Understanding Semiconductor diodes
1. Conductors are materials which allow current to flow through them easily. This is because conductors have free electrons which can drift between their atoms.
2. Insulators are materials which do not conduct electrical current.
3. Semiconductor is a material whose resistance is between those of good conductors and those of good insulators.
Doping
1. The conductivity of a semiconductor can be increased by adding a small amount of certain substances (impurities).
2. DOPING is the process of adding a small amount of impurities into the crystalline lattice of semiconductors.
Semiconductors
1. There are 2 types of semiconductors: p-type and n-type.
2. p-type semiconductor:
i. the holes (positive charge) are the majority carriers.
ii. The trivalent atoms are called acceptor atoms because they accept any free electrons to fill the holes.
iii. E.g. boron, indium and gallium.
3. n-type semiconductor:
i. the free electrons (negative charge) are the majority carriers.
ii. The pentavalent atoms are called donor atoms because they supply free electrons.
Showing posts with label Nota Fizik. Show all posts
Showing posts with label Nota Fizik. Show all posts
2008-09-09
2008-08-07
Understanding Total Internal Reflection of Light
1. If the angle of incidence is allowed to exceed the critical angle, it is found that light rays are not refracted. This is because all of the light rays are reflected back.
2.This phenomenon is called total internal reflection.
3. Total Internal Reflection occurs when:
a. Light rays travel from a denser medium to a less dense medium.
b. The angle of incidence is greater than the critical angle.
Light ray which travels from a denser medium to a less dense medium will be refracted away from the normal.
Here are some Q and A session:
Q: What happens when light passes from a transparent medium into air?
A: When light passes from a transparent medium into air, it bends away from the normal. It is refracted.
Q: Why the angle of refraction becomes 90° and not more? What do we call the angle of incidence at this limit?
A: This is the limit the light ray can be refracted in air because the angle in air cannot be larger than 90°. The angle of incidence in the denser medium at this limit is called the critical angle, c.
Q: What happens when the angle of incidence is more than the critical angle?
A: When the angle of incidence is greater than the critical angle, all the light undergoes reflection.
Later we will study the Relationship between Critical angle and Refractive Index
2.This phenomenon is called total internal reflection.
3. Total Internal Reflection occurs when:
a. Light rays travel from a denser medium to a less dense medium.
b. The angle of incidence is greater than the critical angle.
Light ray which travels from a denser medium to a less dense medium will be refracted away from the normal.
Here are some Q and A session:
A: When light passes from a transparent medium into air, it bends away from the normal. It is refracted.
Q: Why the angle of refraction becomes 90° and not more? What do we call the angle of incidence at this limit?
A: This is the limit the light ray can be refracted in air because the angle in air cannot be larger than 90°. The angle of incidence in the denser medium at this limit is called the critical angle, c.
Q: What happens when the angle of incidence is more than the critical angle?
A: When the angle of incidence is greater than the critical angle, all the light undergoes reflection.
Later we will study the Relationship between Critical angle and Refractive Index
2008-07-30
Reflection of Light on a Curved Surface: Method to draw ray diagrams
1. There are two main types of curved mirrors, namely:
(a) Convex Mirror
(b) Concave Mirror
2. On a Concave mirror, the rays that are parallel and close to the main axis (small opening) converge to a point F (main or principal focus) and the distance FP is known as the focal distance of the concave mirror. (P is the surface of the mirror)
More notes can be found here:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/class/refln/u13l3d.html
3. On a Convex mirror, parallel rays that are close to the main axis, diverge from the surface of reflection. The rays are seen to diverge from a poinf F (main focus) behind the mirror. The distance FP is known as the focal length of the mirror.
More notes can be found here:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/class/refln/u13l4a.html
(a) Convex Mirror
(b) Concave Mirror
2. On a Concave mirror, the rays that are parallel and close to the main axis (small opening) converge to a point F (main or principal focus) and the distance FP is known as the focal distance of the concave mirror. (P is the surface of the mirror)
More notes can be found here:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/class/refln/u13l3d.html
3. On a Convex mirror, parallel rays that are close to the main axis, diverge from the surface of reflection. The rays are seen to diverge from a poinf F (main focus) behind the mirror. The distance FP is known as the focal length of the mirror.
