Current rating of fuses and MCB's.

CURRENT RATING OF FUSES AND MCBS Name of Instructor: Miss. B.S.K. Subasinghe Name : Perera K.N.S. Index No : 020287 Field : ENTC Date of Per. : 10/12/2003 Date of Sub.: 19/12/2003 CALCULATIONS: For the fuse For MCB From graphs drawn, Fusing current for 5A fuse = Tripping current for 2A MCB = RESULTS Fusing Factor Tripping Factor DISCUSSION: Fuses and Miniature Circuit Breakers (MCBs) are used to protect electrical equipment and for the safety of the users. The conditions that require circuit protection are direct shorts, excessive current and excessive heat. When one or more of these conditions occur the above protective devices (connected in series with the supply) are able to disconnect the circuit thus preventing the danger. Fuses Circuit symbol: This provides protection by melting due to the heat produced because of ohmic resistance, when a higher than a rated current flows through it. There are three main types of fuses, Re-wirable fuses These have a thin wire that is held on a ceramic holder. The wire is designed to burn when a high current passes. An advantage is the reusability but it is vulnerable to mishandling where incorrect fusing elements can be fitted by inexperienced people, putting users in danger. Other Problems with this type are the oxidization (causes the cross section of the wire to reduce

  • Word count: 1356
  • Level: AS and A Level
  • Subject: Science
Access this essay

The advantages and limitations of electron microscopy.

The advantages and limitations of electron microscopy There are two main branches of microscopy that are pertinent to cell biology. These branches arise from the two types of microscope; the light microscope and the electron microscope. The basic principles of light microscopy have been known since circa 17th century, however improvements in lens manufacture in circa 19th century allowed the use of microscopy to be much more practically available and useful. This is increased ability inspired rapid research into both the design of microscopes and the preparation of specimens. However, the light microscope can only magnify objects bigger than 0.2 micrometres; due to its limited resolving powers. This is because it utilises a beam of light. Relatively, light has a long wavelength, this means that when there are two small points close together there is too much refraction and wave front overlap, the eye then only sees one point. This can also be considered in terms of objects "crossing the path" of the wavelength. The smallest wavelength of visible light is 400nm, the diameter of mitochondria is 1000nm, and therefore mitochondria cross the path of the light wave. However ribosomes have a diameter of 22nm, and do not cross the path of the light wave and are therefore not seen by the light microscope. As biologists came to realise these limitations they understood that the

  • Ranking:
  • Word count: 1308
  • Level: AS and A Level
  • Subject: Science
Access this essay

investigating the relationship between the diameter and the current in a wire at its melting point

Investigation Report Aim Theory Electrical resistance is a measure of the degree to which an object opposes the passage of an electric current. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured in siemens. Resistance is the property of any object or substance of resisting or opposing the flow of an electrical current. The quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit. Some formulae for resistance are where R is the resistance of the object / ? V is the potential difference across the object / V I is the current passing through the object / A (Ref. http://en.wikipedia.org/wiki/Electrical_resistance) where R is the resistance/ ? ? is the resistivity / ?m l is the length of the wire / m A is the cross section area of the wire / m A = ?() = ? where A is area / m d is the diameter / m Putting the formulae together, so (Ref. http://physics.bu.edu/~duffy/PY106/Resistance.html) Aim of investigation The aim of this work is to investigate the relationship between the resistance and the diameter of the wire. Variables Variable Independent / Controlled / Dependent Resistance D Resistivity C Length of wire C Diameter I Prediction Since the theory suggests that So So the resistance should be

  • Ranking:
  • Word count: 1203
  • Level: AS and A Level
  • Subject: Science
Access this essay

Experiment to measure deflection when a force is applied to a cantilever.

