Physics Form 5: Chapter 4 - P-N Junction of Semiconductor

A small quantity of electrons on the n-side of the junction are attracted by the "holes" in the p-side. They drift across the junction, and fill available holes. This causes a region across the junction to be depleted in carriers of current (that is, electrons and "holes"). This region is called the DEPLETION LAYER, because it has been depleted in majority carriers. The depletion zone is a few micrometers thick, and, since it has no majority carriers, acts as an insulating barrier.

It is important to realise that when electrons moves from the n-side of the junction to the p-side, the n-side becomes positively charged (since neutral atoms have lost electrons), while the p-side of the junction now becomes negatively charged (since neutral atoms have now acquired negatively charged electrons). A potential difference now exists across the junction. This potential difference is about 0.6 V for silicon, and about 0.2 V for germanium. This is called the BARRIER POTENTIAL.

Physics Form 5: Chapter 4 - The Doping of Semiconductor

An extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping, which alters the electrical properties of the semiconductor. Doping process can improve semiconductor's electrical conductivity. Doping process produces two groups of semiconductor: the negative charge conductor (n-type) and the positive charge conductor (p-type). 

N-type semiconductor

Doped by pentavalent impurities which has 5 valence electrons to produce n-type semiconductors by contributing extra electrons. The addition such as antimony, arsenic or phosphorus contributes free electrons, greatly increasing the conductivity of the intrinsic semiconductor. 

This allows four of the five electrons to bond with its neighbouring silicon atoms leaving one "free electron" to move about when an electrical voltage is applied (electron flow).

P-type semiconductor

Doped by trivalent impurities which has 3 valence electrons to produce p-type semiconductors by producing a "HOLE". The addition such as boron, aluminium or gallium to an intrinsic semiconductor creates deficiencies of valence electrons, called "hole".

As there is a hole an adjoining free electron is attracted to it and will try to move into the hole to fill it. However, the electron filling the hole leaves another hole behind it as it moves. This in turn attracts another electron which in turn creates another hole behind, and so forth giving the appearance that the holes are moving as a positive charge through the crystal structure


Conclusion

Physics Form 5: Chapter 4 - Semiconductor

Semiconductor is a material where its electrical conductivity lie between conductors and insulators. In semiconductors, thermal energy is enough to cause a small number of electrons to escape from the valence band of atom to the higher energy of conduction band, in which they are relatively free to move. The resulting gaps in the valence band are called holes.

Usually, semiconductors are made from semi-metal or called metalloid from the Periodic Table. 

Silicon is the most preferred material for semiconductors because:

• ease of availability
• low cost of processing 
• higher temperature range
• high resistivity than other counterparts 
• low leakage current

Semiconductors are widely use in making diode, transistor and integrated circuit

Physics Form 4: Chapter 5 - Concave Lens Ray Diagrams

Concave lens is a diverging lens. The image form is smaller than the object, virtual and upright. Concave lens always produce images that share these characteristics. The location of the object does not affect the characteristic of the image.

Physics Form 4: Chapter 1 - Vernier Calipers

A vernier caliper can measure to the nearest 0.1 mm or 0.01 cm. The ten divisions of the vernier scale on the vernier caliper are spaced over 0.9 cm of the main scale and the aim is to select the vernier graduation which is nearest to being in line with a main scale graduation. 

• The inner jaws is used to measure inner diameter of the object.
• The outer jaws is used to measure outer diameter of the object.

How to read a vernier caliper:

Reading = main scale + vernier scale

How about this one?

Reading = 1.2 + 0.03

                 = 1.23 cm

Click on the diagram below to play!

Physics Form 4: Chapter 3 - Application of Bernoulli principle (WindSurfing)

 

• The air flow over the sail causes an increase in pressure on the windward side and a decrease on the leeward side
• Area of leeward side has a low pressure because of the high speed of the wind.
• A resultant force acts in the direction of F.
• This resultant force can be resolved into component to the right and left.
• The component to the right can be balanced by the surfer who pulls it to the left.
• Therefore, there exists a resultant force to the front so that the surfer moves to the front.
• Factors affect the resultant force is the strength of the wind and the shape of the sail. 

Physics Form 5: Chapter 3 - Application of Electromagnetic Induction (Torchlight)

Electromagnetic induction is the production of induced current by changing magnetic field. By using kinetic energy of shaking hand, electrical energy is produced to power the flash light through electromagnetic induction.

Kinetic energy ------> Electrical energy

• A powerful permanent magnet such as neodymium magnet is used because of small size with strong magnetic field. The permanent magnet is placed inside a plastic track which allow it to slide up and down.
• The shaking hands move the strong magnet to cut through the copper coils causing electromagnetic induction. 
• The electrical energy produced is stored in a capacitor that can be charged hundreds of thousands times.
• The bulb is an energy efficient ultra bright white LED that can produce a beam of light for several minutes after shaking the moving magnet for 30 seconds.

For more information, click below video

Physics Form 5: Chapter 3 - Application of Electromagnet (Telephone Earpiece)

When you listen to your telephone, the receiver in the earpiece reverses the electrical signals from the telephone wire back into sound that we can hear.

How does a telephone earpiece work?

Click on the diagram below to play!