More notes can be found here:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/class/refln/u13l4a.html
Characteristics of Image formed by a plane mirror
Characteristics of image formed in a plane mirror.
(a) It is virtual
(b) Has the same size as the object
(c) Is laterally inverted (i.e. inverted sideways)
(d) The distance of the object from the mirror is equal to the distance of the image form the mirror.
(a) It is virtual
(b) Has the same size as the object
(c) Is laterally inverted (i.e. inverted sideways)
(d) The distance of the object from the mirror is equal to the distance of the image form the mirror.
2008-07-23
Understanding the Reflection of Light: Law of Reflection of Light
1. The reflection of light can be studied by using light ray(s) and a plane of mirror which is placed on a piece of white paper.
2. When the ray of light is incident onto the surface of a plane mirror, the light ray does not pass through the mirror but is reflected back by the plane mirror.
3. The phenomena of ths experiment shows the phenomena of reflected light.
The Law of Reflection of Light States that:
1. The incident Ray, the reflected ray and the normal all lie in the same plane.
2. The angle of incidence is equal to the angle of reflection.
Image courtesy:
http://www.curriki.org/xwiki/bin/download/Coll_Athabasca/Unit3-Lesson2TheMovementofLight/reflection.jpg
More information at:
www.hsphys.com/ light_and_optics.html
Characteristics of Image that is formed on a plane mirror
1) It is upright
2) It is virtual
3) The distance form the object to the mirror is the same as the distance from the image to the mirror.
4) It is the same size as the object
5) It is laterally inverted
All the best!
2008-07-14
Understanding the Gas Laws: Gas Laws and Kinetic Theory of Gases
Gas theory can be explained by way of the kinetic energy.
When gas molecules hit the walls of the container and bounce back, a change in momentum occurs in a split second. This is obviously a very very fast action.
The end result of the above momentum is that the walls of the container experience a force.
Pressure is defined as the force that acts on a unit surface area. Therefore, all surfaces that are knocked by air will experience a pressure. In order for this to take effect all of the gases molecules in the container or free surface must be moving swiftly in a very short time and hit the surface repeatedly.
This pressure is called gas pressure.
Kinetic Theory of Gases
Gas molecules are continually in random and independent motion in all directions at high and different speed.
The motion of gas molecules follows all of the Newton Laws of Motion.
All collisions between the gas molecules (i.e. one with another) and the walls of the container are assumed to be perfectly elastic. Therefore, momentum and kinetic energy are conserved during collision.
The volume of the molecules can be conserved compared to the volume occupied by the gas.
The force among the gas molecules can be neglected except during collision.
The time period of a collision can be neglected when compared with the time interval between two collisions.
When gas molecules hit the walls of the container and bounce back, a change in momentum occurs in a split second. This is obviously a very very fast action.
The end result of the above momentum is that the walls of the container experience a force.
Pressure is defined as the force that acts on a unit surface area. Therefore, all surfaces that are knocked by air will experience a pressure. In order for this to take effect all of the gases molecules in the container or free surface must be moving swiftly in a very short time and hit the surface repeatedly.
This pressure is called gas pressure.
Kinetic Theory of Gases
The basic assumption for the kinetic theory of gas is as follows:
Gas is composed of molecules.
Gas is composed of molecules.
Gas molecules are continually in random and independent motion in all directions at high and different speed.
The motion of gas molecules follows all of the Newton Laws of Motion.
All collisions between the gas molecules (i.e. one with another) and the walls of the container are assumed to be perfectly elastic. Therefore, momentum and kinetic energy are conserved during collision.
The volume of the molecules can be conserved compared to the volume occupied by the gas.
The force among the gas molecules can be neglected except during collision.
The time period of a collision can be neglected when compared with the time interval between two collisions.
2008-06-22
Application of Specific Heat capacity
As we have read (supposedly) about the concept of heat capacity and specific heat capacity, we will discuss briefly about the application of Specific Heat capacity in daily situations.
1. Substances having a small specific heat capacity can be quickly heated up, it also experience a big change in temperature even though only small amount of heat is supplied.
2. Substances having a small specific heat capacity, are very useful as material in cooking instruments such as frying pans, pots, kettles and so on, because, they can be quickly heated up even when small amount oh heat is supplied.
