## June 22, 2011

### 4.2 The Different Types of Energy

Describe energy transfers involving  the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

The Nine types of energy that we should know are: (as mentioned in the syllabus statement)

• Thermal (heat) energy
• Light energy
• Electrical energy
• Sound energy
• Kinetic energy
• Chemical energy
• Nuclear energy
• Elastic Potential energy
• Gravitational Potential energy

Digital signals are capable of carrying more information than analogue signals because digital signals make use of the bandwidth more efficiently by closely approximating the original analogue signal...

## June 11, 2011

### Exam Correction list & things I need to remember

.... the majority of the time I simply didn't read the question properly or didn't think about my answer enough... but the places where i genuinly screwed up are....

1. Things that affect the size of the current:
Resistors
Battery/power supply
2. In physics write things to the same d.p or s.g.f as in the question... and ignore the years of intense training your math teacher has put you through to make you write everything to 3s.g.f and degree's to 1 d.p.

DONE!....Well that was easy.

## June 6, 2011

### 3.24 Advantages of Digital signals

Describe the advantages of using digital signals rather than analogue signals.

When a signal is transmitted from one place to another it gains noise, noise is where the signal becomes distorted during transmission. In analogue signals distorted signals can not be regenerated into their original form because it is impossible to calculate what it originally looked like. But because digital signals only have a value of 1 or 0 if they were distorted it is quite obvious as to there previous value... as shown in the below diagram.

### 3.23 Analogue and Digital

Understand the difference between analogue and digital signals.

An Analogue signal is continuous in time and value, this means that it can have any value at any one time.

On the other hand Digital signals are discrete and only have values of either 1 or 0.

## June 2, 2011

### 3.22 Critical angle and refractive index

Recall and use the relationship between critical angle and refractive index:

$\textup{sin}\, c = \frac{1}{n}$

c is the critical angle (in degrees,°)
n is Refractive index (no units)

Examples:
What is the refractive index of glass that has a critical angle of 42°?

$\textup{sin}\, c = \frac{1}{n}$

What is the critical angle for diamond? (Refractive index of diamond = 2.4)

$\textup{sin}\, c = \frac{1}{n}$

$\textup{sin}^{-1} \left (\frac{1}{2.4} \right ) = c$

$c = 24.6243...$

### 3.21 Critical angle

Recall the meaning of critical angle $c$

The Critical angle is the smallest angle of incidence for which Total Internal Reflection occurs. So if the angle of incidence is larger than the critical angle total internal reflection will occur.

### 3.20 Optical fibres

Describe the role of total internal reflection in transmitting information along optical fibre and in prisms.

because of Total internal reflection when light is sent down an optical fibre it will reflect off of the inside surface of the fibre until it reaches the end, this is a great way to transmit information at high speed because the waves travel at almost the speed of light; 300,000,000m/s; it travels slightly slower than the speed of light because of the refractive index of the optical fibre (it only travels at 300,000,000m/s in a vacuum

### 3.19 calculating the refractive index

Describe an experiment to determine the refractive index of glass, using a glass block.

Using the formula for refractive index isn't too hard once you've tried it a few times...

taking the glass block from the worksheet in the previous post...
the angle of incidence is 40°
and the angle of refraction is 25°
so:
$n = \frac{\textup{sin}\, i}{\textup{sin}\, r}$

$n = \frac{\textup{sin}\, 40}{\textup{sin}\, 25}$

$n = \frac{0.6427...}{0.4226...}$

$n = 1.5209...$

$n \approx 1.52$

so the refractive index of a perspex block is roughly 1.52 (but remember there aren't any units)

### 3.18 Refractive Index

Recall and use the relationship between refractive index, angle of incidence and angle of refraction...

Refractive index is The ratio of the velocity of light in a vacuum to its velocity in a specified medium or simply put: how much the light is bent/refracted when it enters a specific medium.

to calculate the refractive index we use the formula:

$n = \frac{\textup{sin}\, i}{\textup{sin}\, r}$

n is the refractive index (this is purely a number and has no units)
i is the angle of incidence (in degrees °)
r is the angle of refraction (in degrees,
°)