracts the light. The ciliary muscle controls the shape of the lens
4. The refracted light forms an image on the back part of the eye called the retina
5. The light is converted into electrical impulses and is sent along the optic nerve to the brain
6. You ‘see’ the object

Question 22

What does the ciliary muscle do

Answer 22

Change the size of the lens. This will bring into focus objects that are different distances away

Question 23

What is short sightedness

Answer 23

It occurs when the image forms before it reaches the retina. Lenses can be used to refract the light in the opposite direction before it reaches the eye.

Question 24

What lenses are used to correct short sightedness

Answer 24

Concave lenses. They have a negative power

Question 25

What are used to correct long sightedness

Answer 25

Convex lenses. They have a positive power

Question 26

What is long sightedness

Answer 26

It occurs when the image forms after it reaches the retina. It is when the eyeball is too short

Question 27

What is the far point

Answer 27

It is the furthest an object can be from the eye without it appearing blurred. The human far point is infinity.

Question 28

What is the human near point

Answer 28

Closest an object can be from the eye without being blurred. The human near point is 25cm

Question 29

Where can lenses be found

Answer 29

• eyes
• microscopes
• telescopes
• glasses
• cameras