Sc1 Investigation - bending of a Cantilever. Experiment to measure deflection when a force is applied to a cantilever. Introductory Diagram Aim To find out whether varying the load has any affect on the deflection (?d) of the ruler. Theory Elasticity is the property, which allows a material to regain its shape after being distorted. Some materials like, rubber bands, are much more elastic than others. The elastic limit of a material is the maximum amount by which it can be stretched and still regain its original shape after the distorting forces are removed. If a material is stretched beyond its elastic limit its shape is permanently changed. ' The deformation of a material is proportional to the force is applied to it, provided the elastic limit is not exceeded'. This is known as Hooke's Law, named after its discoverer, Robert Hooke, a 17th century scientist. Young's Modulus When stress is applied to a material, strain is produced in the material. The strain is proportional to the stress, provided the stress does not exceed a limit known simply as the 'limit of proportionality'. Within this limit, the value of is a constant for that material, and is known as the Young Modulus for the material. The Young Modulus (E) = Provided the limit of proportionality is not exceeded. Before we can work out the Young Modulus we need to know about stress and strain.

  • Word count: 981
  • Level: AS and A Level
  • Subject: Science
Access this essay

Force of friction

Kwun Tong Government Secondary School Advanced Level Physics (TAS) Experiment Report Experiment No.: 1 Title: Force of friction Date of Experiment: 2006/10/31 Mark: Sch. Code 2114 TAS Group 5 Name: Chan Man Lok Class: S.6C Class No.: 6 Objective: . To study the effects of the normal force, and surface area on the force of friction using a block. 2. To estimate the coefficients of static and kinetic friction. Apparatus: Instrument Description Wooden block x 4 200g x 4 Spring balance x 1 DCS/PL/2-2 0 - 10N The smallest division = 0.2 N Tripe beam balance x 1 0 - 500g The smallest division = 0.1g Frictional paper x 1 / Rubber band Several / Theory: Limiting static friction : Friction always opposes motion. Larger forces tending to produce the motion, larger friction is. However, it cannot increase indefinitely. For example, when a body is in contact with a rough surface frictional forces arise at the contact surface if the body is subjected to an applied force. When the applied force exceeds the limiting static friction , the body will start to slip over the rough surface. And the value of is roughly proportional to the normal force R. where is the coefficient of static friction at maximum at the contact surface. Kinetic friction : However, the friction acting on a resting block

  • Word count: 1635
  • Level: AS and A Level
  • Subject: Science
Access this essay

How the resistance of an ammeter changed when introduced into a circuit.

DC MEASUREMENTS The experiment was to find out how the resistance of both an ammeter and voltmeter, using both an ammeter and voltmeter changed when introduced into a circuit. From doing this it was found that the resistance of the ammeter decreases as both the emf and current decrease, however the avometer suggested that internal resistance increases with the voltage. Introduction Voltmeter's and ammeter's use a moving coil galvanometer to take the current and a mechanical pointer to display the current. When using analogue components an important factor to consider is full-scale deflection, which is when the maximum deflection of an analogue instrument such as a moving coil meter is reached. At present the full-scale deflection of most instruments is 10-50 ?A, but to overcome this shunting resistors are placed in parallel to carry the excess current. To take the voltage of an object, the shunting resistor must be placed in series, as the resistance of the moving-coil galvanometer is not very high. Some formulae which may be useful during this experiment is: Method The experiment firstly started by looking at calculating the resistance of the voltmeter. This was done by setting the circuit up as below: E = d.c. power supply M = Voltmeter being tested Rm = Voltmeter resistance I = Current The avometer was then placed upon successive ranges of 3v, 10v, 30v,

  • Word count: 789
  • Level: AS and A Level
  • Subject: Science
Access this essay

Investigating the depression of a ruler when force is applied.

Investigating the depression of a ruler when force is applied Investigation: Measuring the depression of a ruler when force is acted upon it and when the length of overhang is altered. Planning First of all it was important before starting anything that the environment where the experiment was taking place was a safe one and that I was not in any danger whilst doing my investigation. I will make sure that the desk is clear with only the required apparatus present and also make sure that no more weight than 6N is put on the ruler otherwise it might snap and a splinter could come up into my eye. There are three independent variables in this experiment. These are the over-hang of the ruler, the mass added to the ruler and where the mass is positioned on the ruler. I will be investigating two of these independent variables, which are the alteration in overhang and the mass added to the end of the ruler. These will then produce a Dependant variable. This is the amount the ruler bends. For this experiment I will set up a one-meter ruler lying horizontally off the side of the work desk with a block of wood on top of it and a G Clamp holding it in place so it does not move. I will then add individual weights of 1 Newton to a piece of string hanging on the end of the overhanging ruler. I will measure the distance that the ruler has bent by using another ruler lying vertically

