Light

Question 1

What is the speed of light?

Answer 1

3 x 10⁸ m/s

Question 2

What are the properties of a image from a plane mirror? (4)

Answer 2

• virtual
• same size
• laterally inverted
• same distance from mirror

Question 3

What is an angle of incidence?

Answer 3

The angle between the incident ray and the normal

Question 4

What is an angle of reflection?

Answer 4

The angle between the reflected ray and the normal

Question 5

What is the relationship between angle of incidence and angle of reflection?

Answer 5

Both are equal in size

Question 6

How does refraction from air to glass work?

Answer 6

Slows down and bends light towards the normal

Question 7

How does refraction from glass to air work?

Answer 7

Speeds up and bends light away from the normal

Question 8

How does refraction relate to change of speed?

Answer 8

The greater the refraction, the greater the change of speed

Question 9

What is dispersion? (2)

Answer 9

• Separation of white light into a spectrum of colours.
• Due to the fact different colours of light travel at different speeds and take different paths

Question 10

What are the colours of the colour spectrum?

Answer 10

Red
Orange
Yellow
Green
Blue
Indigo
Violet

Question 11

What happens through light dispersion in a prism?

Answer 11

Red slows down the least so is refracted the least,

while violet slows down the most so is refracted the most

Question 12

What are the types of lenses?

Answer 12

Convex (converging)

And

Concave (diverging)

Question 13

What are the two pneumonics for mediums for refraction?

Answer 13

Less dense
Towards normal
More dense

More dense
Away from normal
Less dense

(In relation to the normal)

Question 14

Where are the incident and reflected angles measured from?

Answer 14

The normal (and incident/reflected rays)

Question 15

What are the two pneumonics for speed of waves after refraction?

Answer 15

Fast
Towards normal
Slow

Slow
Away from normal
Fast

Question 16

in the equation V = fw (w should be lambda), what is the relationship between frequency and wavelength? (2)

Answer 16

• directly proportional, as one increases the other increases
• goes through the origin

Question 17

Define Critical angle

Answer 17

The angle of incidence that results in a 90° angle of refraction

(not visible - along the semi circular glass block)

Question 18

What is Total Internal Reflection (T.I.R)? (2)

Answer 18

• The complete reflection of light
• back into its original material

Question 19

When does total internal reflection occur?

Answer 19

• When the angle of incidence is larger than the critical angle
• when moving from a more dense to less dense medium

Question 20

What happens when a ray of light enters a medium at 90º?

Answer 20

There is no change in direction (unidirectional)

Question 21

In a biconcave lens, where does light appear to come from?

Answer 21

The focal point

Question 22

In a biconvex lens, where does light travel to?

Answer 22

Light converges at the focal point

Question 23

What does SSDM stand for

Answer 23

Short
Sight
Diverging
Myopia

Question 24

What does HLSC stand for

Answer 24

Hyperopia
Long
Sight
Converging

Question 25

What does **LXC** stand for

Answer 25

**L**ens Conve**x** **C**onverging

Question 26

What does **LED** stand for

Answer 26

**L**ens Concav**E** **D**iverging

Question 27

Why does **short sight** occur? (**2**)

Answer 27

- short sight usually occurs when the eyes **grow slightly too long** - so that light **doesn’t focus** on the light-sensitive tissue (**retina**) at the back of the eye properly

Question 28

What is the effect of **short sight** (**2**)

Answer 28

- the light rays **focus just in front of the retina**, - resulting in **distant objects** appearing **blurred**

Question 29

What form of **lens** is used to **correct short sight**?

Answer 29

A **diverging** (concave) lens v | ^.

Question 30

What form of **lens** is used to **correct long sight**?

Answer 30

A **converging** (convex) lens ^. | V

Question 31

Why does **long sight** occur? (**3**)

Answer 31

- long sight usually occurs when the **eyeball is too short** - or the **lens cannot** be made **thick enough** - to focus the light rays **on the retina**

Question 32

What is the effect of **long sight** (**2**)

Answer 32

- the light rays would focus **behind the retina** - so that **nearby objects** appear **blurred**

Question 33

What are the **properties of convex lenses**? (**3**)

Answer 33

- **D**iminished - **R**eal image - **I**nverted

Question 34

What are the **properties of concave lenses**? (**3**)

Answer 34

- **E**rect - **V**irtual image - **D**iminished

Question 35

What is the **straight travel of light** called?

Answer 35

The principal of **linear wave propegation**

Question 36

What is the **principal focus/focal point**?

Answer 36

- The **focus** of a lens - where light rays **appear** - to **converge or diverge** from

Question 37

What is a **real image**?

Answer 37

An image that can be **projected onto a screen**

Question 38

What is a **virtual image**? (**2**)

Answer 38

- An image that **appears** to come from **the object** - **cannot** be **projected onto** a **screen**

Question 39

Where do you find the **image** from a **concave** (*diverging*) lens **on a ray diagram**?

Answer 39

**Trace the rays** on the **left** of the diagram **Where they meet** is where the **image** comes from

Question 40

Where do you find the **image** from a **convex** (*converging*) lens **on a ray diagram**?

Answer 40

**Two lines** from *the **top** of an object*: - One **through the origin** - One **through the focal point** *after hitting the y axis* - *where they meet is the* **image**

Question 41

Explain what happens when the **angle of Incidence** is: 1. **less** than the **critical angle** 2. **equal** to the **critical angle** 3. **more** than the **critical angle**

Answer 41

1. Refraction occurs, weak reflection 2. **90º angle of refraction** 3. Total internal reflection - no refraction

Question 42

After **dispersion in a prism**, what **colour** is **top** and what **colour** is **bottom**?

Answer 42

- Red on top (least refraction) - Violet on bottom (most refraction)

Question 43

Name an **application** of **converging (convex) lenses**

Answer 43

- Projectors - Magnifying glasses

Question 44

Name an **application** of **diverging (concave) lenses**

Answer 44

Telescopes

Question 45

What are **optic fibres**? How do they work?

Answer 45

- Lengths of *solid glass core* with an **outer plastic sheath** - **total internal reflection** at the *surface* of the *glass core*

Question 46

What are **optic fibres** used for in **medicine**?

Answer 46

Endoscopes - allow doctors to see inside a patient’s body

Question 47

What are optical fibres used for? (**2**)

Answer 47

- endoscopes - carrying video and telephone signals over long distances

Question 48

What is the name of the **centre point** of a **lens**?

Answer 48

The **optical centre**