Physics Form 5: Chapter 1 - Application of Reflection of Sound

Echoes are caused by the reflection of sound. A sound wave will continue to bounce around or reverberate until it has lost all its energy. A wave has some of its energy absorbed by the objects it hits. The rest lost as heat energy.

The phenomenon of the reflection of sound is used to determine the distance between the two objects, for example depth of seabed, depth of cave or width of a valley. The type of sound used must be ultrasound.

Sonar (Sound Navigation and Ranging). Sonar is used to detect underwater objects (corals / fishes) or to determine the depth of the water by means of an echo. Sonar equipment emits a high frequency sound signal which is reflected by the object in the water. The reflected sound wave is received by the sonar receiver. The time taken for the echo to return is used to determine the distance of the object below the water surface. 

Sonar waves of high frequency is used because it possesses more energy, high penetration power and can travel further through water.

Click on the diagram below to play!

Physics Form 4: Chapter 5 - Ray Diagrams of Convex Lens

Ray Diagram Rules for Convex Lens

1. Any incident ray travelling parallel to the principal axis of a convex lens will refract through the lens and travel through the focal point on the opposite side of the lens.
2. Any incident ray travelling through the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.
3. Any incident ray passes through the center of the lens will in affect continue in the same direction that it had when it entered the lens.

Examples of ray diagram with different object distance

Physics Form 5: Chapter 1 - Loudness of Sound

2. Loudness - Amplitude

The loudness of a sound depends on the wave's amplitude.
The louder the sound, the higher the amplitude. So, amplitude is also a way of measuring the energy has.


The higher the energy, the higher the amplitude resulting a louder sound.


The system used to measure the loudness of sounds is the decibel system, given the unit dB.

Range (dB)	Description	Examples
0 - 30	Very Quiet	This is the threshold of human hearing, up to the sound of a quiet whisper.
31 - 50	Quiet	This is an average quiet house, with maybe the sound of a fridge running or someone moving around.
51 - 70	Normal	Regular daily sounds like people talking.
71 - 90	Loud	This is the point where a sound becomes annoying or distracting. Vacuums or a noisy car on a busy street are at these levels.
91 - 110	Very Loud	Most people will try to avoid being in areas this loud. Prolonged exposure can cause permanent ear damage. Temporary effects, like "stereo hiss", may happen.
111 +	Painful!!!	Even limited exposure to levels this high will cause permanent hearing loss.

Amplifier is a device to increase the loudness of sound by use of an external energy source. It drives the loudspeakers used in PA system to make the human voice louder.

Physics Form 5: Chapter 1 - Pitch of the Sound

Generally, there are three characteristics of sound:

• frequency affects pitch of the sound
• amplitude affects loudness of the sound
• wave form affects quality of the sound

1. Frequency - Pitch

The frequency of a wave is measured as the number of complete vibrations of particles of a medium per unit time. A commonly used unit for frequency is Hertz.

Pitch is an auditory sensation in which listener assigns musical tones to relative positions on a musical scale based on the frequency of sound. A high pitch sound corresponds to a high frequency sound wave and low pitch sound corresponds to a low frequency sound wave.

Changing Pitch:

Click on the diagram below to play!

A string vibrates with a particular fundamental frequency. It is possible, however, to produce pitches with different frequencies from the same string. The four properties of the string that affect its frequency are length, diameter, tension, and density. These properties are described below:

1. When the length of a string is changed, it will vibrate with a different frequency. Shorter strings have higher frequency and therefore higher pitch. 
2. Diameter is the thickness of the string. Thick strings with large diameters vibrate slower and have lower frequencies than thin ones. 
3. Tightening the string gives it a higher frequency while loosening it lowers the frequency. 
4. The density of a string will also affect its frequency. Remember that dense molecules vibrate at slower speeds. The more dense the string is, the slower it will vibrate, and the lower its frequency will be. Instruments often have strings made of different materials. The strings used for low pitches will be made of a more dense material than the strings used for high pitches.

Name	Frequency Range (Hz)	Characteristics
Infrasonic	0 - 20	Very low frequencies of sound that the human ear can’t detect, but you mayfeel the rumbling of the waves through your body.
Sonic (AKA Audio)	20 - 20 000	Normal range for human ears, although not everyone (especially the elderly) will hear to the extremes of this range.
Ultrasonic	20 000 +	Beyond normal hearing for humans, although some animals (like dogs) hear part ways into this range. Also used in medicine (e.g. ultrasounds for pregnant women).

Can you sing this high-pitched song?

Rest In Peace Whitney Houston

This page is dedicated to you on my lesson about the pitch of the sound. God really loves you and gives you the gift of high-pitched sound. Thanks for your song!

Physics Form 4: Chapter 1 - Micrometer Screw Gauge

Ratchet exerts correct amount of pressure on the object to be measured. 

How to take reading from micrometer screw gauge?

Click on the diagram below to play!

Physics Form 4: Chapter 5 - Refraction of Light

• Refraction is the phenomenon of light bending when it travels from one medium to another medium.
• Refraction occurs because the velocity of light changes when it travels from a medium into another medium.

The law of refraction states that:

1. The incident and refracted rays are on opposite sides of the normal at the point of incidence and all three are in the same plane.
2. The ration of sin i / sin r is a constant. This constant is called refractive index.

Click on the diagram below to play!