  • Word count: 2580
  • Level: AS and A Level
  • Subject: Science
Access this essay

physics investigation- stopping distance

Physics Investigation Introduction In my investigation I intend to gather enough evidence and explanation to see if and how the mass of a ball will affect its stopping distance. I will carry out a series of tests starting with changing the mass of the ball then changing height which it's dropped from. Predictions I predict that the mass of a ball will most defiantly affect the distance it takes to stop because as the mass increases, the amount of friction with the surface will increase which will slow down the ball sooner. I believe if the mass of the ball is doubled the friction with the surface it's on will double and therefore half the distance taken to stop. Equipment For my investigation the equipment I will require is: * A ramp and stand ( 1 metre long) * Carpet (2 by 0.5 metres) * 2 balls of different masses but same size ( ball 1, 2.8g and ball 2, 44.9g) * 2 metre rules My setup My setup is pretty simple I will use a ramp with a rule along it and some carpet for the balls to roll along I will then use another rule to measure the distance taken to stop. When I first set up my equipment the balls where rolling around everywhere, to overcome this problem I decided to curl the carpet into a half bowl shape the balls then rolled smoothly down the ramp and along the carpet. Procedure Firstly I will drop the lighter ball 1, and measure its stopping distance

  • Word count: 1474
  • Level: AS and A Level
  • Subject: Science
Access this essay

Investigation into the resistance of a filament lamp.

Investigation into the resistance of a filament lamp Aim To investigate Characteristics of a filament lamp Background Knowledge Filament bulb The tungsten filament in a modern light bulb is supported by several molybdenum wires. The ends of the support wires are imbedded in a glass button at the top of the glass support rod. The copper and nickel lead-in wires, which carry the current to the filament, are supported by a glass support stem. One lead-in wire is soldered to the metal contact at the base of the bulb, while the other is electrically connected to the side socket contact. The contacts are separated by an insulating plate. An electrical current can pass in either direction through the filament. The filament of a light bulb is a resistor. When a current passes through the resistor electrical energy is converted into heat. A light bulb converts current into power by the resistive element inside the light bulb. When the power level is sufficient to raise the temperature to above 1000 degrees Kelvin, visible light is produced, which can help us to estimate the temperature of the filament. The length of time that you leave the light bulb on determines the total amount of energy that has been used. The hot filament then radiates a fraction of this energy in the form of light. The current through the light bulb is not proportional to the voltage across it. This is

  • Word count: 4216
  • Level: AS and A Level
  • Subject: Science
Access this essay

To determine the acceleration of gravity in a free fall experiment.

ACCELERATION OF GRAVITY AIM To determine the acceleration of gravity in a free fall experiment. DIAGRAM METHOD * The experiment is carried out using the apparatus, as set up above. * The switch is used to open and close one circuit at a time. * The distance for the ball to fall is measured between the ball and the trapdoor with a ruler; a set square is used to see where the ball coincides with the ruler, making it a more accurate measurement. * Adjusting the height of the trapdoor can change the distance. * When circuit A is closed the power supply travels to the electromagnet, which magnetises the ball. * The timer is set to zero. * As the switch is moved, braking circuit A and closing circuit B, the power supply is cut off to the electromagnet and the ball falls. The power supply now travels to the timer and timing commences. The two actions happen simultaneously. * When the ball falls through the trapdoor the circuit is broken and timing stops as there is no power supply. * The time shown on the timer represents how long it took for the ball to reach the trapdoor. * The experiment is repeated several times at different heights, with 2 readings for each height. * Results are put into a table showing the distance, times, an average time and a time. RESULTS Distance/m Time/s Time/s Av.Time/s Time/s 0.55 0.318 0.323 0.3205 0.103 0.521 0.320

  • Word count: 1104
  • Level: AS and A Level
  • Subject: Science
Access this essay