3. Sensitive thermometers also must be made from materials with small specific heat capacity so that it can detect and show a change of temperature rapidly and accurately.
4. Substances that have a high specific heat capacity is suitable as a material for constructing kettle handlers, insulators and oven covers, because, a high amount of heat will cause only a small change in temperature aka the material won't get hot too fast!
5. Heat storage instruments are very useful and they are usually made of substances with a high specific heat capacity.
6. Water as a cooling agent acts excellent as a cooling agent in engines. Water is also used in houses in cold climate countries because as it is heated up (boiled) it tends to retain heat and warm the house due to its high specific heat capacity.
1. Substances having a small specific heat capacity can be quickly heated up, it also experience a big change in temperature even though only small amount of heat is supplied.
2. Substances having a small specific heat capacity, are very useful as material in cooking instruments such as frying pans, pots, kettles and so on, because, they can be quickly heated up even when small amount oh heat is supplied.
3. Sensitive thermometers also must be made from materials with small specific heat capacity so that it can detect and show a change of temperature rapidly and accurately.
4. Substances that have a high specific heat capacity is suitable as a material for constructing kettle handlers, insulators and oven covers, because, a high amount of heat will cause only a small change in temperature aka the material won't get hot too fast!
5. Heat storage instruments are very useful and they are usually made of substances with a high specific heat capacity.
6. Water as a cooling agent acts excellent as a cooling agent in engines. Water is also used in houses in cold climate countries because as it is heated up (boiled) it tends to retain heat and warm the house due to its high specific heat capacity.
2008-06-15
Understanding Specific Heat Capacity: idea of Specific Heat Capacity
Understanding Specific Heat Capacity
Heat Capacity
1. The heat capacity,C , of a substance is the heat which is required to increase the temperature of the substance by 1°C.
2. The unit for heat capacity is J° / C.
3. For example, the heat capacity for 100 g of water is 420 J°/ C. This means that 420 J of heat energy is required to raise the temperature of 100 g water by 1°C. To increase temperature by 2°C, 840 J are needed and so on.
4. Different substance, materials or body has different specific heat capacity.
5. If a body absorbs a lot of heat but there is only a slight increase in temperature, then the body is said to posses a large heat capacity.
6. On the other hand, if a body absorbs a little amount of heat but shows a big rise in temperature, then the body is said to posses a small heat capacity.
7. The relationship between heat capacity, C and specific heat capacity, c is shown by the following equation.
C = mc
Specific Heat Capacity
1. Specific heat capacity, c, of a body is the heat that is needed to increase the heat of a unit of mass or the substance by 1°C or 1K.
2. The unit of specific heat capacity is J kg-1°C-1.
3. For example, the specific heat capacity of water is 4200 J kg-1°C-1 . This means that 4200 J of heat is needed to increase the temperature of 1 Kg of water by 1°C.
4. Therefore, when a body of a mass m and specific heat capacity, c, absorbs a quantity of Heat, H, then its heat will increase by θ.
5. Therefore H = mc θ.
6. On the contrary, when the heat of a body falls by θ, the quantity of heat that disappears or lost is also H = mc θ.
7. The specific heat capacity is dependent upon the type of substances. Different substances have different specific heat capacity.
8. By knowing the specific heat capacity, we can determine the mass and also the change of temperature of a body if we know the amount of heat that is transferred.
9. Total heat transferred H = mc θ.
10. Generally, liquid has more specific heat capacity than solids. This means that liquids need more heat energy than solids to show the same value of rise in temperature.
Hope this helps!
Heat Capacity
1. The heat capacity,C , of a substance is the heat which is required to increase the temperature of the substance by 1°C.
2. The unit for heat capacity is J° / C.
3. For example, the heat capacity for 100 g of water is 420 J°/ C. This means that 420 J of heat energy is required to raise the temperature of 100 g water by 1°C. To increase temperature by 2°C, 840 J are needed and so on.
4. Different substance, materials or body has different specific heat capacity.
5. If a body absorbs a lot of heat but there is only a slight increase in temperature, then the body is said to posses a large heat capacity.
6. On the other hand, if a body absorbs a little amount of heat but shows a big rise in temperature, then the body is said to posses a small heat capacity.
7. The relationship between heat capacity, C and specific heat capacity, c is shown by the following equation.
C = mc
Specific Heat Capacity
1. Specific heat capacity, c, of a body is the heat that is needed to increase the heat of a unit of mass or the substance by 1°C or 1K.
2. The unit of specific heat capacity is J kg-1°C-1.
3. For example, the specific heat capacity of water is 4200 J kg-1°C-1 . This means that 4200 J of heat is needed to increase the temperature of 1 Kg of water by 1°C.
4. Therefore, when a body of a mass m and specific heat capacity, c, absorbs a quantity of Heat, H, then its heat will increase by θ.
5. Therefore H = mc θ.
6. On the contrary, when the heat of a body falls by θ, the quantity of heat that disappears or lost is also H = mc θ.
7. The specific heat capacity is dependent upon the type of substances. Different substances have different specific heat capacity.
8. By knowing the specific heat capacity, we can determine the mass and also the change of temperature of a body if we know the amount of heat that is transferred.
9. Total heat transferred H = mc θ.
10. Generally, liquid has more specific heat capacity than solids. This means that liquids need more heat energy than solids to show the same value of rise in temperature.
Hope this helps!
2008-06-10
Types of Thermometer
There are several types of thermometer, here, I explain only a few of the possibly many types of thermometer.
Mercury thermometer
1. The physical quantity that is used to determine the temperature of a body by means of a mercury thermometer is the length of the thread mercury, or to be more exact, the volume of mercury.
2. When the temperature increases, the volume of the mercury increases too.
3. The sensitivity of a mercury thermometer can be increased by
a. reducing the diameter of the capillary tube.
b. increasing the size of the bulb.
c. using a thinner-walled glass bulb.
4. Normally mercury is used in a thermometer because it:
a. Expands uniformly.
b. has a higher boiling limit.
c. is opaque and therefore it is easier to read off the temperature.
d. is a good conductor of heat.
e. does not stick to the glass.
5. One weakness of the mercury thermometer in the measurement of an accurate temperature is that the glass of the capillary tube also expands when the temperature expands.
In addition to that, it is extremely dangerous if the glass tube breaks because mercury is very poisonous.
Mercury thermometer is suitable to measure temperature between -30 degree celsius to 300 degree celcius.
Resistance thermometer
1. Thermometers which use liquids inside the glass are not suitable to be used for measuring a wide range of temperature. e.g temperature ranging from -250 degree celcius to about 700 degree celsius.
2. A suitable thermometer which is used for the above range of temperatures is a resistance thermometer.
3. A resistance thermometer uses the property of the change in the platinum wire with a change in temperature.
4. The current flowing in the wire experiences more resistance when the wire becomes hot.
5. The change in the resistance of the wire is directly proportional to the change in temperature.
6. A milliammeter can and should be calibrated before hand to measure the temperature.
7. Its calibration of the melting limit of water and the boiling point of water at a pressure of 1 atmosphere is able to convert the milliameter scale to a temperature scale in degree celsius.
8. Therefore, this thermometer is very accurate.
Thermocouple thermometer
1. An electromotive force (e.m.f) will be produced in a thermocouple when there is a temperature difference between the hot junction and the cold junction. Once this happens, a current will flow.
2. This thermometer is very sensitive and responds towards slight change in temperature.
3. Since the physical quantity which is used to measure the temperature is the e.m.f, this thermometer can be connected to other electrical circuits to control or record the surrounding temperature.
4. A thermocouple thermometer is a very sensitive thermometer which is suitable for measuring temperatures ranging from -250 degree celsius to 1600 degree celsius.
Mercury thermometer
1. The physical quantity that is used to determine the temperature of a body by means of a mercury thermometer is the length of the thread mercury, or to be more exact, the volume of mercury.
2. When the temperature increases, the volume of the mercury increases too.
3. The sensitivity of a mercury thermometer can be increased by
a. reducing the diameter of the capillary tube.
b. increasing the size of the bulb.
c. using a thinner-walled glass bulb.
4. Normally mercury is used in a thermometer because it:
a. Expands uniformly.
b. has a higher boiling limit.
c. is opaque and therefore it is easier to read off the temperature.
d. is a good conductor of heat.
e. does not stick to the glass.
5. One weakness of the mercury thermometer in the measurement of an accurate temperature is that the glass of the capillary tube also expands when the temperature expands.
In addition to that, it is extremely dangerous if the glass tube breaks because mercury is very poisonous.
Mercury thermometer is suitable to measure temperature between -30 degree celsius to 300 degree celcius.
Resistance thermometer
1. Thermometers which use liquids inside the glass are not suitable to be used for measuring a wide range of temperature. e.g temperature ranging from -250 degree celcius to about 700 degree celsius.
2. A suitable thermometer which is used for the above range of temperatures is a resistance thermometer.
3. A resistance thermometer uses the property of the change in the platinum wire with a change in temperature.
4. The current flowing in the wire experiences more resistance when the wire becomes hot.
5. The change in the resistance of the wire is directly proportional to the change in temperature.
6. A milliammeter can and should be calibrated before hand to measure the temperature.
7. Its calibration of the melting limit of water and the boiling point of water at a pressure of 1 atmosphere is able to convert the milliameter scale to a temperature scale in degree celsius.
8. Therefore, this thermometer is very accurate.
Thermocouple thermometer
2. This thermometer is very sensitive and responds towards slight change in temperature.
3. Since the physical quantity which is used to measure the temperature is the e.m.f, this thermometer can be connected to other electrical circuits to control or record the surrounding temperature.
4. A thermocouple thermometer is a very sensitive thermometer which is suitable for measuring temperatures ranging from -250 degree celsius to 1600 degree celsius.
2008-06-09
Thermometers and calibration of Thermometers
The definition of temperature as a physical quantity is based on the principle of thermal equilibrium.
Let say there are Thermometer A, Liquid B and Liquid C.
We put thermometer A into liquid B and then after thermal equilibrium is achieved we record the value.
We put thermometer A again into liquid C and after thermal equilibrium is achieved we record the value of reading in the thermometer.
If the temperature in both cases are the same, then liquid B and liquid C are in thermal equilibrium with one another. Eventhough, the two liquids (B and C) are not in thermal contact, they are in thermal equilibrium because their temperatures are the same.
Therefore Temperature is a physical quantity which determines whether or not two objects are in thermal equilibrium.
We measure temperature using a thermometer.
Thermometers must be calibrated before they can be used to measure temperatures.
The calibration of an instrument refers to the process of marking-up a scale on the instrument to be used as measurement.
To produce a scale on a thermometer, two fixed points must be determined first. Then the two points must be the temperatures which can easily and correctly reproduced in any part of the world.
On the Celsius scale, the two fixed points are the ice point (0°C) and the steam/boiling point (100°C).
The ice point (0°C), or lower fixed point is the melting temperature of pure ice at standard atmospheric pressure (760 mm Hg).
The steam point (100°C), or upper fixed point is the temperature of steam at standard atmospheric pressure (760 mm Hg).
After obtaining, the highest point and the lowest point. We divide the length between them to equal parts / scale.
2007-08-20
Introductory Notes
Ok..Ok.. I know this sound as if you don't have somewhere else to go or something else to do.
But, Frankly...this blog is designed to help students to understand the Physics syllabus taught in Malaysian secondary school education system..(at least) and pass the exam..for SPM or GCE O Level Equivalent only.
This Blog is NOT intended for students who wants to score for the Physics Paper.To score you must do Tons of exercises and lots of questioning and research. All the best!
Blog Administrator
Disclaimer:
All the images and diagrams used in the blog are from the website. If the owner of the image does not permit the image to be used please inform the admin. Please note that this is a free website and the blog admin only wants to help in the spread of knowledge.
But, Frankly...this blog is designed to help students to understand the Physics syllabus taught in Malaysian secondary school education system..(at least) and pass the exam..for SPM or GCE O Level Equivalent only.
This Blog is NOT intended for students who wants to score for the Physics Paper.To score you must do Tons of exercises and lots of questioning and research. All the best!
Blog Administrator
Disclaimer:
All the images and diagrams used in the blog are from the website. If the owner of the image does not permit the image to be used please inform the admin. Please note that this is a free website and the blog admin only wants to help in the spread of knowledge.
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